Add debug method to manually set controller address (e.g. for bench testing)

Offload TX data section to DMA (releases up to 12.5ms back to RTOS)
Migrate to FreeRTOS
2026-11-01 23:07:41 +00:00 · 2026-09-28 11:36:01 -07:00 · 2026-09-28 11:36:01 -07:00 · 2026-09-28 11:36:01 -07:00 · 2026-09-20 15:08:19 -07:00 · 2026-09-20 15:08:15 -07:00
41 changed files with 3703 additions and 909 deletions
@@ -16,13 +16,17 @@ Checks: |
  -modernize-avoid-c-arrays,
  -modernize-use-std-print,
  -readability-magic-numbers,
+  -readability-function-cognitive-complexity,
+  -misc-non-private-member-variables-in-classes
 WarningsAsErrors: ""
-ExcludeHeaderFilterRegex: 'out/build'
-HeaderFilterRegex: '^src/.*'
+ExcludeHeaderFilterRegex: "out/build"
+HeaderFilterRegex: "^src/.*"
 SystemHeaders: false
 # AnalyzeTemporaryDtors: false
 FormatStyle: none
 CheckOptions:
+  - key: modernize-deprecated-headers.CheckHeaderFile
+    value: "false"
  - key: readability-magic-numbers.IgnorePowersOf2IntegerValues
    value: "true"
  - key: readability-magic-numbers.IgnoredIntegerValues
@@ -0,0 +1,14 @@
+CompileFlags:
+  Remove:
+    - -mlongcalls
+    - -fno-shrink-wrap
+    - -fstrict-volatile-bitfields
+    - -fno-tree-switch-conversion
+    - -fanalyzer
+    - -ffixed-r2
+    - -ffixed-r3
+    - -ffixed-r4
+    - -fzero-init-padding-bits
+    - -fno-malloc-dce
+  Add:
+    - -Wno-missing-field-initializers
@@ -5,7 +5,17 @@
 	// Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
 	"image": "mcr.microsoft.com/devcontainers/base:alpine-3.22",
 	// Features to add to the dev container. More info: https://containers.dev/features.
-	"features": {},
+	"features": {
+		"ghcr.io/anthropics/devcontainer-features/claude-code:1": {}
+	},
+	"mounts": [
+		"source=${localEnv:HOME}/.claude,target=/home/vscode/.claude,type=bind,consistency=cached",
+		// ~/.claude/skills/* are symlinks into ~/.agents/skills — mount it too or they dangle
+		"source=${localEnv:HOME}/.agents,target=/home/vscode/.agents,type=bind,consistency=cached"
+	],
+	"containerEnv": {
+		"CLAUDE_CONFIG_DIR": "/home/vscode/.claude"
+	},
 	// Use 'forwardPorts' to make a list of ports inside the container available locally.
 	// "forwardPorts": [],
 	// Use 'postCreateCommand' to run commands after the container is created.
@@ -17,28 +27,25 @@
 			"extensions": [
 				"ms-vscode.cpptools-extension-pack",
 				"rockcat.avr-support",
-				"harikrishnan94.cxx-compiler-explorer"
+				"harikrishnan94.cxx-compiler-explorer",
+				"llvm-vs-code-extensions.vscode-clangd",
+				"Anthropic.claude-code"
 			],
 			"settings": {
-				"editor.formatOnSave": true,
-				"C_Cpp.codeAnalysis.clangTidy.checks.disabled": [
-					"clang-analyzer-core.NullDereference"
-				],
-				"C_Cpp.files.exclude": {
-					"build/**": true
-				},
 				"files.associations": {
 					"*.S": "avr"
 				},
-				"cmake.configureOnOpen": true,
-				"compilerexplorer.compilationDirectory": "${workspaceFolder}/build"
+				"clangd.path": "/usr/bin/clangd",
+				"clangd.arguments": [
+					"--compile-commands-dir=${workspaceFolder}/out/build"
+				]
 			}
 		}
-	}
-	// "runArgs": [
-	// 	"--device=/dev/ttyUSB0",
-	// 	"--device=/dev/ttyUSB1"
-	// ]
+	},
+	"runArgs": [
+		"--device=/dev/ttyUSB0",
+		"--network=host"
+	]
 	// Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
 	// "remoteUser": "root"
 }
@@ -12,3 +12,4 @@ __pycache__/
 ~*
 \#*
 /CMakeUserPresets.json
+.cache/
@@ -1,20 +1,34 @@
-cmake_minimum_required(VERSION 3.24)
+cmake_minimum_required(VERSION 3.30)

-project(avclan-mockingboard VERSION 1.1 LANGUAGES C CXX)
+include(FetchContent)
+
+if(AVCLAN_TARGET_SDK_FILE)
+include(${AVCLAN_TARGET_SDK_FILE})
+endif()
+
+project(avclan-mockingboard VERSION 1.2 LANGUAGES C CXX ASM)
+
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+set(BUILD_TESTING OFF CACHE BOOL "" FORCE)
+
+# Hardware target (port) selection. The chosen target/<name>/ directory supplies
+# the port implementation sources, the per-target include path, and all
+# hardware-specific build configuration (compile defs/options, device-pack
+# handling, flashing) via its own CMakeLists, pulled in with add_subdirectory
+# below. The matching cross-compiler is selected separately by a toolchain file
+# (e.g. cmake/avr-gcc-toolchain.cmake) named in a CMake preset. Adding a new
+# board = a sibling target/ directory + a toolchain file + a preset wiring them.
+set(AVCLAN_TARGET avr-attiny3216 CACHE STRING "Hardware target (port) to build")
+set_property(CACHE AVCLAN_TARGET PROPERTY STRINGS "avr-attiny3216" "pico2" "esp32")
+
+# --- Firmware configuration options ----------------------------------------
+set(AVCLAN_MSG_QUEUE_SIZE 16 CACHE STRING "Size of incoming/outgoing queues")
+set(AVCLAN_FRAME_POOL_N 14 CACHE STRING "Pool allocator capacity for avclan::Frame (must be <= incoming/outgoing queue size)")

 set(CMAKE_C_STANDARD 23)
 set(CMAKE_CXX_STANDARD 23)
 set(CMAKE_C_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
-set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
-
-add_compile_options(
-    -Wall -Wswitch-enum -Werror
-    $<$<COMPILE_LANGUAGE:CXX>:-fno-threadsafe-statics>
-    $<$<COMPILE_LANGUAGE:CXX>:-fno-exceptions>
-    $<$<COMPILE_LANGUAGE:CXX>:-fno-rtti>
-    $<$<CONFIG:Debug>:-fanalyzer>
-    $<$<CONFIG:Debug>:-Wno-analyzer-use-of-uninitialized-value>)

 if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
  if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "13")
@@ -47,15 +61,6 @@ if(INSTALL_GIT_HOOKS AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/.git")
  endif()
 endif()

-# Hardware target (port) selection. The chosen target/<name>/ directory supplies
-# the port implementation sources, the per-target include path, and all
-# hardware-specific build configuration (compile defs/options, device-pack
-# handling, flashing) via its own CMakeLists, pulled in with add_subdirectory
-# below. The matching cross-compiler is selected separately by a toolchain file
-# (e.g. cmake/avr-gcc-toolchain.cmake) named in a CMake preset. Adding a new
-# board = a sibling target/ directory + a toolchain file + a preset wiring them.
-set(AVCLAN_TARGET avr-attiny3216 CACHE STRING "Hardware target (port) to build")
-
 # The AVC-LAN stack as a static library: the target-agnostic generic core (no
 # <avr/...>, no register access). The selected target's port sources and flags
 # are contributed by its subdirectory.
@@ -65,6 +70,21 @@ add_library(avclan STATIC
    src/avclan/bus.cc
 )

+target_compile_definitions(avclan PUBLIC
+    AVCLAN_FRAME_POOL_N=${AVCLAN_FRAME_POOL_N}
+    AVCLAN_MSG_QUEUE_SIZE=${AVCLAN_MSG_QUEUE_SIZE}
+)
+
+target_compile_options(avclan PUBLIC
+    -Wall -Wswitch-enum -Werror
+
+    # Debug must not be -O0: both the vendored usart.h and avr-libc's
+    # <util/delay.h> #warning when __OPTIMIZE__ is undefined, and -Werror makes
+    # that fatal.
+    $<$<CONFIG:Debug>:-Og>
+    $<$<CONFIG:Debug>:-fanalyzer>
+    $<$<CONFIG:Debug>:-Wno-analyzer-use-of-uninitialized-value>)
+
 # avclan exports its public generic headers (src/avclan) to consumers and
 # reaches into src/ for sibling headers (stdio.h, board.h) during its own
 # build. The selected target adds its own per-target include path.
@@ -76,8 +96,91 @@ target_include_directories(avclan PUBLIC
 # flashing target. Added after the targets above so it can extend them.
 add_subdirectory(src/avclan/target/${AVCLAN_TARGET})

-add_executable(mockingboard
-    src/sniffer.cc
-)
+if(NOT TARGET mockingboard)
+  add_executable(mockingboard
+      src/sniffer.cc
+  )
+  target_link_libraries(mockingboard avclan)
+endif()

-target_link_libraries(mockingboard avclan)
+# Report firmware section sizes on every build, when the toolchain provides a
+# size tool (CMAKE_SIZE). A standalone custom target (rather than a POST_BUILD
+# command on mockingboard) so it prints even when the link is up to date:
+# custom targets with no output are always considered stale and re-run.
+# add_dependencies orders it after the link.
+if(TARGET mockingboard AND CMAKE_SIZE)
+    add_custom_target(mockingboard-size ALL
+        COMMAND ${CMAKE_SIZE} $<TARGET_FILE:mockingboard>
+        COMMENT "Section sizes: mockingboard firmware"
+        VERBATIM
+    )
+    add_dependencies(mockingboard-size mockingboard)
+endif()
+
+# --- Polyfill headers for std facilities the toolchain may lack -------------
+# tl::expected / tl::optional back-fill std::expected / std::optional (with
+# C++23 monadic ops) when the build's stdlib predates them. Runs after the port
+# subdirectory to provide a port-supplied freestanding stdlib via
+# CMAKE_REQUIRED_INCLUDES, if necessary.
+include(CheckCXXSourceCompiles)
+find_program(GIT_EXECUTABLE git REQUIRED)
+
+if(TARGET libstdcpp)
+    get_target_property(_stdlib_incs libstdcpp INTERFACE_INCLUDE_DIRECTORIES)
+    set(CMAKE_REQUIRED_INCLUDES ${_stdlib_incs})
+endif()
+
+check_cxx_source_compiles("
+    #include <version>
+    #if !defined(__cpp_lib_expected) || __cpp_lib_expected < 202211L
+      #error no std::expected
+    #endif
+    int main() { return 0; }" HAVE_STD_EXPECTED)
+# check_cxx_source_compiles("
+#     #include <version>
+#     #if !defined(__cpp_lib_optional) || __cpp_lib_optional < 202110L
+#       #error no C++23 std::optional
+#     #endif
+#     int main() { return 0; }" HAVE_STD_OPTIONAL)
+unset(CMAKE_REQUIRED_INCLUDES)
+
+if(NOT HAVE_STD_EXPECTED)
+    FetchContent_Declare(
+        tl_expected
+        GIT_REPOSITORY https://github.com/TartanLlama/expected.git
+        GIT_TAG 1770e3559f2f6ea4a5fb4f577ad22aeb30fbd8e4
+        PATCH_COMMAND ${CMAKE_COMMAND}
+            -DGIT_EXECUTABLE=${GIT_EXECUTABLE}
+            -DPATCH_FILE=${CMAKE_CURRENT_SOURCE_DIR}/cmake/tl-expected-no-exception-header.patch
+            -P ${CMAKE_CURRENT_SOURCE_DIR}/cmake/apply-patch.cmake
+        SYSTEM
+    )
+    set(EXPECTED_BUILD_TESTS OFF)
+    set(EXPECTED_BUILD_PACKAGE OFF)
+    FetchContent_MakeAvailable(tl_expected)
+    add_library(tl_expected_hdr INTERFACE)
+    target_include_directories(tl_expected_hdr
+        INTERFACE ${tl_expected_SOURCE_DIR}/include)
+    target_link_libraries(avclan PUBLIC tl_expected_hdr)
+endif()
+
+# std/tl::optional not currently used
+# if(NOT HAVE_STD_OPTIONAL)
+#     FetchContent_Declare(
+#         tl_optional
+#         GIT_REPOSITORY https://github.com/TartanLlama/optional.git
+#         GIT_TAG 3a1209de8370bf5fe16362934956144b49591565
+#         PATCH_COMMAND ${CMAKE_COMMAND}
+#             -DGIT_EXECUTABLE=${GIT_EXECUTABLE}
+#             -DPATCH_FILE=${CMAKE_CURRENT_SOURCE_DIR}/cmake/tl-optional-no-exception-header.patch
+#             -P ${CMAKE_CURRENT_SOURCE_DIR}/cmake/apply-patch.cmake
+#         SYSTEM
+#     )
+#     set(OPTIONAL_BUILD_TESTS OFF)
+#     set(OPTIONAL_BUILD_PACKAGE OFF)
+#     FetchContent_MakeAvailable(tl_optional)
+#     add_library(tl_optional_hdr INTERFACE)
+#     target_include_directories(tl_optional_hdr
+#         INTERFACE ${tl_optional_SOURCE_DIR}/include)
+#     target_link_libraries(avclan PUBLIC tl_optional_hdr)
+# endif()
@@ -1,6 +1,24 @@
 {
-    "version": 3,
+    "version": 9,
    "configurePresets": [
+        {
+            "name": "debug-base",
+            "hidden": true,
+            "description": "Debug build settings",
+            "generator": "Ninja",
+            "cacheVariables": {
+                "CMAKE_BUILD_TYPE": "Debug"
+            }
+        },
+        {
+            "name": "relwithdebinfo-base",
+            "hidden": true,
+            "description": "RelWithDebInfo build settings",
+            "inherits": "debug-base",
+            "cacheVariables": {
+                "CMAKE_BUILD_TYPE": "RelWithDebInfo"
+            }
+        },
        {
            "name": "usb0",
            "hidden": true,
@@ -22,7 +40,7 @@
            "hidden": true,
            "description": "AVR ATtiny3216 cross-compile toolchain + matching port",
            "toolchainFile": "${sourceDir}/cmake/avr-gcc-toolchain.cmake",
-            "binaryDir": "${sourceDir}/out/build/attiny3216",
+            "binaryDir": "${sourceDir}/out/build/avr-attiny3216",
            "cacheVariables": {
                "AVCLAN_TARGET": "avr-attiny3216",
                "FREQSEL": "20MHz",
@@ -31,31 +49,64 @@
            }
        },
        {
-            "name": "debug-base",
+            "name": "pico2",
            "hidden": true,
-            "description": "Debug build settings",
-            "generator": "Unix Makefiles",
-            "binaryDir": "${sourceDir}/out/build",
+            "binaryDir": "${sourceDir}/out/build/pico2",
+            "inherits": "debug-base",
            "cacheVariables": {
-                "CMAKE_BUILD_TYPE": "Debug"
+                "AVCLAN_TARGET": "pico2",
+                "AVCLAN_FRAME_POOL_N": "14",
+                "AVCLAN_TARGET_SDK_FILE": "${sourceDir}/cmake/pico_sdk_import.cmake",
+                "PICO_SDK_FETCH_FROM_GIT": true
+            },
+            "environment": {
+                "PICO_PLATFORM": "rp2350-arm-s",
+                "PICO_BOARD": "pimoroni_pico_plus2_w_rp2350"
            }
        },
        {
-            "name": "relwithdebinfo-base",
-            "hidden": true,
-            "description": "RelWithDebInfo build settings",
-            "inherits": "debug-base",
-            "cacheVariables": {
-                "CMAKE_BUILD_TYPE": "RelWithDebInfo"
+            "name": "pico2-gcc",
+            "displayName": "Pico 2W (GCC)",
+            "inherits": "pico2",
+            "description": "",
+            "generator": "Ninja",
+            "environment": {
+                "PICO_COMPILER": "pico_arm_gcc"
            }
        },
+        {
+            "name": "pico2-clang",
+            "displayName": "Pico 2W (Clang)",
+            "inherits": "pico2",
+            "description": "",
+            "environment": {
+                "PICO_COMPILER": "pico_arm_clang"
+            }
+        },
+        {
+            "name": "attiny3216-relwithdebinfo",
+            "hidden": true,
+            "description": "ATtiny3216 RelWithDebInfo build,",
+            "inherits": [
+                "avr-attiny3216",
+                "relwithdebinfo-base"
+            ]
+        },
+        {
+            "name": "attiny3216-debug",
+            "hidden": true,
+            "description": "ATtiny3216 Debug build",
+            "inherits": [
+                "avr-attiny3216",
+                "debug-base"
+            ]
+        },
        {
            "name": "attiny3216-relwithdebinfo-usb0",
            "displayName": "ATtiny3216 RelWithDebInfo (ttyUSB0)",
            "description": "ATtiny3216 RelWithDebInfo build, program over /dev/ttyUSB0",
            "inherits": [
-                "avr-attiny3216",
-                "relwithdebinfo-base",
+                "attiny3216-relwithdebinfo",
                "usb0"
            ]
        },
@@ -64,8 +115,25 @@
            "displayName": "ATtiny3216 RelWithDebInfo (ttyUSB1)",
            "description": "ATtiny3216 RelWithDebInfo build, program over /dev/ttyUSB1",
            "inherits": [
-                "avr-attiny3216",
-                "relwithdebinfo-base",
+                "attiny3216-relwithdebinfo",
+                "usb1"
+            ]
+        },
+        {
+            "name": "attiny3216-debug-usb0",
+            "displayName": "ATtiny3216 Debug (ttyUSB0)",
+            "description": "ATtiny3216 Debug build, program over /dev/ttyUSB0",
+            "inherits": [
+                "attiny3216-debug",
+                "usb0"
+            ]
+        },
+        {
+            "name": "attiny3216-debug-usb1",
+            "displayName": "ATtiny3216 Debug (ttyUSB1)",
+            "description": "ATtiny3216 Debug build, program over /dev/ttyUSB1",
+            "inherits": [
+                "attiny3216-debug",
                "usb1"
            ]
        }
@@ -0,0 +1,18 @@
+# Idempotent patch driver for FetchContent PATCH_COMMAND steps.
+#
+# Usage: cmake -DGIT_EXECUTABLE=<git> -DPATCH_FILE=<patch> -P apply-patch.cmake
+# (run with CWD = the populated source directory, as PATCH_COMMAND does).
+#
+# FetchContent re-runs PATCH_COMMAND after its update step on reconfigure, so a
+# bare `git apply` fails the second time around. Skip if the patch is already
+# applied (the reverse-apply dry run succeeds); otherwise apply it for real.
+execute_process(
+    COMMAND "${GIT_EXECUTABLE}" apply --reverse --check --ignore-whitespace
+        "${PATCH_FILE}"
+    RESULT_VARIABLE _already_applied
+    OUTPUT_QUIET ERROR_QUIET)
+if(NOT _already_applied EQUAL 0)
+    execute_process(
+        COMMAND "${GIT_EXECUTABLE}" apply --ignore-whitespace "${PATCH_FILE}"
+        COMMAND_ERROR_IS_FATAL ANY)
+endif()
@@ -13,6 +13,9 @@
 ##########################################################################
 find_program(AVR_CC avr-gcc REQUIRED)
 find_program(AVR_CXX avr-g++ REQUIRED)
+# Section-size reporter; consumed by an optional POST_BUILD in the top-level
+# CMakeLists (left unset -> no size report) so the top level stays HW-agnostic.
+find_program(CMAKE_SIZE avr-size)

 set(CMAKE_SYSTEM_NAME Generic)
 set(CMAKE_SYSTEM_PROCESSOR avr)
@@ -0,0 +1,121 @@
+# This is a copy of <PICO_SDK_PATH>/external/pico_sdk_import.cmake
+
+# This can be dropped into an external project to help locate this SDK
+# It should be include()ed prior to project()
+
+# Copyright 2020 (c) 2020 Raspberry Pi (Trading) Ltd.
+#
+# Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
+# following conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following
+# disclaimer.
+#
+# 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following
+# disclaimer in the documentation and/or other materials provided with the distribution.
+#
+# 3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products
+# derived from this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+# INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+# WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+if (DEFINED ENV{PICO_SDK_PATH} AND (NOT PICO_SDK_PATH))
+    set(PICO_SDK_PATH $ENV{PICO_SDK_PATH})
+    message("Using PICO_SDK_PATH from environment ('${PICO_SDK_PATH}')")
+endif ()
+
+if (DEFINED ENV{PICO_SDK_FETCH_FROM_GIT} AND (NOT PICO_SDK_FETCH_FROM_GIT))
+    set(PICO_SDK_FETCH_FROM_GIT $ENV{PICO_SDK_FETCH_FROM_GIT})
+    message("Using PICO_SDK_FETCH_FROM_GIT from environment ('${PICO_SDK_FETCH_FROM_GIT}')")
+endif ()
+
+if (DEFINED ENV{PICO_SDK_FETCH_FROM_GIT_PATH} AND (NOT PICO_SDK_FETCH_FROM_GIT_PATH))
+    set(PICO_SDK_FETCH_FROM_GIT_PATH $ENV{PICO_SDK_FETCH_FROM_GIT_PATH})
+    message("Using PICO_SDK_FETCH_FROM_GIT_PATH from environment ('${PICO_SDK_FETCH_FROM_GIT_PATH}')")
+endif ()
+
+if (DEFINED ENV{PICO_SDK_FETCH_FROM_GIT_TAG} AND (NOT PICO_SDK_FETCH_FROM_GIT_TAG))
+    set(PICO_SDK_FETCH_FROM_GIT_TAG $ENV{PICO_SDK_FETCH_FROM_GIT_TAG})
+    message("Using PICO_SDK_FETCH_FROM_GIT_TAG from environment ('${PICO_SDK_FETCH_FROM_GIT_TAG}')")
+endif ()
+
+if (PICO_SDK_FETCH_FROM_GIT AND NOT PICO_SDK_FETCH_FROM_GIT_TAG)
+  set(PICO_SDK_FETCH_FROM_GIT_TAG "master")
+  message("Using master as default value for PICO_SDK_FETCH_FROM_GIT_TAG")
+endif()
+
+set(PICO_SDK_PATH "${PICO_SDK_PATH}" CACHE PATH "Path to the Raspberry Pi Pico SDK")
+set(PICO_SDK_FETCH_FROM_GIT "${PICO_SDK_FETCH_FROM_GIT}" CACHE BOOL "Set to ON to fetch copy of SDK from git if not otherwise locatable")
+set(PICO_SDK_FETCH_FROM_GIT_PATH "${PICO_SDK_FETCH_FROM_GIT_PATH}" CACHE FILEPATH "location to download SDK")
+set(PICO_SDK_FETCH_FROM_GIT_TAG "${PICO_SDK_FETCH_FROM_GIT_TAG}" CACHE FILEPATH "release tag for SDK")
+
+if (NOT PICO_SDK_PATH)
+    if (PICO_SDK_FETCH_FROM_GIT)
+        include(FetchContent)
+        set(FETCHCONTENT_BASE_DIR_SAVE ${FETCHCONTENT_BASE_DIR})
+        if (PICO_SDK_FETCH_FROM_GIT_PATH)
+            get_filename_component(FETCHCONTENT_BASE_DIR "${PICO_SDK_FETCH_FROM_GIT_PATH}" REALPATH BASE_DIR "${CMAKE_SOURCE_DIR}")
+        endif ()
+        FetchContent_Declare(
+                pico_sdk
+                GIT_REPOSITORY https://github.com/raspberrypi/pico-sdk
+                GIT_TAG ${PICO_SDK_FETCH_FROM_GIT_TAG}
+        )
+
+        if (NOT pico_sdk)
+            message("Downloading Raspberry Pi Pico SDK")
+            # GIT_SUBMODULES_RECURSE was added in 3.17
+            if (${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.17.0")
+                FetchContent_Populate(
+                        pico_sdk
+                        QUIET
+                        GIT_REPOSITORY https://github.com/raspberrypi/pico-sdk
+                        GIT_TAG ${PICO_SDK_FETCH_FROM_GIT_TAG}
+                        GIT_SUBMODULES_RECURSE FALSE
+
+                        SOURCE_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-src
+                        BINARY_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-build
+                        SUBBUILD_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-subbuild
+                )
+            else ()
+                FetchContent_Populate(
+                        pico_sdk
+                        QUIET
+                        GIT_REPOSITORY https://github.com/raspberrypi/pico-sdk
+                        GIT_TAG ${PICO_SDK_FETCH_FROM_GIT_TAG}
+
+                        SOURCE_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-src
+                        BINARY_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-build
+                        SUBBUILD_DIR ${FETCHCONTENT_BASE_DIR}/pico_sdk-subbuild
+                )
+            endif ()
+
+            set(PICO_SDK_PATH ${pico_sdk_SOURCE_DIR})
+        endif ()
+        set(FETCHCONTENT_BASE_DIR ${FETCHCONTENT_BASE_DIR_SAVE})
+    else ()
+        message(FATAL_ERROR
+                "SDK location was not specified. Please set PICO_SDK_PATH or set PICO_SDK_FETCH_FROM_GIT to on to fetch from git."
+                )
+    endif ()
+endif ()
+
+get_filename_component(PICO_SDK_PATH "${PICO_SDK_PATH}" REALPATH BASE_DIR "${CMAKE_BINARY_DIR}")
+if (NOT EXISTS ${PICO_SDK_PATH})
+    message(FATAL_ERROR "Directory '${PICO_SDK_PATH}' not found")
+endif ()
+
+set(PICO_SDK_INIT_CMAKE_FILE ${PICO_SDK_PATH}/pico_sdk_init.cmake)
+if (NOT EXISTS ${PICO_SDK_INIT_CMAKE_FILE})
+    message(FATAL_ERROR "Directory '${PICO_SDK_PATH}' does not appear to contain the Raspberry Pi Pico SDK")
+endif ()
+
+set(PICO_SDK_PATH ${PICO_SDK_PATH} CACHE PATH "Path to the Raspberry Pi Pico SDK" FORCE)
+
+include(${PICO_SDK_INIT_CMAKE_FILE})
@@ -0,0 +1,36 @@
+diff --git a/include/tl/expected.hpp b/include/tl/expected.hpp
+index 59e59aa..75857bd 100644
+--- a/include/tl/expected.hpp
+++ b/include/tl/expected.hpp
+@@ -20,7 +20,7 @@
+ #define TL_EXPECTED_VERSION_MINOR 3
+ #define TL_EXPECTED_VERSION_PATCH 1
+ 
+-#include <exception>
+#include <cstdlib>
+ #include <functional>
+ #include <type_traits>
+ #include <utility>
+@@ -222,7 +222,7 @@ static constexpr unexpect_t unexpect{};
+ #ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
+ #define TL_EXPECTED_THROW_EXCEPTION(e) throw((e));
+ #else
+-#define TL_EXPECTED_THROW_EXCEPTION(e) std::terminate();
+#define TL_EXPECTED_THROW_EXCEPTION(e) std::abort();
+ #endif
+ 
+ namespace detail {
+@@ -1249,11 +1249,11 @@ template <class T, class E> struct expected_default_ctor_base<T, E, false> {
+ };
+ } // namespace detail
+ 
+-template <class E> class bad_expected_access : public std::exception {
+template <class E> class bad_expected_access {
+ public:
+   explicit bad_expected_access(E e) : m_val(std::move(e)) {}
+ 
+-  virtual const char *what() const noexcept override {
+  virtual const char *what() const noexcept {
+     return "Bad expected access";
+   }
+ 
@@ -0,0 +1,21 @@
+diff --git a/include/tl/optional.hpp b/include/tl/optional.hpp
+index e9c59c2..1ff3d4a 100644
+--- a/include/tl/optional.hpp
+++ b/include/tl/optional.hpp
+@@ -21,7 +21,6 @@
+ #define TL_OPTIONAL_VERSION_MINOR 1
+ #define TL_OPTIONAL_VERSION_PATCH 0
+ 
+-#include <exception>
+ #include <functional>
+ #include <new>
+ #include <type_traits>
+@@ -664,7 +663,7 @@ struct nullopt_t {
+ static constexpr nullopt_t nullopt{nullopt_t::do_not_use{},
+                                    nullopt_t::do_not_use{}};
+ 
+-class bad_optional_access : public std::exception {
+class bad_optional_access {
+ public:
+   bad_optional_access() = default;
+   const char *what() const noexcept { return "Optional has no value"; }
@@ -1,2 +1,2 @@
-sudo apk add make cmake avrdude avr-libc gcc-avr tshark
+sudo apk add make cmake avrdude avr-libc gcc-avr tshark clang-extra-tools

@@ -203,14 +203,16 @@ local function bcd2dec(b)
 end

 -- Format a BCD-encoded mm:ss pair, falling back to raw hex when a byte isn't
-- valid BCD (e.g. a 0xff sentinel for "time unknown").
-local function bcd_time(min_b, sec_b)
+-- valid BCD (e.g. a 0xff sentinel for "time unknown"). `negative` (the CD
+-- NEGATIVE flag) only controls the sign, so it applies to the raw fallback too.
+local function bcd_time(min_b, sec_b, negative)
+    local sign = negative and "-" or ""
    local m = bcd2dec(min_b)
    local s = bcd2dec(sec_b)
    if m == nil or s == nil then
-        return string.format("%02x:%02x (raw)", min_b, sec_b)
+        return string.format("%s%02x:%02x (raw)", sign, min_b, sec_b)
    end
-    return string.format("%02d:%02d", m, s)
+    return string.format("%s%02d:%02d", sign, m, s)
 end

 local known_devices = {
@@ -478,6 +480,15 @@ local f_cd_flag_repeat = ProtoField.bool("avclan.cd.flags.repeat", "REPEAT", 8,
 local f_cd_flag_disk_scan = ProtoField.bool("avclan.cd.flags.disk_scan", "DISK_SCAN", 8, nil, 0x20)
 local f_cd_flag_scan = ProtoField.bool("avclan.cd.flags.scan", "SCAN", 8, nil, 0x40)

+-- Second CD flags byte (last byte of the playback status frame). Resting value
+-- is 0x80; 0x40 (NEGATIVE) makes the reported play time count below zero, as
+-- seen when rewinding past the start of a track: ..., 00:01, 00:00, then the
+-- byte flips to 0xc0 and the time climbs again as -00:01, -00:02, ...
+-- [msgdumps/rewind-negative.txt].
+local f_cd_flags2 = ProtoField.uint8("avclan.cd.flags2", "CD player flags (byte 2)")
+local f_cd_flag_negative = ProtoField.bool("avclan.cd.flags2.negative", "NEGATIVE", 8, nil, 0x40)
+local f_cd_flag2_unknown7 = ProtoField.bool("avclan.cd.flags2.unknown7", "UNKNOWN7", 8, nil, 0x80)
+
 local f_tape_present = ProtoField.uint8("avclan.tape.present", "Tape deck slot", base.HEX, {[0x01] = "FILLED", [0x00] = "EMPTY"})
 local f_tape_state = ProtoField.uint8("avclan.tape.state", "Tape deck state")
 local f_tape_seeking_rev = ProtoField.bool("avclan.tape.state.seeking_rev", "SEEKING_REVERSE", 8, nil, 0x01)
@@ -553,6 +564,9 @@ avclanproto.fields = {
    f_cd_flag_repeat,
    f_cd_flag_disk_scan,
    f_cd_flag_scan,
+    f_cd_flags2,
+    f_cd_flag_negative,
+    f_cd_flag2_unknown7,
    f_tape_present,
    f_tape_state,
    f_tape_seeking_rev,
@@ -809,7 +823,7 @@ end
 local function decode_cd(subtree, buffer, offset, action)
    if action == known_actions_names["PLAYBACK_STATUS"] or
        action == known_actions_names["PLAYBACK_RESP"] then
-        local cdtree = subtree:add(avclanproto, buffer(offset,9), "Device: CD player")
+        local cdtree = subtree:add(avclanproto, buffer(offset,-1), "Device: CD player")
        local cd_slots = cdtree:add(f_cd_slots, buffer(offset+3,1))
        cd_slots:add(f_cd_slot1, buffer(offset+3,1))
        cd_slots:add(f_cd_slot2, buffer(offset+3,1))
@@ -825,6 +839,12 @@ local function decode_cd(subtree, buffer, offset, action)
        cd_state:add(f_cd_playback, buffer(offset+4,1))
        cd_state:add(f_cd_seeking_track, buffer(offset+4,1))
        cd_state:add(f_cd_loading, buffer(offset+4,1))
+        -- The sign of the play time lives in the trailing flags byte, so read it
+        -- before formatting the time (older/shorter reports may omit it).
+        local negative = false
+        if buffer:len() > offset+10 then
+            negative = bit.band(buffer(offset+10,1):uint(), 0x40) ~= 0
+        end
        local cd_status = cdtree:add(avclanproto, buffer(offset+5,-1), "")
        cd_status:add(f_cd_disc, buffer(offset+5,1))
        cd_status:add(f_cd_track, buffer(offset+6,1))
@@ -832,7 +852,7 @@ local function decode_cd(subtree, buffer, offset, action)
        cd_status:add(f_cd_sec, buffer(offset+8,1))
        cd_status:append_text("Disc " .. field_cd_disc().value .. ", ")
        cd_status:append_text("track " .. tostring(buffer(offset+6,1)):gsub("(.)(.)", "%1%2") .. ", ")
-        cd_status:append_text("time " .. bcd_time(buffer(offset+7,1):uint(), buffer(offset+8,1):uint()))
+        cd_status:append_text("time " .. bcd_time(buffer(offset+7,1):uint(), buffer(offset+8,1):uint(), negative))
        local cd_flags = cdtree:add(f_cd_flags, buffer(offset+9,1))
        cd_flags:add(f_cd_flag_disk_random, buffer(offset+9,1))
        cd_flags:add(f_cd_flag_random, buffer(offset+9,1))
@@ -840,6 +860,14 @@ local function decode_cd(subtree, buffer, offset, action)
        cd_flags:add(f_cd_flag_repeat, buffer(offset+9,1))
        cd_flags:add(f_cd_flag_disk_scan, buffer(offset+9,1))
        cd_flags:add(f_cd_flag_scan, buffer(offset+9,1))
+        if buffer:len() > offset+10 then
+            local cd_flags2 = cdtree:add(f_cd_flags2, buffer(offset+10,1))
+            cd_flags2:add(f_cd_flag_negative, buffer(offset+10,1))
+            cd_flags2:add(f_cd_flag2_unknown7, buffer(offset+10,1))
+            if negative then
+                cd_flags2:append_text(" (play time is negative)")
+            end
+        end
    elseif action == known_actions_names["LOADING_STATUS"] or
        action == known_actions_names["LOADING_RESP"] then
        local cdtree = subtree:add(avclanproto, buffer(offset,9), "Device: CD player")
@@ -49,6 +49,7 @@ still bypasses it.
 import argparse
 import os
 import re
+import subprocess
 import sys

 # ---- locations -------------------------------------------------------------
@@ -227,10 +228,16 @@ def find_address_spec(root):


 def iter_src_files(root):
-    for dirpath, _dirs, files in os.walk(os.path.join(root, SRC_REL)):
-        for fn in sorted(files):
-            if fn.endswith(SRC_EXTS):
-                yield os.path.join(dirpath, fn)
+    """List source files under src/, via `git ls-files` so paths excluded by
+    .gitignore (e.g. the ESP32 port's CMake build directory, which vendors
+    FetchContent'd third-party code) are never walked into."""
+    out = subprocess.run(
+        ["git", "-C", root, "ls-files", "-z", "--cached", "--others",
+         "--exclude-standard", "--", SRC_REL],
+        capture_output=True, check=True, text=True,
+    ).stdout
+    paths = sorted(p for p in out.split("\0") if p.endswith(SRC_EXTS))
+    return [os.path.join(root, p) for p in paths]

 # ---- lint ------------------------------------------------------------------

@@ -471,8 +478,6 @@ def main():
    lua_path = os.path.join(root, LUA_REL)
    lua_lines = read_lines(lua_path)
    specs, have_address = build_specs(root)
-    if not have_address:
-        print("note: no Address enum found in src/ -- addresses not synced")

    # ---- lint (all modes) ----
    lint_failed = False
@@ -487,6 +492,8 @@ def main():
            print_lint(spec, LUA_REL, problems)

    if args.lint:
+        if not have_address:
+            print("note: no Address enum found in src/ -- addresses not synced")
        if lint_failed:
            print("lint: FAILED")
            return 1
@@ -503,6 +510,8 @@ def main():
    has_drift = any(not d.clean() for _s, _e, d in drifts)

    if args.fix:
+        if not have_address:
+            print("note: no Address enum found in src/ -- addresses not synced")
        if lint_failed:
            print("fix aborted: resolve the dissector name problems above first")
            return 1
@@ -525,16 +534,17 @@ def main():
        print("fix: applied" if has_drift else "fix: already in sync")
        return 0

-    # ---- default: report ----
+    # ---- default: report (silent on success -- this is the pre-commit hook) ----
+    if not (lint_failed or has_drift):
+        return 0
+    if not have_address:
+        print("note: no Address enum found in src/ -- addresses not synced")
    for spec, _entries, drift in drifts:
        if not drift.clean():
            print("%s drift:" % spec["name"])
            print_drift(drift)
-    if lint_failed or has_drift:
-        print("out of sync -- run: scripts/sync_avclan_enums.py --fix")
-        return 1
-    print("enums in sync with the dissector")
-    return 0
+    print("out of sync -- run: scripts/sync_avclan_enums.py --fix")
+    return 1


 if __name__ == "__main__":
@@ -121,6 +121,12 @@ enum AVCLAN_ENUM_CLASS MediaAction : uint8_t {
 };

 #ifdef __cplusplus
+enum class Device : uint8_t;
+
+// Sentinel for a frame with no owning device.
+// Compile-time collision check lives in device.hpp
+inline constexpr Device NoDevice = Device{0xFF};
+
 namespace detail {
 struct Error {
 #endif
@@ -137,9 +143,12 @@ struct Error {
    BAD_CONTROLLER_PARITY,
    BAD_CONTROL_PARITY,
    BAD_PARITY, // generic bad parity has max severity
-    STARTBIT_TOO_SHORT,
+    STARTBIT_MISSED,
+    STARTBIT_MALFORMED,
    STARTBIT_TOO_LONG,
    BAD_STARTBIT,
+    NO_FRAME,
+    POOL_EMPTY, // non-bus error
  };

  enum AVCLAN_ENUM_CLASS Send : uint8_t {
@@ -147,7 +156,10 @@ struct Error {
    NAK_MESSAGE_LENGTH,
    NAK_CONTROL,
    NAK_ADDRESS,
+    NAK_TOO_LONG,
    NAK, // generic NAK has max severity
+    CONTENDED_BUS,
+    LOST_ARBITRATION,
    BUSY,
    MUTED,
  };
@@ -160,13 +172,13 @@ struct Error {

 #ifdef __cplusplus
 };
-#endif

-enum AVCLAN_ENUM_CLASS Bit : uint8_t {
-  bit_zero = 0x00,
-  bit_one = 0x01,
-  bit_start = 0x10
+struct SendError {
+  Device owning_device;
+  uint8_t reaction;
+  Error::Send err;
 };
+#endif

 #ifdef __cplusplus
 } // namespace detail
@@ -26,30 +26,31 @@
       | 1 │ *Acknowledge*
       *repeat `n` times*

-  No acknowledge bits are sent for broadcast frames.
+  For broadcast frames the acknowledge (one) bit is sent, but an ACK response
+  (zero) is not expected.
 */

-#include <concepts>
+#include <cstdint>
 #include <cstdio>
+#include <memory>
+
+#include "FreeRTOS.h" // IWYU pragma: export

 #include "avclan.h"
 #include "bus.hpp"
 #include "frame.hpp"
 #include "hal/phy.h"
+#include "stdshim.hpp"

 namespace {
 using Read = avclan::detail::Error::Read;
 using Send = avclan::detail::Error::Send;
-using Bit = avclan::detail::Bit;

-struct trailer_bits_t {};
-struct no_parity_t : trailer_bits_t {};   // raw bits (the broadcast bit)
-struct with_parity_t : trailer_bits_t {}; // bits + parity (controller address)
-struct with_ack_t : trailer_bits_t {
-}; // bits + parity + ACK slot (all other fields)
-inline constexpr no_parity_t no_parity{};
-inline constexpr with_parity_t with_parity{};
-inline constexpr with_ack_t with_ack{};
+// The bus spec has a unit that loses arbitration retry rather than fail: "if
+// the unit loses in arbitration, the frame is automatically reset up twice
+// (three times in total)". Only an attempt that is outbid every time is an
+// error worth reporting.
+constexpr uint8_t SEND_ATTEMPTS = 3;
 } // namespace

 namespace avclan {
@@ -68,217 +69,142 @@ public:
  Handle(const Handle &) = delete;
  Handle(Handle &&) = delete;

-  // NOLINTNEXTLINE(readability-convert-member-functions-to-static)
-  Send sendstartbit() { return phy_send_startbit(); };
-  // NOLINTNEXTLINE(readability-convert-member-functions-to-static)
-  Read readstartbit() { return phy_read_startbit(); };
-
-  template <auto N, std::unsigned_integral T,
-            std::derived_from<trailer_bits_t> Trailer>
-    requires(sizeof(T) < 3 && N < 16 && !std::same_as<Trailer, with_ack_t>)
-  Send send(T bits, Trailer /*tag*/) {
-    const Bit parity = sendbits<N>(bits);
-
-    if constexpr (std::is_same_v<Trailer, with_parity_t>)
-      sendbits<1>(to_underlying(parity));
-
-    return Send{0};
+  // Forward to phy API (organized so that hal/phy.h isn't public/visible at the
+  // C++/library level)
+  // NOLINTBEGIN(readability-convert-member-functions-to-static)
+  Read read_header(bool *is_unicast) { return phy_read_header(is_unicast); };
+  Read read_controller_addr(uint16_t *addr) {
+    return phy_read_controller_addr(addr);
+  };
+  Read read_peripheral_addr(uint16_t *addr) {
+    return phy_read_peripheral_addr(addr);
+  };
+  Read read_control(uint8_t *control) { return phy_read_control(control); };
+  Read read_length(uint8_t *length) { return phy_read_length(length); };
+  Read read_data(uint8_t *data, uint8_t length, uint8_t *data_index) {
+    return phy_read_data(data, length, data_index);
  };

-  template <auto N, std::unsigned_integral T>
-    requires(sizeof(T) < 3 && N < 16)
-  Send send(T bits, with_ack_t /*tag*/, bool expect_ack) {
-    send<N>(bits, with_parity);
-
-    if (expect_ack)
-      return read_ACK();
-
-    sendbits<1>(1U); // still need to fill the ack bit slot
-    return Send{0};
+  Send send_header(bool is_unicast) { return phy_send_header(is_unicast); };
+  Send send_controller_addr(uint16_t addr) {
+    return phy_send_controller_addr(addr);
  };
-
-  template <auto N, std::unsigned_integral T,
-            std::derived_from<trailer_bits_t> Trailer>
-    requires(sizeof(T) < 3 && N < 16 && !std::same_as<Trailer, with_ack_t>)
-  Read read(T *bits, Trailer /*tag*/) {
-    const Bit calc_parity = readbits<N>(bits);
-    if constexpr (std::is_same_v<Trailer, with_parity_t>) {
-      uint8_t read_parity;
-      readbits<1>(&read_parity);
-      if (to_underlying(calc_parity) != read_parity)
-        return Read::BAD_PARITY;
-    }
-    return Read{0};
+  Send send_peripheral_addr(uint16_t addr, bool expect_ack) {
+    return phy_send_peripheral_addr(addr, expect_ack);
  };
-
-  template <auto N, std::unsigned_integral T, class F>
-    requires(sizeof(T) < 3 && N < 16)
-  Read read(T *bits, with_ack_t /*tag*/, F &&ack) {
-    if (read<N>(bits, with_parity) == Read::BAD_PARITY)
-      return Read::BAD_PARITY;
-
-    if (ack()) {
-      send_ACK();
-    } else {
-      uint8_t slot;
-      readbits<1>(&slot);
-    }
-
-    return Read{0};
+  Send send_control(uint8_t control, bool expect_ack) {
+    return phy_send_control(control, expect_ack);
  };
-  template <auto N, std::unsigned_integral T>
-    requires(sizeof(T) < 3 && N < 16)
-  Read read(T *bits, with_ack_t /*tag*/, bool ack) {
-    return read<N>(bits, with_ack, [=]() { return ack; });
-  }
-
-private:
-  static void send_ACK() { phy_send_ack(); };
-  static Send read_ACK() { return phy_read_ack(); };
-
-  template <auto N, class T> Bit sendbits(T bits);
-  template <auto N, class T> Bit readbits(T *bits);
-
-  template <auto N>
-    requires(N > 1 && N < 8)
-  Bit sendbits(uint8_t bits) {
-    return phy_send_bits_u8(&bits, N);
+  Send send_length(uint8_t length, bool expect_ack) {
+    return phy_send_length(length, expect_ack);
  };
-  template <auto N>
-    requires(N <= 16)
-  Bit sendbits(uint16_t bits) {
-    return phy_send_bits_u16(&bits, N);
-  };
-  template <auto N>
-    requires(N < 8)
-  Bit readbits(uint8_t *bits) {
-    return static_cast<Bit>(phy_read_bits_u8(bits, N));
-  };
-  template <auto N>
-    requires(N <= 16)
-  Bit readbits(uint16_t *bits) {
-    return static_cast<Bit>(phy_read_bits_u16(bits, N));
+  Send send_data(const uint8_t *data, uint8_t length, bool expect_ack,
+                 uint8_t *data_index) {
+    return phy_send_data(data, length, expect_ack, data_index);
  };
+  // NOLINTEND(readability-convert-member-functions-to-static)
 };

-template <> inline Bit Bus::Handle::sendbits<8>(uint8_t bits) {
-  return phy_send_byte(&bits);
-};
-template <> inline Bit Bus::Handle::sendbits<1>(uint8_t bits) {
-  const Bit bit{static_cast<Bit>(bits & 1U)};
-  phy_send_bit(bit);
-  return bit;
-};
-template <> inline Bit Bus::Handle::readbits<8>(uint8_t *bits) {
-  return phy_read_byte(bits);
-};
-
-void Bus::init() {
+void Bus::init(uint16_t address) {
  // Idempotent: the single Bus is shared by reference, so every Peripheral's
  // ctor calls init() on it — but the hardware must be brought up exactly once
  // (phy_init is not assumed re-entrant/idempotent).
  if (inited_)
    return;
-  phy_init();
+  phy_init(address);
  muted_ = false; // phy_init leaves the bus TX unmuted
  inited_ = true;
 };

-// NOLINTNEXTLINE(readability-convert-member-functions-to-static)
-bool Bus::is_active() const { return phy_active(); };
 void Bus::mute(bool mute) {
  phy_mute(mute);
  muted_ = mute; // Only update muted_ *AFTER* hardware has finished muting
 };
+// NOLINTNEXTLINE(readability-convert-member-functions-to-static)
+void Bus::deafen(bool deaf) { phy_deafen(deaf); }

-auto Bus::read(uint16_t address, Frame *in, Frame::Print print) -> Read {
+auto Bus::read(Frame::Print print)
+    -> expected<std::unique_ptr<Frame>, Error::Read> {
  struct errtype {
-    Read errno;
+    Read type;
    uint16_t val;
  } err = {};

  using enum Read;

+  std::unique_ptr<Frame> in = Frame::acquire();
+  if (!in) {
+    err.type = POOL_EMPTY;
+    goto handle_err;
+  }
+
+  phy_wait_frame(portMAX_DELAY);
+
  { // bound handle lifetime
    auto handle = get();

-    bool shouldACK = false;
-    uint8_t tmp = 0;
-
-    err.errno = handle.readstartbit();
-    if (err.errno != Read{0})
+    err.type = handle.read_header(&in->is_unicast);
+    if (err.type != Read{0})
      goto handle_err;

-    handle.read<1>(&tmp, no_parity);
-    in->is_unicast = (tmp != 0U);
-
-    if (auto rerr = handle.read<12>(&in->controller_addr, with_parity);
-        rerr == BAD_PARITY) {
-      err.errno = BAD_CONTROLLER_PARITY;
+    err.type = handle.read_controller_addr(&in->controller_addr);
+    if (err.type != Read{0}) {
      if (print.verbose)
        err.val = in->controller_addr;

      goto handle_err;
    }

-    // Using lambda for delayed evaluation of peripheral_addr field
-    // deref, which will be written by the time the lambda is evaluated
-    auto should_ack_lambda = [&]() {
-      shouldACK = !is_muted() && (in->peripheral_addr == address);
-      return shouldACK;
-    };
-    if (auto rerr =
-            handle.read<12>(&in->peripheral_addr, with_ack, should_ack_lambda);
-        rerr == BAD_PARITY) {
-      err.errno = BAD_PERIPHERAL_PARITY;
+    err.type = handle.read_peripheral_addr(&in->peripheral_addr);
+    if (err.type != Read{0}) {
      if (print.verbose)
        err.val = in->peripheral_addr;

      goto handle_err;
    }

-    if (auto rerr = handle.read<4>(&in->control, with_ack, shouldACK);
-        rerr == BAD_PARITY) {
-      err.errno = BAD_CONTROL_PARITY;
+    err.type = handle.read_control(&in->control);
+    if (err.type != Read{0}) {
      if (print.verbose)
        err.val = in->control;

      goto handle_err;
    }

-    if (auto rerr = handle.read<8>(&in->length, with_ack, shouldACK);
-        rerr == BAD_PARITY) {
-      err.errno = BAD_LENGTH_PARITY;
+    err.type = handle.read_length(&in->length);
+    if (err.type != Read{0}) {
      if (print.verbose)
        err.val = in->length;

      goto handle_err;
-    }
-
-    if (in->length == 0 || in->length > Frame::MAXLENGTH) {
-      err.errno = BAD_LENGTH_RANGE;
+    } else if (in->length == 0 || in->length > Frame::MAXLENGTH) {
+      err.type = BAD_LENGTH_RANGE;
      err.val = in->length;
      goto handle_err;
    }

-    for (uint8_t i = 0; i < in->length; i++) {
-      if (auto rerr = handle.read<8>(&in->data[i], with_ack, shouldACK);
-          rerr == BAD_PARITY) {
-        err.errno = BAD_DATA_PARITY;
-        if (print.verbose)
-          err.val = in->data[i];
+    uint8_t data_i = 0;
+    err.type = handle.read_data(in->data, in->length, &data_i);
+    if (err.type != Read{0}) {
+      if (print.verbose)
+        err.val = in->data[data_i];

-        goto handle_err;
-      }
+      goto handle_err;
    }
  } // destroy handle

  if (false) { // NOLINT(readability-simplify-boolean-expr)
  handle_err:;
+    if (err.type == NO_FRAME)
+      return unexpected{NO_FRAME};
    fputs("ERR(read): ", stdout);
-    switch (err.errno) {
+    switch (err.type) {
+      case POOL_EMPTY: puts("failed Frame alloc"); break;
      case BAD_STARTBIT: fputs("bad start bit (other)", stdout); break;
-      case STARTBIT_TOO_SHORT: fputs("bad start bit (short)", stdout); break;
+      case STARTBIT_MISSED: fputs("missed start bit", stdout); break;
+      case STARTBIT_MALFORMED:
+        fputs("malformed start bit (external cause)", stdout);
+        break;
      case STARTBIT_TOO_LONG: fputs("bad start bit (long)", stdout); break;
      case BAD_CONTROLLER_PARITY:
        fputs("reading controller addr.", stdout);
@@ -288,109 +214,120 @@ auto Bus::read(uint16_t address, Frame *in, Frame::Print print) -> Read {
        goto VERBOSE;
      case BAD_CONTROL_PARITY: fputs("reading control", stdout); goto VERBOSE;
      case BAD_LENGTH_PARITY: fputs("reading length", stdout); goto VERBOSE;
-      case BAD_LENGTH_RANGE: printf("bad length 0x%02X", err.val); break;
+      case BAD_LENGTH_RANGE: printf("bad length 0x%02X:", err.val); break;
      case BAD_DATA_PARITY: fputs("reading data", stdout); goto VERBOSE;
+      case NO_FRAME:
      case BAD_PARITY:
        __builtin_unreachable();
      VERBOSE:
        if (print.verbose) {
-          printf("; read 0x%02X", err.val);
+          printf("; read 0x%02X:", err.val);
        }
    }
    putchar('\n');
  }

  // Only print if some data has been correctly received
-  if (print.print && (err.errno < STARTBIT_TOO_SHORT)) {
-    if (err.errno > BAD_DATA_PARITY)
+  if (print.print && (err.type < STARTBIT_MISSED)) {
+    if (err.type > BAD_DATA_PARITY)
      in->length = 0;
    in->print(print);
  }

-  return err.errno;
+  if (err.type != Read{0})
+    return unexpected(err.type);
+
+  return in;
 }

-auto Bus::send(const Frame *out, Frame::Print print) -> Send {
+auto Bus::send(const Frame &out, Frame::Print print) -> Send {
  struct errtype {
    // Error enum is ordered such that a lower numeric value corresponds to
    // more success
-    Send errno;
+    Send type;
    uint8_t val;
  } err = {};

  using enum Send;

  if (is_muted()) {
-    err.errno = MUTED;
+    err.type = MUTED;
    goto handle_err;
  }

-  { // bound handle lifetime
-    auto handle = get();
+  for (uint8_t attempt = 0; attempt < SEND_ATTEMPTS; attempt++) {
+    auto handle = get(); // bound handle lifetime

-    if (handle.sendstartbit() == BUSY) {
-      // Some other device is already driving the bus
-      err.errno = BUSY;
+    err.type = Send{0};
+
+    err.type = handle.send_header(out.is_unicast);
+    if (err.type != Send{0}) // BUSY or LOST_ARBITRATION (broadcast)
+      continue;
+
+    err.type = handle.send_controller_addr(out.controller_addr);
+    if (err.type != Send{0}) // LOST_ARBITRATION: other device has lower address
+      continue;
+
+    err.type = handle.send_peripheral_addr(out.peripheral_addr, out.is_unicast);
+    if (err.type != Send{0})
+      goto handle_err;
+
+    err.type = handle.send_control(out.control, out.is_unicast);
+    if (err.type != Send{0})
+      goto handle_err;
+
+    err.type = handle.send_length(out.length, out.is_unicast);
+    if (err.type != Send{0})
+      goto handle_err;
+
+    err.type = handle.send_data(out.data, out.length, out.is_unicast, &err.val);
+    if (err.type != Send{0})
+      goto handle_err;
+
+    // A phy that only queued the fields above settles them here
+    uint8_t data_i = 0;
+    err.type = phy_send_done(&data_i);
+    if (err.type == BUSY || err.type == LOST_ARBITRATION) // Queued header
+      continue;
+    if (err.type != Send{0}) {
+      err.val = data_i;
      goto handle_err;
    }

-    handle.send<1>(static_cast<uint8_t>(out->is_unicast), no_parity);
+    break; // Sent
+  }

-    handle.send<12>(out->controller_addr, with_parity);
-
-    if (auto serr =
-            handle.send<12>(out->peripheral_addr, with_ack, out->is_unicast);
-        serr == NAK) {
-      err.errno = NAK_ADDRESS;
-      goto handle_err;
-    }
-
-    if (auto serr = handle.send<4>(out->control, with_ack, out->is_unicast);
-        serr == NAK) {
-      err.errno = NAK_CONTROL;
-      goto handle_err;
-    }
-
-    if (auto serr = handle.send<8>(out->length, with_ack, out->is_unicast);
-        serr == NAK) {
-      err.errno = NAK_MESSAGE_LENGTH;
-      goto handle_err;
-    }
-
-    for (uint8_t i = 0; i < out->length; i++) {
-      // Based on the µPD6708 datasheet, ACK bit for broadcast doesn't seem
-      // necessary (i.e. This deviates from the previous broadcast specific
-      // function that sent an extra `1` bit after each byte/parity)
-      // Explanation for why audio-group broadcast state report isn't working?
-      if (auto serr = handle.send<8>(out->data[i], with_ack, out->is_unicast);
-          serr == NAK) {
-        err.errno = NAK_DATA;
-        err.val = i;
-        goto handle_err;
-      }
-    }
-  } // destroy handle
+  if (err.type != Send{0})
+    goto handle_err; // Outbid (or busy) on every attempt

  // back to read mode
  if (false) { // NOLINT(readability-simplify-boolean-expr)
  handle_err:;
    fputs("Error", stdout);
-    switch (err.errno) {
+    switch (err.type) {
      case MUTED: fputs(": Device muted", stdout); break;
      case BUSY: fputs(": Busy bus", stdout); break;
+      case CONTENDED_BUS:
+        fputs(": bus contended after arbitration", stdout);
+        break;
+      case LOST_ARBITRATION: fputs(": lost arbitration", stdout); break;
      case NAK_ADDRESS:
      case NAK_CONTROL:
      case NAK_MESSAGE_LENGTH:
      case NAK_DATA:
+      case NAK_TOO_LONG:
      case NAK:
        fputs(" NAK: ", stdout);
-        switch (err.errno) {
+        switch (err.type) {
          case NAK_ADDRESS: fputs("address", stdout); break;
          case NAK_CONTROL: fputs("Control", stdout); break;
          case NAK_MESSAGE_LENGTH: fputs("Message length", stdout); break;
          case NAK_DATA: printf(" data[%u]", err.val); break;
+          case NAK_TOO_LONG: fputs("too long", stdout); break;
          case NAK:
          case MUTED:
+          case CONTENDED_BUS:
+          case LOST_ARBITRATION:
          case BUSY: __builtin_unreachable();
        }
        break;
@@ -399,18 +336,33 @@ auto Bus::send(const Frame *out, Frame::Print print) -> Send {
  }

  if (print.print)
-    out->print(print);
+    out.print(print);

-  return err.errno;
+  return err.type;
 }

 Bus::Handle Bus::get() { return Handle{*this}; };

-#ifndef NDEBUG
-// Debug bit-timing measurement on the one physical bus; instance-scoped for the
-// same reason as is_active().
+#if !defined(NDEBUG)
+
+void Bus::set_dominant() { phy_set_dominant(); }
+void Bus::set_recessive() { phy_set_recessive(); }
+
+Send Bus::sendbyte(uint8_t byte, bool ack) {
+  auto handle = get();
+  uint8_t data_i = 0;
+  if (const Send serr = handle.send_data(&byte, 1, ack, &data_i);
+      serr != Send{0})
+    return serr;
+  return phy_send_done(&data_i);
+}
+
+  #ifdef MEASURE_BUS
+// Debug bit-timing measurement on the one physical bus; instance-scoped like
+// deafen().
 // NOLINTNEXTLINE(readability-convert-member-functions-to-static)
 void Bus::measure() { phy_measure(); }
+  #endif
 #endif

 } // namespace avclan
@@ -48,9 +48,11 @@
 #pragma once

 #include <cstdint>
+#include <memory>

 #include "avclan.h"
 #include "frame.hpp"
+#include "stdshim.hpp"

 namespace avclan {

@@ -67,18 +69,27 @@ public:
  Bus(const Bus &) = delete;
  Bus &operator=(const Bus &) = delete;

-  void init();
+  // `address` is our own peripheral address; the phy keeps it and acknowledges
+  // frames addressed to it without further instruction. One address per bus.
+  void init(uint16_t address);

-  bool is_active() const;
+  // Prevent the device from being active on the bus
  void mute(bool mute);
  bool is_muted() const { return muted_; };

+  // Set the device to be deaf to (ie don't react to) bus activity. It is
+  // orthogonal to mute — a deaf device can still send frames.
+  void deafen(bool deaf);
+
 #ifndef NDEBUG
  void measure();
+  detail::Error::Send sendbyte(uint8_t byte, bool ack = false);
+  void set_dominant();
+  void set_recessive();
 #endif

-  Error::Read read(uint16_t address, Frame *in, Frame::Print print);
-  Error::Send send(const Frame *out, Frame::Print print);
+  expected<std::unique_ptr<Frame>, Error::Read> read(Frame::Print print);
+  Error::Send send(const Frame &out, Frame::Print print);

 private:
  class Handle;
@@ -3,18 +3,22 @@
 // Copyright (C) 2015 Allen Hill <allenofthehills@gmail.com>
 // SPDX-License-Identifier: GPL-3.0-or-later

+#include <algorithm>
+#include <chrono>
 #include <cstdint>
 #include <cstring>
+#include <memory>
+#include <mutex>

 #include "avclan.h"
 #include "cdchanger.hpp"
 #include "device.hpp"
 #include "frame.hpp"
-#include "hal/cd_timer.h"
 #include "hal/media.h"

 namespace {
 using namespace avclan;
+using namespace std::chrono_literals;

 constexpr uint8_t cdloading_resp[] = {to_underlying(Device::CD_CHANGER),
                                      to_underlying(Device::STATUS),
@@ -27,73 +31,83 @@ constexpr uint8_t cdloading_resp[] = {to_underlying(Device::CD_CHANGER),
                                      0x01,
                                      0x02};

-constexpr int WIRE_SIZE = 8;  // cd state report size in bytes
-constexpr int TIME_SKIP = 15; // seconds
+constexpr int WIRE_SIZE = 8; // cd state report size in bytes
+constexpr auto TIME_SKIP = 15s;
 constexpr int TWODIGIT_MAX = 99;
+constexpr auto MAX_TIME = std::chrono::minutes{TWODIGIT_MAX} + 59s;

-/* Pack a 0–TWODIGIT_MAX count into 2-digit BCD. Values >TWODIGIT_MAX (sentinels
-   such as 0xFF / 0x7F meaning "no time") pass through unchanged so they survive
-   the wire round-trip. */
+// Pack a 0–TWODIGIT_MAX count into 2-digit BCD
 constexpr uint8_t toBCD(uint8_t val) {
-  if (val > TWODIGIT_MAX)
-    return val;
  return (uint8_t)(((val / 10) << 4) | (val % 10));
 }

-extern "C" void incrementTime_callback(void *self) {
-  static_cast<avclan::CDChanger *>(self)->incrementTime();
-}
-
-extern "C" bool isPlaying_callback(void *self) {
-  return static_cast<avclan::CDChanger *>(self)->isPlaying();
+// Whole seconds, saturated to the displayable range
+constexpr std::chrono::seconds displaySeconds(std::chrono::milliseconds t) {
+  return std::clamp(std::chrono::floor<std::chrono::seconds>(t), -MAX_TIME,
+                    MAX_TIME);
 }
 } // namespace

 namespace avclan {

-void CDChanger::init() {
+void CDChanger::init(Notifier notif) {
  media_init();
-  cdtimer_init(this, &incrementTime_callback, &isPlaying_callback);
+  notifier = notif;
+  statusTimer = xTimerCreate(
+      "cd status", pdMS_TO_TICKS(1000), true, this, [](TimerHandle_t timer) {
+        auto &self = *static_cast<CDChanger *>(pvTimerGetTimerID(timer));
+        // Timer callbacks must not block; a refused request is re-made next
+        // tick
+        if (!self.statusQueued.exchange(true) && !self.notifier.notify(0, 0))
+          self.statusQueued = false;
+      });
+  configASSERT(statusTimer);
 }

-void CDChanger::handle(const Frame *in, Frame *out) {
-  if (in->length < 4)
+void CDChanger::handle(const Frame &in, Frame &out) {
+  if (in.length < 4)
    return; // [Currently known] valid CDChanger frames have at least 4 bytes

-  const uint8_t *data = &in->data[1];
+  std::optional<MediaAction> media;
+
+  const uint8_t *data = &in.data[1];
  const auto from = static_cast<Device>(*data++);
  /* const auto to = */ data++;
  const auto action = static_cast<Action>(*data++);

  static const uint8_t function_change_resp[] = {
-      0x00, to_underlying(Device::CD_CHANGER), to_underlying(from), 0xFF, 0x01};
+      0x00, to_underlying(Device::CD_CHANGER), 0xFF, 0xFF, 0x01};

  using enum Action;
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wswitch-enum"
  // Unicast to CD changer: bytes are (0x00, from, to, action, [extra...]).
-  switch (action) {
+  switch (const std::lock_guard lock(mutex); action) {
    case Enable_Function_Req:
-      out->is_unicast = true;
-      out->length = sizeof(function_change_resp);
-      memcpy(out->data, function_change_resp, sizeof(function_change_resp));
-      out->data[3] = to_underlying(Enable_Function_Resp);
+      out.is_unicast = true;
+      out.length = sizeof(function_change_resp);
+      memcpy(out.data, function_change_resp, sizeof(function_change_resp));
+      out.data[2] = to_underlying(from);
+      out.data[3] = to_underlying(Enable_Function_Resp);
      state = 0;
      flags2 = 0x80;
-      out->reaction = r_StatusReport;
+      out.reaction = r_StatusReport;
      break;
    case Disable_Function_Req:
-      // No change/response needed if we're already not playing
+      // Head unit always expects a response, but the state change can be
+      // conditional
+      out.is_unicast = true;
+      out.length = sizeof(function_change_resp);
+      memcpy(out.data, function_change_resp, sizeof(function_change_resp));
+      out.data[2] = to_underlying(from);
+      out.data[3] = to_underlying(Disable_Function_Resp);
      if (isPlaying()) {
-        stopPlaying();
-        out->length = sizeof(function_change_resp);
-        memcpy(out->data, function_change_resp, sizeof(function_change_resp));
-        out->data[3] = to_underlying(Disable_Function_Resp);
+        media = stopPlaying();
        state = 0;
        flags2 = 0x80;
-        out->is_unicast = true;
-        out->reaction = r_StatusReport;
-      }
+        out.reaction = r_StatusReport;
+      } else
+        out.reaction = r_SendOnly;
      break;
    case Eject: {
      // "Eject" label is multiply wrong; proper meaning unclear:
@@ -106,20 +120,20 @@ void CDChanger::handle(const Frame *in, Frame *out) {
      if (static_cast<bool>(state & SEEKING)) { // FF/RW button released
        state &= ~SEEKING;
      } else {
-        out->is_unicast = true;
+        out.is_unicast = true;
        {
          const uint8_t msg[] = {0x00, to_underlying(Device::CD_CHANGER),
                                 to_underlying(Device::CMD_SW),
                                 to_underlying(Insertion), 0x01};
-          out->length = sizeof(msg);
-          memcpy(out->data, msg, sizeof(msg));
+          out.length = sizeof(msg);
+          memcpy(out.data, msg, sizeof(msg));
        }
-        out->reaction = r_SendOnly;
+        out.reaction = r_SendOnly;
      }
      break;
    }
    case Initial_Report_Req: {
-      out->is_unicast = true;
+      out.is_unicast = true;
      // No knowledge/understanding of field meaning/interpretation
      const uint8_t cdinitreport_resp[] = {0x00,
                                           to_underlying(Device::CD_CHANGER),
@@ -130,29 +144,29 @@ void CDChanger::handle(const Frame *in, Frame *out) {
                                           0x10,
                                           0x01,
                                           0x01};
-      out->length = sizeof(cdinitreport_resp);
-      memcpy(out->data, cdinitreport_resp, sizeof(cdinitreport_resp));
-      out->reaction = r_SendOnly;
+      out.length = sizeof(cdinitreport_resp);
+      memcpy(out.data, cdinitreport_resp, sizeof(cdinitreport_resp));
+      out.reaction = r_SendOnly;
      break;
    }
    case Playback_Req:
-      out->data[0] = 0x00;
-      out->data[1] = to_underlying(Device::CD_CHANGER);
-      out->data[2] = to_underlying(from);
-      out->data[3] = to_underlying(Playback_Resp);
-      out->length = WIRE_SIZE + 4;
-      serialize(&out->data[4]);
-      out->is_unicast = true;
-      out->reaction = r_SendOnly;
+      out.data[0] = 0x00;
+      out.data[1] = to_underlying(Device::CD_CHANGER);
+      out.data[2] = to_underlying(from);
+      out.data[3] = to_underlying(Playback_Resp);
+      out.length = WIRE_SIZE + 4;
+      serialize(&out.data[4]);
+      out.is_unicast = true;
+      out.reaction = r_SendOnly;
      break;
    case Loading_Req:
-      out->data[0] = 0x00;
-      out->length = sizeof(cdloading_resp) + 1;
-      memcpy(&out->data[1], cdloading_resp, sizeof(cdloading_resp));
-      out->data[2] = to_underlying(from);
-      out->data[3] = to_underlying(Loading_Resp);
-      out->is_unicast = true;
-      out->reaction = r_SendOnly;
+      out.data[0] = 0x00;
+      out.length = sizeof(cdloading_resp) + 1;
+      memcpy(&out.data[1], cdloading_resp, sizeof(cdloading_resp));
+      out.data[2] = to_underlying(from);
+      out.data[3] = to_underlying(Loading_Resp);
+      out.is_unicast = true;
+      out.reaction = r_SendOnly;
      break;
    case Track_Seek_Up:
      state = SEEKING_TRACK;
@@ -160,256 +174,287 @@ void CDChanger::handle(const Frame *in, Frame *out) {
        ++track;
      else
        track = 1;
-      mins = 0xff;
-      secs = 0x7f;
-      flags2 = 0xc0;
+      time.reset();
      generateStatus(out, true, Device::CMD_SW);
-      media_action(MediaAction::Track_Next);
-      out->reaction = r_TrackChange;
+      media = MediaAction::Track_Next;
+      out.reaction = r_TrackChange;
      break;
    case Track_Seek_Down:
      state = SEEKING_TRACK;
      // Track down returns to track beginning if in ~middle of song
-      if (mins == 0 && secs < 5) {
+      if (const auto t = trackTime(); t && *t < 5s) {
        if (track > 1)
          --track;
        else
          track = TWODIGIT_MAX;

-        media_action(MediaAction::Track_Prev);
+        media = MediaAction::Track_Prev;
      }
-      mins = 0xff;
-      secs = 0x7f;
-      flags2 = 0xc0;
+      time.reset();
      generateStatus(out, true, Device::CMD_SW);
-      out->reaction = r_TrackChange;
+      out.reaction = r_TrackChange;
      break;
    case Track_Fast_Forward: {
      state |= SEEKING;
-      secs += TIME_SKIP;
-      if (secs > 59) {
-        secs -= 60;
-        ++mins;
-      }
+      seek(TIME_SKIP);
      generateStatus(out, true, Device::CMD_SW);
-      media_action(MediaAction::Skip_Forward);
-      cdtimer_reset(); // Skipped to a whole/round sec; ensure next tick
-                       // is ~1 sec from now
-      out->reaction = r_SendOnly;
+      media = MediaAction::Skip_Forward;
+      out.reaction = r_SendOnly;
      break;
    }
    case Track_Rewind: {
      state |= SEEKING;
-      if (secs < TIME_SKIP) {
-        if (mins > 0) {
-          const uint8_t dif = TIME_SKIP - secs;
-          secs = 60 - dif;
-          --mins;
-        } else {
-          mins = 0;
-          secs = 0;
-        }
-      } else
-        secs -= TIME_SKIP;
+      seek(-TIME_SKIP);
      generateStatus(out, true, Device::CMD_SW);
-      media_action(MediaAction::Skip_Backward);
-      cdtimer_reset(); // Skipped to a whole/round sec; ensure next tick
-                       // is ~1 sec from now
-      out->reaction = r_SendOnly;
+      media = MediaAction::Skip_Backward;
+      out.reaction = r_SendOnly;
      break;
    }
    case CD_Enable_Random:
      flags |= RANDOM;
      generateStatus(out, true, Device::CMD_SW);
-      out->reaction = r_StatusReport;
+      out.reaction = r_StatusReport;
      break;
    case CD_Disable_Random:
      flags &= ~RANDOM;
      generateStatus(out, true, Device::CMD_SW);
-      out->reaction = r_StatusReport;
+      out.reaction = r_StatusReport;
      break;
    case CD_Enable_Repeat:
      flags |= REPEAT;
      generateStatus(out, true, Device::CMD_SW);
-      out->reaction = r_StatusReport;
+      out.reaction = r_StatusReport;
      break;
    case CD_Disable_Repeat:
      flags &= ~REPEAT;
      generateStatus(out, true, Device::CMD_SW);
-      out->reaction = r_StatusReport;
+      out.reaction = r_StatusReport;
      break;
    case CD_Enable_Disk_Random:
      flags |= DISK_RANDOM;
      generateStatus(out, true, Device::CMD_SW);
-      out->reaction = r_StatusReport;
+      out.reaction = r_StatusReport;
      break;
    case CD_Disable_Disk_Random:
      flags &= ~DISK_RANDOM;
      generateStatus(out, true, Device::CMD_SW);
-      out->reaction = r_StatusReport;
+      out.reaction = r_StatusReport;
      break;
    case CD_Enable_Disk_Repeat:
      flags |= DISK_REPEAT;
      generateStatus(out, true, Device::CMD_SW);
-      out->reaction = r_StatusReport;
+      out.reaction = r_StatusReport;
      break;
    case CD_Disable_Disk_Repeat:
      flags &= ~DISK_REPEAT;
      generateStatus(out, true, Device::CMD_SW);
-      out->reaction = r_StatusReport;
+      out.reaction = r_StatusReport;
+      break;
+    case CD_Enable_Scan:
+      flags |= SCAN;
+      generateStatus(out, true, Device::CMD_SW);
+      out.reaction = r_StatusReport;
+      break;
+    case CD_Disable_Scan:
+      flags &= ~SCAN;
+      generateStatus(out, true, Device::CMD_SW);
+      out.reaction = r_StatusReport;
+      break;
+    case CD_Enable_Disk_Scan:
+      flags |= DISK_SCAN;
+      generateStatus(out, true, Device::CMD_SW);
+      out.reaction = r_StatusReport;
+      break;
+    case CD_Disable_Disk_Scan:
+      flags &= ~DISK_SCAN;
+      generateStatus(out, true, Device::CMD_SW);
+      out.reaction = r_StatusReport;
      break;
    default: break;
  }
 #pragma GCC diagnostic pop
+
+  // Media action handled outside of switch to minimize lock duration
+  if (media)
+    media_action(*media);
 }

-void CDChanger::react(Frame *out, detail::Error::Send err) {
-  auto resp = static_cast<reaction_t>(out->reaction);
-  out->reaction = r_Nothing;
-  switch (resp) {
-    case r_StateReport:
-      if (err == detail::Error::Send::NAK_ADDRESS &&
-          ++failedStatusReports > 1) {
-        failedStatusReports = 0;
-        stopPlaying(); // Disable periodic updates if e.g. no-one's
-                       // listening (car was turned off?)
-      }
-      break;
-    case r_Ejection: {
-      const uint8_t play[] = {0x00,
-                              to_underlying(Device::COMM_CTRL),
-                              to_underlying(Device::COMMUNICATION_V1),
-                              to_underlying(Action::Insertion),
-                              to_underlying(Device::CD_CHANGER),
-                              0x01};
-      out->length = sizeof(play);
-      memcpy(out->data, play, sizeof(play));
+std::unique_ptr<Frame>
+CDChanger::react(expected<std::unique_ptr<Frame>, detail::SendError> exp) {
+  std::optional<MediaAction> media;
+  std::unique_ptr<Frame> next;
+
+  if (const std::lock_guard lock(mutex); !exp) {
+    if (exp.error().reaction == to_underlying(r_StateReport) &&
+        exp.error().err == detail::Error::Send::NAK_ADDRESS &&
+        ++failedStatusReports > 1) {
+      failedStatusReports = 0;
+      media = stopPlaying(); // Disable periodic updates if e.g. no-one's
+                             // listening (car was turned off?)
    }
-      out->reaction = r_Report_Load;
-      break;
-    case r_Report_Load:
-      out->is_unicast = false;
-      out->peripheral_addr = 0x1FF;
-      out->length = sizeof(cdloading_resp) + 1;
-      memcpy(out->data, cdloading_resp, sizeof(cdloading_resp));
-      out->data[1] = to_underlying(Device::STATUS);
-      out->data[2] = to_underlying(Action::Loading_Status);
-      out->reaction = r_SendOnly;
-      break;
-    case r_TrackChange:
-      setTime(0, 0);
-      cdtimer_reset(); // Skipped to a whole/round sec; ensure next tick is
-                       // ~1 sec from now
-      [[fallthrough]];
-    case r_NormalizeState:
-      normalizeState();
-      generateStatus(out, false, Device::STATUS);
-      out->reaction = r_SendOnly;
-      break;
-    case r_StartPlaying:
-      normalizeState();
-      generateStatus(out, false, Device::STATUS);
-      out->reaction = r_BeganPlaying;
-      break;
-    case r_BeganPlaying:
-      startPlaying(); // only start PIT after normalizing state
-      out->reaction = r_Nothing;
-      break;
-    case r_StatusReport:
-      generateStatus(out, false, Device::STATUS);
-      out->reaction = r_SendOnly;
-      break;
-    case r_SendOnly: [[fallthrough]];
-    case r_Nothing: [[fallthrough]];
-    default: out->reaction = r_Nothing;
+  } else {
+    auto out = std::move(exp.value());
+    auto resp = static_cast<reaction_t>(out->reaction);
+    out->reaction = r_Nothing;
+    switch (resp) {
+      case r_Ejection: {
+        const uint8_t play[] = {0x00,
+                                to_underlying(Device::COMM_CTRL),
+                                to_underlying(Device::COMMUNICATION_V1),
+                                to_underlying(Action::Insertion),
+                                to_underlying(Device::CD_CHANGER),
+                                0x01};
+        out->length = sizeof(play);
+        memcpy(out->data, play, sizeof(play));
+      }
+        out->reaction = r_Report_Load;
+        break;
+      case r_Report_Load:
+        out->is_unicast = false;
+        out->peripheral_addr = 0x1FF;
+        out->length = sizeof(cdloading_resp) + 1;
+        memcpy(out->data, cdloading_resp, sizeof(cdloading_resp));
+        out->data[1] = to_underlying(Device::STATUS);
+        out->data[2] = to_underlying(Action::Loading_Status);
+        out->reaction = r_SendOnly;
+        break;
+      case r_TrackChange:
+        setTime(0ms);
+        // Track starts at a whole sec; next status is ~1 sec out
+        xTimerReset(statusTimer, 0);
+        [[fallthrough]];
+      case r_NormalizeState:
+        normalizeState();
+        generateStatus(*out, false, Device::STATUS);
+        out->reaction = r_SendOnly;
+        break;
+      case r_StartPlaying:
+        normalizeState();
+        generateStatus(*out, false, Device::STATUS);
+        out->reaction = r_BeganPlaying;
+        break;
+      case r_BeganPlaying:
+        media = startPlaying(); // only start status timer after normalizing
+        out->reaction = r_Nothing;
+        break;
+      case r_StatusReport:
+        generateStatus(*out, false, Device::STATUS);
+        out->reaction = r_SendOnly;
+        break;
+      case r_StateReport: [[fallthrough]];
+      case r_SendOnly: [[fallthrough]];
+      case r_Nothing: [[fallthrough]];
+      default: break;
+    }
+
+    if (out->reaction > r_Nothing)
+      next = std::move(out);
  }
+
+  if (media)
+    media_action(*media);
+  return next;
 }

-void CDChanger::enable(Frame *out) {
+void CDChanger::enable(Frame &out) {
  if (!isPlaying()) {
-    if (mins > TWODIGIT_MAX)
-      mins = 0;
-    if (secs > TWODIGIT_MAX)
-      secs = 0;
+    const std::lock_guard lock(mutex);
+    if (!time)
+      setTime(0ms);
    state = SEEKING | SEEKING_TRACK;
-    flags2 = 0xc0;
+    flags2 = 0x80;
    generateStatus(out, false, Device::STATUS);
-    out->reaction = r_StartPlaying;
+    out.reaction = r_StartPlaying;
  }
 }

-bool CDChanger::pending() { return cdtimer_pending(); }
-void CDChanger::resolvepending() { cdtimer_clear(); }
-
-void CDChanger::emit(Frame *out, uint16_t peripheral) {
-  out->owning_device = id; // so react() routes r_StateReport back here
-  out->peripheral_addr = peripheral;
+void CDChanger::emit(Frame &out, uint32_t /*payload*/) {
+  statusQueued = false; // Clear first so a tick during emit() queues anew
+  const std::lock_guard lock(mutex);
  generateStatus(out, false, Device::STATUS);
-  out->reaction = r_StateReport;
+  out.reaction = r_StateReport;
 }

 bool CDChanger::isPlaying() const { return playing; }

-// Sets CD_mode to play and resets timer count (so that the next interrupt is in
-// 1 sec)
-void CDChanger::startPlaying() {
+// Starts track time and the ~1 Hz status report (the first ~1 sec from now)
+std::optional<MediaAction> CDChanger::startPlaying() {
  static bool havePlayed = false;
+  std::optional<MediaAction> media;
  if (havePlayed)
-    media_action(MediaAction::Play);
+    media = MediaAction::Play;
  havePlayed |= true;
+  if (!playing)
+    refTick = xTaskGetTickCount();
  playing = true;
-  cdtimer_reset();
+  xTimerReset(statusTimer, 0);
+  return media;
 }

-void CDChanger::stopPlaying() {
-  cdtimer_disable();
+MediaAction CDChanger::stopPlaying() {
+  xTimerStop(statusTimer, 0);
+  time = trackTime();
  playing = false;
-  media_action(MediaAction::Pause);
+  return MediaAction::Pause;
+}
+
+std::optional<std::chrono::milliseconds> CDChanger::trackTime() const {
+  if (!time || !playing)
+    return time;
+  return *time + std::chrono::milliseconds{
+                     pdTICKS_TO_MS(xTaskGetTickCount() - refTick)};
+}
+
+void CDChanger::setTime(std::chrono::milliseconds t) {
+  time = t;
+  refTick = xTaskGetTickCount();
+}
+
+// Seek `by` from the current whole second; no-op while no time is shown
+void CDChanger::seek(std::chrono::seconds by) {
+  const auto t = trackTime();
+  if (!t)
+    return;
+  setTime(displaySeconds(*t + by));
+  if (playing) // Seeked to a whole sec; next status is ~1 sec out
+    xTimerReset(statusTimer, 0);
 }

 // Serialize cd_status into the wire format.
 // track/mins/secs, need converted from decimal to BCD
 void CDChanger::serialize(uint8_t *dst) const {
+  uint8_t mins = 0xFF; // "no time" sentinels
+  uint8_t secs = 0x7F;
+  bool negative = false;
+  if (const auto t = trackTime()) {
+    const auto sec = displaySeconds(*t);
+    const auto magnitude = std::chrono::abs(sec);
+    const auto wholeMins = std::chrono::floor<std::chrono::minutes>(magnitude);
+    mins = toBCD((uint8_t)wholeMins.count());
+    secs = toBCD((uint8_t)(magnitude - wholeMins).count());
+    negative = sec < 0s;
+  }
+
  *dst++ = cds;
  *dst++ = state;
  *dst++ = disc;
  *dst++ = toBCD(track);
-  *dst++ = toBCD(mins);
-  *dst++ = toBCD(secs);
+  *dst++ = mins;
+  *dst++ = secs;
  *dst++ = flags;
-  *dst++ = flags2;
-}
-
-void CDChanger::setTime(uint8_t min, uint8_t sec) {
-  mins = min;
-  secs = sec;
-}
-
-void CDChanger::incrementTime() {
-  // Sentinel values (>TWODIGIT_MAX) mean "no time"; leave them alone until
-  // setTime() replaces them with a real count.
-  if (secs > TWODIGIT_MAX)
-    return;
-  if (secs == 59) {
-    secs = 0;
-    if (mins == TWODIGIT_MAX)
-      mins = 0;
-    else
-      mins++;
-  } else
-    secs++;
+  *dst++ = negative ? (flags2 | NEGATIVE) : (flags2 & ~NEGATIVE);
 }

 // Used for changed status messages
-void CDChanger::generateStatus(Frame *status, bool is_unicast,
+void CDChanger::generateStatus(Frame &status, bool is_unicast,
                               Device to) const {
-  status->is_unicast = is_unicast;
+  status.is_unicast = is_unicast;
  if (!is_unicast)
-    status->peripheral_addr = 0x1FF;
-  status->control = 0xF;
-  status->length = WIRE_SIZE + ((is_unicast) ? 4 : 3);
+    status.peripheral_addr = 0x1FF;
+  status.control = 0xF;
+  status.length = WIRE_SIZE + ((is_unicast) ? 4 : 3);

-  uint8_t *data = status->data;
+  uint8_t *data = status.data;
  if (is_unicast)
    *data++ = 0x00;
  *data++ = to_underlying(Device::CD_CHANGER);
@@ -419,13 +464,10 @@ void CDChanger::generateStatus(Frame *status, bool is_unicast,
 }

 void CDChanger::normalizeState() {
-  if (mins > TWODIGIT_MAX)
-    mins = 0;
-  if (secs > TWODIGIT_MAX)
-    secs = 0;
+  if (!time)
+    setTime(0ms);
  state = PLAYBACK;
  flags &= (uint8_t)~(DISK_SCAN | SCAN);
-  flags2 = 0x80;
 }

 #ifndef NDEBUG
@@ -5,7 +5,15 @@

 #pragma once

+#include <atomic>
+#include <chrono>
 #include <cstdint>
+#include <memory>
+#include <optional>
+
+#include "FreeRTOS.h" // IWYU pragma: export
+#include "semphr.h"
+#include "timers.h"

 #include "avclan.h"
 #include "device.hpp"
@@ -38,6 +46,7 @@ public:
    REPEAT = 1 << 4,
    DISK_SCAN = 1 << 5,
    SCAN = 1 << 6,
+    NEGATIVE = 1 << 6,
  };

  /// Message state machine
@@ -58,16 +67,17 @@ public:
  };

  static constexpr Device id = Device::CD_CHANGER;
-  void init();
+  CDChanger() : mutex(xSemaphoreCreateMutex()) {}
+  CDChanger(const CDChanger &) = delete;

-  void handle(const Frame *in, Frame *out);
-  void react(Frame *out, detail::Error::Send err);
-  void enable(Frame *out);
-  void disable(Frame *out);
-  static bool pending();
-  static void resolvepending();
-  void emit(Frame *out, uint16_t peripheral);
-  void incrementTime();
+  void init(Notifier notifier);
+
+  void handle(const Frame &in, Frame &out);
+  std::unique_ptr<Frame>
+  react(expected<std::unique_ptr<Frame>, detail::SendError> exp);
+  void enable(Frame &out);
+  void disable(Frame &out);
+  void emit(Frame &out, uint32_t payload);
  bool isPlaying() const;
 #ifndef NDEBUG
  void media_action(MediaAction action);
@@ -76,23 +86,45 @@ public:
 #endif

 private:
-  void startPlaying();
-  void stopPlaying();
+  // Implements the BasicLockable named requirements for an xSemaphore
+  class xMutex {
+  public:
+    explicit xMutex(SemaphoreHandle_t mutex) : mutex_{mutex} {}
+    xMutex(const xMutex &) = delete;
+
+    void lock() noexcept { xSemaphoreTake(mutex_, portMAX_DELAY); }
+    void unlock() noexcept { xSemaphoreGive(mutex_); }
+
+  private:
+    SemaphoreHandle_t mutex_ = nullptr;
+  };
+
+  std::optional<MediaAction> startPlaying();
+  MediaAction stopPlaying();
+  std::optional<std::chrono::milliseconds> trackTime() const;
+  void setTime(std::chrono::milliseconds t);
+  void seek(std::chrono::seconds by);
  void serialize(uint8_t *dst) const;
-  void setTime(uint8_t mins, uint8_t secs);
-  void generateStatus(Frame *status, bool is_unicast, Device to) const;
+  void generateStatus(Frame &status, bool is_unicast, Device to) const;
  void normalizeState();

+  Notifier notifier{};
+  TimerHandle_t statusTimer = nullptr;
+  std::atomic<bool> statusQueued = false; // coalesces status emit requests
+  xMutex mutex;
+
+  // Track time is a stopwatch: `time` is relative to `refTick`, and
+  // advances while `playing`. nullopt means no time is shown.
+  std::optional<std::chrono::milliseconds> time;
+  TickType_t refTick = 0;
  bool playing = false;
  int failedStatusReports = 0;
  uint8_t cds = CD1;
  uint8_t state = SEEKING | SEEKING_TRACK;
  uint8_t disc = 1;
-  uint8_t track = 1;   // Decimal storage; serialize to BCD
-  uint8_t mins = 0xFF; // Decimal storage; serialize to BCD
-  uint8_t secs = 0x7F; // Decimal storage; serialize to BCD
+  uint8_t track = 1; // Decimal storage; serialize to BCD
  uint8_t flags = 0;
-  uint8_t flags2 = 0xC0;
+  uint8_t flags2 = 0x80;
 };

 } // namespace avclan
@@ -5,9 +5,14 @@

 #include <concepts>
 #include <cstdint>
+#include <memory>
+
+#include "FreeRTOS.h" // IWYU pragma: export
+#include "queue.h"

 #include "avclan.h"
 #include "frame.hpp"
+#include "stdshim.hpp"

 namespace avclan {

@@ -45,17 +50,34 @@ enum class Device : uint8_t {
  TRIP_INFO = 0xE5,
 };

+// Notifies the Peripheral to emit for a device at `index`. Requests are served
+// in order, one `emit()` each; coalescing is up to the device. `val` (24 bits)
+// is device-defined. Returns whether the request was accepted within `wait`.
+class Notifier {
+public:
+  Notifier() = default;
+  Notifier(QueueHandle_t queue, uint8_t index) : queue{queue}, index{index} {}
+
+  bool notify(uint32_t val = 0, TickType_t wait = portMAX_DELAY) const {
+    const uint32_t item = (val << 8) | index;
+    return xQueueSend(queue, &item, wait) == pdPASS;
+  }
+
+private:
+  QueueHandle_t queue = nullptr;
+  uint8_t index = 0;
+};
+
 template <class T>
 concept DeviceInterface =
    requires { std::integral_constant<Device, T::id>{}; } &&
-    requires(T dev, const Frame *in, Frame *out, detail::Error::Send err,
-             uint16_t peripheral) {
-      dev.init();
+    requires(T dev, Notifier notifier, const Frame &in, Frame &out,
+             expected<std::unique_ptr<Frame>, detail::SendError> exp,
+             uint32_t payload) {
+      dev.init(notifier);
      dev.handle(in, out);
      dev.enable(out);
-      dev.react(out, err);
-      { dev.pending() } -> std::convertible_to<bool>;
-      dev.resolvepending();
-      dev.emit(out, peripheral);
+      { dev.react(std::move(exp)) } -> std::same_as<std::unique_ptr<Frame>>;
+      dev.emit(out, payload);
    };
 } // namespace avclan
@@ -6,8 +6,53 @@
 #include <cstdint>
 #include <cstdio>
 #include <cstring>
+#include <memory>
+#include <new>
+#include <type_traits>
+
+#include "FreeRTOS.h" // IWYU pragma: export
+#include "task.h"

 #include "frame.hpp"
+#include "hal/stdio.h"
+#include "stdshim.hpp"
+
+#if defined(AVCLAN_FRAME_POOL_N)
+  #include <array>
+  #include <cstddef>
+  #include <limits>
+
+namespace {
+template <class T, std::uint8_t N>
+  requires(N >= 1 && N <= std::numeric_limits<uint8_t>::max())
+class Pool {
+public:
+  constexpr Pool() {
+    for (uint8_t i = 0; i < N; ++i)
+      ptrs_[i] = &storage_[i];
+  }
+
+  T *acquire() {
+    if (top_ == 0)
+      return nullptr;
+    return ptrs_[--top_];
+  }
+
+  void release(T *ptr) {
+    // Properly would need an origin check/confirmation if this was used more
+    // generally
+    ptrs_[top_++] = ptr;
+  }
+
+private:
+  std::array<T, N> storage_;
+  std::array<T *, N> ptrs_;
+  uint8_t top_ = N;
+};
+
+Pool<avclan::Frame, AVCLAN_FRAME_POOL_N> pool;
+} // namespace
+#endif

 namespace {
 using Error = avclan::detail::Error;
@@ -15,52 +60,135 @@ using enum Error::Parse;
 } // namespace

 namespace avclan {
+
+#if defined(AVCLAN_FRAME_POOL_N)
+void *Frame::operator new(std::size_t /*count*/,
+                          const std::nothrow_t & /*tag*/) noexcept {
+  taskENTER_CRITICAL();
+  Frame *frame = pool.acquire();
+  taskEXIT_CRITICAL();
+  return frame;
+}
+// NOLINTNEXTLINE(misc-new-delete-overloads) false-positive
+void Frame::operator delete(void *ptr) noexcept {
+  taskENTER_CRITICAL();
+  pool.release(static_cast<Frame *>(ptr));
+  taskEXIT_CRITICAL();
+}
+#endif
+
+std::unique_ptr<Frame> Frame::acquire() {
+  std::unique_ptr<Frame> frame(new (std::nothrow) Frame);
+  for (uint8_t retries = 0; !frame && retries < 3; retries++) {
+    vTaskDelay(pdMS_TO_TICKS(2));
+    frame.reset(new (std::nothrow) Frame);
+  }
+  return frame;
+}
+
+namespace {
+// Emit `value` as at least `width` (lowercase, as to_chars emits) hex digits,
+// zero-padded. `width` must be <= 3 (see the padding below); every call site
+// reserves its field's worst case in the destination buffer, so this can't
+// overflow.
+template <class T>
+  requires std::is_unsigned_v<T>
+char *put_hex(char *dest, T value, uint8_t width) {
+  // to_chars emits the minimum number of digits, so work out up front how many
+  // that will be to know how much zero padding goes in front of them. At most
+  // two iterations for the field widths used here.
+  uint8_t ndigits = 1;
+  for (T rest = value; rest >= 16; rest /= 16)
+    ndigits++;
+
+  // At most two pad digits (width <= 3). Written out rather than as a counted
+  // loop because GCC turns that into a memset() call — call overhead an order
+  // of magnitude above the one or two stores it replaces.
+  if (ndigits < width) {
+    *dest++ = '0';
+    if (ndigits + 1 < width)
+      *dest++ = '0';
+  }
+
+  return to_chars(dest, dest + ndigits, value, 16).ptr;
+}
+
+// " 0xNNN" for each field, plus the leading unicast digit and trailing newline
+constexpr uint8_t LINE_MAX = 1 + (4 * 6) + (Frame::MAXLENGTH * 5) + 1;
+// The same buffer serves the binary branch, which is the shorter of the two
+static_assert(LINE_MAX >= 8 + Frame::MAXLENGTH + 2);
+} // namespace
+
 void Frame::print(Frame::Print print) const {
+  // The AVC-LAN read loop polls for start bits between calls, so emitting per
+  // character (~3 µs each through stdio) would blow past a start bit's ~169 µs
+  // and lose the next frame.
+  char buffer[LINE_MAX];
+  char *bptr = buffer;
+
  if (print.binary) {
-    uint8_t buffer[8];
-    uint8_t *bptr = buffer;
    *bptr++ = 0x10; // Data Link Escape, signaling binary data forthcoming
-    *bptr++ = static_cast<uint8_t>(is_unicast);
+    *bptr++ = static_cast<char>(is_unicast);

    // Send addresses in big-endian order
-    *bptr++ = static_cast<uint8_t>(controller_addr >> 8);
-    *bptr++ = static_cast<uint8_t>(controller_addr);
-    *bptr++ = static_cast<uint8_t>(peripheral_addr >> 8);
-    *bptr++ = static_cast<uint8_t>(peripheral_addr);
+    *bptr++ = static_cast<char>(controller_addr >> 8);
+    *bptr++ = static_cast<char>(controller_addr);
+    *bptr++ = static_cast<char>(peripheral_addr >> 8);
+    *bptr++ = static_cast<char>(peripheral_addr);

-    *bptr++ = control;
-    *bptr++ = length;
-    fwrite(buffer, 1, 8, stdout);
-    fwrite(data, 1, length, stdout);
+    *bptr++ = static_cast<char>(control);
+    *bptr++ = static_cast<char>(length);
+
+    memcpy(bptr, data, length);
+    bptr += length;

-    bptr = buffer;
    *bptr++ = 0x17; // End of transmission block
    *bptr++ = 0x0A; // \n
-    fwrite(buffer, 1, 2, stdout);
-  } else {
-    printf("%X", static_cast<unsigned>(is_unicast));
-    printf(" 0x%03X", static_cast<unsigned>(controller_addr & 0x0FFF));
-    printf(" 0x%03X", static_cast<unsigned>(peripheral_addr & 0x0FFF));
-    printf(" 0x%X", static_cast<unsigned>(control & 0x0F));
-    printf(" 0x%X", static_cast<unsigned>(length & 0x0F));

-    for (uint8_t i = 0; i < length; i++) {
-      printf(" 0x%02X", static_cast<unsigned>(data[i]));
-    }
-    putchar('\n');
+    stdio_write_nonblock(buffer, static_cast<size_t>(bptr - buffer));
+    return;
  }
+
+  struct field_t {
+    uint16_t value;
+    uint8_t width; // minimum digits, matching the old %03x / %x formats
+  };
+
+  *bptr++ = is_unicast ? '1' : '0';
+  for (const field_t field :
+       {field_t{.value = static_cast<uint16_t>(controller_addr & 0x0FFF),
+                .width = 3},
+        field_t{.value = static_cast<uint16_t>(peripheral_addr & 0x0FFF),
+                .width = 3},
+        field_t{.value = static_cast<uint16_t>(control & 0x0F), .width = 1},
+        field_t{.value = static_cast<uint16_t>(length & 0x0F), .width = 1}}) {
+    *bptr++ = ' ';
+    *bptr++ = '0';
+    *bptr++ = 'x';
+    bptr = put_hex(bptr, field.value, field.width);
+  }
+
+  for (uint8_t i = 0; i < length; i++) {
+    *bptr++ = ' ';
+    *bptr++ = '0';
+    *bptr++ = 'x';
+    bptr = put_hex(bptr, data[i], 2);
+  }
+  *bptr++ = '\n';
+
+  stdio_write_nonblock(buffer, static_cast<size_t>(bptr - buffer));
 }

 Error::Parse Frame::parse(const uint8_t *bytes, uint8_t len) {
  struct errtype {
-    Error::Parse errno;
+    Error::Parse type;
    uint8_t val;
  } err = {};

  const uint8_t *last = bytes + len;

  if (len < Frame::MIN_SIZE) {
-    err.errno = TOO_SHORT;
+    err.type = TOO_SHORT;
    goto handle_err;
  }

@@ -73,7 +201,7 @@ Error::Parse Frame::parse(const uint8_t *bytes, uint8_t len) {
  length = *bytes++;

  if (length > MAXLENGTH) {
-    err.errno = LENGTH_TOO_BIG;
+    err.type = LENGTH_TOO_BIG;
    err.val = length;
    goto handle_err;
  }
@@ -81,14 +209,14 @@ Error::Parse Frame::parse(const uint8_t *bytes, uint8_t len) {
  if ((bytes + length) <= last) {
    memcpy(data, bytes, length);
  } else {
-    err.errno = MISMATCH_LENGTH;
+    err.type = MISMATCH_LENGTH;
    goto handle_err;
  }

  if (false) { // NOLINT(readability-simplify-boolean-expr)
  handle_err:;
    fputs("ERR(parse): ", stdout);
-    switch (err.errno) {
+    switch (err.type) {
      case TOO_SHORT: puts("not enough bytes too fill AVCLAN frame"); break;
      case MISMATCH_LENGTH:
        puts("frame->length is longer than remaining data");
@@ -101,6 +229,6 @@ Error::Parse Frame::parse(const uint8_t *bytes, uint8_t len) {
    }
  }

-  return err.errno;
+  return err.type;
 }
 } // namespace avclan
@@ -6,9 +6,15 @@
 #pragma once

 #include <cstdint>
+#include <memory>

 #include "avclan.h"

+#if defined(AVCLAN_FRAME_POOL_N)
+  #include <cstddef>
+  #include <new>
+#endif
+
 namespace avclan {
 enum class Device : uint8_t;

@@ -25,13 +31,27 @@ struct Frame {
  Error::Parse parse(const uint8_t *bytes, uint8_t len);
  void print(Print print) const;

-  uint8_t reaction;
-  Device owning_device;
+  // Retries every 2ms up to 3 times (max 6ms wait); null if still exhausted
+  static std::unique_ptr<Frame> acquire();
+
+#if defined(AVCLAN_FRAME_POOL_N)
+  // O(1) heapless pooled allocation. Only `new (std::nothrow) Frame` is
+  // supported.
+  static void *operator new(std::size_t) = delete;
+  static void *operator new(std::size_t, const std::nothrow_t &) noexcept;
+  // NOLINTNEXTLINE(misc-new-delete-overloads) false-positive
+  static void operator delete(void *) noexcept;
+#endif
+
+  // reaction has a Device-defined interpretation, with the sole invariant that
+  // 0 == inactive/non-sendable frame
+  uint8_t reaction = 0;
+  Device owning_device = NoDevice;
  bool is_unicast;
  uint16_t controller_addr; // formerly "master"
  uint16_t peripheral_addr; // formerly "slave"
  uint8_t control = 0xF;
-  uint8_t length;
+  uint8_t length = 0;
  uint8_t data[MAXLENGTH];
 };
 } // namespace avclan
@@ -1,32 +0,0 @@
-// Copyright (C) 2026 Allen Hill <allenofthehills@gmail.com>
-// SPDX-License-Identifier: GPL-3.0-or-later
-
-// CDChanger periodic-timer HAL: the ~1 Hz tick that drives the CD changer's
-// status updates. The timer hardware is target-specific; the CD changer owns
-// what a tick means (see cdchanger.cc). The device polls cdtimer_pending() and
-// clears the tick with cdtimer_clear().
-
-#pragma once
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-// One-time hardware bring-up. Leaves the tick disabled.
-void cdtimer_init(void *ptr, void(clbk)(void *), bool(isplay)(void *));
-
-// Reset the count so the next tick is ~1 s out, and enable the tick.
-void cdtimer_reset(void);
-
-// Restore / disable the ~1 Hz tick.
-void cdtimer_restore(void);
-void cdtimer_disable(void);
-
-extern volatile bool cdtimer_pending_flag;
-
-static inline bool cdtimer_pending() { return cdtimer_pending_flag; }
-static inline void cdtimer_clear() { cdtimer_pending_flag = false; }
-
-#ifdef __cplusplus
-}
-#endif
@@ -7,21 +7,23 @@

 #include <stdint.h>

+#include "FreeRTOS.h" // IWYU pragma: export
+
 #include "avclan.h"

 #ifdef __cplusplus
 using Read = avclan::detail::Error::Read;
 using Send = avclan::detail::Error::Send;
-using Bit = avclan::detail::Bit;
 extern "C" {
 #else
 typedef enum Read Read;
 typedef enum Send Send;
-typedef enum Bit Bit;
 #endif

 // One-time bring-up of the bus hardware. Leaves the bus idle and TX unmuted.
-void phy_init(void);
+//
+// `address` is our device address.
+void phy_init(uint16_t address);

 // Mute/unmute device TX. "Muted" means transmission is disabled (RX is
 // unchanged/still allowed)
@@ -30,56 +32,83 @@ void phy_mute(bool mute);
 // Non-mutating (e.g. theoretically const qualified/-able)
 bool phy_is_muted(void);

-// True when bus is driven/"dominant" (logical 0)
-bool phy_active(void);
+// Do not respond to or log incoming frames. Can still send frames.
+void phy_deafen(bool deaf);
+
+// Blocks until a frame is ready
+void phy_wait_frame(TickType_t xTicksToWait);

 // Bus-transaction guard: quiesce the other async sources (e.g. interrupts)
 // so that bus read/send timing isn't disturbed. Re-enable relevant async
-// sources with `phy_guard_leave`. May be a no-op on a target where contention
-// isn't a concern.
+// sources with `phy_guard_leave`.
+//  - May be a no-op on a target where concurrency/preemption isn't a concern.
 void phy_guard_enter(void);
 void phy_guard_leave(void);

-// Start-bit handling, factored out of read/sendframe so the framing layer holds
-// no bus-timing or hardware-recovery logic.
-// - phy_read_startbit waits for and validates an incoming start bit, doing
-//   any target-specific bus recovery; see avclan::detail::Error::Read.
-// - phy_send_startbit acquires the bus and emits a start bit; may return BUSY
-Read phy_read_startbit(void);
-Send phy_send_startbit(void);
+/* Per-field frame I/O.
+ *
+ * All send functions may have asynchronous implementations (e.g. return before
+ * the send has completed on the bus). Success is indicated by a zero value
+ * `Read` or `Send` enum. Non-zero error codes indicate a synchronously
+ * completed send failure. Otherwise, `phy_send_done` must be called to block
+ * until all queued send's have completed, and may return the error code for a
+ * previous (queued) send failure; a success return value indicates that all
+ * queued send's have finished sending over the bus.
+ *
+ * The read functions are similarly optionally asynchronous, and may return the
+ * results of buffered reads. When this is the case, phy_read_header returns the
+ * relevant error for the entire frame.
+ *
+ * It is invalid to call any later read or send function after getting an
+ * error (e.g. calling `phy_read_data` after `phy_read_length` errored).
+ *
+ * `expect_ack` indicates whether the recipient should be ACK'ing; false for
+ * broadcast frames which don't have a single recipient.
+ */

-/* Returns 0 (`(Send)0`) if the peripheral sent an ACK bit, otherwise returns
-NAK. An ACK bit is a cooperative bit, where the sender starts (drives the bus)
-for the sync period, and allows the receiver to drive the bus (or not) to
-finish a "1" bit.
-*/
-Send phy_read_ack(void);
-void phy_send_ack(void);
+// Returns NO_FRAME when there is no frame to read.
+Read phy_read_header(bool *is_unicast);
+Read phy_read_controller_addr(uint16_t *addr);
+Read phy_read_peripheral_addr(uint16_t *addr);
+Read phy_read_control(uint8_t *control);
+Read phy_read_length(uint8_t *length);
+// Read `length` data bytes. `data_index` is only written to on error, with the
+// index of the failed byte.
+Read phy_read_data(uint8_t *data, uint8_t length, uint8_t *data_index);

-// Per-symbol I/O. The send* helpers return the even parity of the bits sent;
-// the read* helpers return the even parity of the bits read. The _u8/_u16
-// suffixes name the source-operand width. The function implementations need not
-// all be separate/independent (e.g. all send functions could be redirect to a
-// single phy_send_bits_u16, etc).
-// N.B: `len` is the number of bits  to send. The
-// C++ send/readbits templates are the only consumers and use constraints to
-// enforce valid len values, so runtime checks are unnecessary.
+// Send start and broadcast bits. Returns success or one of these error values:
+// MUTED, BUSY, or LOST_ARBITRATION (if another device overrides our frame with
+// a broadcast).
+Send phy_send_header(bool is_unicast);

-// Intended for sending parity bits
-void phy_send_bit(Bit bit);
+// Send the controller address. Returns success or LOST_ARBITRATION (a device
+// with a lower device is sending a frame).
+Send phy_send_controller_addr(uint16_t addr);
+Send phy_send_peripheral_addr(uint16_t addr, bool expect_ack);
+Send phy_send_control(uint8_t control, bool expect_ack);
+Send phy_send_length(uint8_t length, bool expect_ack);
+// Send `length` data bytes. `data_index` is only written to for NAK_DATA.
+Send phy_send_data(const uint8_t *data, uint8_t length, bool expect_ack,
+                   uint8_t *data_index);

-// Variants available to minimize unnecessary work for max runtime efficiency
-Bit phy_send_bits_u8(const uint8_t *bits, int8_t len);
-Bit phy_send_bits_u16(const uint16_t *bits, int8_t len);
-Bit phy_send_byte(const uint8_t *byte);
-
-Bit phy_read_bits_u8(uint8_t *bits, uint8_t len);
-Bit phy_read_bits_u16(uint16_t *bits, int8_t len);
-Bit phy_read_byte(uint8_t *byte);
+// Allows asynchronous ports to block until the phy has finished sending the
+// frame. Returns success or the relevant field-specific NAK (e.g. NAK_ADDRESS,
+// etc) or CONTENDED_BUS; a port that queues the header and controller address
+// also reports their BUSY or LOST_ARBITRATION here. `data_index` is only
+// written to for NAK_DATA. A fully synchronous port should always report
+// success.
+Send phy_send_done(uint8_t *data_index);

 #ifndef NDEBUG
+
+// Hold the bus at a level until the matching call.
+void phy_set_dominant(void);
+void phy_set_recessive(void);
+
+  #ifdef MEASURE_BUS
 // Sample and dump bus bit timing over the serial link (REPL `M`).
 void phy_measure(void);
+  #endif
 #endif

 #ifdef __cplusplus
@@ -3,18 +3,36 @@

 #pragma once

+#include <stddef.h>
+#include <stdint.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif

 // Generic stdio interface initialization. All user I/O goes through <stdio.h>
 // functions. Assumptions/invariants:
-//  - stdin MUST be non-blocking (ie. getchar() returns EOF immediately when
-//    empty). Necessary to avoid stalling the REPL poll loop.
-//  - stdout is *raw* — no '\n' -> "\r\n" translation: bare LF and binary frame
-//    payloads (fwrite) are emitted verbatim
+//  - A libc read of stdin blocks the calling task (not the CPU) until at least
+//    one byte is available.
+//  - stdout is *raw*. There is no '\n' -> "\r\n" translation. The port does not
+//    change a bare LF or a binary frame payload. Writes through
+//    <stdio.h> and writes through stdio_write_nonblock() must reach the same
+//    stream, in order.
 void stdio_init(void);

+// Queue a buffer onto stdout--if it has space, or return false.
+//
+// If stdout cannot accept all `len` bytes now, the function queues
+// a "\n!\n" indicator onto stdout, overwriting the last 3 chars if stdout is
+// full. The caller must not assume that the buffer went out.
+//
+// A port MUST emit that indicator for every dropped buffer, and MUST be able to
+// emit it even if stdout is full. A reader detects the loss as a line that
+// holds only '!'. In the overwrite case the buffer in front of that line is
+// truncated, so a reader MUST tolerate one malformed buffer there. The return
+// value is useful only for diagnostics.
+bool stdio_write_nonblock(const void *buf, uint8_t len);
+
 #ifdef __cplusplus
 }
 #endif
@@ -4,73 +4,125 @@
 // SPDX-License-Identifier: GPL-3.0-or-later
 #pragma once

+#include <algorithm>
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <cstring>
+#include <memory>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+#include "FreeRTOS.h" // IWYU pragma: export
+#include "queue.h"
+
 #include "avclan.h"
 #include "bus.hpp"
 #include "device.hpp"
 #include "frame.hpp"
-
-#include <cstdint>
-#include <cstring>
-#include <tuple>
+#include "stdshim.hpp"

 namespace avclan {
+namespace detail {
+enum class Party : uint8_t { Sender, Recipient };
+}
+
 template <DeviceInterface... Devs> class Peripheral {
+  using Party = detail::Party;
+  using enum Party;
+
 public:
  using Error = detail::Error;

-  Peripheral(Bus &bus, uint16_t address) : bus{bus}, address_{address} {
-    bus.init();
-    (std::get<Devs>(devices_).init(), ...);
+  // lack of static reflection until C++26 limits our methods of doing a
+  // compile-time collision check. Within Peripheral, we can at least assert no
+  // collision with Devices *used in a particular instantiation* but it is not a
+  // universal check against all Device enum values
+  static_assert(((Devs::id != NoDevice) && ...),
+                "a registered Device id collides with the NoDevice sentinel; "
+                "update the sentinel value in avclan.h");
+  static_assert(
+      sizeof...(Devs) <= 0x100,
+      "too many devices: Notifier packs the device index into 8 bits");
+
+  static constexpr UBaseType_t EMIT_QUEUE_LEN = 2 * sizeof...(Devs);
+
+  Peripheral(Bus &bus, uint16_t address)
+      : bus{bus}, address_{address},
+        emit_requests_{xQueueCreate(EMIT_QUEUE_LEN, sizeof(uint32_t))} {
+    configASSERT(emit_requests_);
+    bus.init(address);
+    (std::get<Devs>(devices_).init(Notifier{emit_requests_, index_of<Devs>()}),
+     ...);
  }
+  Peripheral(const Peripheral &) = delete;

  uint16_t controller() const { return controller_; };
  template <DeviceInterface Dev> Dev &device() {
    return std::get<Dev>(devices_);
  }

-  bool bus_is_active() const { return bus.is_active(); };
  void mute(bool mute) { bus.mute(mute); };
  bool is_muted() const { return bus.is_muted(); };

 #ifndef NDEBUG
  Bus &get_bus() { return bus; }
+  void set_controller(uint16_t addr) { controller_ = addr; }
 #endif

-  Error::Read read(Frame *in, Frame::Print print) {
-    return bus.read(address_, in, print);
+  expected<std::unique_ptr<Frame>, Error::Read>
+  read(Frame::Print print = Frame::Print{}) {
+    return bus.read(print);
  };
-  Error::Send send(Frame *out, Frame::Print print) {
+
+  expected<std::unique_ptr<Frame>, detail::SendError>
+  send(std::unique_ptr<Frame> out, Frame::Print print = Frame::Print{}) {
    // To "forge" a controller_addr, instantiate a new/different Peripheral
-    postmark(out);
-    return bus.send(out, print);
+    stamp<Sender>(*out);
+    out->control = 0xF;
+    auto err = bus.send(*out, print);
+    if (err != Error::Send{0})
+      return unexpected{detail::SendError{.owning_device = out->owning_device,
+                                          .reaction = out->reaction,
+                                          .err = err}};
+
+    return out;
  };

 #define PACK3(a, b, c) (((uint32_t)(a) << 16) | ((uint32_t)(b) << 8) | (c))

-  void route(const Frame *in, Frame *out) {
+  // expected needed to distinguish don't vs can't respond
+  expected<std::unique_ptr<Frame>, Error::Read> route(const Frame &in) {
    using enum Device;
    using enum Action;
-    out->reaction = 0;

-    if (is_muted() || in->length < 3)
-      return;
+    if (is_muted() || in.length < 3)
+      return {};
+
+    std::unique_ptr<Frame> out = Frame::acquire();
+    if (!out) {
+      puts("!! failed Frame alloc in route !!");
+      return unexpected{Error::Read::POOL_EMPTY};
+    }

    // 0xFF placeholders are variant bytes filled by writing directly to
    // out->data[N] after memcpy.
    static const uint8_t lancheck_resp[] = {0x00, to_underlying(COMM_CTRL),
                                            to_underlying(LAN), 0xFF, 0xFF};

-    out->peripheral_addr = controller_;
+    stamp<Recipient>(*out);

-    const uint8_t *data = in->data;
+    const uint8_t *data = in.data;
    const uint8_t b0 = *data++;
    const uint8_t b1 = *data++;
    const uint8_t b2 = *data++;
-    uint8_t b3 = 0;
-    if (in->length > 3) // the shortest known/valid messages are 3 bytes long
-      b3 = *data++;

-    if (!in->is_unicast) {
+    // the shortest known/valid messages are 3 bytes long
+    const uint8_t b3 = (in.length > 3) ? *data++ : 0;
+
+    if (!in.is_unicast) {
      const auto from = b0;
      const auto to = b1;
      const auto action = b2;
@@ -103,15 +155,14 @@ public:
        case PACK3(COMMUNICATION_V1, COMM_CTRL,
                   to_underlying(Advertise_Function)):
        case PACK3(COMMUNICATION_V2, COMM_CTRL,
-                   to_underlying(Advertise_Function)):
+                   to_underlying(Advertise_Function)): {
+          auto enable_d = [](auto &d, auto &out) { d.enable(out); };
          ((Devs::id == static_cast<Device>(b3)
-            ? [&] {
-                out->owning_device = Devs::id;
-                std::get<Devs>(devices_).enable(out);
-              }()
-            : void()),
+                ? originate(std::get<Devs>(devices_), *out, enable_d)
+                : void()),
           ...);
          break;
+        }
        case PACK3(COMMUNICATION_V1, COMM_CTRL, to_underlying(Ping_Req)):
        case PACK3(COMMUNICATION_V2, COMM_CTRL, to_underlying(Ping_Req)): {
          out->is_unicast = true;
@@ -127,8 +178,8 @@ public:
                   to_underlying(List_Functions_Req)):
        case PACK3(COMMUNICATION_V2, COMM_CTRL,
                   to_underlying(List_Functions_Req)): {
-          controller_ = in->controller_addr;
-          out->peripheral_addr = controller_;
+          controller_ = in.controller_addr;
+          stamp<Recipient>(*out); // re-stamp now that controller_ is known
          out->is_unicast = true;
          const uint8_t list_functions_resp[] = {
              0x00, to_underlying(COMM_CTRL), from,
@@ -141,49 +192,78 @@ public:
        // case Restart_Lan: not handled
        default: break;
      }
-    } else if (in->peripheral_addr == address_ && b0 == 0x00) {
+    } else if (in.peripheral_addr == address_ && b0 == 0x00) {
+      auto handle_d = [&](auto &d, auto &out) { d.handle(in, out); };
      ((Devs::id == static_cast<Device>(b2)
-        ? device_preroute(std::get<Devs>(devices_), in, out),
-        0 : 0),
+            ? originate(std::get<Devs>(devices_), *out, handle_d)
+            : void()),
       ...);
    }
+
+    if (out->reaction > 0)
+      return out;
+
+    return {};
  }

 #undef PACK3

-  void react(Frame *out, Error::Send err) {
-    if (((Devs::id == out->owning_device) || ...))
-      ((Devs::id == out->owning_device
-        ? std::get<Devs>(devices_).react(out, err),
-        0 : 0),
-       ...);
-    else
-      out->reaction = 0;
+  std::unique_ptr<Frame>
+  react(expected<std::unique_ptr<Frame>, detail::SendError> exp) {
+    const Device from =
+        exp ? exp.value()->owning_device : exp.error().owning_device;
+
+    std::unique_ptr<Frame> next;
+    ((Devs::id == from &&
+      (next = std::get<Devs>(devices_).react(std::move(exp)))) ||
+     ...);
+    return next;
  }

-  template <class F> void poll_devices(F &&fun) {
-    (poller(std::get<Devs>(devices_), fun), ...);
+  // Blocks until a device requests an emit; requests are served in order.
+  std::unique_ptr<Frame> poll() {
+    std::unique_ptr<Frame> out = Frame::acquire();
+    if (!out) {
+      puts("!! failed Frame alloc in poll !!");
+      return {};
+    }
+
+    uint32_t val;
+    xQueueReceive(emit_requests_, &val, portMAX_DELAY);
+    const uint8_t index = val & 0xFF;
+
+    auto emit_d = [val](auto &d, auto &out) { d.emit(out, val >> 8); };
+    [&]<std::size_t... Is>(std::index_sequence<Is...>) {
+      ((Is == index ? originate(std::get<Is>(devices_), *out, emit_d) : void()),
+       ...);
+    }(std::index_sequence_for<Devs...>{});
+    return out;
  }

 private:
-  void postmark(Frame *out) const {
-    out->controller_addr = address_;
-    out->control = 0xF;
+  // Dev's position in Devs
+  template <class Dev> static constexpr uint8_t index_of() {
+    constexpr std::array is_dev{std::is_same_v<Dev, Devs>...};
+    return std::ranges::find(is_dev, true) - is_dev.begin();
  }

-  template <DeviceInterface Dev, class F> void poller(Dev &dev, F &&fun) {
-    if (dev.pending() && fun(dev))
-      dev.resolvepending();
+  template <Party P> void stamp(Frame &out) const {
+    if constexpr (P == Sender)
+      out.controller_addr = address_;
+    else
+      out.peripheral_addr = controller_;
  }
-  template <DeviceInterface Dev>
-  void device_preroute(Dev &dev, const Frame *in, Frame *out) {
-    out->owning_device = Dev::id;
-    dev.handle(in, out);
+
+  void originate(DeviceInterface auto &dev, Frame &out, auto &&fill) {
+    out.owning_device = std::remove_reference_t<decltype(dev)>::id;
+    stamp<Recipient>(out); // default set FIRST; fill() may override
+    fill(dev, out);
  }

  Bus &bus;
  uint16_t controller_ = 0;
  const uint16_t address_;
  std::tuple<Devs...> devices_;
+  QueueHandle_t emit_requests_;
 };
 } // namespace avclan
@@ -0,0 +1,72 @@
+// Copyright (C) 2026 Allen Hill <allenofthehills@gmail.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+#pragma once
+
+#include <version>
+
+#if !defined(__cpp_lib_expected) || __cpp_lib_expected < 202211L
+  #include <tl/expected.hpp>
+
+namespace avclan {
+template <class T, class E> using expected = tl::expected<T, E>;
+template <class E> using unexpected = tl::unexpected<E>;
+using tl::unexpect;
+using tl::unexpect_t;
+} // namespace avclan
+#else
+  #include <expected>
+
+namespace avclan {
+template <class T, class E> using expected = std::expected<T, E>;
+template <class E> using unexpected = std::unexpected<E>;
+using std::unexpect;
+using std::unexpect_t;
+} // namespace avclan
+#endif
+
+#if !defined(__cpp_lib_to_chars) || __cpp_lib_to_chars < 201611L
+  #include <cstdint>
+  #include <type_traits>
+
+namespace avclan {
+// No <charconv> (nor the <system_error> its result type needs) in the
+// freestanding stdlib, so mirror the std API surface for the unsigned-integral
+// overload — the only one used here. Values are those of std::errc, so call
+// sites written against either spelling behave the same.
+enum class errc : uint8_t { value_too_large = 75 };
+
+struct to_chars_result {
+  char *ptr;
+  errc ec;
+};
+
+template <class T>
+  requires std::is_integral_v<T> && std::is_unsigned_v<T>
+constexpr to_chars_result to_chars(char *first, char *last, T value,
+                                   int base = 10) {
+  char digits[sizeof(T) * 8]; // worst case: base 2
+  uint8_t ndigits = 0;
+  do {
+    const auto digit = static_cast<unsigned>(value % static_cast<T>(base));
+    digits[ndigits++] =
+        static_cast<char>(digit < 10 ? '0' + digit : 'a' + (digit - 10));
+    value = static_cast<T>(value / static_cast<T>(base));
+  } while (value != 0);
+
+  if ((last - first) < ndigits)
+    return {.ptr = last, .ec = errc::value_too_large};
+
+  while (ndigits > 0)
+    *first++ = digits[--ndigits];
+  return {.ptr = first, .ec = errc{}};
+}
+} // namespace avclan
+#else
+  #include <charconv>
+
+namespace avclan {
+using errc = std::errc;
+using std::to_chars;
+using std::to_chars_result;
+} // namespace avclan
+#endif
@@ -12,6 +12,11 @@ target_sources(avclan PRIVATE
    )

 target_include_directories(avclan PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+target_compile_options(avclan PUBLIC
+    $<$<COMPILE_LANGUAGE:CXX>:-fno-threadsafe-statics>
+    $<$<COMPILE_LANGUAGE:CXX>:-fno-exceptions>
+    $<$<COMPILE_LANGUAGE:CXX>:-fno-rtti>
+)

 find_program(AVRDUDE avrdude)
 set(AVR_PROGRAMMER serialupdi CACHE STRING "avrdude programmer hardware")
@@ -85,11 +90,14 @@ FetchContent_Declare(
    avr_libstdcpp
    GIT_REPOSITORY https://github.com/modm-io/avr-libstdcpp.git
    GIT_TAG 5354296040a2289c911062daa82336762231e897
+    SYSTEM
 )
 FetchContent_MakeAvailable(avr_libstdcpp)
-add_library(libstdcpp INTERFACE)
-target_include_directories(libstdcpp SYSTEM
-    INTERFACE ${avr_libstdcpp_SOURCE_DIR}/include)
+add_library(libstdcpp STATIC ${avr_libstdcpp_SOURCE_DIR}/src/new_handler.cc)
+target_include_directories(libstdcpp
+    PUBLIC ${avr_libstdcpp_SOURCE_DIR}/include)
+# Let --gc-sections drop the unused set/get_new_handler functions.
+target_compile_options(libstdcpp PRIVATE -ffunction-sections -fdata-sections)
 target_link_libraries(avclan PUBLIC libstdcpp)

 if(NOT LIBC_VERSION_TEST)
@@ -131,6 +139,7 @@ target_compile_definitions(jnk0le_uart
    PRIVATE F_CPU=${FREQSEL}
 )
 target_compile_options(jnk0le_uart PUBLIC
+    $<$<CONFIG:Debug>:-Og>
    -ffixed-r2 -ffixed-r3 -ffixed-r4) # reserved ISR scratch (SREG=r4, Z=r2:r3)
 target_link_libraries(avclan PUBLIC jnk0le_uart)

@@ -9,13 +9,17 @@
 #include <stdint.h>
 #include <util/atomic.h>

+#include "avclan.h"
 #include "hal/cd_timer.h" // statustimer_enable/disable (guard)
 #include "hal/phy.h"
 #include "media_avr.h" // media_sync_during_mask (guard)

 // F_CPU + TICK_US (timing.h) defined here; F_CPU potentially needed by
 // avr-libc.
-#include "timing_avr.h"
+#include "timing_avr.h" // IWYU pragma: keep
+
+enum bit_t : uint8_t { bit_zero = 0x00, bit_one = 0x01, bit_start = 0x10 };
+typedef enum bit_t Bit;

 // USART0 TX ring indices owned by the jnk0le lib; the guard consults them to
 // decide whether to resume the TX drain (DRE interrupt) on leave.
@@ -79,8 +83,12 @@ bool phy_is_muted() {
  return (((VPORTA_DIR & PIN4_bm) | (VPORTA_DIR & PIN0_bm)) == 0);
 }

+// No-op: acks are driven from inside the synchronous read path, which a deaf
+// caller never enters.
+void phy_deafen([[maybe_unused]] bool deaf) {}
+
 // True when the bus is being driven (i.e. not idle/floating).
-bool phy_active() { return !BUS_IS_IDLE; }
+bool phy_frame_pending() { return (!BUS_IS_IDLE) != 0; }

 // Mute device TX on AVCLAN bus
 void phy_mute(bool mute) {
@@ -112,11 +120,9 @@ static void set_AVC_logic_for(uint8_t val, uint16_t period) {
    AVCLAN_setBusDriven();
  }
  while (TCB1.CNT <= period) {};
-
-  return;
 }

-void phy_send_bit(Bit bit) {
+static void phy_send_bit(Bit bit) {
  uint16_t zero_length, one_length;
  switch (bit) {
    case bit_zero:
@@ -137,7 +143,7 @@ void phy_send_bit(Bit bit) {
  set_AVC_logic_for(1, one_length);
 }

-void phy_send_ack() {
+static void phy_send_ack() {
  TCB1.CNT = 0;

  // Wait for controller to begin ACK bit
@@ -151,7 +157,7 @@ void phy_send_ack() {
  phy_send_bit(bit_zero);
 }

-Send phy_read_ack() {
+static Send phy_read_ack() {
  TCB1.CNT = 0;                              // Double reset of TCB1.CNT: here
  set_AVC_logic_for(0, AVCLAN_BIT1_LOGIC_0); // And here (within)
  AVCLAN_setBusIdle();                       // Stop driving bus
@@ -166,13 +172,13 @@ Send phy_read_ack() {
  // Check/wait in case we get here before peripheral finishes ACK bit
  while (!BUS_IS_IDLE) {
    if (TCB1.CNT > AVCLAN_BIT_LENGTH_MAX)
-      return NAK;
+      return NAK_TOO_LONG;
  }
  return (Send)0;
 }

 // Send `len` bits on the AVCLAN bus; returns the even parity
-Bit phy_send_bits_u8(const uint8_t *bits, int8_t len) {
+static Bit phy_send_bits_u8(const uint8_t *bits, int8_t len) {
  uint8_t b = *bits;
  uint8_t parity = 0;
  int8_t len_mod8 = 8;
@@ -191,17 +197,19 @@ Bit phy_send_bits_u8(const uint8_t *bits, int8_t len) {
      b <<= 1;
    }
    len_mod8 = 8;
-    b = *--bits;
+    // Avoid under-read for last byte
+    if (len > 0)
+      b = *--bits;
  }
  return (parity & 1);
 }

 // Send `len` bits on the AVCLAN bus; returns the even parity
-Bit phy_send_bits_u16(const uint16_t *bits, int8_t len) {
+static Bit phy_send_bits_u16(const uint16_t *bits, int8_t len) {
  return phy_send_bits_u8((const uint8_t *)bits + 1, len);
 }

-Bit phy_send_byte(const uint8_t *byte) {
+static Bit phy_send_byte(const uint8_t *byte) {
  uint8_t b = *byte;
  uint8_t parity = 0;

@@ -225,19 +233,22 @@ ISR(TCB0_INT_vect) {
  //   last_tcb1 = cur_tcb1;
  // #endif

-  READING_BYTE <<= 1;
  // If the logical `0` pulse was less than the sync + data period threshold,
  // bit was a 1
-  pulsewidth = TCB0.CCMP;
-  if (pulsewidth < (uint16_t)AVCLAN_READBIT_THRESHOLD) {
-    READING_BYTE++;
-    READING_PARITY++;
+  uint16_t tmp = pulsewidth = TCB0.CCMP; // non-volatile tmp saves re-read in
+                                         // read-bit-threshold comparison
+  if (READING_NBITS) {
+    READING_BYTE <<= 1;
+    if (tmp < (uint16_t)AVCLAN_READBIT_THRESHOLD) {
+      READING_BYTE++;
+      READING_PARITY++;
+    }
+    READING_NBITS--;
  }
-  READING_NBITS--;
 }

 // Read `len` bits on the AVCLAN bus; returns the even parity
-Bit phy_read_bits_u8(uint8_t *bits, uint8_t len) {
+static Bit phy_read_bits_u8(uint8_t *bits, uint8_t len) {
  uint8_t parity;
  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
    READING_BYTE = 0;
@@ -264,7 +275,7 @@ Bit phy_read_bits_u8(uint8_t *bits, uint8_t len) {
 }

 // Read `len` bits on the AVCLAN bus; returns the even parity
-Bit phy_read_bits_u16(uint16_t *bits, int8_t len) {
+static Bit phy_read_bits_u16(uint16_t *bits, int8_t len) {
  uint8_t parity = 0;
  if (len > 8) {
    uint8_t over = len - 8;
@@ -277,7 +288,7 @@ Bit phy_read_bits_u16(uint16_t *bits, int8_t len) {
 }

 // Read a byte on the AVCLAN bus
-Bit phy_read_byte(uint8_t *byte) {
+static Bit phy_read_byte(uint8_t *byte) {
  uint8_t parity;
  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
    READING_BYTE = 0;
@@ -303,7 +314,16 @@ Bit phy_read_byte(uint8_t *byte) {
  return (Bit)(parity & 1);
 }

-void phy_init() {
+// Our own peripheral address, and whether the frame being read is addressed to
+// it. hal/phy.h puts the ACK decision in the phy, so the latch that used to
+// live in Bus::read lives here now: set when the peripheral address comes in,
+// and reused by every field after it.
+static uint16_t own_address_;
+static bool acking_;
+
+void phy_init(uint16_t address) {
+  own_address_ = address;
+
  // Set pin 6 and 7 as input
  PORTA.DIRCLR = (PIN6_bm | PIN7_bm);
  // Disable input buffer; recommended when using AC
@@ -338,15 +358,36 @@ void phy_init() {
  phy_mute(false); // unmute AVCLAN bus TX
 }

-// Wait for and validate an incoming start bit. On an over-long "driven" bus
-// (AC2 latched high because the bus is actually floating) this kicks PA7 hard
-// high to unlatch the comparator. The framing layer maps the result to its own
-// error reporting; no printing happens here.
-Read phy_read_startbit() {
-  uint16_t startbitlen = TCB1.CNT = 0;
+static Read phy_read_startbit() {
+  // Following HAL header docs, this function is only called after a driven bus
+  // was ~recently detected.
+  // Two main (designed) entry flows, depending on timing of pulse end w.r.t.
+  // beginning this function:
+  //  - Bus is still driven or ISR is pending
+  //    - Wait for pulse to end if needed
+  //      - On an over-long "driven" bus (AC2 latched high when bus is floating)
+  //      kick PA7 hard high to try unlatching the comparator
+  //    - Grab updated `pulsewidth`
+  //  - Bus is idle
+  //    - `pulsewidth` holds duration of most recent pulse.
+
+  TCB1.CNT = 0;
+
+  // "stale"ness indicates that the current `pulsewidth` value is out of date
+  bool stale = true;
+
+  uint16_t startbitlen;
+  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+    // pulsewidth won't/can't be updated during atomic block, but pulse may end
+    // and store an IRQ. If bus is idle and no pending ISR, then pulsewidth
+    // currrently holds the duration of the most recent pulse (stale = false).
+    stale = (((!BUS_IS_IDLE) | (TCB0.INTFLAGS & TCB_CAPT_bm)) != 0);
+    // Read ~atomically, to prevent torn reads
+    startbitlen = pulsewidth;
+  }
+
  while (!BUS_IS_IDLE) {
-    startbitlen = TCB1.CNT;
-    if (startbitlen > (uint16_t)AVCLAN_STARTBIT_LOGIC_0 * 1.2) {
+    if (TCB1.CNT > (uint16_t)AVCLAN_STARTBIT_LOGIC_0 * 1.2) {
      Read result = STARTBIT_TOO_LONG;
      while (!BUS_IS_IDLE) {
        // If bus is "driven" too long, assume the AC2 is latched (e.g.
@@ -367,24 +408,48 @@ Read phy_read_startbit() {
      return result;
    }
  }
+
+  TCB1.CNT = 0;
+  while (stale) { // bus was driven, or a capture was still unconsumed, at entry
+    uint16_t old_pulsewidth = startbitlen;
+    // `pulsewidth` updates once the TCB0_INT_vect ISR runs for this pulse.
+    // Read ~atomically, to prevent torn reads
+    ATOMIC_BLOCK(ATOMIC_RESTORESTATE) { startbitlen = pulsewidth; }
+    if (startbitlen != old_pulsewidth)
+      break;
+
+    // Exit for potential false-negative: ISR writes for identical mid-frame
+    // bits (e.g. double 0 or 1 bits) can't be detected, but the ISR should
+    // definitely have run after ~6μs (i.e. startbitlen is actually current).
+    // The delay is ultimately free since mid-frame entry is directed to the
+    // "wait-for-message-completion" stall loop anyways
+    if (TCB1.CNT > (uint16_t)AVCLAN_BIT0_LOGIC_1)
+      break;
+  }
+
  if (startbitlen < (uint16_t)(AVCLAN_STARTBIT_LOGIC_0 * 0.8)) {
-    // We missed the beginning of this message; wait for it to finish (bus
-    // continuously idle for >1 bit length) before returning, so we don't have
-    // multiple false-starts while the in-progress message keeps sending more
-    // bits.
+    // Not a start bit; wait for the message to finish (bus continuously idle
+    // for >1 bit length) before returning, so we only report one error (instead
+    // of e.g. repeated "bad (short) start bit" errors)
    TCB1.CNT = 0;
    while (TCB1.CNT < (uint16_t)(AVCLAN_BIT_LENGTH_MAX * 1.2)) {
      if (!BUS_IS_IDLE)
-        TCB1.CNT = 0;
+        TCB1.CNT = 0; // (Re)start count from when bus was last driven
    }
-    return STARTBIT_TOO_SHORT;
+    // A pulse no wider than a normal bit means we merely tuned in mid-frame and
+    // this was a data bit; a wider-but-still-sub-start pulse means some other
+    // device emitted a wonky pulse.
+    return (startbitlen < (uint16_t)AVCLAN_BIT_LENGTH_MAX) ? STARTBIT_MISSED
+                                                           : STARTBIT_MALFORMED;
  }
+  if (startbitlen > (uint16_t)(AVCLAN_STARTBIT_LOGIC_0 * 1.2))
+    return STARTBIT_TOO_LONG;
  return (Read)0; // that was a start bit
 }

 // Acquire the bus and emit a start bit. Returns false if another device is
 // already driving the bus (we can't yet do proper CSMA/CD).
-Send phy_send_startbit() {
+static Send phy_send_startbit() {
  // wait for free line
  TCB1.CNT = 0;
  while (BUS_IS_IDLE) {
@@ -413,6 +478,144 @@ Send phy_send_startbit() {
  return (Send)0;
 }

+// Field bits, then the wire's parity bit, checked against what we counted.
+static Read read_parity(Bit calc, Read bad) {
+  uint8_t wire = 0;
+  phy_read_bits_u8(&wire, 1);
+  return ((uint8_t)calc != wire) ? bad : (Read)0;
+}
+
+// An acknowledge slot follows the field whether or not we drive it, so a frame
+// that isn't ours still has to have the slot read away.
+static void ack_slot(void) {
+  if (acking_) {
+    phy_send_ack();
+  } else {
+    uint8_t slot = 0;
+    phy_read_bits_u8(&slot, 1);
+  }
+}
+
+Read phy_read_header(bool *is_unicast) {
+  acking_ = false; // New frame; nothing is addressed to us yet
+
+  const Read err = phy_read_startbit();
+  if (err != (Read)0)
+    return err;
+
+  uint8_t bit = 0;
+  phy_read_bits_u8(&bit, 1); // Broadcast bit: one bare bit, no parity
+  *is_unicast = (bit != 0);
+  return (Read)0;
+}
+
+Read phy_read_controller_addr(uint16_t *addr) {
+  // No acknowledge slot: this field is the arbitration window.
+  return read_parity(phy_read_bits_u16(addr, 12), BAD_CONTROLLER_PARITY);
+}
+
+Read phy_read_peripheral_addr(uint16_t *addr) {
+  const Read err =
+      read_parity(phy_read_bits_u16(addr, 12), BAD_PERIPHERAL_PARITY);
+  if (err != (Read)0)
+    return err;
+
+  // The one field that decides the ack; every field after it reuses the answer.
+  acking_ = !phy_is_muted() && (*addr == own_address_);
+  ack_slot();
+  return (Read)0;
+}
+
+Read phy_read_control(uint8_t *control) {
+  const Read err =
+      read_parity(phy_read_bits_u8(control, 4), BAD_CONTROL_PARITY);
+  if (err != (Read)0)
+    return err;
+  ack_slot();
+  return (Read)0;
+}
+
+Read phy_read_length(uint8_t *length) {
+  const Read err = read_parity(phy_read_byte(length), BAD_LENGTH_PARITY);
+  if (err != (Read)0)
+    return err;
+  ack_slot();
+  return (Read)0;
+}
+
+Read phy_read_data(uint8_t *data, uint8_t length, uint8_t *data_index) {
+  for (uint8_t i = 0; i < length; i++) {
+    const Read err = read_parity(phy_read_byte(&data[i]), BAD_DATA_PARITY);
+    if (err != (Read)0) {
+      *data_index = i;
+      return err;
+    }
+    ack_slot();
+  }
+  return (Read)0;
+}
+
+// `expect_ack` is "a NAK here is worth reporting", not "emit the slot": the
+// slot goes out either way, and a broadcast frame simply has nobody to fill it.
+static Send send_ack_slot(bool expect_ack, Send nak) {
+  if (expect_ack) {
+    const Send err = phy_read_ack();
+    return err == NAK ? nak : err;
+  }
+
+  const uint8_t fill = 1U;
+  phy_send_bits_u8(&fill, 1);
+  return (Send)0;
+}
+
+Send phy_send_header(bool is_unicast) {
+  const Send err = phy_send_startbit();
+  if (err != (Send)0)
+    return err;
+
+  const uint8_t bit = (is_unicast) ? 1U : 0U;
+  phy_send_bits_u8(&bit, 1); // Broadcast bit: one bare bit, no parity
+  return (Send)0;
+}
+
+Send phy_send_controller_addr(uint16_t addr) {
+  // No acknowledge slot: this field is the arbitration window.
+  phy_send_bit(phy_send_bits_u16(&addr, 12));
+  return (Send)0;
+}
+
+Send phy_send_peripheral_addr(uint16_t addr, bool expect_ack) {
+  phy_send_bit(phy_send_bits_u16(&addr, 12));
+  return send_ack_slot(expect_ack, NAK_ADDRESS);
+}
+
+Send phy_send_control(uint8_t control, bool expect_ack) {
+  phy_send_bit(phy_send_bits_u8(&control, 4));
+  return send_ack_slot(expect_ack, NAK_CONTROL);
+}
+
+Send phy_send_length(uint8_t length, bool expect_ack) {
+  phy_send_bit(phy_send_byte(&length));
+  return send_ack_slot(expect_ack, NAK_MESSAGE_LENGTH);
+}
+
+Send phy_send_data(const uint8_t *data, uint8_t length, bool expect_ack,
+                   uint8_t *data_index) {
+  for (uint8_t i = 0; i < length; i++) {
+    phy_send_bit(phy_send_byte(&data[i]));
+    const Send err = send_ack_slot(expect_ack, NAK_DATA);
+    if (err != (Send)0) {
+      *data_index = i;
+      return err;
+    }
+  }
+  return (Send)0;
+}
+
+// Every field above is on the wire, and has reported its own outcome, by the
+// time it returns: nothing is left to wait out or attribute.
+Send phy_send_done([[maybe_unused]] uint8_t *data_index) { return (Send)0; }
+
 /* Disable non-read related interrupts (USART RX, RTC status tick, mic timer)
   during AVCLAN bus transactions so framing isn't disturbed. TCB0 must remain
   enabled. */
@@ -433,9 +636,30 @@ void phy_guard_leave() {
 }

 #ifndef NDEBUG
-  // Only used immediately below
-  #define XSTR(x) #x
-  #define STR(x)  XSTR(x)
+
+// Hold the bus at a given level.
+// Overrides and restores mute state upon release (i.e. set recessive).
+static void phy_set_state(bool dominant) {
+  static bool saved_mute = false;
+  if (dominant) {
+    saved_mute = phy_is_muted();
+    AVCLAN_setBusDriven();
+    phy_mute(false);
+  } else {
+    AVCLAN_setBusIdle();
+    phy_mute(saved_mute);
+  }
+}
+
+void phy_set_dominant(void) { phy_set_state(true); }
+void phy_set_recessive(void) { phy_set_state(false); }
+
+  #ifdef MEASURE_BUS
+    #include <stdio.h> // phy_measure() reporting (debug builds only)
+
+    // Only used immediately below
+    #define XSTR(x) #x
+    #define STR(x)  XSTR(x)

 static uint16_t pulses[100];
 static uint16_t periods[100];
@@ -468,4 +692,6 @@ void phy_measure() {

  phy_guard_leave();
 }
+
+  #endif
 #endif
@@ -4,11 +4,27 @@
 #include <avr/io.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h>
+#include <util/atomic.h>

 #include "hal/stdio.h"
 #include "timing_avr.h" // IWYU pragma: export
 #include "usart.h"      // jnk0le AVR-UART-lib

+// TX ring owned by the jnk0le lib. `tx0_Head` is the index of the last byte
+// written, so the next write goes to head+1. The DRE ISR reads tail+1 and then
+// advances `tx0_Tail`. The ring is empty when the two indexes are equal. The
+// ring holds at most TX0_BUFFER_SIZE-1 bytes.
+extern char tx0_buffer[TX0_BUFFER_SIZE];
+
+// stdio_write_nonblock() is all-or-nothing. If the ring cannot hold the largest
+// buffer that the app writes, the function drops every buffer and queues none.
+// The largest buffer is a text frame log line (Frame::print). That line is
+// ~186 bytes at MAXLENGTH=32. The ring therefore needs headroom above this
+// size.
+static_assert(TX0_BUFFER_SIZE - 1 >= 192,
+              "TX ring too small to hold a whole frame log line");
+
 // Raw stdout backend: emit the byte verbatim, no '\n' -> "\r\n" translation
 // (unlike the lib's uart_putchar). Keeps binary frame payloads intact.
 static int stdio_putchar(char data, FILE *stream) {
@@ -17,6 +33,67 @@ static int stdio_putchar(char data, FILE *stream) {
  return 0;
 }

+bool stdio_write_nonblock(const void *buf, uint8_t len) {
+  if (len == 0)
+    return true;
+
+  // A single unguarded read of each index is enough:
+  //  - Only main writes tx0_Head.
+  //  - Only the DRE ISR writes tx0_Tail.
+  //  - 8-bit accesses are atomic on AVR.
+  // If the ISR advances the tail during this function, the ring has more free
+  // space than this function measured. That direction is safe.
+  const uint8_t head = tx0_Head;
+  const uint8_t space = (uint8_t)((tx0_Tail - head - 1) & TX0_BUFFER_MASK);
+  if (len > space) {
+    // The ring cannot take the whole buffer, so drop it and queue the indicator
+    // instead. A buffer may be refused because it is larger than
+    // available space or because the ring is full. For the former case, the
+    // full indicator can be appended without truncating previously queued
+    // bytes.
+    // Goal is for the bang-indicator to be on its own line
+    uint8_t tmp = head;
+    if (space >= 3) {
+      // Room for 3 normally implies the current head ends with a newline
+      // (avoids an unneeded double newline in most cases)
+      tmp = (tmp + 1) & TX0_BUFFER_MASK;
+      tx0_buffer[tmp] = '!';
+      tmp = (tmp + 1) & TX0_BUFFER_MASK;
+      tx0_buffer[tmp] = '\n';
+      tx0_Head = tmp;
+      ATOMIC_BLOCK(ATOMIC_RESTORESTATE) { USART0.CTRLA |= USART_DREIE_bm; }
+    } else {
+      // No room for even the indicator, so it goes over the last three queued
+      // bytes. The ISR already drains the ring, so DREIE needs no change.
+      // Write in reverse order to more efficiently decrement
+      tx0_buffer[tmp] = '\n';
+      tmp = (tmp - 1) & TX0_BUFFER_MASK;
+      tx0_buffer[tmp] = '!';
+      tmp = (tmp - 1) & TX0_BUFFER_MASK;
+      tx0_buffer[tmp] = '\n';
+    }
+    return false;
+  }
+
+  const uint8_t start = (uint8_t)((head + 1) & TX0_BUFFER_MASK);
+  const uint8_t contiguous = TX0_BUFFER_SIZE - start;
+
+  if (len <= contiguous) {
+    memcpy(&tx0_buffer[start], buf, len);
+  } else { // wraps the end of the ring
+    memcpy(&tx0_buffer[start], buf, contiguous);
+    memcpy(&tx0_buffer[0], (const char *)buf + contiguous, len - contiguous);
+  }
+
+  // Publish the bytes only after all of them are in place. This is a single
+  // store, so the ISR never sees a partly filled buffer.
+  tx0_Head = (uint8_t)((head + len) & TX0_BUFFER_MASK);
+
+  // The ISR also writes CTRLA (to clear DREIE when it drains the last byte).
+  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) { USART0.CTRLA |= USART_DREIE_bm; }
+  return true;
+}
+
 // Non-blocking stdin backend: next received byte, or _FDEV_EOF when the RX ring
 // is empty (uart0_getData() returns a negative value when there is no data).
 static int stdio_getchar(FILE *stream) {
@@ -34,14 +111,14 @@ void stdio_init(void) {
  // The lib's uart0_init configures the USART registers/baud but not the pins;
  // keep the ATtiny3216 pin-mux the old driver did.
  PORTMUX.CTRLB = PORTMUX_USART0_ALTERNATE_gc; // TxD/RxD on PA1/PA2
-  PORTA.DIRSET = PIN1_bm;                       // TxD output
-  PORTA.DIRCLR = PIN2_bm;                       // RxD input
+  PORTA.DIRSET = PIN1_bm;                      // TxD output
+  PORTA.DIRCLR = PIN2_bm;                      // RxD input

-  #ifdef USE_DOUBLE_SPEED
+#ifdef USE_DOUBLE_SPEED
  uart0_init(DOUBLE_BAUD_CALC(1200000));
-  #else
+#else
  uart0_init(BAUD_CALC(1200000));
-  #endif
+#endif

  stdout = stdin = &stdio_stream; // printf/fputs/fwrite + non-blocking getchar
 }
@@ -63,4 +63,4 @@
 // TCB_TICK is nanoseconds/tick; the generic timing.h wants microseconds/tick.
 #define TICK_US (TCB_TICK / 1000.0)

-#include "timing.h"
+#include "timing.h" // IWYU pragma: export
@@ -108,11 +108,11 @@

 // Size of the ring buffers, must be power of 2
 // default 32
-#define RX_BUFFER_SIZE 64
+#define RX_BUFFER_SIZE 128

 // Size of the ring buffers, must be power of 2
 // default 32
-#define TX_BUFFER_SIZE 128
+#define TX_BUFFER_SIZE 256

 /*******************config for multiple USART * mcu's*************************/

@@ -0,0 +1,79 @@
+pico_sdk_init()
+
+include_directories(
+    ${CMAKE_CURRENT_LIST_DIR}
+    include
+)
+FetchContent_Declare( freertos_kernel
+  EXCLUDE_FROM_ALL
+  GIT_REPOSITORY https://github.com/FreeRTOS/FreeRTOS-Kernel.git
+  GIT_TAG        3a22924e0a9ddbbc8b0758881c33b3422a5cc20d # v11.3.1
+)
+add_library(freertos_config INTERFACE)
+target_include_directories(freertos_config SYSTEM
+  INTERFACE
+    include
+)
+target_compile_definitions(freertos_config
+  INTERFACE
+    projCOVERAGE_TEST=0
+)
+target_compile_options(freertos_config
+  INTERFACE
+    $<$<COMPILE_LANGUAGE:CXX>:-Wno-volatile>
+)
+
+set( FREERTOS_PORT "GCC_RP2040" CACHE STRING "" FORCE)
+FetchContent_MakeAvailable(freertos_kernel)
+set(FREERTOS_KERNEL_PATH "${freertos_kernel_SOURCE_DIR}" CACHE STRING "" FORCE)
+include(${freertos_kernel_SOURCE_DIR}/portable/ThirdParty/GCC/RP2040/FreeRTOS_Kernel_import.cmake)
+
+target_sources(avclan PRIVATE
+    phy.cc
+    media.cc
+    board.cc
+    stdio.cc
+    )
+pico_generate_pio_header(avclan ${CMAKE_CURRENT_LIST_DIR}/iebus.pio)
+
+target_link_libraries(avclan PUBLIC
+    hardware_pio
+    hardware_dma
+    pico_stdlib 
+    pico_stdio_usb
+    pico_multicore
+    pico_async_context_freertos
+    freertos_config
+    FreeRTOS-Kernel-Heap4
+)
+pico_enable_stdio_usb(avclan 1)
+
+# stdio_write_nonblock() is all-or-nothing and the largest buffer is a ~186 byte
+# frame log line; the SDK default of 64 would drop every one. PUBLIC so the
+# TinyUSB sources compiled into `mockingboard` agree on the FIFO size.
+target_compile_definitions(avclan PUBLIC CFG_TUD_CDC_TX_BUFSIZE=256)
+
+# Needs separate/new executable target because `pico_add_extra_outputs` only
+# works on locally (to this file/directory) defined targets
+add_executable(mockingboard
+    ${avclan-mockingboard_SOURCE_DIR}/src/sniffer.cc
+)
+target_link_libraries(mockingboard PUBLIC
+    avclan
+)
+
+# Silence warnings in TinyUSB, and only there.
+file(GLOB_RECURSE _tinyusb_sources ${PICO_TINYUSB_PATH}/src/*.c)
+set_source_files_properties(${_tinyusb_sources}
+    TARGET_DIRECTORY avclan mockingboard
+    PROPERTIES COMPILE_OPTIONS "-w")
+unset(_tinyusb_sources)
+
+pico_add_extra_outputs(mockingboard)
+
+pico_set_program_description(mockingboard
+    "Emulate an external CD Changer on an AVCLAN bus to add Bluetooth and aux-input audio to older Toyota's"
+)
+pico_set_program_version(mockingboard 
+    "${avclan-mockingboard_VERSION}")
+pico_set_program_url(mockingboard "https://github.com/halleysfifthinc/AVCLAN-Mockingboard")
@@ -0,0 +1,5 @@
+#include "hal/board.h"
+
+extern "C" void board_init() {}
+
+extern "C" void board_enable_interrupts() {}
@@ -0,0 +1,268 @@
+.define public ack_latch        4   ; (PIO0, internal) frame is addressed to us
+.define public ack_irq          5   ; (PIO1) rx -> iebus_ack: hold this slot low
+
+; This is used to set the clkdiv.
+; The delay cycle counts in read_bit (AVCLAN_READBIT_THRESHOLD) and iebus_tx's
+; ack_drive (AVCLAN_BIT0_LOGIC_0) must be updated in sync with this variable
+.define public CYCLES_PER_READBIT_PERIOD 64
+
+.pio_version 1
+
+.program iebus_rx
+
+; TX encoding: one read per word
+; |   31    | 30:16 | 15:0  |
+; | has ACK | zeros | Instr |
+;
+; Instr must be `out x, (14 - N)` for a read of N bits + parity, or `jmp rx_startbit`.
+; The `out` zeroes x (the parity accumulator) and leaves exactly N + 1 bits before
+; the OSR reaches its threshold, which ends the read loop. "has ACK" marks a field
+; followed by an acknowledge slot.
+;
+; RX encoding: one read per word (RX FIFO can hold max 4 reads)
+; | 31:16 | 15:0 |
+; | zeros | slot |
+;
+; where each slot is encoded as
+; | MSB .................... LSB |
+; | 15-N zeros | N bits | parity |
+;
+; Parity is validated by this SM, but is still reported in the LSB. `y` is reserved
+; for the address match below.
+
+.in 1 left
+; OSR threshold set to 31 so that the OSRE is reached when all the data+parity bits
+; have been read
+.out 0 right 31
+.mov_status irq set ack_latch
+
+;;; Start-bit read (auto-resets until a proper start bit is observed)
+; A start bit is dominant for AVCLAN_STARTBIT_LOGIC_0 (~169us) and recessive for
+; AVCLAN_STARTBIT_LOGIC_0 (~20us) more.
+; The bus state is polled as fast as target bounds (80% and 120%) can be evenly
+; divided (must be faster than shortest recessive period  AVCLAN_BIT0_LOGIC_1 to
+; detect/distinguish normal bits mid-frame).
+public rx_startbit:
+    wait 1 pin 0
+leading_edge:
+    wait 0 pin 0
+    set x 29
+dominant:
+    jmp pin leading_edge [10]  ; Pin HIGH == released before 0.8x: not a start bit
+                            ; Polled every 11 cycles, starting 2 cycles after leading edge
+                            ; Last poll at 332 cycles (~80% * AVCLAN_STARTBIT_LOGIC_0)
+    jmp x-- dominant        ; Cycle 333 on fall-through
+    set x 18                ; 334
+recessive:
+    jmp pin valid_startbit  ; Pin HIGH == released within bounds
+    jmp x-- recessive [8]   ; + 19 * 9 = 506 total (~120% * AVCLAN_STARTBIT_LOGIC_0)
+                            ; Delay on decrement jmp to keep the release jmp quick
+    jmp rx_startbit         ; Still dominant: too long to be proper start bit
+valid_startbit:
+    irq clear ack_latch     ; Once per frame, before any address can set it
+
+.wrap_target
+wait_read:
+    pull
+    out exec, 16            ; Set up the read (zero x and set up output shift 
+                            ; count as bit count), or jmp to rx_startbit
+
+read_bit:
+;;; Resynchronize at each leading (recessive => dominant) edge
+    wait 1 pin 0
+    ; Worst-case (slowest) path to return here is for non-ACK flow.
+    wait 0 pin 0 [31]
+    out null, 1  [31]       ; Count this bit
+    ; Read bus state ~AVCLAN_READBIT_THRESHOLD after bus goes dominant
+    in pins, 1
+    jmp pin counted         ; Fall through for recessive (i.e. a one bit)
+    mov x, ~x               ; Accumulate parity over the zero bits
+counted:
+    jmp !osre read_bit
+
+;;; Check parity
+; Every parity-checked field is an odd number of bits, so even parity (an even
+; number of ones) is an odd number of zeros: x == ~0. The broadcast bit has no
+; parity; its verdict can only clear a latch that was never set.
+    jmp x-- parity_ok
+    irq clear ack_latch     ; NAK this field and the rest of the frame
+
+;;; Check if we're the frame recipient
+; Our peripheral address can only appear in individual 12-bit reads as the
+; controller or peripheral address. We should only ack if we're the frame recipient.
+; y is preset in phy_init to our peripheral address + parity, and temporarily
+; inverted when we are sending (so we don't self-ACK)
+parity_ok:
+    mov x, isr          ; Save read value before clobbering the ISR with push
+    jmp x!=y push_slot  ; Fall-through to set ACK latch only if the read matches 
+                        ; our address + parity
+    irq set ack_latch   ; Set before the push, so the driver's veto can't be overwritten
+
+push_slot:
+    push
+
+;;; Consume the ack slot if has ACK, driving it if ACK latch is set
+    out x, 1                ; Load "has ACK"
+    jmp !x wait_read
+    wait 1 pin 0
+    wait 0 pin 0 [30]       ; Sender begins the ACK bit, and will hold it dominant
+                            ; for ~48 cycles (~AVCLAN_BIT1_LOGIC_0) before releasing
+                            ; for peripheral to take over
+                            ; Delay reloading ack_latch to give the driver as much
+                            ; time as possible to veto an ACK (i.e. clear it for
+                            ; e.g. a bad length)
+    mov x, status           ; Load ack_latch state into x
+    jmp !x wait_read
+    irq next set ack_irq    ; The ack SM (iebus_tx's ack_entry, on the other (TX)
+                            ; PIO) is released 32 cycles after sender began bit,
+                            ; and its jmp to ack_drive takes the slot over at 34
+                            ; (~70% of AVCLAN_BIT1_LOGIC_0), holding it dominant.
+.wrap
+
+; Can execute one streamed instruction every 3 cycles
+; An even number of instructions must be executed to maintain the correct shift-count/autopull
+; when returning to normal reads after exec'ing. Pad instructions with `nop` as needed.
+; public do_exec:
+;     out exec, 16        ; Cycle 1: Load the streamed instruction
+;                         ; Cycle 2: Execute the streamed instruction
+;     jmp x-- do_exec     ; Cycle 3: Restart loop (if x != 0)
+;     jmp wait_read
+
+.program iebus_tx
+.fifo tx
+
+; TX Encoding (8 deep TX FIFO):
+; | MSB ............................................. LSB |
+; |   4 bits   | N bits | 5 bits |  1 bit  | 22 - N bits |
+; | Length (N) | Data+P |  Next  | NAK ok  |   padding   |
+;
+; Parity is generated by the driver and appended as the last (least significant)
+; bit of the data field. "Next" should be the address of `reset` or `ack_drive`
+
+.in 1 left
+.out 1 left
+
+.define public nak_irq      7
+.define public lost_arb_irq 6
+.define public eof_irq      3   ; An acknowledge slot is over
+
+;;; Emit or synchronize to a start bit
+; Reached by a CPU initiated force exec jmp to tx_startbit, with x = JOIN_SAMPLES
+; and y = IDLE_SAMPLES. We originate once the bus has stayed recessive for the
+; idle window. A dominant pulse is joined only if it outlasts every bit's
+; dominant period (i.e. it's a start bit); otherwise the bus is busy, reported as
+; a lost bid before any word is pulled.
+.define public IDLE_SAMPLES 11  ; 12 * 16 = 192 cycles (~2 * AVCLAN_BIT_LENGTH_MAX)
+; TODO: Explore tightening the idle window to 3 * AVCLAN_STARTBIT_LOGIC_1 (the
+; longest recessive period within a frame)
+.define public JOIN_SAMPLES 8   ; 9 * 12 = 108 cycles (> 1.2 * AVCLAN_BIT0_LOGIC_0)
+
+idle_ok:
+    jmp y-- tx_startbit [14]    ; Sampled every 16 cycles
+    set x 31                    ; Idle: originate
+    set pins, 0     [30]
+public tx_startbit:
+    jmp pin idle_ok
+hold:
+    jmp pin lost            ; Released too soon for a start bit (never while we drive)
+    jmp x-- hold    [10]    ; Sampled every 12 cycles, within a zero bit's recessive
+                            ; period (~AVCLAN_BIT0_LOGIC_1). Ours is 31 + 1 + 32 * 12
+                            ; = 416 total (~AVCLAN_STARTBIT_LOGIC_0)
+    set pins, 1             ; Release
+    wait 1 pin 0    [31]    ; The start bit's trailing edge, whoever drove it
+    jmp reset       [16]    ; 51 cycles from that edge to reset's first
+                            ; `set pins, 0` (~AVCLAN_STARTBIT_LOGIC_1)
+
+handle_nak:
+    jmp x-- ack_done        ; Slot is over either way if a NAK was expected
+    irq wait nak_irq
+
+;;; Close the acknowledge slot
+; The peripheral owns this slot's trailing edge, so the recessive period that
+; ends the slot is timed from its release rather than from our leading edge --
+; the one bit in a frame we don't drive to completion ourselves. A slot nobody
+; answered is already recessive and falls straight through.
+ack_done:
+    wait 1 pin 0    [11]    ; 15 cycles from the release to `set pins, 0` below
+                            ; (~AVCLAN_BIT0_LOGIC_1)
+    irq set eof_irq
+
+reset:
+.wrap_target
+    pull
+    out x, 4
+
+send_bit:
+    set pins, 0     [31]    ; OUT pin remains low/dominant for 32+16 cycles (~AVCLAN_BIT1_LOGIC_0)
+    out y, 1        [15]    ; Save output bit to y
+    mov pins, y     [15]    ; Output the bit
+    ; Read bus state ~AVCLAN_READBIT_THRESHOLD after bus goes dominant
+    jmp pin bit_end [13]    ; JMP_PIN must be the IEBUS_RX pin (TX activity will mirror
+                            ; back to the RX pin). The delay burns the common duration 
+                            ; between the one and zero bits.
+
+bit_zero:
+    ; This branch catches a difference between what we intended to send and what is actually
+    ; present on the bus (a difference is only expected/allowed during send arbitration, 
+    ; where lower addresses have higher priority: since one bits are recessive, another 
+    ; device sending a zero will "override" the value of that bit)
+    jmp !y bit_end  [2]     ; Delay 3 more cycles before releasing bus at ~AVCLAN_BIT0_LOGIC_0
+    ; Fall through means we lost arbitration (we read a zero, when we expected a one)
+lost:
+    irq wait lost_arb_irq
+.wrap
+
+bit_end:
+    set pins, 1         [9]     ; Delay must be common to all following control flow paths
+    jmp x-- slow_jmp            ; Fall through once x (the bit count) is exhausted
+    out pc, 5           [1]     ; "Next": reset, or ack_drive to read ACK
+
+;;; read ack
+public ack_drive:
+    set pins, 0         [31]    ; Start ACK bit with a AVCLAN_BIT1_LOGIC_0 length pulse
+    out x, 1            [15]    ; Preload NAK ok
+public ack_release:
+    set pins, 1         [15]    ; Release bus
+    jmp pin handle_nak  [13]    ; Sampled at 64 cycles (~AVCLAN_READBIT_THRESHOLD);
+                                ; both flow paths reach ack_done one instr later
+    jmp ack_done
+
+slow_jmp:
+    jmp send_bit        [3]     ; 15 cycles from bit_end to `set pins, 0`, the same
+                                ; as the last bit's path through `out pc` and reset
+
+;;; Send an ack for iebus_rx
+; Run by its own SM, wrapping from ack_release back to ack_entry: it borrows
+; ack_drive's 48-cycle pulse to hold the slot dominant for *less than* a complete
+; AVCLAN_BIT0_LOGIC_0, releasing at ~AVCLAN_BIT0_LOGIC_0 after the slot's
+; leading edge.
+public ack_entry:
+    wait 1 irq ack_irq          ; Released by iebus_rx after bus goes dominant
+    jmp ack_drive
+
+; `mov pins, pins` reads the IN mapping (bit 0 == in base) and writes the OUT
+; mapping (out base, 1 pin), so one program instance serves any src->dst pair;
+; give each pair its own SM with its own pin mapping.
+.program pin_mirror
+    mov pins, ~pins
+
+; === IDIOMS ===
+
+;;; Isolate first bit (for left shifting)
+;   mov osr, ::isr      ; Reverse ISR so its LSB becomes the MSB in osr
+;   out x, 1            ; Set LSB of x from MSB of osr
+
+;;; Incrementing (counting up)
+;   set x 0
+;   set x ~x            ; x == 0xffffffff
+;   jmp x-- label       ; "Increment"
+;   set x ~x            ; Re-inversing gives the actual count
+
+;;; Multiplying delays/counts (e.g. 2*20)
+;   set y 1
+; loop1:
+;   set x 19
+; loop2:
+;   jmp x-- loop2
+
+
@@ -0,0 +1,161 @@
+/*
+ * FreeRTOS V202111.00
+ * Copyright (C) 2020 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ * http://www.FreeRTOS.org
+ * http://aws.amazon.com/freertos
+ *
+ * 1 tab == 4 spaces!
+ */
+
+#ifndef FREERTOS_CONFIG_EXAMPLES_COMMON_H
+#define FREERTOS_CONFIG_EXAMPLES_COMMON_H
+
+/*-----------------------------------------------------------
+ * Application specific definitions.
+ *
+ * These definitions should be adjusted for your particular hardware and
+ * application requirements.
+ *
+ * THESE PARAMETERS ARE DESCRIBED WITHIN THE 'CONFIGURATION' SECTION OF THE
+ * FreeRTOS API DOCUMENTATION AVAILABLE ON THE FreeRTOS.org WEB SITE.
+ *
+ * See http://www.freertos.org/a00110.html
+ *----------------------------------------------------------*/
+
+/* Scheduler Related */
+#define configUSE_PREEMPTION     1
+#define configUSE_TICKLESS_IDLE  0
+#define configCPU_CLOCK_HZ       (150000000UL)
+#define configTICK_RATE_HZ       ((TickType_t)1000)
+#define configMAX_PRIORITIES     32
+#define configMINIMAL_STACK_SIZE (configSTACK_DEPTH_TYPE)512
+#define configIDLE_SHOULD_YIELD  1
+#define configUSE_16_BIT_TICKS   0
+#define configUSE_IDLE_HOOK      0
+#define configUSE_TICK_HOOK      0
+
+/* Synchronization Related */
+#define configUSE_MUTEXES                       1
+#define configUSE_RECURSIVE_MUTEXES             1
+#define configUSE_APPLICATION_TASK_TAG          0
+#define configUSE_COUNTING_SEMAPHORES           1
+#define configQUEUE_REGISTRY_SIZE               8
+#define configUSE_QUEUE_SETS                    1
+#define configUSE_TIME_SLICING                  1
+#define configUSE_NEWLIB_REENTRANT              0
+#define configENABLE_BACKWARD_COMPATIBILITY     0
+#define configNUM_THREAD_LOCAL_STORAGE_POINTERS 5
+
+/* System */
+#define configSTACK_DEPTH_TYPE           uint32_t
+#define configMESSAGE_BUFFER_LENGTH_TYPE size_t
+
+/* Memory allocation related definitions. */
+#ifndef configSUPPORT_STATIC_ALLOCATION
+  #define configSUPPORT_STATIC_ALLOCATION 0
+#endif
+#ifndef configSUPPORT_DYNAMIC_ALLOCATION
+  #define configSUPPORT_DYNAMIC_ALLOCATION 1
+#endif
+#define configTOTAL_HEAP_SIZE            (128 * 1024)
+#define configAPPLICATION_ALLOCATED_HEAP 0
+
+/* Hook function related definitions. */
+#define configCHECK_FOR_STACK_OVERFLOW     0
+#define configUSE_MALLOC_FAILED_HOOK       0
+#define configUSE_DAEMON_TASK_STARTUP_HOOK 0
+
+/* Run time and task stats gathering related definitions. */
+#define configGENERATE_RUN_TIME_STATS        0
+#define configUSE_TRACE_FACILITY             1
+#define configUSE_STATS_FORMATTING_FUNCTIONS 0
+
+/* Co-routine related definitions. */
+#define configUSE_CO_ROUTINES           0
+#define configMAX_CO_ROUTINE_PRIORITIES 1
+
+/* Software timer related definitions. */
+#define configUSE_TIMERS             1
+#define configTIMER_TASK_PRIORITY    (configMAX_PRIORITIES - 1)
+#define configTIMER_QUEUE_LENGTH     10
+#define configTIMER_TASK_STACK_DEPTH 1024
+
+/* Interrupt nesting behaviour configuration. */
+/*
+#define configKERNEL_INTERRUPT_PRIORITY         [dependent of processor]
+#define configMAX_SYSCALL_INTERRUPT_PRIORITY    [dependent on processor and
+application] #define configMAX_API_CALL_INTERRUPT_PRIORITY   [dependent on
+processor and application]
+*/
+
+#if FREE_RTOS_KERNEL_SMP // set by the RP2xxx SMP port of FreeRTOS
+  /* SMP port only */
+  #ifndef configNUMBER_OF_CORES
+    #define configNUMBER_OF_CORES 2
+  #endif
+  #define configNUM_CORES               configNUMBER_OF_CORES
+  #define configTICK_CORE               0
+  #define configRUN_MULTIPLE_PRIORITIES 1
+  #if configNUMBER_OF_CORES > 1
+    #define configUSE_CORE_AFFINITY 1
+  #endif
+  #define configUSE_PASSIVE_IDLE_HOOK 0
+#endif
+
+/* RP2040 specific */
+#define configSUPPORT_PICO_SYNC_INTEROP 1
+#define configSUPPORT_PICO_TIME_INTEROP 1
+
+#include <assert.h>
+/* Define to trap errors during development. */
+#define configASSERT(x) assert(x)
+
+/* Set the following definitions to 1 to include the API function, or zero
+to exclude the API function. */
+#define INCLUDE_vTaskPrioritySet            1
+#define INCLUDE_uxTaskPriorityGet           1
+#define INCLUDE_vTaskDelete                 1
+#define INCLUDE_vTaskSuspend                1
+#define INCLUDE_vTaskDelay                  1
+#define INCLUDE_xTaskDelayUntil             1
+#define INCLUDE_xTaskGetSchedulerState      1
+#define INCLUDE_xTaskGetCurrentTaskHandle   1
+#define INCLUDE_uxTaskGetStackHighWaterMark 1
+#define INCLUDE_xTaskGetIdleTaskHandle      1
+#define INCLUDE_eTaskGetState               1
+#define INCLUDE_xTimerPendFunctionCall      1
+#define INCLUDE_xTaskAbortDelay             1
+#define INCLUDE_xTaskGetHandle              1
+#define INCLUDE_xTaskResumeFromISR          1
+#define INCLUDE_xQueueGetMutexHolder        1
+
+#if PICO_RP2350
+  #define configENABLE_MPU                     0
+  #define configENABLE_TRUSTZONE               0
+  #define configRUN_FREERTOS_SECURE_ONLY       1
+  #define configENABLE_FPU                     1
+  #define configMAX_SYSCALL_INTERRUPT_PRIORITY 16
+#endif
+
+/* A header file that defines trace macro can be included here. */
+
+#endif /* FREERTOS_CONFIG_H */
@@ -0,0 +1,10 @@
+#include "hal/media.h"
+
+extern "C" void media_init(void) {}
+
+extern "C" void media_action(MediaAction fn) {}
+
+#ifndef NDEBUG
+extern "C" bool media_mic_toggle(void) { return false; }
+extern "C" bool media_busy(void) { return false; }
+#endif
@@ -0,0 +1,96 @@
+
+#include <cerrno>
+#include <cstdio>
+#include <unistd.h>
+
+#include "FreeRTOS.h" // IWYU pragma: export
+#include "semphr.h"
+
+#include "hal/stdio.h"
+#include "pico/stdio.h"
+#include "pico/stdio_usb.h"
+#include "pico/time.h"
+#include "tusb.h" // IWYU pragma: export
+
+// stdio_write_nonblock() is all-or-nothing. The CDC TX FIFO must hold the
+// largest buffer the app writes; that is a text frame log line (Frame::print),
+// ~186 bytes at MAXLENGTH=32.
+static_assert(CFG_TUD_CDC_TX_BUFSIZE >= 256,
+              "CDC TX FIFO too small to hold a whole frame log line");
+
+namespace {
+// Set when a dropped buffer had no room for its indicator; the next call emits
+// it. The AVR port instead overwrites the last three queued bytes, which
+// collapses a burst of drops to a single '!' line in exactly the same way.
+bool drop_indicator_pending = false;
+
+// stdout's only backend here is the usb driver, which writes into the same CDC
+// TX FIFO measured below, so printf and this share one stream and one order.
+void queue(const char *str, int len) {
+  stdio_put_string(str, len, false, false);
+}
+
+SemaphoreHandle_t rx_ready = nullptr;
+
+// Called from the stdio_usb background IRQ after each tud_task() with RX data
+// pending.
+void on_rx([[maybe_unused]] void *param) {
+  BaseType_t woken = false;
+  xSemaphoreGiveFromISR(rx_ready, &woken);
+  portYIELD_FROM_ISR(woken);
+}
+} // namespace
+
+extern "C" void stdio_init() {
+  rx_ready = xSemaphoreCreateBinary();
+  stdio_usb_init();
+  stdio_set_chars_available_callback(on_rx, nullptr);
+  stdio_set_translate_crlf(&stdio_usb, false);
+  // pico_stdio wraps printf/puts/putchar straight onto the CDC, but not
+  // fputs/fwrite. Unbuffered stdout keeps the newlib path in step with them
+  // instead of stranding whole strings in the FILE buffer.
+  setvbuf(stdout, nullptr, _IONBF, 0);
+}
+
+// Overrides the SDK's weak newlib hook, which busy-waits.
+extern "C" int _read(int handle, char *buffer, int length) {
+  if (handle != STDIN_FILENO) {
+    errno = EBADF;
+    return -1;
+  }
+
+  while (true) {
+    const int count = stdio_get_until(buffer, length, make_timeout_time_us(0));
+    if (count > 0)
+      return count;
+    xSemaphoreTake(rx_ready, portMAX_DELAY);
+  }
+}
+
+extern "C" bool stdio_write_nonblock(const void *buf, uint8_t len) {
+  uint32_t avail = tud_cdc_write_available();
+
+  if (drop_indicator_pending) {
+    if (avail < 3)
+      return false;
+    queue("!\n", 2);
+    drop_indicator_pending = false;
+    avail -= 2;
+  }
+
+  if (len == 0)
+    return true;
+
+  if (len <= avail) {
+    queue(static_cast<const char *>(buf), len);
+    return true;
+  }
+
+  // Every buffer ends with '\n', so the FIFO already sits at a line boundary.
+  if (avail >= 3)
+    queue("!\n", 2);
+  else
+    drop_indicator_pending = true;
+
+  return false;
+}
@@ -3,101 +3,39 @@

 #pragma once

-#include <array>
-#include <concepts>
-#include <cstdint>
-#include <limits>
 #include <memory>

-namespace detail {
-template <class T, auto N> struct Deleter;
-}
-
-template <class T, std::integral auto N, bool Owning = false>
-  requires((N & (N - 1)) == 0 && N <= std::numeric_limits<uint8_t>::max())
-class Queue {
-  using Deleter = detail::template Deleter<T, N>;
-  friend Deleter;
+#include "FreeRTOS.h" // IWYU pragma: export
+#include "queue.h"

+// Owning FIFO of `T`s, safe to share between tasks
+template <class T> class Queue {
 public:
-  // Only full and copy-convert-from-full construction is allowed
-  Queue() = delete;
+  explicit Queue(UBaseType_t length)
+      : handle{xQueueCreate(length, sizeof(T *))} {
+    configASSERT(handle);
+  }
  Queue(const Queue &) = delete;

-  // Moving is unsupported due to being self-referential
-  Queue(Queue &&) = delete;
-  Queue &operator=(Queue &&) = delete;
-
-  constexpr Queue(T (&items)[N])
-    requires(Owning)
-      : owner{this}, write{N} {
-    for (uint8_t i = 0; i < N; ++i)
-      buf[i] = &items[i];
-  }
-  constexpr Queue(Queue<T, N, true> &queue)
-    requires(!Owning)
-      : owner{&queue} {}
-
-  bool isEmpty() const { return write == read; }
-  uint8_t size() const { return write - read; }
-  uint8_t capacity() const { return N; }
-  bool isFull() const { return size() == capacity(); }
-
-  uint8_t push(std::unique_ptr<T, Deleter> x)
-    requires(!Owning)
-  {
-    // structurally unnecessary; empty construction from same size parent
-    // guarantees
-    // !isFull assert(!isFull());
-
-    if (!x || !x.get_deleter().is_owned_by(owner))
-      return 1;
-
-    reclaim(x.release());
-
-    return 0;
+  // Blocks until accepted (INCLUDE_vTaskSuspend: portMAX_DELAY never times out)
+  void push(std::unique_ptr<T> x) {
+    T *ptr = x.release();
+    xQueueSend(handle, &ptr, portMAX_DELAY);
  }

-  const T *peek() const {
-    if (isEmpty())
-      return nullptr;
-
-    return buf[mask(read)];
+  std::unique_ptr<T> pop(TickType_t wait = portMAX_DELAY) {
+    T *ptr = nullptr;
+    xQueueReceive(handle, &ptr, wait);
+    return std::unique_ptr<T>(ptr);
  }

-  std::unique_ptr<T, Deleter> pop() {
-    if (isEmpty())
-      return nullptr;
-
-    if constexpr (Owning)
-      return {buf[mask(read++)], {this}};
-    else
-      return {buf[mask(read++)], {owner}};
+  // The front item stays owned by the queue
+  const T *peek(TickType_t wait = portMAX_DELAY) const {
+    T *ptr = nullptr;
+    xQueuePeek(handle, &ptr, wait);
+    return ptr;
  }

 private:
-  uint8_t mask(uint8_t pos) const { return pos & (N - 1); }
-  void reclaim(T *x) { buf[mask(write++)] = x; }
-
-  std::array<T *, N> buf = {};
-  Queue<T, N, true> *const owner;
-  uint8_t read = 0;
-  uint8_t write = 0;
+  QueueHandle_t handle;
 };
-
-template <class T, auto N> Queue(Queue<T, N, true> &) -> Queue<T, N, false>;
-template <class T, auto N> Queue(T (&items)[N]) -> Queue<T, N, true>;
-
-namespace detail {
-template <class T, auto N> struct Deleter {
-  Deleter() = default;
-  constexpr Deleter(Queue<T, N, true> *owner) : owner{owner} {}
-  void operator()(T *x) const { owner->reclaim(x); }
-  constexpr bool is_owned_by(const Queue<T, N, true> *parent) const {
-    return owner == parent;
-  }
-
-private:
-  Queue<T, N, true> *const owner = nullptr;
-};
-} // namespace detail
@@ -7,6 +7,10 @@
 #include <cstdint>
 #include <cstdio>
 #include <cstring>
+#include <utility>
+
+#include "FreeRTOS.h" // IWYU pragma: export
+#include "task.h"

 #include "cdchanger.hpp"
 #include "frame.hpp"
@@ -14,19 +18,32 @@
 #include "hal/stdio.h"
 #include "peripheral.hpp"
 #include "queue.hpp"
-
-const char *const offon[] = {"OFF", "ON"};
-
-constexpr uint8_t CACHE_SIZE = 32;
+#include "stdshim.hpp"

 using namespace avclan;

 namespace {
-Frame frames[CACHE_SIZE];
+using Periph = Peripheral<CDChanger>;

-constinit Queue cache(frames);
-constinit Queue incoming = cache;
-constinit Queue outgoing = cache;
+const char *const offon[] = {"OFF", "ON"};
+
+constexpr uint8_t CACHE_SIZE = AVCLAN_MSG_QUEUE_SIZE;
+// A queue that can hold the entire Frame pool is never full, so the sender's
+// blocking push of a follow-up frame onto its own queue can't deadlock
+static_assert(CACHE_SIZE >= AVCLAN_FRAME_POOL_N,
+              "CACHE_SIZE must be >= avclan::Frame allocator pool capacity");
+
+// Must be ranked such that queues deterministically tend to empty
+constexpr UBaseType_t SendPriority = tskIDLE_PRIORITY + 3;
+constexpr UBaseType_t RoutePriority = tskIDLE_PRIORITY + 2;
+constexpr UBaseType_t PollPriority = tskIDLE_PRIORITY + 2;
+constexpr UBaseType_t ReceivePriority = tskIDLE_PRIORITY + 1;
+
+struct Context {
+  Periph &peripheral;
+  Queue<Frame> &incoming;
+  Queue<Frame> &outgoing;
+};

 uint8_t hexChars[2];
 uint8_t hexDigit = 0; // current digit being written to hexChars
@@ -59,63 +76,60 @@ void set_flag(bool *flag, bool val, const char *msg) {

 void Setup();
 void print_help();
-} // namespace

-int main() {
-  Bus phy;
+[[noreturn]] void vReceiverTask(void *pvParameters) {
+  using Print = Frame::Print;
+  auto &[peripheral, incoming, outgoing] =
+      *static_cast<Context *>(pvParameters);
+  while (true) {
+    if (auto msg = peripheral.read(Print{.print = printAllFrames,
+                                         .binary = printBinary,
+                                         .verbose = verbose}))
+      incoming.push(std::move(*msg));
+  }
+}
+
+[[noreturn]] void vRoutingTask(void *pvParameters) {
+  auto &[peripheral, incoming, outgoing] =
+      *static_cast<Context *>(pvParameters);
+  while (true) {
+    const Frame *in = incoming.peek();
+    if (auto resp = peripheral.route(*in)) {
+      incoming.pop();
+      if (*resp)
+        outgoing.push(std::move(*resp));
+    }
+  }
+}
+
+[[noreturn]] void vPollTask(void *pvParameters) {
+  auto &[peripheral, incoming, outgoing] =
+      *static_cast<Context *>(pvParameters);
+  while (true) {
+    if (auto msg = peripheral.poll())
+      outgoing.push(std::move(msg));
+  }
+}
+
+[[noreturn]] void vSenderTask(void *pvParameters) {
+  using Print = Frame::Print;
+  auto &[peripheral, incoming, outgoing] =
+      *static_cast<Context *>(pvParameters);
+  while (true) {
+    auto result = peripheral.send(
+        outgoing.pop(), Print{.print = printAllFrames, .binary = printBinary});
+    if (auto next = peripheral.react(std::move(result)))
+      outgoing.push(std::move(next));
+  }
+}
+
+[[noreturn]] void vREPLTask(void *pvParameters) {
  using enum Action;
  using enum Device;
-  Peripheral<CDChanger> peripheral(phy, 0x360);
-  using Error = decltype(peripheral)::Error;
-  using Print = Frame::Print;
-
-  Setup();
-  print_help();
-
+  auto &[peripheral, incoming, outgoing] =
+      *static_cast<Context *>(pvParameters);
  while (true) {
-    if (peripheral.bus_is_active()) {
-      if (auto msg = cache.pop()) {
-        auto err = peripheral.read(msg.get(), Print{.print = printAllFrames,
-                                                    .binary = printBinary,
-                                                    .verbose = verbose});
-        if (err == Error::Read{0x00})
-          incoming.push(std::move(msg));
-      } else {
-        puts("!! Dropping an incoming message; cache is empty !!");
-      }
-    }
-
-    if (const auto *in = incoming.peek()) {
-      if (auto out = cache.pop()) {
-        peripheral.route(in, out.get());
-        incoming.pop();
-
-        if (out->reaction > 0)
-          outgoing.push(std::move(out));
-      } else {
-        puts("!! Unable to respond; cache is empty !!");
-      }
-    }
-
-    peripheral.poll_devices([&](auto &dev) {
-      if (auto status = cache.pop()) {
-        dev.emit(status.get(), peripheral.controller());
-        outgoing.push(std::move(status));
-        return true;
-      }
-      return false;
-    });
-
-    if (auto out = outgoing.pop()) {
-      auto err = peripheral.send(
-          out.get(), Print{.print = printAllFrames, .binary = printBinary});
-      peripheral.react(out.get(), err);
-      if (out->reaction > 0)
-        outgoing.push(std::move(out));
-    }
-
-    // stdin must be non-blocking: yielding EOF when idle/empty
-    if (int readkey = getchar(); readkey != EOF) {
+    if (int readkey = fgetc(stdin); readkey != EOF) {
      switch (readkey) {
        case '?': print_help(); break;
        case 'v': toggle_flag(&verbose, "Verbose errors:"); break;
@@ -133,7 +147,7 @@ int main() {
        case 'x': set_flag(&printBinary, false, "Binary:"); break;

        case 'E': // Beep
-          if (auto out = cache.pop()) {
+          if (auto out = Frame::acquire()) {
            out->is_unicast = true;
            out->peripheral_addr = peripheral.controller();
            {
@@ -145,10 +159,10 @@ int main() {
            out->reaction = 1;
            outgoing.push(std::move(out));
          } else
-            puts("!! Cache empty; unable to queue beep request");
+            puts("!! failed Frame alloc for Beep !! ");
          break;
        case 'P':
-          if (auto out = cache.pop()) {
+          if (auto out = Frame::acquire()) {
            out->is_unicast = true;
            out->peripheral_addr = peripheral.controller();
            {
@@ -163,7 +177,8 @@ int main() {
            }
            out->reaction = CDChanger::reaction_t::r_Ejection;
            outgoing.push(std::move(out));
-          }
+          } else
+            puts("!! failed Frame alloc for Play !! ");
          break;

 #ifndef NDEBUG
@@ -189,7 +204,19 @@ int main() {
          while (peripheral.device<CDChanger>().media_busy()) {}
          puts("end");
          break;
+        case '+':
+          peripheral.get_bus().deafen(true);
+          peripheral.get_bus().set_dominant();
+          puts("Set bus dominant...");
+          break;
+        case '-':
+          peripheral.get_bus().set_recessive();
+          peripheral.get_bus().deafen(false);
+          puts("Set bus recessive...");
+          break;
+  #ifdef MEASURE_BUS
        case 'M': peripheral.get_bus().measure(); break;
+  #endif
 #endif

        case 0x10: // Signals binary sequence incoming
@@ -218,41 +245,80 @@ int main() {
          hexChars[0] = hexChars[1] = 0;
          seqIsUnicast = false;
          break;
+        case '\r': // Eat carriage return too
+          if (readBinary)
+            goto DEFAULT;
+          [[fallthrough]];
        case '\n':
+          if (readSeq && !readBinary && seqIdx == 0) {
+            // Nothing to send, so leave the mode instead: an escape for an
+            // entry started by accident.
+            readSeq = false;
+            hexDigit = hexChars[0] = hexChars[1] = 0;
+            printAllFrames = lastPrintAllFrames;
+            break;
+          }
          if (readSeq && seqIdx > 0) {
            if (readBinary) {
              if (data_tmp[seqIdx - 1] == 0x17) {
-                if (auto out = cache.pop()) {
+                if (auto out = Frame::acquire()) {
                  if (out->parse(data_tmp, --seqIdx) ==
                      Frame::Error::Parse{0}) {
                    out->reaction = 1;
                    outgoing.push(std::move(out));
+                    readSeq = readBinary = false;
                  }
-                }
-                readSeq = readBinary = false;
+                } else
+                  puts("!! failed Frame alloc for input message !!");
              } else
                goto DEFAULT; // reading binary and this is a real data byte;
                              // fall through to default
-            } else if (seqIdx <= Frame::MAXLENGTH) {
-              if (auto out = cache.pop()) {
+            } else {          // ASCII message
+              if (auto out = Frame::acquire()) {
+                const uint8_t sendLen =
+                    seqIdx <= Frame::MAXLENGTH ? seqIdx : Frame::MAXLENGTH;
                out->is_unicast = seqIsUnicast;
                out->peripheral_addr =
                    seqIsUnicast ? peripheral.controller() : 0x1FF;
-                out->length = seqIdx;
-                memcpy(out->data, data_tmp, seqIdx);
+                out->length = sendLen;
+                memcpy(out->data, data_tmp, sendLen);
                out->reaction = 1;
                outgoing.push(std::move(out));
-              }
-              printAllFrames = lastPrintAllFrames;
+
+                if (seqIdx > Frame::MAXLENGTH)
+                  printf("!! sequence too long (%u > %u), truncated !!\n",
+                         static_cast<unsigned>(seqIdx),
+                         static_cast<unsigned>(Frame::MAXLENGTH));
+
+                // Only leave hex-entry mode and restore logging once the
+                // message actually sent, so a failed alloc can be retried
+                // with '\n' instead of silently dropping the entry.
+                readSeq = false;
+                seqIdx = hexDigit = 0;
+                printAllFrames = lastPrintAllFrames;
+              } else
+                puts("!! failed Frame alloc for input message !!");
            }
            break;
          }
        DEFAULT:
        default:
-          if (readSeq && seqIdx < (Frame::MAXLENGTH + sizeof(Frame))) {
+          if (readSeq) {
+            // Binary mode carries the full wire preamble; hex mode is payload
+            // only, so it stops one past MAXLENGTH to let '\n' report overflow.
+            if (seqIdx >= (readBinary ? sizeof(data_tmp)
+                                      : uint8_t{Frame::MAXLENGTH + 1})) {
+              puts("!! sequence buffer full, ignoring further input !!");
+              break;
+            }
+
            if (readBinary) {
              data_tmp[seqIdx++] = readkey;
            } else {
+              // Only take valid hex digits
+              if (isxdigit(readkey) == 0)
+                break;
+
              hexChars[hexDigit++] = readkey;

              if (hexDigit == 2) {
@@ -277,9 +343,38 @@ int main() {
            }
          }
      } // switch (readkey)
+    } else {
+      clearerr(stdin);
    } // if (readkey != EOF)
  }
-  return 0;
+}
+
+} // namespace
+
+int main() {
+  Setup();
+  print_help();
+
+  // Static: the scheduler reclaims main's stack for ISRs
+  static Bus phy;
+  static Periph peripheral(phy, 0x360);
+  static Queue<Frame> incoming(CACHE_SIZE);
+  static Queue<Frame> outgoing(CACHE_SIZE);
+  static Context ctx{
+      .peripheral = peripheral, .incoming = incoming, .outgoing = outgoing};
+
+  xTaskCreateAffinitySet(vSenderTask, "send/react", configMINIMAL_STACK_SIZE,
+                         &ctx, SendPriority, 0b01, nullptr);
+  xTaskCreateAffinitySet(vRoutingTask, "router", configMINIMAL_STACK_SIZE, &ctx,
+                         RoutePriority, 0b01, nullptr);
+  xTaskCreateAffinitySet(vPollTask, "poll", configMINIMAL_STACK_SIZE, &ctx,
+                         PollPriority, 0b01, nullptr);
+  xTaskCreateAffinitySet(vReceiverTask, "receiver", configMINIMAL_STACK_SIZE,
+                         &ctx, ReceivePriority, 0b01, nullptr);
+  xTaskCreateAffinitySet(vREPLTask, "repl", configMINIMAL_STACK_SIZE, &ctx,
+                         tskIDLE_PRIORITY, 0b01, nullptr);
+
+  vTaskStartScheduler();
 }

 namespace {
@@ -291,8 +386,8 @@ void Setup() {

 void print_help() {
  puts("AVCLAN Mockingboard v1");
-  puts("U - begin reading for unicast message\n"
-       "B - begin reading for broadcast message\n"
+  puts("U - begin reading for unicast message (send with Enter key)\n"
+       "B - begin reading for broadcast message (send with Enter key)\n"
       "m - Toggle mute for mockingboard bus activity\n"
       "v - Toggle verbose error logging\n"
       "l - Toggle message logging\n"
@@ -307,6 +402,8 @@ void print_help() {
       "s - MIC skip forward\n"
       "b - MIC skip backward\n"
       "M - Measure bit-timing (pulse-widths and periods)\n"
+       "+ - Set bus driven/dominant\n"
+       "- - Set bus idle/recessive\n"
 #endif
       "? - Print this message");
 }
Author	SHA1	Message	Date
Allen Hill	e64fe519d6	Add debug method to manually set controller address (e.g. for bench testing)	2026-09-28 11:36:01 -07:00
Allen Hill	598f6ede0e	Offload TX data section to DMA (releases up to 12.5ms back to RTOS)	2026-09-28 11:36:01 -07:00
Allen Hill	c24bab7a80	Migrate to FreeRTOS	2026-09-28 11:36:01 -07:00
Allen Hill	5b9cb1da8b	Add single byte send debug function	2026-09-20 15:08:19 -07:00
Allen Hill	fbf5811496	Refine (further) the Phy API - Refactor send/read data to read entire array instead of byte-oriented reads - Simplify/improve consistency of asynchrony (all send functions now optionally async) - Fix start-bit TX (now actually validate joinable start-bits) Assisted-by: Claude Code (Opus 5)	2026-09-20 15:08:15 -07:00
Allen Hill	7252e6bfdd	fixup PIO comment rewriting oops	2026-09-20 15:08:15 -07:00
Allen Hill	6b22f14e6d	Fix `deafen` semantics	2026-09-20 15:08:15 -07:00
Allen Hill	2c85305c0d	Finish Pico/PIO phy layer Assisted-by: Claude Code (Opus 5)	2026-09-20 15:08:11 -07:00
Allen Hill	8a47b5b776	Refactor peripheral/bus/phy APIs (prep for pico/PIO) - Refactor PHY to be higher-level with a field focus (controller/peripheral address, control byte, etc) - Phy layer is now device address aware (ACK's automatically) (Hardens previously ~implicit design to only support emulating one AVCLAN unit per mockingboard build) - Redesign `phy_active` => `phy_frame_pending` (to allow asynchronous/buffered frame reads on pico) and embed within Peripheral::read - Add `deafen` function: like mute, but also ignore incoming messages (i.e. don't receive/process at all). Makes `Bus::is_active` always return `false`. - Add debug bus driving functions Assisted-by: Claude Code (Opus 5)	2026-09-20 15:07:42 -07:00
Allen Hill	9efbb01ccf	PIO proof-of-concept	2026-09-20 15:03:31 -07:00
Allen Hill	53c5abb3e9	Fix compile errors due to non-portable code	2026-09-03 16:07:27 -07:00
Allen Hill	ac47cebe86	Add ~empty implementation of HAL for pico2	2026-09-03 16:06:57 -07:00
Allen Hill	e30dbc501d	initial build system tweaks for pico hardware	2026-09-03 12:50:00 -07:00
Allen Hill	6c460aa3a0	more infra/clangd updates	2026-08-19 11:45:06 -07:00
Allen Hill	6ce4c2cc21	Improve `stdio_write_nonblock` perf and indicator printing	2026-08-19 11:38:08 -07:00
Allen Hill	b9f7978d3e	react to [disk] scan button presses	2026-08-13 20:46:57 -07:00
Allen Hill	cd68ee7267	misc infra/clangd updates	2026-08-13 17:55:46 -07:00
Allen Hill	ee5b4a955c	Update Lua dissector for newly understood bit flag (NEGATIVE time) Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>	2026-08-13 17:50:21 -07:00
Allen Hill	5d6b5f4ce0	Handle flag for NEGATIVE time; unify time incrementing	2026-08-13 17:47:31 -07:00
Allen Hill	0bef565564	Speed up Frame printing to (finally) solve missing AVCLAN bus frames Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>	2026-08-13 17:34:15 -07:00
Allen Hill	66dd441610	Max the UART TX buffer size	2026-08-13 16:48:44 -07:00
Allen Hill	3ea7c2d44a	Improve correctness of phy_read_startbit invariants/assumptions	2026-08-13 16:31:03 -07:00
Allen Hill	95dae572a0	Tighten up non-reading TCB0 ISR timing	2026-08-13 16:27:22 -07:00
Allen Hill	f45a0f5e92	Shorten time to next phy_active check (early continue)	2026-08-13 16:25:50 -07:00
Allen Hill	994759dd39	Free up some ram	2026-08-13 16:24:55 -07:00
Allen Hill	eab535db98	fixup `7871e92`	2026-08-03 13:30:14 -07:00
Allen Hill	f3d0d99ce4	Update Disable_Function_Req response	2026-08-01 13:15:06 -07:00
Allen Hill	76f5da0125	Restore dynamic from device in function change resp	2026-08-01 13:14:38 -07:00
Allen Hill	7871e92dbe	Fix Debug builds	2026-07-31 17:53:31 -07:00
Allen Hill	fb17b7e75b	Update gitignore and silence some tidy warnings	2026-07-25 11:22:33 -07:00
Allen Hill	ae539e27f6	Fix some overflow behavior when reading input msgs	2026-07-23 12:41:00 -07:00
Allen Hill	a99fe56aae	Fix intermittent, early boot short start bit errors	2026-07-21 13:22:19 -07:00
Allen Hill	909915730b	Not all error conditions print a message	2026-07-21 12:52:25 -07:00
Allen Hill	5bbbb6c011	Party should be ~private	2026-07-21 12:51:49 -07:00
Allen Hill	8950bd6917	Make b3 const	2026-07-21 12:51:18 -07:00
Allen Hill	56936aed10	Switch to using references where possible	2026-07-17 14:31:54 -07:00
Allen Hill	5208e083f3	Redesign (simplify) top-level avclan interface to use expected/nullable unique_ptr - Peripheral::read/send now return `expected<unique_ptr<Frame>, Error>` for a unified success/error interface. - Peripheral::route returns `expected<unique_ptr<Frame>, Error>` to distinguish intent: (intentional) non-response vs unable to respond - Other functions with optional message semantics (handle,poll,react) return a unique_ptr whose ownership-state indicates response intent (i.e. send new message) Bundled necessary changes: - Switch Frame allocation from global to local (enabled via member function new/delete) - Add new header-library tl::expected to shim avr-libstdcpp Unrelated: Defensive `continue` added after `route`, to reduce Bus activity check latency Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>	2026-07-17 14:47:47 -07:00
Allen Hill	200a225add	Unify frame metadata setting (addrs and owning_device)	2026-07-16 13:35:25 -07:00
Allen Hill	568c2af9e6	Only check tracked files and don't print on empty lint	2026-07-16 13:35:06 -07:00