Add C++ Bus class for the physical layer interface

CMakeLists.txt

@@ -35,6 +35,7 @@ add_library(avclan STATIC
     src/avclan/avclan_protocol.c
     src/avclan/cdchanger.c
     src/avclan/peripheral.cc
+    src/avclan/bus.cc
 )
 
 # avclan exports its public generic headers (src/avclan) to consumers and

src/avclan/bus.cc

@@ -0,0 +1,32 @@
+// copyright (C) 2006 Marcin Slonicki <marcin@softservice.com.pl>
+// copyright (C) 2007 Louis Frigon
+// Copyright (C) 2015 Allen Hill <allenofthehills@gmail.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "bus.hpp"
+#include "avclan_defs.h"
+#include "avclan_phy.h" // bridge until phy has been ported
+
+namespace avclan {
+void Bus::init() { AVCLAN_busInit(); };
+void Bus::mute(bool mute) { AVCLAN_muteDevice(mute); };
+bool Bus::is_muted() const { return AVCLAN_ismuted(); };
+Bus::Handle Bus::get() { return {}; };
+
+bool Bus::Handle::sendstartbit() { return AVCLAN_sendstartbit(); };
+Bus::Error::Read Bus::Handle::readstartbit() {
+  using enum Error::Read;
+  auto err = AVCLAN_readstartbit();
+  if (err == rSTARTBIT_TOO_LONG)
+    return STARTBIT_TOO_LONG;
+  else if (err == rLATCHED_COMPARATOR)
+    return BAD_STARTBIT;
+  else if (err == rSTARTBIT_TOO_SHORT)
+    return STARTBIT_TOO_SHORT;
+  else
+    return Read{0};
+};
+void Bus::Handle::send_ACK() { AVCLAN_sendbit_ACK(); };
+uint8_t Bus::Handle::read_ACK() { return AVCLAN_readbit_ACK(); };
+
+} // namespace avclan

src/avclan/bus.hpp

@@ -0,0 +1,178 @@
+// copyright (C) 2006 Marcin Slonicki <marcin@softservice.com.pl>
+// copyright (C) 2007 Louis Frigon
+// Copyright (C) 2015 Allen Hill <allenofthehills@gmail.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+/*
+                                AVC LAN Theory
+
+  The AVC LAN bus is an implementation of the IEBus (mode 1) which is a
+  differential signal; IEBus is electrically (but not logically) compatible with
+  CAN bus.
+
+  - Logical `1`: Potential difference between bus lines (BUS+ pin and BUS– pin)
+    is 20 mV or lower (floating).
+  - Logical `0`: Potential difference between bus lines (BUS+ pin and BUS– pin)
+    is 120 mV or higher (driving).
+
+  A nominal bit length is 39 us, composed of 3 periods: preparation,
+  synchronization, data.
+
+                                Figure 1. AVCLAN Bus bit format
+
+                             │ Prep │<─ Sync ─>│<─ Data ─>│ ...
+    Driving (logical `0`)           ╭──────────╮──────────╮
+                                    │          │          │
+    Floating (logical `1`) ─────────╯          ╰──────────╰─────────
+                             │ 6 μs │── 19 μs ─│─ 13 μs ──│
+
+  The logical value during the data period signifies the bit value, e.g. a bit
+  `0` continues the logical `0` (high potential difference between bus lines) of
+  the sync period thru the data period, and a bit `1` has a logical `1`
+  (low/floating potential between bus lines) during the data period. Using the
+  TCB pulse-width and frequency measure mode, the total bit length differs for
+  bit `1` and `0`; detailed bit timing can be found in "timing.h". The bus
+  idles at low potential (floating).
+
+  A start bit is nominally 169 us high followed by 20 us low.
+
+  A bit `0` is dominant on the bus, which is a design choice that affects
+  bit/interpretation:
+    - Low addresses have priority upon transmission conflicts
+    - The broadcast bit is `1` (floating, no effort) for normal communication
+    - For acknowledge bits, the receiver extends the logical '0' of the sync
+      period to the length of a normal bit `0`. Hence, a NAK (bit `1`) is
+      literally the absence of an ACK.
+*/
+
+#pragma once
+
+#include <concepts>
+
+#include "avclan_defs.h"
+#include "avclan_phy.h" // bridge until phy has been ported
+
+namespace avclan {
+class Bus {
+public:
+  struct Error {
+    enum class Read : uint8_t {
+      BAD_PARITY = 0x01,
+      STARTBIT_TOO_SHORT = 0x80, // Start *well* above Peripher::Error::Read
+                                 // (which ~inherits these values)
+      STARTBIT_TOO_LONG,
+      BAD_STARTBIT,
+    };
+
+    enum class Send : uint8_t {
+      NAK = 0x01,
+    };
+  };
+  class Handle;
+
+  void init();
+  void mute(bool mute);
+  bool is_muted() const;
+  Handle get();
+};
+
+class Bus::Handle {
+  Handle() { AVCLAN_stopEvent(); }
+  friend Bus;
+
+public:
+  ~Handle() { AVCLAN_startEvent(); }
+  Handle(const Handle &) = delete;
+  Handle(Handle &&) = delete;
+
+  bool sendstartbit();
+  Error::Read readstartbit();
+
+  template <auto N, std::unsigned_integral T>
+    requires(sizeof(T) < 3 && N < 16)
+  Error::Send send(T bits, bool ack) {
+    const auto parity = sendbits<N>(bits);
+    sendbits<1>(static_cast<uint8_t>(parity));
+
+    if (ack && !read_ACK())
+      return Send::NAK;
+
+    return Send{0};
+  };
+
+  template <auto N, std::unsigned_integral T, class F>
+    requires(sizeof(T) < 3 && N < 16)
+  Error::Read read(T *bits, F &&ack) {
+    const auto calc_parity = readbits<N>(bits);
+    uint8_t read_parity;
+    readbits<1>(&read_parity);
+    if (calc_parity != read_parity) {
+      return Read::BAD_PARITY;
+    } else if (ack()) {
+      send_ACK();
+    } else
+      readbits<1>(&read_parity);
+
+    return Read{0};
+  };
+  template <auto N, std::unsigned_integral T>
+    requires(sizeof(T) < 3 && N < 16)
+  Error::Read read(T *bits, bool ack) {
+    return read<N>(bits, [=]() { return ack; });
+  }
+
+private:
+  using Read = Error::Read;
+  using Send = Error::Send;
+
+  // A single bus symbol. bit_zero/bit_one carry data (and double as parity
+  // values); bit_start marks a frame start bit.
+  enum class avclan_bit : uint8_t {
+    bit_zero = 0x00,
+    bit_one = 0x01,
+    bit_start = 0x10
+  };
+
+  void send_ACK();
+  uint8_t read_ACK();
+
+  template <auto N, class T> avclan_bit_t sendbits(T bits);
+  template <auto N, class T> avclan_bit_t readbits(T *bits);
+
+  // Temporary specializations bridging to legacy C API
+  // Replace with proper (single?) template when phy has been ported
+  template <auto N>
+    requires(N > 1 && N < 8)
+  avclan_bit_t sendbits(uint8_t bits) {
+    return AVCLAN_sendbitsi(&bits, N);
+  };
+  template <auto N>
+    requires(N <= 16)
+  avclan_bit_t sendbits(uint16_t bits) {
+    return AVCLAN_sendbitsl(&bits, N);
+  };
+  template <auto N>
+    requires(N < 8)
+  avclan_bit_t readbits(uint8_t *bits) {
+    return static_cast<avclan_bit_t>(AVCLAN_readbitsi(bits, N));
+  };
+  template <auto N>
+    requires(N <= 16)
+  avclan_bit_t readbits(uint16_t *bits) {
+    return static_cast<avclan_bit_t>(AVCLAN_readbitsl(bits, N));
+  };
+};
+
+template <> inline avclan_bit_t Bus::Handle::sendbits<8>(uint8_t byte) {
+  return AVCLAN_sendbyte(&byte);
+};
+template <> inline avclan_bit_t Bus::Handle::sendbits<1>(uint8_t byte) {
+  const avclan_bit_t b{static_cast<avclan_bit_t>(byte & 1u)};
+  AVCLAN_sendbit(b);
+  return b;
+};
+template <> inline avclan_bit_t Bus::Handle::readbits<8>(uint8_t *byte) {
+  return static_cast<avclan_bit_t>(AVCLAN_readbyte(byte));
+};
+
+} // namespace avclan

src/avclan/peripheral.cc

@@ -6,8 +6,8 @@
 #include "peripheral.hpp"
 #include "avclan_defs.h"
 #include "avclan_frame.h"
-#include "avclan_phy.h" // bus symbol I/O + transaction guard (target-provided)
-#include "com232.h"     // error logging
+#include "bus.hpp"
+#include "com232.h" // error logging
 
 #include <cstdint>
 
@@ -26,104 +26,83 @@ Peripheral::Error::Read Peripheral::read(AVCLAN_frame_t *in, log_t print) {
   } err = {};
 
   using enum Error::Read;
+  auto BAD_PARITY = Bus::Error::Read::BAD_PARITY;
 
-  AVCLAN_stopEvent(); // quiesce contending sources during the read
+  { // bound handle lifetime
+    auto handle = bus.get();
 
-  bool shouldACK = false;
-  uint8_t tmp = 0, parity = 0;
+    bool shouldACK = false;
+    uint8_t tmp = 0;
 
-  err.errno = Error::Read{AVCLAN_readstartbit()};
-  if (static_cast<uint8_t>(err.errno))
-    goto handle_err;
+    err.errno = Error::Read{static_cast<uint8_t>(handle.readstartbit())};
+    if (static_cast<uint8_t>(err.errno))
+      goto handle_err;
 
-  AVCLAN_readbits<1>(&tmp);
-  in->is_unicast = tmp;
+    handle.read<1>(&tmp, false);
+    in->is_unicast = tmp;
 
-  parity = AVCLAN_readbits<12>(&in->controller_addr);
-  AVCLAN_readbits<1>(&tmp);
-  if (parity != (tmp &= 1)) {
-    err.errno = BAD_CONTROLLER_PARITY;
-    if (print.verbose) {
-      err.read_val = in->controller_addr;
-      err.parity = tmp;
-    }
-    goto handle_err;
-  }
-
-  parity = AVCLAN_readbits<12>(&in->peripheral_addr);
-  AVCLAN_readbits<1>(&tmp);
-  if (parity != (tmp &= 1)) {
-    err.errno = BAD_PERIPHERAL_PARITY;
-    if (print.verbose) {
-      err.read_val = in->peripheral_addr;
-      err.parity = tmp;
-    }
-    goto handle_err;
-  }
-
-  shouldACK = !AVCLAN_ismuted() && (in->peripheral_addr == address);
-
-  if (shouldACK)
-    AVCLAN_sendbit_ACK();
-  else
-    AVCLAN_readbits<1>(&tmp);
-
-  parity = AVCLAN_readbits<4>(&in->control);
-  AVCLAN_readbits<1>(&tmp);
-  if (parity != (tmp &= 1)) {
-    err.errno = BAD_CONTROL_PARITY;
-    if (print.verbose) {
-      err.read_val = in->control;
-      err.parity = tmp;
-    }
-    goto handle_err;
-  } else if (shouldACK) {
-    AVCLAN_sendbit_ACK();
-  } else {
-    AVCLAN_readbits<1>(&tmp);
-  }
-
-  parity = AVCLAN_readbyte(&in->length);
-  AVCLAN_readbits<1>(&tmp);
-  if (parity != (tmp &= 1)) {
-    err.errno = BAD_LENGTH_PARITY;
-    if (print.verbose) {
-      err.read_val = in->length;
-      err.parity = tmp;
-    }
-    goto handle_err;
-  } else if (shouldACK) {
-    AVCLAN_sendbit_ACK();
-  } else {
-    AVCLAN_readbits<1>(&tmp);
-  }
-
-  if (in->length == 0 || in->length > MAXMSGLEN) {
-    err.errno = BAD_LENGTH_RANGE;
-    err.val = in->length;
-    goto handle_err;
-  }
-
-  for (uint8_t i = 0; i < in->length; i++) {
-    parity = AVCLAN_readbits<8>(&in->data[i]);
-    AVCLAN_readbits<1>(&tmp);
-    if (parity != (tmp &= 1)) {
-      err.errno = BAD_DATA_PARITY;
+    if (auto rerr = handle.read<12>(&in->controller_addr, false);
+        rerr == BAD_PARITY) {
+      err.errno = BAD_CONTROLLER_PARITY;
       if (print.verbose) {
-        err.read_val = in->data[i];
-        err.parity = tmp;
+        err.read_val = in->controller_addr;
       }
       goto handle_err;
-    } else if (shouldACK) {
-      AVCLAN_sendbit_ACK();
-    } else {
-      AVCLAN_readbits<1>(&tmp);
     }
-  }
+
+    if (auto rerr = handle.read<12>(&in->peripheral_addr,
+                                    [&]() {
+                                      return !bus.is_muted() &&
+                                             (in->peripheral_addr == address);
+                                    });
+        rerr == BAD_PARITY) {
+      err.errno = BAD_PERIPHERAL_PARITY;
+      if (print.verbose) {
+        err.read_val = in->peripheral_addr;
+      }
+      goto handle_err;
+    }
+
+    shouldACK = !bus.is_muted() && (in->peripheral_addr == address);
+
+    if (auto rerr = handle.read<4>(&in->control, shouldACK);
+        rerr == BAD_PARITY) {
+      err.errno = BAD_CONTROL_PARITY;
+      if (print.verbose) {
+        err.read_val = in->control;
+      }
+      goto handle_err;
+    }
+
+    if (auto rerr = handle.read<8>(&in->length, shouldACK);
+        rerr == BAD_PARITY) {
+      err.errno = BAD_LENGTH_PARITY;
+      if (print.verbose) {
+        err.read_val = in->length;
+      }
+      goto handle_err;
+    }
+
+    if (in->length == 0 || in->length > MAXMSGLEN) {
+      err.errno = 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], shouldACK);
+          rerr == BAD_PARITY) {
+        err.errno = BAD_DATA_PARITY;
+        if (print.verbose) {
+          err.read_val = in->data[i];
+        }
+        goto handle_err;
+      }
+    }
+  } // destroy handle
 
   if (false) {
   handle_err:;
-    AVCLAN_startEvent();
     RS232_Print("ERR(read): ");
     switch (err.errno) {
       case BAD_STARTBIT: RS232_Print("bad start bit (other)"); break;
@@ -153,8 +132,6 @@ Peripheral::Error::Read Peripheral::read(AVCLAN_frame_t *in, log_t print) {
         }
     }
     RS232_Print("\n");
-  } else {
-    AVCLAN_startEvent();
   }
 
   // Only print if some data has been correctly received
@@ -177,70 +154,60 @@ Peripheral::Error::Send Peripheral::send(const AVCLAN_frame_t *out,
   } err = {};
 
   using enum Error::Send;
-
-  avclan_bit_t parity;
+  auto NAK = Bus::Error::Send::NAK;
 
   if (AVCLAN_ismuted()) {
     err.errno = MUTED;
     goto handle_err;
   }
 
-  AVCLAN_stopEvent();
+  { // bound handle lifetime
+    auto handle = bus.get();
 
-  if (!AVCLAN_sendstartbit()) {
-    // Some other device is already driving the bus
-    err.errno = BUSY;
-    goto handle_err;
-  }
-
-  AVCLAN_sendbits<1>(static_cast<uint8_t>(out->is_unicast));
-
-  parity = AVCLAN_sendbits<12>(out->controller_addr);
-  AVCLAN_sendbit(parity);
-
-  parity = AVCLAN_sendbits<12>(address);
-  AVCLAN_sendbit(parity);
-
-  if (out->is_unicast && !AVCLAN_readbit_ACK()) {
-    err.errno = NAK_ADDRESS;
-    goto handle_err;
-  }
-
-  parity = AVCLAN_sendbits<4>(out->control);
-  AVCLAN_sendbit(parity);
-
-  if (out->is_unicast && !AVCLAN_readbit_ACK()) {
-    err.errno = NAK_CONTROL;
-    goto handle_err;
-  }
-
-  parity = AVCLAN_sendbits<8>(out->length); // data length
-  AVCLAN_sendbit(parity);
-
-  if (out->is_unicast && !AVCLAN_readbit_ACK()) {
-    err.errno = NAK_MESSAGE_LENGTH;
-    goto handle_err;
-  }
-
-  for (uint8_t i = 0; i < out->length; i++) {
-    parity = AVCLAN_sendbits<8>(out->data[i]);
-    AVCLAN_sendbit(parity);
-    // 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)
-    if (out->is_unicast && !AVCLAN_readbit_ACK()) {
-      err.errno = NAK_DATA;
-      err.val = i;
+    if (!handle.sendstartbit()) {
+      // Some other device is already driving the bus
+      err.errno = BUSY;
       goto handle_err;
     }
-    // else
-    //   AVCLAN_sendbit_1();
-  }
+
+    handle.send<1>(static_cast<uint8_t>(out->is_unicast), false);
+
+    handle.send<12>(out->controller_addr, false);
+
+    if (auto serr = handle.send<12>(out->controller_addr, out->is_unicast);
+        serr == NAK) {
+      err.errno = NAK_ADDRESS;
+      goto handle_err;
+    }
+
+    if (auto serr = handle.send<4>(out->control, out->is_unicast);
+        serr == NAK) {
+      err.errno = NAK_CONTROL;
+      goto handle_err;
+    }
+
+    if (auto serr = handle.send<8>(out->length, 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], out->is_unicast);
+          serr == NAK) {
+        err.errno = NAK_DATA;
+        err.val = i;
+        goto handle_err;
+      }
+    }
+  } // destroy handle
 
   // back to read mode
   if (false) {
   handle_err:;
-    AVCLAN_startEvent();
     RS232_Print("Error");
     switch (err.errno) {
       case MUTED: RS232_Print(": Device muted"); break;
@@ -265,8 +232,6 @@ Peripheral::Error::Send Peripheral::send(const AVCLAN_frame_t *out,
         break;
     }
     RS232_Print("\n");
-  } else {
-    AVCLAN_startEvent();
   }
 
   if (print.print)

src/avclan/peripheral.hpp

@@ -5,6 +5,8 @@
 #pragma once
 
 #include "avclan_defs.h"
+#include "bus.hpp"
+
 #include <cstdint>
 
 namespace avclan {
@@ -14,33 +16,38 @@ public:
     // Error enums are ordered such that a lower numeric value corresponds to
     // more progress/success before an error occured, with 0 being no errors
     enum class Read : uint8_t {
-      BAD_DATA_PARITY = rBAD_DATA_PARITY, // = 0x01
-      BAD_LENGTH_RANGE = rBAD_LENGTH_RANGE,
-      BAD_LENGTH_PARITY = rBAD_LENGTH_PARITY,
-      BAD_PERIPHERAL_PARITY = rBAD_PERIPHERAL_PARITY,
-      BAD_CONTROLLER_PARITY = rBAD_CONTROLLER_PARITY,
-      BAD_CONTROL_PARITY = rBAD_CONTROL_PARITY,
-      STARTBIT_TOO_SHORT = rSTARTBIT_TOO_SHORT,
-      STARTBIT_TOO_LONG = rSTARTBIT_TOO_LONG,
-      BAD_STARTBIT = rLATCHED_COMPARATOR,
+      BAD_DATA_PARITY = 0x01,
+      BAD_LENGTH_RANGE,
+      BAD_LENGTH_PARITY,
+      BAD_PERIPHERAL_PARITY,
+      BAD_CONTROLLER_PARITY,
+      BAD_CONTROL_PARITY,
+      STARTBIT_TOO_SHORT =
+          static_cast<uint8_t>(Bus::Error::Read::STARTBIT_TOO_SHORT),
+      STARTBIT_TOO_LONG =
+          static_cast<uint8_t>(Bus::Error::Read::STARTBIT_TOO_LONG),
+      BAD_STARTBIT = static_cast<uint8_t>(Bus::Error::Read::BAD_STARTBIT),
     };
 
     enum class Send : uint8_t {
-      NAK_DATA = sNAK_DATA, // = 0x01
-      NAK_MESSAGE_LENGTH = sNAK_MESSAGE_LENGTH,
-      NAK_CONTROL = sNAK_CONTROL,
-      NAK_ADDRESS = sNAK_ADDRESS,
-      BUSY = sBUSY,
-      MUTED = sMUTED,
+      NAK_DATA = 0x01,
+      NAK_MESSAGE_LENGTH,
+      NAK_CONTROL,
+      NAK_ADDRESS,
+      BUSY,
+      MUTED,
     };
   };
 
-  Peripheral(uint16_t address) : address{address} {}
+  Peripheral(Bus bus, uint16_t address) : bus{bus}, address{address} {
+    bus.init();
+  }
 
   Error::Read read(AVCLAN_frame_t *in, log_t print);
   Error::Send send(const AVCLAN_frame_t *out, log_t print);
 
 private:
+  Bus bus;
   const uint16_t address;
 };
 } // namespace avclan

src/avclan/target/avr-attiny3216/phy_avr.c

@@ -3,48 +3,6 @@
 // Copyright (C) 2015 Allen Hill <allenofthehills@gmail.com>
 // SPDX-License-Identifier: GPL-3.0-or-later
 
-/*
-                                AVC LAN Theory
-
-  The AVC LAN bus is an implementation of the IEBus (mode 1) which is a
-  differential signal; IEBus is electrically (but not logically) compatible with
-  CAN bus.
-
-  - Logical `1`: Potential difference between bus lines (BUS+ pin and BUS– pin)
-    is 20 mV or lower (floating).
-  - Logical `0`: Potential difference between bus lines (BUS+ pin and BUS– pin)
-    is 120 mV or higher (driving).
-
-  A nominal bit length is 39 us, composed of 3 periods: preparation,
-  synchronization, data.
-
-                                Figure 1. AVCLAN Bus bit format
-
-                             │ Prep │<─ Sync ─>│<─ Data ─>│ ...
-    Driving (logical `0`)           ╭──────────╮──────────╮
-                                    │          │          │
-    Floating (logical `1`) ─────────╯          ╰──────────╰─────────
-                             │ 6 μs │── 19 μs ─│─ 13 μs ──│
-
-  The logical value during the data period signifies the bit value, e.g. a bit
-  `0` continues the logical `0` (high potential difference between bus lines) of
-  the sync period thru the data period, and a bit `1` has a logical `1`
-  (low/floating potential between bus lines) during the data period. Using the
-  TCB pulse-width and frequency measure mode, the total bit length differs for
-  bit `1` and `0`; detailed bit timing can be found in "timing.h". The bus
-  idles at low potential (floating).
-
-  A start bit is nominally 169 us high followed by 20 us low.
-
-  A bit `0` is dominant on the bus, which is a design choice that affects
-  bit/interpretation:
-    - Low addresses have priority upon transmission conflicts
-    - The broadcast bit is `1` (floating, no effort) for normal communication
-    - For acknowledge bits, the receiver extends the logical '0' of the sync
-      period to the length of a normal bit `0`. Hence, a NAK (bit `1`) is
-      literally the absence of an ACK.
-*/
-
 #include <avr/interrupt.h>
 #include <avr/io.h>
 #include <avr/sfr_defs.h>

src/sniffer.cc

@@ -71,7 +71,8 @@ int main() {
 
   const AVCLAN_frame_t *lastStatus = nullptr;
 
-  avclan::Peripheral cd_changer(0x360);
+  avclan::Bus phy;
+  avclan::Peripheral cd_changer(phy, 0x360);
   using Error = avclan::Peripheral::Error;
 
   Setup();