Decouple hardware specific code from generic, agnostic code

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

@@ -0,0 +1,158 @@
+/*
+                        AVCLAN-Mockingboard
+    Copyright (C) 2015 Allen Hill <allenofthehills@gmail.com>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+#include <avr/interrupt.h>
+#include <avr/io.h>
+#include <stdint.h>
+#include <util/atomic.h>
+
+#include "media_avr.h"   // mediacontrol_syncDuringMask (used by the bus guard)
+#include "mediacontrol.h"
+
+// F_CPU defined in timing_avr.h; the mic tick constants below are derived from
+// it (this hardware generation's TCA0/PB1 button-press implementation).
+#include "timing_avr.h"
+
+// pending WO1 toggles (even); signed to avoid underflows from a stray OVF
+static volatile int8_t mic_ntoggles = 0;
+
+// Target pulse length is ~40-150ms, with interval between pulses of
+// ~100-200ms
+// TCA0 period (CMP0/TOP) in ticks at F_CPU with the CLKSEL=DIV1024 prescaler.
+// A press phase is ~100 ms; the final LOW phase is stretched to
+// mic_refractory_period (~333 ms) so consecutive presses stay distinct
+static constexpr uint16_t mic_press_ticks = (uint16_t)((F_CPU / 1024UL) / 10UL);
+static constexpr uint16_t mic_refractory_period =
+    (uint16_t)((F_CPU / 1024UL) / 3UL);
+
+// the longest AVCLAN frame duration is ~15ms
+static constexpr uint16_t close_thresh =
+    (uint16_t)(mic_press_ticks * 15UL / 100UL);
+
+#ifndef NDEBUG
+// Toggle PB1 and return its new level.
+bool AVCLAN_micToggle() {
+  // Take manual control of PB1 (CMP1EN gives TCA0 control of WO1/PB1 level)
+  TCA0.SINGLE.CTRLB &= ~TCA_SINGLE_CMP1EN_bm;
+  VPORTB.OUT ^= PIN1_bm;
+  return (VPORTB.OUT & PIN1_bm) != 0;
+}
+
+bool AVCLAN_isMediaFunctioning() { return mic_ntoggles != 0; }
+#endif
+
+// Begin a press waveform of `nphases` × 100 ms level segments.
+// - ~Immediately toggles high, alternates each phase (1 = single HIGH press, 3
+//   = skip H/L/H, etc).
+// - Halting the timer freezes WO1 at its last level; must run even number of
+// phases to ensure we return to low
+static void mic_pulse(uint8_t nphases) {
+  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+    if (mic_ntoggles) // Skip if already pulsing
+      return;
+
+    // must be even to return to idle-low
+    mic_ntoggles = (nphases & 0x01) ? nphases + 1 : nphases;
+    TCA0.SINGLE.CTRLB |=
+        TCA_SINGLE_CMP1EN_bm; // Reassert TCA control of WO1/PB1
+    TCA0.SINGLE.CTRLC = 0;    // Reset WO1 level just in case
+    TCA0.SINGLE.CNT = 0;
+    TCA0.SINGLE.CMP0 =   // TOP
+        mic_press_ticks; // always restore default ~100 ms period
+    TCA0.SINGLE.INTFLAGS = TCA_SINGLE_OVF_bm; // clear any stale flag
+    TCA0.SINGLE.INTCTRL |= TCA_SINGLE_OVF_bm;
+    TCA0.SINGLE.CTRLA |= TCA_SINGLE_ENABLE_bm;
+  }
+}
+
+// OVF ISR body function:
+//  - counts phases
+//  - stretches the final LOW phase as a refractory period, to keep separate
+//    pulse trains distinct
+//  - stops the timer after the last phase
+static inline void mic_timer_isr_body(bool is_early) {
+  if (--mic_ntoggles == 1) {
+    // Stretch final phase to a ~333 ms idle-low so back-to-back presses stay
+    // distinct
+    // Invariant: mic_refractory_period > mic_press_ticks, so counter can never
+    // silently wrap
+    TCA0.SINGLE.CMP0 = mic_refractory_period;
+  } else if (mic_ntoggles <= 0) {
+    TCA0.SINGLE.CTRLA &= ~TCA_SINGLE_ENABLE_bm;
+    TCA0.SINGLE.CTRLC = 0; // Timer must be disabled before (re)setting
+                           // CTRLC/WO1 level (§20.5.3)
+    mic_ntoggles = 0;      // clamp to avoid perma-lockout in mic_pulse
+  }
+  if (is_early)
+    TCA0.SINGLE.CNT = 0;
+
+  // OVF FLAG must be cleared via write. MUST BE PERFORMED LAST.
+  // This function is called in two cases:
+  //  - ISR, triggered by actual OVF: OVF FLAG is set and needs clearing
+  //  - stopEvent, running ISR body ~early: OVF flag may be set while in
+  //    ATOMIC_BLOCK (either in stopEvent, or earlier in this function body).
+  //    Clear OVF FLAG as a precaution to prevent erroneous ISR runs
+  TCA0.SINGLE.INTFLAGS = TCA_SINGLE_OVF_bm;
+}
+
+ISR(TCA0_OVF_vect) { mic_timer_isr_body(false); }
+
+// Emulate a transport-control button press on the source device. Each action
+// maps to a press-train of a given length on MIC_CONTROL.
+void AVCLAN_mediaFunction(AVCLAN_media_fn_t fn) {
+  switch (fn) {
+    case MEDIA_PLAY_PAUSE: mic_pulse(1); break;    // single press
+    case MEDIA_SKIP_FORWARD: mic_pulse(3); break;  // double-press
+    case MEDIA_SKIP_BACKWARD: mic_pulse(5); break; // triple-press
+  }
+}
+
+// Pre-emptively "overflow" and run the OVF ISR body early if a press is in
+// progress and likely to overflow within the masked window. This maintains:
+//  - a rough absolute time for the pulse train
+//  - peripheral WO1 toggles and mic_ntoggles kept in sync
+//  - maximum frame duration is ~15ms, "early" OVF remains within acceptable
+//    ranges for either high/low pulses
+// Caller (AVCLAN_stopEvent) guarantees interrupts are disabled.
+void mediacontrol_syncDuringMask() {
+  if (mic_ntoggles && TCA0.SINGLE.CNT >= (TCA0.SINGLE.CMP0 - close_thresh))
+    mic_timer_isr_body(true);
+}
+
+void mediacontrol_init() {
+  // PB1 needs to be set as an output for TCA0 to set the level
+  PORTB.DIRSET = PIN1_bm;
+
+  // Experimentally, a press should be ~100ms; multiple presses can be separated
+  // by the same ~100ms (but separate pulse trains need more separation to
+  // remain distinct)
+  TCA0.SINGLE.CTRLA = TCA_SINGLE_CLKSEL_DIV1024_gc;
+
+  // In frequency (FRQ) mode, channel N compare match triggers "UPDATE"
+  // When CMPnEN is set, TCA0 has control of the output level for the channel's
+  // pin, and UPDATE toggles the level
+  // Channel 1 controls WO1, which is mapped to PB1
+  TCA0.SINGLE.CTRLB = TCA_SINGLE_WGMODE_FRQ_gc | TCA_SINGLE_CMP1EN_bm;
+  TCA0.SINGLE.CTRLC = 0; // Preset WO1 level low just to be sure
+  mic_ntoggles = 0;
+
+  // toggle WO1 ~immediately after each period start; should go low => high
+  TCA0.SINGLE.CMP1 = 2;
+  TCA0.SINGLE.INTFLAGS = TCA_SINGLE_OVF_bm; // Clear OVF flag just in case
+  TCA0.SINGLE.INTCTRL = 0;
+}