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diff --git a/platforms/avr/drivers/audio_pwm_hardware.c b/platforms/avr/drivers/audio_pwm_hardware.c
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+/* Copyright 2016 Jack Humbert
+ * Copyright 2020 JohSchneider
+ *
+ * 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 2 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 <http://www.gnu.org/licenses/>.
+ */
+
+#if defined(__AVR__)
+# include <avr/pgmspace.h>
+# include <avr/interrupt.h>
+# include <avr/io.h>
+#endif
+
+#include "audio.h"
+
+extern bool playing_note;
+extern bool playing_melody;
+extern uint8_t note_timbre;
+
+#define CPU_PRESCALER 8
+
+/*
+ Audio Driver: PWM
+
+ drive up to two speakers through the AVR PWM hardware-peripheral, using timer1 and/or timer3 on Atmega32U4.
+
+ the primary channel_1 can be connected to either pin PC4 PC5 or PC6 (the later being used by most AVR based keyboards) with a PMW signal generated by timer3
+ and an optional secondary channel_2 on either pin PB5, PB6 or PB7, with a PWM signal from timer1
+
+ alternatively, the PWM pins on PORTB can be used as only/primary speaker
+*/
+
+#if defined(AUDIO_PIN) && (AUDIO_PIN != C4) && (AUDIO_PIN != C5) && (AUDIO_PIN != C6) && (AUDIO_PIN != B5) && (AUDIO_PIN != B6) && (AUDIO_PIN != B7) && (AUDIO_PIN != D5)
+# error "Audio feature enabled, but no suitable pin selected as AUDIO_PIN - see docs/feature_audio under the AVR settings for available options."
+#endif
+
+#if (AUDIO_PIN == C4) || (AUDIO_PIN == C5) || (AUDIO_PIN == C6)
+# define AUDIO1_PIN_SET
+# define AUDIO1_TIMSKx TIMSK3
+# define AUDIO1_TCCRxA TCCR3A
+# define AUDIO1_TCCRxB TCCR3B
+# define AUDIO1_ICRx ICR3
+# define AUDIO1_WGMx0 WGM30
+# define AUDIO1_WGMx1 WGM31
+# define AUDIO1_WGMx2 WGM32
+# define AUDIO1_WGMx3 WGM33
+# define AUDIO1_CSx0 CS30
+# define AUDIO1_CSx1 CS31
+# define AUDIO1_CSx2 CS32
+
+# if (AUDIO_PIN == C6)
+# define AUDIO1_COMxy0 COM3A0
+# define AUDIO1_COMxy1 COM3A1
+# define AUDIO1_OCIExy OCIE3A
+# define AUDIO1_OCRxy OCR3A
+# define AUDIO1_PIN C6
+# define AUDIO1_TIMERx_COMPy_vect TIMER3_COMPA_vect
+# elif (AUDIO_PIN == C5)
+# define AUDIO1_COMxy0 COM3B0
+# define AUDIO1_COMxy1 COM3B1
+# define AUDIO1_OCIExy OCIE3B
+# define AUDIO1_OCRxy OCR3B
+# define AUDIO1_PIN C5
+# define AUDIO1_TIMERx_COMPy_vect TIMER3_COMPB_vect
+# elif (AUDIO_PIN == C4)
+# define AUDIO1_COMxy0 COM3C0
+# define AUDIO1_COMxy1 COM3C1
+# define AUDIO1_OCIExy OCIE3C
+# define AUDIO1_OCRxy OCR3C
+# define AUDIO1_PIN C4
+# define AUDIO1_TIMERx_COMPy_vect TIMER3_COMPC_vect
+# endif
+#endif
+
+#if defined(AUDIO_PIN) && defined(AUDIO_PIN_ALT) && (AUDIO_PIN == AUDIO_PIN_ALT)
+# error "Audio feature: AUDIO_PIN and AUDIO_PIN_ALT on the same pin makes no sense."
+#endif
+
+#if ((AUDIO_PIN == B5) && ((AUDIO_PIN_ALT == B6) || (AUDIO_PIN_ALT == B7))) || ((AUDIO_PIN == B6) && ((AUDIO_PIN_ALT == B5) || (AUDIO_PIN_ALT == B7))) || ((AUDIO_PIN == B7) && ((AUDIO_PIN_ALT == B5) || (AUDIO_PIN_ALT == B6)))
+# error "Audio feature: PORTB as AUDIO_PIN and AUDIO_PIN_ALT at the same time is not supported."
+#endif
+
+#if defined(AUDIO_PIN_ALT) && (AUDIO_PIN_ALT != B5) && (AUDIO_PIN_ALT != B6) && (AUDIO_PIN_ALT != B7)
+# error "Audio feature: the pin selected as AUDIO_PIN_ALT is not supported."
+#endif
+
+#if (AUDIO_PIN == B5) || (AUDIO_PIN == B6) || (AUDIO_PIN == B7) || (AUDIO_PIN_ALT == B5) || (AUDIO_PIN_ALT == B6) || (AUDIO_PIN_ALT == B7) || (AUDIO_PIN == D5)
+# define AUDIO2_PIN_SET
+# define AUDIO2_TIMSKx TIMSK1
+# define AUDIO2_TCCRxA TCCR1A
+# define AUDIO2_TCCRxB TCCR1B
+# define AUDIO2_ICRx ICR1
+# define AUDIO2_WGMx0 WGM10
+# define AUDIO2_WGMx1 WGM11
+# define AUDIO2_WGMx2 WGM12
+# define AUDIO2_WGMx3 WGM13
+# define AUDIO2_CSx0 CS10
+# define AUDIO2_CSx1 CS11
+# define AUDIO2_CSx2 CS12
+
+# if (AUDIO_PIN == B5) || (AUDIO_PIN_ALT == B5)
+# define AUDIO2_COMxy0 COM1A0
+# define AUDIO2_COMxy1 COM1A1
+# define AUDIO2_OCIExy OCIE1A
+# define AUDIO2_OCRxy OCR1A
+# define AUDIO2_PIN B5
+# define AUDIO2_TIMERx_COMPy_vect TIMER1_COMPA_vect
+# elif (AUDIO_PIN == B6) || (AUDIO_PIN_ALT == B6)
+# define AUDIO2_COMxy0 COM1B0
+# define AUDIO2_COMxy1 COM1B1
+# define AUDIO2_OCIExy OCIE1B
+# define AUDIO2_OCRxy OCR1B
+# define AUDIO2_PIN B6
+# define AUDIO2_TIMERx_COMPy_vect TIMER1_COMPB_vect
+# elif (AUDIO_PIN == B7) || (AUDIO_PIN_ALT == B7)
+# define AUDIO2_COMxy0 COM1C0
+# define AUDIO2_COMxy1 COM1C1
+# define AUDIO2_OCIExy OCIE1C
+# define AUDIO2_OCRxy OCR1C
+# define AUDIO2_PIN B7
+# define AUDIO2_TIMERx_COMPy_vect TIMER1_COMPC_vect
+# elif (AUDIO_PIN == D5) && defined(__AVR_ATmega32A__)
+# pragma message "Audio support for ATmega32A is experimental and can cause crashes."
+# undef AUDIO2_TIMSKx
+# define AUDIO2_TIMSKx TIMSK
+# define AUDIO2_COMxy0 COM1A0
+# define AUDIO2_COMxy1 COM1A1
+# define AUDIO2_OCIExy OCIE1A
+# define AUDIO2_OCRxy OCR1A
+# define AUDIO2_PIN D5
+# define AUDIO2_TIMERx_COMPy_vect TIMER1_COMPA_vect
+# endif
+#endif
+
+// C6 seems to be the assumed default by many existing keyboard - but sill warn the user
+#if !defined(AUDIO1_PIN_SET) && !defined(AUDIO2_PIN_SET)
+# pragma message "Audio feature enabled, but no suitable pin selected - see docs/feature_audio under the AVR settings for available options. Don't expect to hear anything... :-)"
+// TODO: make this an error - go through the breaking-change-process and change all keyboards to the new define
+#endif
+// -----------------------------------------------------------------------------
+
+#ifdef AUDIO1_PIN_SET
+static float channel_1_frequency = 0.0f;
+void channel_1_set_frequency(float freq) {
+ if (freq == 0.0f) // a pause/rest is a valid "note" with freq=0
+ {
+ // disable the output, but keep the pwm-ISR going (with the previous
+ // frequency) so the audio-state keeps getting updated
+ // Note: setting the duty-cycle 0 is not possible on non-inverting PWM mode - see the AVR data-sheet
+ AUDIO1_TCCRxA &= ~(_BV(AUDIO1_COMxy1) | _BV(AUDIO1_COMxy0));
+ return;
+ } else {
+ AUDIO1_TCCRxA |= _BV(AUDIO1_COMxy1); // enable output, PWM mode
+ }
+
+ channel_1_frequency = freq;
+
+ // set pwm period
+ AUDIO1_ICRx = (uint16_t)(((float)F_CPU) / (freq * CPU_PRESCALER));
+ // and duty cycle
+ AUDIO1_OCRxy = (uint16_t)((((float)F_CPU) / (freq * CPU_PRESCALER)) * note_timbre / 100);
+}
+
+void channel_1_start(void) {
+ // enable timer-counter ISR
+ AUDIO1_TIMSKx |= _BV(AUDIO1_OCIExy);
+ // enable timer-counter output
+ AUDIO1_TCCRxA |= _BV(AUDIO1_COMxy1);
+}
+
+void channel_1_stop(void) {
+ // disable timer-counter ISR
+ AUDIO1_TIMSKx &= ~_BV(AUDIO1_OCIExy);
+ // disable timer-counter output
+ AUDIO1_TCCRxA &= ~(_BV(AUDIO1_COMxy1) | _BV(AUDIO1_COMxy0));
+}
+#endif
+
+#ifdef AUDIO2_PIN_SET
+static float channel_2_frequency = 0.0f;
+void channel_2_set_frequency(float freq) {
+ if (freq == 0.0f) {
+ AUDIO2_TCCRxA &= ~(_BV(AUDIO2_COMxy1) | _BV(AUDIO2_COMxy0));
+ return;
+ } else {
+ AUDIO2_TCCRxA |= _BV(AUDIO2_COMxy1);
+ }
+
+ channel_2_frequency = freq;
+
+ AUDIO2_ICRx = (uint16_t)(((float)F_CPU) / (freq * CPU_PRESCALER));
+ AUDIO2_OCRxy = (uint16_t)((((float)F_CPU) / (freq * CPU_PRESCALER)) * note_timbre / 100);
+}
+
+float channel_2_get_frequency(void) { return channel_2_frequency; }
+
+void channel_2_start(void) {
+ AUDIO2_TIMSKx |= _BV(AUDIO2_OCIExy);
+ AUDIO2_TCCRxA |= _BV(AUDIO2_COMxy1);
+}
+
+void channel_2_stop(void) {
+ AUDIO2_TIMSKx &= ~_BV(AUDIO2_OCIExy);
+ AUDIO2_TCCRxA &= ~(_BV(AUDIO2_COMxy1) | _BV(AUDIO2_COMxy0));
+}
+#endif
+
+void audio_driver_initialize() {
+#ifdef AUDIO1_PIN_SET
+ channel_1_stop();
+ setPinOutput(AUDIO1_PIN);
+#endif
+
+#ifdef AUDIO2_PIN_SET
+ channel_2_stop();
+ setPinOutput(AUDIO2_PIN);
+#endif
+
+ // TCCR3A / TCCR3B: Timer/Counter #3 Control Registers TCCR3A/TCCR3B, TCCR1A/TCCR1B
+ // Compare Output Mode (COM3An and COM1An) = 0b00 = Normal port operation
+ // OC3A -- PC6
+ // OC3B -- PC5
+ // OC3C -- PC4
+ // OC1A -- PB5
+ // OC1B -- PB6
+ // OC1C -- PB7
+
+ // Waveform Generation Mode (WGM3n) = 0b1110 = Fast PWM Mode 14. Period = ICR3, Duty Cycle OCR3A)
+ // OCR3A - PC6
+ // OCR3B - PC5
+ // OCR3C - PC4
+ // OCR1A - PB5
+ // OCR1B - PB6
+ // OCR1C - PB7
+
+ // Clock Select (CS3n) = 0b010 = Clock / 8
+#ifdef AUDIO1_PIN_SET
+ // initialize timer-counter
+ AUDIO1_TCCRxA = (0 << AUDIO1_COMxy1) | (0 << AUDIO1_COMxy0) | (1 << AUDIO1_WGMx1) | (0 << AUDIO1_WGMx0);
+ AUDIO1_TCCRxB = (1 << AUDIO1_WGMx3) | (1 << AUDIO1_WGMx2) | (0 << AUDIO1_CSx2) | (1 << AUDIO1_CSx1) | (0 << AUDIO1_CSx0);
+#endif
+
+#ifdef AUDIO2_PIN_SET
+ AUDIO2_TCCRxA = (0 << AUDIO2_COMxy1) | (0 << AUDIO2_COMxy0) | (1 << AUDIO2_WGMx1) | (0 << AUDIO2_WGMx0);
+ AUDIO2_TCCRxB = (1 << AUDIO2_WGMx3) | (1 << AUDIO2_WGMx2) | (0 << AUDIO2_CSx2) | (1 << AUDIO2_CSx1) | (0 << AUDIO2_CSx0);
+#endif
+}
+
+void audio_driver_stop() {
+#ifdef AUDIO1_PIN_SET
+ channel_1_stop();
+#endif
+
+#ifdef AUDIO2_PIN_SET
+ channel_2_stop();
+#endif
+}
+
+void audio_driver_start(void) {
+#ifdef AUDIO1_PIN_SET
+ channel_1_start();
+ if (playing_note) {
+ channel_1_set_frequency(audio_get_processed_frequency(0));
+ }
+#endif
+
+#if !defined(AUDIO1_PIN_SET) && defined(AUDIO2_PIN_SET)
+ channel_2_start();
+ if (playing_note) {
+ channel_2_set_frequency(audio_get_processed_frequency(0));
+ }
+#endif
+}
+
+static volatile uint32_t isr_counter = 0;
+#ifdef AUDIO1_PIN_SET
+ISR(AUDIO1_TIMERx_COMPy_vect) {
+ isr_counter++;
+ if (isr_counter < channel_1_frequency / (CPU_PRESCALER * 8)) return;
+
+ isr_counter = 0;
+ bool state_changed = audio_update_state();
+
+ if (!playing_note && !playing_melody) {
+ channel_1_stop();
+# ifdef AUDIO2_PIN_SET
+ channel_2_stop();
+# endif
+ return;
+ }
+
+ if (state_changed) {
+ channel_1_set_frequency(audio_get_processed_frequency(0));
+# ifdef AUDIO2_PIN_SET
+ if (audio_get_number_of_active_tones() > 1) {
+ channel_2_set_frequency(audio_get_processed_frequency(1));
+ } else {
+ channel_2_stop();
+ }
+# endif
+ }
+}
+#endif
+
+#if !defined(AUDIO1_PIN_SET) && defined(AUDIO2_PIN_SET)
+ISR(AUDIO2_TIMERx_COMPy_vect) {
+ isr_counter++;
+ if (isr_counter < channel_2_frequency / (CPU_PRESCALER * 8)) return;
+
+ isr_counter = 0;
+ bool state_changed = audio_update_state();
+
+ if (!playing_note && !playing_melody) {
+ channel_2_stop();
+ return;
+ }
+
+ if (state_changed) {
+ channel_2_set_frequency(audio_get_processed_frequency(0));
+ }
+}
+#endif