Playing notes over I2S
This commit is contained in:
Dejvino
+47
-113
@@ -1,133 +1,67 @@
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#include "AudioThread.h"
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#include "SharedState.h"
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#include <I2S.h>
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#include <math.h>
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// --- MIDI ---
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// Create a MIDI object listening on Serial1 (GP0/GP1)
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MIDI_CREATE_INSTANCE(HardwareSerial, Serial1, MIDI);
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// I2S Pin definitions
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// You may need to change these to match your hardware setup (e.g., for a specific DAC).
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const int I2S_BCLK_PIN = 9; // Bit Clock (GP9)
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const int I2S_LRC_PIN = 10; // Left-Right Clock (GP10)
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const int I2S_DOUT_PIN = 11; // Data Out (GP11)
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// --- Forward Declarations ---
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void fill_audio_buffer(int16_t* buffer, size_t buffer_size);
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void handleNoteOn(byte channel, byte note, byte velocity);
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void handleNoteOff(byte channel, byte note, byte velocity);
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// Audio parameters
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const int SAMPLE_RATE = 44100;
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const int16_t AMPLITUDE = 16383; // Use a lower amplitude to avoid clipping (max is 32767 for 16-bit)
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#ifdef TEST_OUT
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// C Natural Minor Scale notes (C3 to C5) for testing
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const byte c_minor_scale_notes[] = {
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48, 50, 51, 53, 55, 56, 58, // C3 octave
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60, 62, 63, 65, 67, 68, 70, // C4 octave
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72 // C5
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// Create an I2S output object
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I2S i2s(OUTPUT);
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// --- Synthesizer State ---
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// Frequencies for a C-Major scale to pick from
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const float NOTE_FREQUENCIES[] = {
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261.63, 293.66, 329.63, 349.23, 392.00, 440.00, 493.88, 523.25
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};
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#endif
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const int NUM_NOTES = sizeof(NOTE_FREQUENCIES) / sizeof(NOTE_FREQUENCIES[0]);
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float currentFrequency = 440.0f;
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double phase = 0.0;
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unsigned long lastNoteChangeTime = 0;
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// ---
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void setupAudio() {
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#ifndef TEST_OUT
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// --- Initialize MIDI ---
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// The optocoupler circuit inverts the signal, so we must enable inverse logic.
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Serial1.setRX(MIDI_RX_PIN);
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Serial1.setTX(0); // Not using TX
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Serial1.begin(31250);
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Serial1.setRXInverse(true);
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MIDI.setHandleNoteOn(handleNoteOn);
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MIDI.setHandleNoteOff(handleNoteOff);
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MIDI.begin(MIDI_CHANNEL_OMNI);
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Serial.println("MIDI Initialized.");
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#else
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Serial.println("TEST_OUT mode enabled. Playing random C minor notes.");
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// Seed random from noise on the volume pot ADC pin
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randomSeed(analogRead(VOL_POT_PIN));
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#endif
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// --- Initialize I2S Audio ---
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// Configure I2S pins
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i2s.setBCLK(I2S_BCLK_PIN);
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i2s.setLRCK(I2S_LRCK_PIN);
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i2s.setDATA(I2S_DATA_PIN);
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i2s.setDATA(I2S_DOUT_PIN);
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// Set the audio callback function
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i2s.setBufferCallback(fill_audio_buffer);
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if (!i2s.begin(I2S_STEREO, SAMPLE_RATE, BITS_PER_SAMPLE)) {
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// Set the sample rate and start I2S communication
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i2s.setFrequency(SAMPLE_RATE);
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if (!i2s.begin()) {
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Serial.println("Failed to initialize I2S!");
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while (1); // Stop forever
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while (1); // Halt on error
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}
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Serial.println("I2S Initialized.");
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// Seed the random number generator from an unconnected analog pin
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randomSeed(analogRead(A0));
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}
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void loopAudio() {
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#ifdef TEST_OUT
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static uint32_t last_note_event = 0;
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static bool is_playing_test_note = false;
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const uint16_t note_duration = 250; // ms
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const uint16_t note_gap = 50; // ms
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unsigned long now = millis();
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// Check if it's time to turn off the current note
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if (is_playing_test_note && (millis() - last_note_event > note_duration)) {
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handleNoteOff(1, 0, 0); // Turn note off
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is_playing_test_note = false;
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last_note_event = millis(); // Reset timer for the gap
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// Every 500ms, pick a new random note to play
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if (now - lastNoteChangeTime > 500) {
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lastNoteChangeTime = now;
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int noteIndex = random(0, NUM_NOTES);
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currentFrequency = NOTE_FREQUENCIES[noteIndex];
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Serial.println("Playing note: " + String(currentFrequency) + " Hz");
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}
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// Check if it's time to play a new note
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if (!is_playing_test_note && (millis() - last_note_event > note_gap)) {
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// Pick a random note from the scale
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int note_index = random(sizeof(c_minor_scale_notes) / sizeof(c_minor_scale_notes[0]));
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byte midi_note = c_minor_scale_notes[note_index];
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// Generate the sine wave sample
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double phaseIncrement = 2.0 * M_PI * currentFrequency / SAMPLE_RATE;
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phase = fmod(phase + phaseIncrement, 2.0 * M_PI);
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int16_t sample = static_cast<int16_t>(AMPLITUDE * sin(phase));
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// Call NoteOn to set frequency and state
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handleNoteOn(1, midi_note, 127); // Channel and velocity don't matter here
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is_playing_test_note = true;
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last_note_event = millis(); // Reset timer for the duration
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}
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#else
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// Listen for incoming MIDI messages
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MIDI.read();
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#endif
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}
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// --- Audio Generation Callback ---
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// This function is called by the I2S library on the second core (by default)
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// to fill the audio buffer. It must be fast and should not do any allocations.
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void fill_audio_buffer(int16_t* buffer, size_t buffer_size) {
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if (!g_note_on || g_note_frequency <= 0.0) {
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// If no note is playing, fill the buffer with silence.
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memset(buffer, 0, buffer_size * sizeof(int16_t));
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return;
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}
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// Calculate how much to increment the phase for each sample to get the desired frequency.
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float phase_increment = (2.0 * PI * g_note_frequency) / SAMPLE_RATE;
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// The maximum amplitude for a 16-bit signed integer.
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const int16_t max_amplitude = 32767;
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for (size_t i = 0; i < buffer_size; i += 2) { // Process in stereo pairs
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// Generate a sawtooth wave sample (-1.0 to 1.0)
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float sample = (g_phase / PI) - 1.0;
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// Increment and wrap the phase
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g_phase += phase_increment;
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if (g_phase >= 2.0 * PI) {
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g_phase -= 2.0 * PI;
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}
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// Apply volume and scale to 16-bit integer range
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int16_t final_sample = static_cast<int16_t>(sample * max_amplitude * g_volume);
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// Write the same sample to both left and right channels
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buffer[i] = final_sample; // Left channel
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buffer[i + 1] = final_sample; // Right channel
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}
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}
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// --- MIDI Callback Functions ---
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void handleNoteOn(byte channel, byte note, byte velocity) {
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// Convert MIDI note number to frequency
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g_note_frequency = 440.0 * pow(2.0, (note - 69.0) / 12.0);
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g_note_on = true;
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g_phase = 0.0; // Reset phase for a clean attack
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}
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void handleNoteOff(byte channel, byte note, byte velocity) {
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g_note_on = false;
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g_note_frequency = 0.0;
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// Write the same sample to both left and right channels (mono audio).
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// This call is blocking and will wait until there is space in the DMA buffer.
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i2s.write(sample);
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i2s.write(sample);
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}
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