buffer_queue.h

#pragma once

// Circular queue of buffers used to produce and consume new blocks of audio data 
// coming from and going to the I2S bus. 
// Current setup is working for 2 channels using i2s or TDM for 4 channels.
class BufferQueue
{
#define BUFFER_QUEUE_SIZE 3
public:
  int32_t channel[CHANNELS][AUDIO_BLOCK_SAMPLES * BUFFER_QUEUE_SIZE];
	int32_t* readPtr[CHANNELS];
	int32_t* writePtr[CHANNELS];

	uint8_t readPos = 0;
	uint8_t writePos = 0;
	int available = 0;

	inline BufferQueue()
	{
		writePtr[0] = &channel[0][writePos * AUDIO_BLOCK_SAMPLES];
		writePtr[1] = &channel[1][writePos * AUDIO_BLOCK_SAMPLES];
    
        readPtr[0] = &channel[0][readPos * AUDIO_BLOCK_SAMPLES];
		readPtr[1] = &channel[1][readPos * AUDIO_BLOCK_SAMPLES];
    
    if (CHANNELS > 2) {
        writePtr[2] = &channel[2][writePos * AUDIO_BLOCK_SAMPLES];
		writePtr[3] = &channel[3][writePos * AUDIO_BLOCK_SAMPLES];

        readPtr[2] = &channel[2][readPos * AUDIO_BLOCK_SAMPLES];
		readPtr[3] = &channel[3][readPos * AUDIO_BLOCK_SAMPLES];
     }
        for (size_t i = 0; i < AUDIO_BLOCK_SAMPLES * BUFFER_QUEUE_SIZE; i++)
        {
            channel[0][i] = 0;
            channel[1][i] = 0;
            
            if (CHANNELS > 2) {
              channel[2][i] = 0;
              channel[3][i] = 0;
            }
        }
        
        for (size_t i = 0; i < BUFFER_QUEUE_SIZE - 1; i++)
        {
            publish();
        }
	}

	// Increases writePos by one and updates the write pointers
	// First, write to the write pointers, then call this function to mark the data as available for reading.
	inline void publish()
	{
		writePos = (writePos + 1) % BUFFER_QUEUE_SIZE;
		writePtr[0] = &channel[0][writePos * AUDIO_BLOCK_SAMPLES];
		writePtr[1] = &channel[1][writePos * AUDIO_BLOCK_SAMPLES];
    
        if (CHANNELS > 2) {
          writePtr[2] = &channel[2][writePos * AUDIO_BLOCK_SAMPLES];
		  writePtr[3] = &channel[3][writePos * AUDIO_BLOCK_SAMPLES];
    }
    available++;

		// writing over the tail of the circular buffer. Should never happen as read and write should be synchronous!
		if (available > BUFFER_QUEUE_SIZE)
			consume(); // consume and discard one block
	}

	// increase ReadPos by one and updates the read pointers.
	// First read from the read pointers, then call this function to mark the data as dispensed.
	inline void consume()
	{
		if (available <= 0)
			return;

		readPos = (readPos + 1) % BUFFER_QUEUE_SIZE;
		readPtr[0] = &channel[0][readPos * AUDIO_BLOCK_SAMPLES];
		readPtr[1] = &channel[1][readPos * AUDIO_BLOCK_SAMPLES];
    
    if (CHANNELS > 2) {
      	readPtr[2] = &channel[2][readPos * AUDIO_BLOCK_SAMPLES];
		readPtr[3] = &channel[3][readPos * AUDIO_BLOCK_SAMPLES];
    }
    available--;
	}
};