// mmap-record.c - Records audio using ALSA mmap and writes to S32_LE WAV file

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <alsa/asoundlib.h>

#define SAMPLE_RATE 48000
#define CHANNELS 2
#define FORMAT SND_PCM_FORMAT_S32_LE
#define BUFFER_TIME 500000   // us
#define PERIOD_TIME 100000   // us
#define DURATION 5           // seconds
#define FILENAME "record_mmap.wav"
#define PCM_DEVICE "hw:0,0"

#define WAV_HEADER_SIZE 44

#define kAudioFrameSamples 256  // This is the audio driver callback rate.  Should not be too huge as it consumes coherent kernel memory.
#define kNumAlsaBuffers 4
snd_pcm_uframes_t periodSize = kAudioFrameSamples;
snd_pcm_uframes_t bufferSize = kAudioFrameSamples * kNumAlsaBuffers; // adjusted in initPcmHandle


void write_wav_header(FILE *f, int data_bytes) {
    int32_t sample_rate = SAMPLE_RATE;
    int16_t bits_per_sample = 32;
    int16_t channels = CHANNELS;
    int32_t byte_rate = sample_rate * channels * bits_per_sample / 8;
    int16_t block_align = channels * bits_per_sample / 8;
    int32_t chunk_size = 36 + data_bytes;

    uint8_t header[WAV_HEADER_SIZE] = {
        'R','I','F','F',
        chunk_size & 0xFF, (chunk_size >> 8) & 0xFF, (chunk_size >> 16) & 0xFF, (chunk_size >> 24) & 0xFF,
        'W','A','V','E','f','m','t',' ',
        16,0,0,0, // Subchunk1Size
        1,0, // PCM
        channels,0,
        sample_rate & 0xFF, (sample_rate >> 8) & 0xFF, (sample_rate >> 16) & 0xFF, (sample_rate >> 24) & 0xFF,
        byte_rate & 0xFF, (byte_rate >> 8) & 0xFF, (byte_rate >> 16) & 0xFF, (byte_rate >> 24) & 0xFF,
        block_align,0,
        bits_per_sample,0,
        'd','a','t','a',
        data_bytes & 0xFF, (data_bytes >> 8) & 0xFF, (data_bytes >> 16) & 0xFF, (data_bytes >> 24) & 0xFF
    };
    fwrite(header, 1, WAV_HEADER_SIZE, f);
}

const char *snd_pcm_state_name(snd_pcm_state_t state)
{
  switch (state)
  {
    case SND_PCM_STATE_OPEN:
      return "SND_PCM_STATE_OPEN";
    case SND_PCM_STATE_SETUP:
      return "SND_PCM_STATE_SETUP";
    case SND_PCM_STATE_PREPARED:
      return "SND_PCM_STATE_PREPARED";
    case SND_PCM_STATE_RUNNING:
      return "SND_PCM_STATE_RUNNING";
    case SND_PCM_STATE_XRUN:
      return "SND_PCM_STATE_XRUN";
    case SND_PCM_STATE_DRAINING:
      return "SND_PCM_STATE_DRAINING";
    case SND_PCM_STATE_PAUSED:
      return "SND_PCM_STATE_PAUSED";
    case SND_PCM_STATE_SUSPENDED:
      return "SND_PCM_STATE_SUSPENDED";
    case SND_PCM_STATE_DISCONNECTED:
      return "SND_PCM_STATE_DISCONNECTED";
    default:
      return "Unknown state";
  }
}

const char *snd_pcm_stream_name_zz(snd_pcm_t *pcmHandle)
{
  snd_pcm_stream_t stream = snd_pcm_stream(pcmHandle);
  switch (stream)
  {
    case SND_PCM_STREAM_PLAYBACK:
      return "SND_PCM_STREAM_PLAYBACK";
    case SND_PCM_STREAM_CAPTURE:
      return "SND_PCM_STREAM_CAPTURE";
    default:
      return "Unknown stream";
  }
}


int handlePcmOverOrUnderRun(snd_pcm_t *pcmHandle, int dbgCauseSource)
{
  // handle overrun or underrun.
  snd_pcm_drop(pcmHandle);
  snd_pcm_recover(pcmHandle, -EPIPE, 0);
  snd_pcm_prepare(pcmHandle);
  usleep(3000);
  snd_pcm_state_t state = snd_pcm_state(pcmHandle);
  printf("Stream %s: state = %s after recovery, source = %d\n",
      snd_pcm_stream_name_zz(pcmHandle), snd_pcm_state_name(state), dbgCauseSource);

  state = snd_pcm_state(pcmHandle);
  printf("Stream %s: state = %s after start, source = %d\n",
      snd_pcm_stream_name_zz(pcmHandle), snd_pcm_state_name(state), dbgCauseSource);

  usleep(3000);
  return 0;
}

void hw_init(snd_pcm_t *handle)
{
  snd_pcm_hw_params_t *hwparams;
    int err;

    snd_pcm_hw_params_malloc(&hwparams);
    snd_pcm_hw_params_any(handle, hwparams);
    snd_pcm_hw_params_set_access(handle, hwparams, SND_PCM_ACCESS_MMAP_INTERLEAVED);
    snd_pcm_hw_params_set_format(handle, hwparams, FORMAT);
    snd_pcm_hw_params_set_rate(handle, hwparams, SAMPLE_RATE, 0);
    snd_pcm_hw_params_set_channels(handle, hwparams, CHANNELS);
    err        = snd_pcm_hw_params_set_period_size_near(handle, hwparams, &periodSize, 0);
    if (err < 0) printf("Error %d with snd_pcm_hw_params_set_period_size_near\n", err);
    bufferSize = periodSize * kNumAlsaBuffers;  // e.g., 4 audio frames in the entire alsa buffer
    err        = snd_pcm_hw_params_set_buffer_size_near(handle, hwparams, &bufferSize);
    if (err < 0) printf("Error %d with snd_pcm_hw_params_set_buffer_size_near\n", err);
    printf("Using period (audio frame) size: %lu and buffer size %lu\n", periodSize, bufferSize);
    snd_pcm_hw_params(handle, hwparams);    
    snd_pcm_hw_params_free(hwparams);
}

void sw_init(snd_pcm_t *handle,const int  audio_frame_size)
{
    snd_pcm_sw_params_t *swparams;
    snd_pcm_sw_params_malloc(&swparams);
    snd_pcm_sw_params_current(handle, swparams);
    snd_pcm_sw_params_set_avail_min(handle, swparams, audio_frame_size);
    snd_pcm_sw_params_set_start_threshold(handle, swparams, 0);
    snd_pcm_sw_params_set_stop_threshold(handle, swparams, 65536);
    snd_pcm_sw_params(handle, swparams);
    snd_pcm_sw_params_free(swparams);

}


void do_capture_samples(snd_pcm_t *handle,const int  audio_frame_size, FILE *fout)
{
  int dir, err;
  int total_frames = SAMPLE_RATE * DURATION;
  int frame_size = CHANNELS * sizeof(int32_t);
  int recorded_frames = 0;
  int attempts = 0;
  const snd_pcm_channel_area_t *areas;
  snd_pcm_uframes_t offset, frames;

  while (recorded_frames < total_frames) 
  {
    frames = audio_frame_size;
    err = snd_pcm_mmap_begin(handle, &areas, &offset, &frames);
    if (err < 0) {
        fprintf(stderr, "mmap_begin error: %s\n", snd_strerror(err));
        break;
    }

    snd_pcm_state_t state = snd_pcm_state(handle);
    if (frames == 0)
    {
      err = snd_pcm_mmap_commit(handle, offset, frames);
      // printf ("commit 0 frames err = %d, state =  %s)\n", err,
      //           snd_pcm_state_name(state));
      if (attempts > 500)
      {
        printf ("Not getting audio frames\n");
        attempts = 0;
      }
      if (attempts > 0)
        ++attempts;
      if (state == SND_PCM_STATE_PREPARED)
      {
        printf("Starting pcm capture stream after %d attempts\n", attempts);
        snd_pcm_start(handle);
      }
      else if (state == SND_PCM_STATE_XRUN) 
      {
        printf("XRUN detected, attempting recovery\n");
        handlePcmOverOrUnderRun(handle, 1);
        continue;
      }
      usleep(4000);
      continue;
    }

    if ((recorded_frames & 0x3FF) == 0)
      printf ("%d frames\n", recorded_frames);
    if (frames > audio_frame_size)
      frames = audio_frame_size;

    if (frames < audio_frame_size) 
    {
      printf ("Short: %d\n", frames);
    }
    // else
    {

      int32_t *samples = (int32_t *)((uint8_t *)areas[0].addr + (offset * (areas[0].step / 8)));
      size_t bytes = frames * frame_size;
      fwrite(samples, 1, bytes, fout);
      recorded_frames += frames;

      err = snd_pcm_mmap_commit(handle, offset, frames);
      if (err < 0) {
          fprintf(stderr, "mmap_commit error: %s\n", snd_strerror(err));
          break;
      }
      usleep(5000);
    }
    attempts = -1;
  }
}

int main()
{
    snd_pcm_t *handle;
    const snd_pcm_channel_area_t *areas;
    snd_pcm_uframes_t offset, frames;
    int dir, err;
    const int audio_frame_size = 256;

    int frame_size = CHANNELS * sizeof(int32_t);
    int total_frames = SAMPLE_RATE * DURATION;
    int recorded_frames = 0;

    err = snd_pcm_open(&handle, PCM_DEVICE, SND_PCM_STREAM_CAPTURE, 0);
        if (err < 0) {
        fprintf(stderr, "Error opening PCM device: %s\n", snd_strerror(err));
        return 1;
    }

    hw_init(handle);
    sw_init(handle, audio_frame_size);

    FILE *fout = fopen(FILENAME, "wb");
    if (!fout) {
        perror("fopen");
        return 1;
    }
    write_wav_header(fout, total_frames * frame_size);

    snd_pcm_prepare(handle);
    do_capture_samples(handle, audio_frame_size, fout);

    snd_pcm_pause(handle, 1);
    fclose(fout);

    snd_pcm_pause(handle, 1);
    snd_pcm_close(handle);
    printf("Wrote %s\n", FILENAME);
    return 0;
}

进行编译、方法是为 SDK 的环境设置脚本提供源代码、然后运行

$｛CC｝McASP-alsa-recor记录-map-main.c -lasound -lm -o McASP-alsa-mmap-record