[alsa-devel] capturing data from the microphone

[Marc Garnier]

Hi,

I have the same kind of problem. I try to capture PCM stream thanks to 
areacord :
# arecord -c 1 -t wav -f S16_LE -r 8000 -d 10 input.wav

30 seconds later I have the folowing message :
# arecord: pcm_read:1629: read error: Input/output error

I can observe the PCM stream on an oscilloscope but no interrupt are 
catched by the system  (AIC ss0 counter remains at zero ) :
# cat /proc/interrupts
           CPU0
  1:     275059         AIC  at91_tick, rtc0, ttyS0
  7:        179         AIC  ttyS2
  9:         11         AIC  mmc0
 13:          0         AIC  atmel_spi.1
 14:          0         AIC  ssc0
 82:          1        GPIO  alerte
107:       9464        GPIO  eth0

Any idea?



Riccardo Magliocchetti wrote:
> [the same message is waiting in moderator queue, sorry if you receive it two times]
>
> Hello,
>
> i'm trying to capture audio data from the microphone, but i'm not able to
> read any frames.
> The frames are always 0 and delay is fixed to 2730. I've tried calling
> snd_pcm_avail_delay,  snd_pcm_avail_update but does not make a difference.
> The soundcard is driven by  snd_hda_intel. The code is more or less the
> same as Paul Davis' tutorial on using the alsa api.
>
> This is the code for init and the loop that tries to read the data:
>
> #define MIC_BUFSIZE 4096
>
> static gpointer snd_pcm_read(gpointer data)
> {
>    int error;
>    snd_pcm_sframes_t frames = MIC_BUFSIZE;
>
>    while (TRUE) {
>
>      if ((error = snd_pcm_wait (pcm_handle, 1000)) < 0) {
>          g_printerr("Failed to poll: %s\n", snd_strerror(error));
>          continue;
>      }
>
>      if ((error = snd_pcm_avail(pcm_handle)) < 0) {
>        if (error == -EPIPE) {
>          g_printerr("xrun! %s\n", snd_strerror(error));
>          continue;
>          //return GINT_TO_POINTER(FALSE);
>        } else {
>          g_printerr("alsa_pcm_avail_update error %s\n", snd_strerror(error));
>          continue;
>          //return GINT_TO_POINTER(FALSE);
>        }
>      }
>
>      frames = error;
>      if (frames == 0)
>        continue;
>
>      frames = frames > MIC_BUFSIZE ? MIC_BUFSIZE : frames;
>      g_printerr ("frames: %ld\n", frames);
>      g_static_mutex_lock(&mutex);
>      error = snd_pcm_readi(pcm_handle, Mic_Buffer[Mic_WriteBuf], frames);
>      g_static_mutex_unlock(&mutex);
>      if (error < 0)
>          error = snd_pcm_recover(pcm_handle, error, 0);
>      if (error < 0) {
>         LOG("snd_pcm_readi FAIL!: %s\n", snd_strerror(error));
>      }
>    }
>
>    return GINT_TO_POINTER(TRUE);
> }
>
> BOOL Mic_Init()
> {
>      snd_pcm_hw_params_t *hwparams;
>      snd_pcm_sw_params_t *swparams;
>      int err;
>
>      if (Mic_Inited)
>          return TRUE;
>
>      // Open the default sound card in capture
>      if ((err = snd_pcm_open(&pcm_handle, "default", SND_PCM_STREAM_CAPTURE,
> /*SND_PCM_NONBLOCK*/ 0)) < 0) {
>          g_printerr("Failed to open device: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      // Allocate the snd_pcm_hw_params_t structure and fill it.
>      snd_pcm_hw_params_alloca(&hwparams);
>      if ((err = snd_pcm_hw_params_any(pcm_handle, hwparams)) < 0) {
>          g_printerr("Failed to setup hw parameters: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      //Set the access
>      if ((err = snd_pcm_hw_params_set_access(pcm_handle, hwparams,
> SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
>          g_printerr("Failed to set access: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      //dir 0 == exacte (Rate = 16K exacte)
>      if ((err = snd_pcm_hw_params_set_rate(pcm_handle, hwparams, 16000, 0)) < 0) {
>          g_printerr("Failed to set rate: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      /* Set sample format */
>      if ((err = snd_pcm_hw_params_set_format(pcm_handle, hwparams, SND_PCM_FORMAT_S8)) < 0) {
>          g_printerr("Failed to set format: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      // Set one channel (mono)
>      if ((err = snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 1)) < 0) {
>          g_printerr("Failed to set channels: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      //Set the params
>      if ((err = snd_pcm_hw_params(pcm_handle, hwparams)) < 0) {
>          g_printerr("Failed to set hw parameters: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      snd_pcm_sw_params_alloca(&swparams);
>      if ((err = snd_pcm_sw_params_current (pcm_handle, swparams)) < 0) {
>          g_printerr("Failed to set current sw parameters: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      if ((err = snd_pcm_sw_params_set_avail_min (pcm_handle, swparams, MIC_BUFSIZE)) < 0) {
>          g_printerr("Failed to set minimum available count: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      if ((err = snd_pcm_sw_params_set_start_threshold (pcm_handle, swparams, 0U)) < 0) {
>          g_printerr("Failed to set start mode: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      if ((err = snd_pcm_sw_params (pcm_handle, swparams)) < 0) {
>          g_printerr("Failed to set sw parameters: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      if ((err = snd_pcm_prepare (pcm_handle)) < 0) {
>          g_printerr("Failed to prepare audio interface to use: %s\n", snd_strerror(err));
>          return FALSE;
>      }
>
>      Mic_Inited = TRUE;
>      Mic_Reset();
>
>      mic_reader = g_thread_create(snd_pcm_read, NULL, TRUE, NULL);
>
>      return TRUE;
> }
>
>
> thanks,
> Riccardo
>
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