[alsa-devel] capturing data from the microphone

[pl bossart]

You haven't specified the buffer/period size in the hw params. See
alsa-lib/test/pcm.c
- Pierre

On Mon, Jan 4, 2010 at 11:39 AM, Riccardo Magliocchetti
<riccardo.magliocchetti at gmail.com> 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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