I wrote a sample program as follows to OPEN ALSA sound device and set its hw params -

Code:

/* Open PCM device for playback. */ rc = snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0); if (rc < 0) { fprintf(stderr, "unable to open pcm device: %s\n", snd_strerror(rc)); return 1; }

/* Allocate a hardware parameters object. */ snd_pcm_hw_params_alloca(&params);

/* Fill it in with default values. */ snd_pcm_hw_params_any(handle, params);

/* Set the desired hardware parameters. */

/* Interleaved mode */ snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);

/* Signed 16-bit little-endian format */ snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);

/* One channel (mono) */ snd_pcm_hw_params_set_channels(handle, params, 1);

/* 8000 bits/second sampling rate */ val = 8000; snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir);

/* Set period size to 32 frames. */ frames = 32; snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir); fflush(stderr);

/* Write the parameters to the driver */ rc = snd_pcm_hw_params(handle, params);

Above lines of code works fine if I run it as an independent test program. When I use the same lines of code in my application, it is failing in snd_pcm_hw_params_any(). It returns "Operation not permitted". So I changed the device name to "plughw:0,0", instead of "default". With this change, its failing at snd_pcm_hw_params_set_rate_near(). It returns some huge value 192000. Also, following snd_pcm_hw_params_set_period_size() also fails with 699050.

Any idea, why I'm getting this error? Is link to some other library or some header file inclusion, in my application causing this error? I am trying to play 8k, 16 bit PCM audio.

Then I changed snd_pcm_hw_set_rate_near() to snd_pcm_hw_set_rate() and also snd_pcm_hw_params_set_period_size_near() to snd_pcm_hw_params_set_period_size(). These 2 calls succeed. But when I check period_size after calling snd_pcm_hw_params(), it is different. My set value was 32 but I got it as 1. Then call to snd_pcm_writei() crashes with - pcm.c:1240: snd_pcm_writei: Assertion `pcm' failed.

Please note my application is multi threaded but opening the device and setting hardware parameters are under one place.

I appreciate your help on this.

Thanks, Latha