> > I've got a simple PCM capture test program below, which is basically > a slightly tweak version of something from: > > http://equalarea.com/paul/alsa-audio.html > > > The program uses two different methods of setting up the capture > handle; one that works (and is complex) and one that doesn't but > seems like it should (and is simple). I'm trying to figure out > why the simple one (using snd_pcm_set_params) doesn't work. > > The program can be compiled and run in two ways: > > gcc -Wall -O2 -DUSE_SET_PARAMS=1 alsa_capture.c -lasound -o alsa_capture > ./alsa_capture > > which fails with: > > Read from audio interface failed (Input/output error) > > and: > > gcc -Wall -O2 -DUSE_SET_PARAMS=0 alsa_capture.c -lasound -o alsa_capture > ./alsa_capture > > which works as expected. > > Questions: > > * Is snd_pcm_set_params() supposed to work on capture handles (I've used > it successfully on playback handles)? > > * Is my use of snd_pcm_set_params() missing something and if so what? Do your sound card driver support 0.5 second buffer? > > * If snd_pcm_set_params() is not supposed to work on capture handles > would it be possible to update the documentation to reflect that? > > > int buffer_frames = 128; > unsigned int rate = 44100; > snd_pcm_t *capture_handle; > snd_pcm_format_t format = SND_PCM_FORMAT_S32_LE; > if (USE_SET_PARAMS) { > if ((err = snd_pcm_set_params (capture_handle, format, SND_PCM_ACCESS_RW_INTERLEAVED, 2, rate, 0, 500000)) < 0) { /* 0.5sec */ > printf ("Capture open error: %s\n", snd_strerror (err)); exit (1) ; > } > } > else { > snd_pcm_hw_params_t *hw_params; > > if ((err = snd_pcm_hw_params_malloc (&hw_params)) < 0) { > printf ("Cannot allocate hardware parameter structure (%s)\n", snd_strerror (err)); exit (1) ; > } > > if ((err = snd_pcm_hw_params_any (capture_handle, hw_params)) < 0) { > printf ("Cannot initialize hardware parameter structure (%s)\n", snd_strerror (err)); exit (1) ; > } > > if ((err = snd_pcm_hw_params_set_access (capture_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) { > printf ("cannot set access type (%s)\n", snd_strerror (err)); exit (1) ; > } > > if ((err = snd_pcm_hw_params_set_format (capture_handle, hw_params, format)) < 0) { > printf ("Cannot set sample format (%s)\n", snd_strerror (err)); exit (1) ; > } > > if ((err = snd_pcm_hw_params_set_rate_near (capture_handle, hw_params, &rate, 0)) < 0) { > printf ("Cannot set sample rate (%s)\n", snd_strerror (err)); exit (1) ; > } > > if ((err = snd_pcm_hw_params_set_channels (capture_handle, hw_params, 2)) < 0) { > printf ("cannot set channel count (%s)\n", snd_strerror (err)); exit (1) ; > } > > if ((err = snd_pcm_hw_params (capture_handle, hw_params)) < 0) { > printf ("cannot set parameters (%s)\n", snd_strerror (err)); exit (1) ; > } If you does not specify period, period_size or buffer size, period_time or buffer_time before calling snd_pcm_hw_params , you have to use use those hw_params_get_* functions after calling snd_pcm_hw_params to get back those values > > buffer = malloc (buffer_frames * snd_pcm_format_width(format) / 8 * 2); > > if ((err = snd_pcm_prepare (capture_handle)) < 0) { > printf ("cannot prepare audio interface for use (%s)\n", snd_strerror (err)); exit (1) ; > } > > for (i = 0; i < 10; ++i) { > if ((err = snd_pcm_readi (capture_handle, buffer, buffer_frames)) != buffer_frames) { > printf ("Read from audio interface failed (%s)\n", snd_strerror (err)); exit (1) ; > break; > } > printf("read %d done\n", i); > } > _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
