At Thu, 21 Jan 2010 12:32:20 +0800, Raymond Yau wrote: > > Refer to > http://www.alsa-project.org/~tiwai/writing-an-alsa-driver/ch05s06.html#pcm-interface-operators-hw-free-callback > > hw_free callback > > static int snd_xxx_hw_free(struct snd_pcm_substream *substream); > > This is called to release the resources allocated via > *hw_params*. For example, releasing the > buffer via snd_pcm_lib_malloc_pages() is done by > calling the following: > snd_pcm_lib_free_pages(substream); > > This function is always called before the close callback is called. > Also, the callback may be called multiple times, too. > Keep track whether the resource was already released. > Nearly all the examples in those ALSA tutorials in the web sites have the code > > > if ((err = snd_pcm_hw_params (playback_handle, hw_params)) < 0) { > fprintf (stderr, "cannot set parameters (%s)\n", > snd_strerror (err)); > exit (1); > } > > snd_pcm_hw_params_free (hw_params); > > This seem to violate "This function is always called before the close > callback is called." > > and those hardware mixing sound cards (e.g cs46xx , au88x0, ... ) use > snd_xxx_hw_free() to deallocate the hardware mixing path in the DSP. > > There are a number of audio package (e.g. gstreamer , wine , .... ) > call snd_pcm_hw_params_free immediately after snd_pcm_hw_params() > > Is this a bug of snd_pcm_hw_params_free() not change the state of the > PCM stream ? Confusingly, snd_pcm_hw_params_free() and snd_pcm_hw_free() are different. The former is just to free the malloced snd_pcm_hw_params struct while the latter corresponds to snd_xxx_hw_free(). Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
