Re: the ALSA state machine

On 8/9/26 00:47, [email protected] wrote:
> Hello,
> 	I am trying to debug some ALSA playback code. I have two playback
> devices,. The first is A USB sound bar and the second is A Bluetooth sound
> bar. The issue I am debugging is truncated output on the Bluetooth sound
> bar. The USB sound bar works fine. I've added assertions to understand how
> my code may be getting out of sync with the ALSA state machine.
> 	For reference, I am using the documentation at
> https://www.alsa-project.org/alsa-doc/alsa-lib/pcm.html
> 	After opening the device, I check its state and it is always in the
> SND_PCM_STATE_OPEN state, as expected. After initializing the h/w and s/w
> params, however, the document says I should be in the SND_PCM_STATE_SETUP
> state. Instead, however, I am in the SND_PCM_STATE_PREPARED state. I then

It's correct per snd_pcm_hw_params() documentation:

"""
  * After this call, #snd_pcm_prepare() is called automatically and
  * the stream is brought to \c #SND_PCM_STATE_PREPARED state.
"""

> call snd_pcm_prepare() and remain in the SND_PCM_STATE_PREPARED state. I
> then call snd_pcm_start(). In the USB version I get an -EPIPE error. In the

EPIPE usually means that there are not enough data (samples) in the ring buffer.

				Jaroslav

-- 
Jaroslav Kysela <[email protected]>
Linux Sound Maintainer; ALSA Project; Red Hat