Enno Fennema wrote:

The documentation says this functions waits for the pcm to become ready for I/O. I am not sure what ready means in this context.

Ready for playback/capture, i.e., some frames are available.

Is there a function to wait for entering the SETUP state. In particular I would like to wait for pcm_snd_drain to finish.

This is not possible. alsa-lib is not thread-safe, so while another thread is executing snd_pcm_drain, you cannot access the same PCM device. Let the other thread send a message after snd_pcm_drain has finished.

Regards, Clemens