xrun and snd_pcm_prepare.

xrun and snd_pcm_prepare.

[Shaju Abraham]

Hi,
    In aplay utility to playback music, we see that if the return value
is -EPIPE, a function xrun() is called. This function does nothing more
than snd_pcm_prepare(handle).  What is the meaning of receiving a -EPIPE
return value to a application? and, Why cannot this be done at the
driver level itself? say in pcm_native.c .

Is it ok if this snd_pcm_prepare is called from pcm_native.c instead of
returning -EPIPE to the application?

--Shaju Abraham


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Re: xrun and snd_pcm_prepare.

[Paul Davis]

>    In aplay utility to playback music, we see that if the return value
>is -EPIPE, a function xrun() is called. This function does nothing more
>than snd_pcm_prepare(handle).  What is the meaning of receiving a -EPIPE
>return value to a application? and, Why cannot this be done at the
>driver level itself? say in pcm_native.c .

EPIPE signals an xrun (over- or under-run). Its analogous to a POSIX
pipe that has either filled up or has nothing to read. It means that
application has failed to keep up with the hardware.

>Is it ok if this snd_pcm_prepare is called from pcm_native.c instead of
>returning -EPIPE to the application?

no, its not.

behaviour when xruns happen is not automatic. sometimes the driver
will do something, sometimes user space wants to know about it and
take care of the situation with its own approach.

--p


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