[alsa-devel] Regarding pointer callback

Pharaoh . pharaoh137 at gmail.com
Wed Feb 20 20:16:30 CET 2008


In Writing an ALSA driver, it is written that
pointer callback is called usually from the buffer-update routine in
the pcm middle layer, which is invoked when snd_pcm_period_elapsed()
is called in the interrupt routine. Then the pcm middle layer updates
the position and calculates the available space, and wakes up the
sleeping poll threads, etc.

I know from a kernel space ALSA driver, the pointer callback is called
after the driver calls snd_pcm_period_elapsed() from the interrupt handler
or after a period is consumed. How pointer function of a user space plugin
is called? I have a user space pcm external plugin which updates the buffer
counter after every period is consumed, but when will it be called? How does
ALSA lib know when to call it since there is no snd_pcm_period_elapsed() in


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