>What do the callbacks do in snd_pcm_ops_t:
the best answers can be found by looking at similar drivers, or even
dissimilar drivers. i wrote two ALSA drivers that way.
> open
someone has called snd_pcm_open() and the named device has resolved to
include this h/w device. you should take ownership of the h/w here, do
anything that needs to be done that isn't related to actually using
the h/w.
> close
the final user of the device has called snd_pcm_close(). release all
resources associated with the device and release the device itself.
> ioctl
implement all (or as many as possible) of the SNDDRV_PCM_IOCTL_* commands.
> hw_params
this is where the hardware based parameters are set. the callback must
attempt to handle these, returning EINVAL if its not possible.
> hw_free
not sure.
> prepare
this is called in response to snd_pcm_prepare(), which is called
before an application can actually start to use the device. this is
where you would do any late setup of the h/w, up to but not including
starting it running.
> trigger
this is called to actually start and stop the h/w.
> pointer
this is called to find out where the h/w pointer is in the ring buffer
used for capture/playback. some devices do not support it, but most do.
--p
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