On 4/3/2013 9:49 AM, Clemens Ladisch wrote:
Patrick Lai wrote:
Data is transferred in chunk equal to period size.
Data is transferred in whatever chunk size the hardware uses.
The period size specifies when the hardware raises an interrupt.
If some application is blocking, this interrupt is the only mechanism
by which userspace is woken up.
At the end of playback, there may not be enough audio data left in the
music stream to fill entire period. If remaining audio data only takes
up very small chunk of period, playback takes longer to stop. Given
that period size I have to deal with is quite large, this problem is
observed easily. If my understanding is correct, what is the standard/
recommended way of handling end of stream case?
I guess you wouldn't ask if your hardware supported smaller periods? ;-)
The hardware can accept smaller period but smaller period would result
in more frequent interrupt to application processor. This leads to
higher power consumption.
Use non-blocking writes, and use some other timer to wait for the actual
data to be played. (But if the hardware cannot report the current
playback position accurately, ALSA won't notice that the playback has
reached the end.)
My concern is not about blocking too long but audio playback ending
longer than necessary. If I understand correctly, you are suggesting
that application, once done transferring residual data, set up timer
according to expected duration of residual data. Upon waking up from
timer, call ALSA library API to get the current hardware pointer.
Is my understanding correct?
Regards,
Clemens
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