[alsa-devel] Monitoring ALSA's write pointer (appl_ptr)?

Brian Welch Brian-Welch at cox.net
Wed Nov 5 04:10:13 CET 2008

>> Is there a definitive/safe way to monitor ALSA's write pointer in the
>> dma_area?  It seems like the ack callback and the appl_ptr is the
>> correct way, but I was told by another developer that appl_ptr doesn't
>> work in all cases.
>> As a future optimization for my hardware, I may want to tell ALSA to use
>> a specific area of physical memory for it's dma_area, what is the best
>> way to do that?
> A good question.  The ack callback is called only when the explicit
> read/write method is used.  When mmap access is used, it won't be
> called.
> One hack would be to check appl_ptr in the pointer callback.  This
> callback is called in snd_pcm_hwsync(), too.  So, if you watch the
> appl_ptr change as frequently as possible, it'd be a good place for
> that.
> Takashi

Thanks.  I'll try reading appl_ptr from within the pointer callback.


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