* Re: Monitoring ALSA's write pointer (appl_ptr)? [not found] <20081103234028.PAVUM.84220.imail@fed1rmwml28> @ 2008-11-04 16:33 ` Takashi Iwai 2008-11-05 3:10 ` Brian Welch 0 siblings, 1 reply; 2+ messages in thread From: Takashi Iwai @ 2008-11-04 16:33 UTC (permalink / raw) To: brian-welch; +Cc: alsa-devel At Mon, 3 Nov 2008 23:40:28 -0500, <brian-welch@cox.net> wrote: > > Hello List, > > My first post, so excuse any ignorance. > > 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 ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Monitoring ALSA's write pointer (appl_ptr)? 2008-11-04 16:33 ` Monitoring ALSA's write pointer (appl_ptr)? Takashi Iwai @ 2008-11-05 3:10 ` Brian Welch 0 siblings, 0 replies; 2+ messages in thread From: Brian Welch @ 2008-11-05 3:10 UTC (permalink / raw) To: Takashi Iwai; +Cc: alsa-devel >> 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. Brian ^ permalink raw reply [flat|nested] 2+ messages in thread
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2008-11-04 16:33 ` Monitoring ALSA's write pointer (appl_ptr)? Takashi Iwai
2008-11-05 3:10 ` Brian Welch
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