[alsa-devel] Help required with debugging
perex at perex.cz
Thu Jul 2 10:08:35 CEST 2009
On Thu, 2 Jul 2009, Harsha, Priya wrote:
> Why is runtime->hw_ptr_jiffies updated in hw_ptr()? This should be only
> updated in the interrupt context right?
The idea of hw_ptr_jiffies is to have a check if real-time clock in sync
with the DMA buffer position. If your hardware does block transfers and is
not able to return fine position in period set SNDRV_PCM_INFO_BATCH flag.
But it's rather a workaround than a proper fix, because timestamps are
updated but the ring buffer position is not moved (which brokes the idea
to have a relation between the ring buffer position and the real-time
I think that this sort of drivers might require to implement the
SNDRV_PCM_POS_KEEP return value in case when position does not change from
last read to notify midlevel PCM code that they're not able to handle fine
Also, hardware with large FIFOs should update properly runtime->delay
Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.
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