[alsa-devel] [PATCH RFC 0/2] da850 mcasp playback ping-pong buffers don't work

Ben Gardiner bengardiner at nanometrics.ca
Mon May 16 21:15:51 CEST 2011

Hi All,

On Fri, May 13, 2011 at 5:26 PM, Ben Gardiner
<bengardiner at nanometrics.ca> wrote:
> [...]
> Does anyone have any clues why ping-pong buffers on da850 to the McASP
> would work? Or any clues why the patches are broken?

To answer my own question: the reason ping-pong buffering was not
working is because the SRAM allocator being used was allocating
buffers from the "ARM local RAM" block @0xFFFF0000 which is not
addressable by the DMA engine -- according to SPRS586.

Ping-pong buffers work when I substitute the allocator for one that
allocates from the 'Shared RAM' block @0x80000000 using Subhasish
Ghosh's patch "davinci: changed SRAM allocator to shared ram."

Best Regards,
Ben Gardiner

Nanometrics Inc.

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