At Sun, 11 Oct 2009 12:48:00 +0200,
Krzysztof Helt wrote:
>
> From: Krzysztof Helt <krzysztof.h1@xxxxx>
>
> The chipsets with the isa_dma_bridge_buggy set do not stop DMA during
> DMA counter reads. The DMA counter is read in two 8-bit read steps
> on x86 platform. Sometimes, such reads happen during higher byte
> change so the lower byte is already decremented (rolled over) but
> the higher byte is not. It introduces an error that position is
> moved 256 bytes ahead of the true position. Thus, the next DMA
> position read can return a lower value then the previous read.
> If the DMA position is decreased (reversed) the ALSA subsystem is
> tricked into the playback underrun error and resets the playback.
> It results in a "pop" during a playback.
>
> Work around the issue by reading the counter twice and choosing a higher
> value.
>
> Signed-off-by: Krzysztof Helt <krzysztof.h1@xxxxx>
> ---
> This issue can be tested with the pcm tool from the alsa-lib's test package.
> The command "pcm -c 2 -b 350000 -p 5800" can easily trigger the original error
> every ten seconds on my system.
> This work around greatly reduces the underrun errors for ogg123 and mpg321
> on VIA Apollo (586) chipset + K6-2 533 MHz (from every few seconds to one per about
> 15 minutes - few songs).
Applied now. The only affecting change is the call of enable_dma(),
but this should be OK.
thanks,
Takashi
>
>
> sound/core/isadma.c | 10 +++++++++-
> 1 files changed, 9 insertions(+), 1 deletions(-)
>
> diff --git a/sound/core/isadma.c b/sound/core/isadma.c
> index 79f0f16..950e19b 100644
> --- a/sound/core/isadma.c
> +++ b/sound/core/isadma.c
> @@ -85,16 +85,24 @@ EXPORT_SYMBOL(snd_dma_disable);
> unsigned int snd_dma_pointer(unsigned long dma, unsigned int size)
> {
> unsigned long flags;
> - unsigned int result;
> + unsigned int result, result1;
>
> flags = claim_dma_lock();
> clear_dma_ff(dma);
> if (!isa_dma_bridge_buggy)
> disable_dma(dma);
> result = get_dma_residue(dma);
> + /*
> + * HACK - read the counter again and choose higher value in order to
> + * avoid reading during counter lower byte roll over if the
> + * isa_dma_bridge_buggy is set.
> + */
> + result1 = get_dma_residue(dma);
> if (!isa_dma_bridge_buggy)
> enable_dma(dma);
> release_dma_lock(flags);
> + if (unlikely(result < result1))
> + result = result1;
> #ifdef CONFIG_SND_DEBUG
> if (result > size)
> snd_printk(KERN_ERR "pointer (0x%x) for DMA #%ld is greater than transfer size (0x%x)\n", result, dma, size);
> --
> 1.6.0.3
>
>
>
> ---------------------------------------------------------------
> Zobacz jak pracuje sie na wysokosciach.
> Kliknij >>> http://link.interia.pl/f2384
>
_______________________________________________
Alsa-devel mailing list
Alsa-devel@xxxxxxxxxxxxxxxx
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
