Re: audio/PCI/mmap oddity (again)
David Olofson (audiality@swipnet.se)
Sun, 25 Jul 1999 23:58:40 +0200
Paul Barton-Davis wrote:
(...)
> >1. You read pattern n. Not overwritten.
> >2. DMA burst overwrites pattern n AND pattern (n + 1).
> >3. You read pattern (n + 1), which has now been overwritten...
> >
>
> this sounds close, but not quite.
>
> first, it doesn't matter what the distance between the patterns is -
> 8, 16, 32, 128, 512, 2048 byte distances all suffer from the same
> problem.
>
> second, the *odd* part is that your point (2) is exactly what is *not*
> happening (i had coded for that situation). that is, we end up with
> pattern n *NOT* overwritten and pattern (n+1) overwritten.
Ok, I thought about suggesting that you tested for that.
> finally, the fact that using an 8bit sample size eliminates the
> problem seems to suggest that the DMA burst size is not it.
Yes, it does...
> did i get something wrong ?
No, I don't think so... This DOES sound a bit weird. Can't think of
anything obvious right now...
Tried different sample rates? Do you have programming specs for the
card? Any hints in the driver source?
//David
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