Messages in this thread | | | Date | Fri, 7 May 2010 10:45:21 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [alsa-devel] USB transfer_buffer allocations on 64bit systems |
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On Fri, 7 May 2010, Daniel Mack wrote:
> > Or to be precise it could be done with coherent memory, but you'd risk > > transfering partially updated buffers, as you cannot know when DMA will > > be done and we don't guarantee that DMA will be done right as we transfer. > > If the memory is coherent, it should be possible. And if buffers are > only partially updated, the audio buffer scheduling is too tight. IOW, > the configured buffer size of audio clients in userspace is too small.
Even with coherent memory, this dynamic updating of buffer contents isn't a good idea. There's no guarantee that coherent memory won't be implemented using a bounce buffer during URB submission.
Alan Stern
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