611x analog out dma

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Dave,

We got dma analog output (and input) working with the NI 611x cards, but I've 
hit two issues with output dma.  How to munge output data that is being dma'd 
directly from the buffer, and how to reliably detect underruns?  

It seems to me the best way to munge the output data would be for the driver 
to provide the comedi module with a munging function it can apply when moving 
data from user space to async->prealloc_buf.  This wouldn't work for 
memory-mapped output though.

To catch underruns without race conditions, it seems we would need to do the 
same kind of thing, where the comedi module would need to be able to poll the 
driver to find out how much it has read, and this would need to happen right 
after moving data from user space to async->prealloc_buf.  Again, this 
wouldn't work for memory-mapped output.

I despise memory mapped buffers :)

- -- 
Frank

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Received on 2002-11-14Z18:13:16