[MPlayer-dev-eng] DMA or not DMA

Daniel Serpell daniel_serpell at yahoo.com
Wed Nov 24 19:37:17 CET 2004


Hi!

El Wed, Nov 24, 2004 at 06:59:33PM +0100, Arpi escribio:
> > 
> > Oh.. sounds fun. 5 DMA channels, all correctly set up and coordinated.
> 
> yeah :)
> 
> btw, is it possible at all to run multiple dma transfers (to
> different cards) in the same time? or bus-mastering is about it?
> (ie only one dma transfer over pci bus)

There should be only one bus-master on the bus at any given time,
so there is bus-arbitration going on. Normally, each bus-master
transfer takes at least about 16 words (ie, 64 bytes in PCI-32)
and then the bus is released. The "latency-timers" on each PCI
card give the bus information about when a master should release
the bus.

So, if you adjust all the latency-timers to the same value, you
will end-up having a round-robbing of bus-master's, giving each
card an equal share of the bus. It's is better to raise the timers,
so the impact of bus adquisition and release is lowered.

Hope it helps,

        Daniel.




More information about the MPlayer-dev-eng mailing list