[MPlayer-dev-eng] DMA or not DMA

[Attila Kinali]

On Wed, 24 Nov 2004 15:37:17 -0300
Daniel Serpell <daniel_serpell at yahoo.com> wrote:


> > 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)

You can set up multiple dma transferes w/o problem, as long as
the dma controller has free channels. Of course, only one transfere
at a time is possible unless you have multiple independent busses.

I dunno how linux handles this, but i guess that linux keeps
it's own buffer for pending dma transferes and processes one
after each other (at least, that would be what i do)

> 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.

Latency is of no concern in this case as you want to show all
frames at the same time. Additionaly it's actualy better to
keep the transferese together to skip the setup phase


 			Attila Kinali