On 8/20/06, Timothy Miller <[EMAIL PROTECTED]> wrote:
The only problem I haven't totally resolved yet (in any case) is that while DMA is going on, you really don't want to try to do a PIO to the same device. This isn't a logical problem so much as a physical one. During the transfer of a DMA burst, the bus is tied up doing something, and it's going to be doing it for a while. Any attempt by the CPU to access the bus is going to suffer a massive latency. Imagine how many CPU cycles are wasted while waiting for 32 PCI bus cycles at 33MHz.
In command stream mode the Radeon chips don't need to do any PIO. You put commands in the command stream that write to the same registers. It is a somewhat general mechanism, commands can write 1,2,3,4,5, etc registers. Command blocks contain pairs of register numbers and values. DMA to/from the cards is overrated. Most apps load their textures into the card and then never use DMA again. DX10 specs virtual VRAM which eliminates even more need for programmed DMA. Only a few apps read textures back from the card. -- Jon Smirl [EMAIL PROTECTED] _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
