Re: [Mesa3d-dev] MMIO/DMA ?

[Stephane M. <ste...@gm...>]

On Tue, Feb 23, 2010 at 22:54, Westermann Fu <wes...@gm...> wrote:
> Thanks very much
>
> As the example when FIFO is full, maybe the 17th or 33th vertex will wait
> for there is room again, so the block happens, I agree. But for correctness,
> need software special handling? I mean after each time a triangle is feeding
> to GPU, then, should software wait for some status register to indicate the
> FIFO is safe? or the 'MOV' instruction itself (or whatever others, here I
> mean no any sync code needed) can promise the correctness automaticly?
> Otherwise I think there is a FIFO overriding risk.
>

[with a proper reply all this time]

On all MMIO GPUs that I know which work like that, the CPU will block
and wait for as long as it takes. But usually you also have a reg you
can poke to know the current filling status of the fifo (full/some
free space), and you can use that to avoid sending too many triangles
and end up in a blocking situation.

Stephane