Intel integrated and derivatives have an actual "frame buffer", in that you set a base pointer to a contiguous block of memory visible to the adapter and scan-out happens from there.

I think the real performance issue for hardware where the frame buffer is in the PCIe shared memory apperture is that writes are write-through/coalesced on their way across the PCIe, but reads can't be, and so incur huge stalls.

Paul


Dec 1, 2008 06:34:59 AM, 9fans@9fans.net wrote:

===========================================


>
> Very true, the only exception to this I know of is some of the modern
> Dual PCIExpress cards which use a bus in each direction.
>

do you have a reference for "dual pciexpress"?  as far as i know,
pcie/agp/pci cards only have a single bus that goes both ways.

my limited understanding was that the reason that reading the
framebuffer was slow, was that there is no framebuffer.  it's an
illusion that the card provides that's easy to write but not so
easy to fake on reads.

someone with real understanding of graphics please correct me.

- erik