[Mesa-dev] Doubt about Streamed Vertex Buffer Write message descriptor in SandyBridge

Ilia Mirkin imirkin at alum.mit.edu
Tue Jul 22 08:38:05 PDT 2014

On Tue, Jul 22, 2014 at 11:25 AM, Samuel Iglesias Gonsálvez
<siglesias at igalia.com> wrote:
> Hello,
> I have a doubt related to Streamed Vertex Buffer Write message and its
> message descriptor in SandyBridge.
> Reading about Stream Output Primitives Written
> (snb_ihd_os_vol2_part1.pdf, pag 175), it says the following:
> "Whenever a GS thread outputs a DataPort Streamed Vertex Buffer Write
> (SVBWrite) message with the Increment Num Prims Written bit set, the
> SO_NUM_PRIMS_WRITTEN register will be incremented."
> According to SNB's spec [0], all the bits in the SVBWrite message
> descriptor are ignored and I have not found the definition of this bit
> in the documentation. Maybe I'm running the wrong pdfgrep command :-/
> After doing some Google searches, I found that in other doc [1] it's
> mentioned the "Increment Num Prims Written" bit inside the SVBWrite
> message descriptor is not ignored for SNB (at least, it doesn't say that
> explicitly).
> Do you know where is the "Increment Num Prims Written" bit defined in
> SNB's doc?

Not 100% sure if this is what you're looking for, but take a look at


Page 23, - SONumPrimsWritten and/or Page 29 -
NumGSPrimsGenerated and perhaps some of the other fields in the
FF_SYNC message.

Or wait until someone who knows what they're talking about replies :)


> Thanks,
> Sam
> [0] snb_ihd_os_vol4_part1.pdf, "3.9.11 Streamed Vertex Buffer Write
> [DevSNB]", page 260.
> [1] http://www.x.org/docs/intel/HD/IHD_OS_Vol_4_Part1_BJS.pdf "5.10.10
> Streamed Vertex Buffer Write [Pre-DevIVB]", page 247.
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