[Openchrome-devel] Some HW related questions to VIA:

[BenjaminPan@viatech.com]

Dear Thomas,

We really appreciate that you can make time available to continue working on the OpenChrome 3D code especially knowing that you have been very busy with regular job. Therefore you bet we want to support you as much as we can.

The reason that we don't have the PS instruction set for you right now is because the existing document was written by engineers during the development the 3D engines long time ago with everything including sample shaders reference to info from Microsoft under NDA at that time. Over the years, no one has asked for shader document so it hasn't been reviewed/researched for how much of those have become public info and how should the rest be rewritten.

That is why Bruce is trying to get some idea about the scope of your work so that we can allocate right resource to support you accordingly. Editing related parts of the document requires different expertise from doing direct translation of each ARB fragment program instruction directly into VX800's native shader code without a compiler.

Regarding EXA, I supposed you want to use 3D engine to accelerate the composite extensions. Since this is a new frontier, there may be info that we can exchange or discuss for what can improve performance and what can not. Do you want to have an IRC session or start a separate subject thread for that?

One quick clarification, although AMD K8 / Athlon64 CPUs have memory attached to the CPU, linear address by direct frame buffer access still needs to be translated into physical address by graphics engine. So the access cycles is routed back-n-forth between CPU which memory is attached to, and chipset where graphics resides. That is why it is so slow compared to true "direct" access of P4 and K7 architectures where both graphics and memory are on the same side of the bus.

VX800 doesn't support frame buffer dynamically allocated out of page-locked system memory as Intel does. So the use of system memory is mainly for texture and command buffers as AGP aperture space before - except now graphics is reported as PCI type hence GART function is part the graphics and not chipset.

Regards,

Benjamin Pan

-----Original Message-----
From: Thomas Hellstr?m [mailto:thomas at tungstengraphics.com] 
Sent: Wednesday, November 12, 2008 6:19 AM
To: Bruce Chang
Cc: thomas at shipmail.org; openchrome-devel at openchrome.org; Benjamin Pan (Fremont); Harald Welte; Vincent Tan
Subject: Re: [Openchrome-devel] Some HW related questions to VIA:

Hi, Bruce.

BruceChang at via.com.tw wrote:
> Hello Thomas:
>     Regarding the pixel shader, can I have the detail question you have? After consult with our engineers, it seems we don't have integrated document for it. Everyone seems to have only small piece information.
>   
Bruce, complete information regarding how to write and execute pixel 
shaders on the VX800 is necessary for anyone working with the 3D driver 
or EXA render acceleration.

Also, is there any information on how to set up "Local Dynamic" memory 
on the VX800, more explicitly: How to program the page tables?

>     For the memory of PM800 / KM400 / K8M800, the architecture of AMD system is different to P4 system. That's why the CPU access difference.
>
>   
OK.

Thanks,
Thomas