From: Christoph Egger <Christoph_Egger@t-online.de>
  To  : ggi-develop@eskimo.com
  Date: Sat, 7 Aug 1999 14:04:46 +0200 (MEST)

Re: Matrox GGI accellerator

On Tue, 3 Aug 1999, Steffen Seeger wrote:

> James Simmons wrote:
>  
> > > I really think that pingpong buffers are the best way to go, given the graphic
> > > card hardware problems that prevent us to mmap fully to userspace without
> > > compromising safety on the one hand, and the latency of ioctl on the other
> > > hand (this is not to neglect even if I agree that ioctl are not so bad
> > > in practice - especially for 2d ops.).
> > 
> > Hum. Can you expalin in detail the ping pong method. I sort of have a
> > idea on how it works but not quite. Thanks.
> 
> You just expose a hardware command buffer to the application which 
> 'compiles' commands into that buffer. Once the buffer is full, you
> deny the application access to it, and give it to the driver to 
> 'execute it'. This means either to start a DMA transfer of the buffer,
> do programmed IO to send the commands to the hardware. This allows all
> the API specific translation of rendering requests to be translated into
> a hardware specific command stream by userspace code. This is why we have
> to consider a modular library like libGGI as a part of the driver.
> 
> The tricky thing about this is just how to detect if the buffer is full
> and when to switch buffers, do context switches etc.. This is worked 
> out at code level and already implemented in KGI-0.9. The parts are 
> tested independently, but the whole thing is not due to lack of drivers
> and time to finish those. It does (in a quite simple but extendible manner)
> what you are trying to implement: virtual graphics processors.

Do you mean with "graphic processor" the chip, which draws things on the
screen, OR do you mean a geometric processor like the OXYGEN GVX1 has?
BTW: I know what you want to say with "virtual".

> 
> Regards,
> 			Steffen
> 
> ----------------- e-mail: seeger@physik.tu-chemnitz.de -----------------
> 

Christoph Egger
E-Mail: Christoph_Egger@t-online.de