Re: virtual flat frame buffer

Hi Eddie,

Eddie McCreary wrote:
>
> I've been playing around with *very* primitive graphics under Vsta
> and I'd like to share as much code as I can between the operations
> that work on memory bitmaps and the those that work on the screen.
> One thing that would go along way to simplifying things would be
> to setup a virtual flat frame buffer. The idea is that you memory
> map the amount of memory you have on your video card and when you
> try to read or write to a portion that isn't mapped in by the
> page registers, a page fault is generated and the code to handle
> video paging is invoked.

This was one of the ideas Gavin Nichol and I thought about earlier on this
year - we actually thought it was a good way to go although it sacrifices a
fair amount of performance. When I actually came to start work on the
bitblt code though I found that as we only blitted data onto the screen and
did all of the raster ops in system RAM it wasn't too much of a problem to
just do the bank switching as we transfered the blt buffers to the video RAM.
FWIW I think that using a flat space would be a neater solution as most new
devices allow a flat linear mapping anyway :-)

> Has anyone done this already? If so, would you mind sharing your
> code? If not, I'd appreciate anyone's suggestions on implementation
> details. I'll probably start looking at it in a day or so.

I wouldn't have thought anyone else will have implemented this as it
requires the intervention of the kernel page handler. I just took a quick
look at the code and I'm pretty sure there's no mechanism there for a
user-installed page fault handler (eg no way to tell the faulting process
where we faulted, etc).

                         Regards,
                        Dave
Received on Wed Nov 23 03:19:54 1994