[Open-graphics] Sample VGA translation code, for nanocontroller

[Patrick McNamara]

Timothy Normand Miller wrote:
> On 9/5/07, Mark <mark at jarvin.net> wrote:
>
>   
>> Could you be more specific about how VGA graphics mode memory accesses
>> aren't standard reads and writes?  I'm reading up on VGA, but I haven't
>> got there yet.
>>     
>
> Patrick did the research on that, so he'll have to fill in the
> details.  But basically there are some raster operators that can be
> applied, and there's a bitblt buffer of some sort, where we put it in
> a mode so that reads and writes cause macro operations.
>
>   
All standard VGA graphics modes except 320x200x256 and 320x240x256 go
through a multistage "pipeline".  You can see a diagram of the read and
write pipelines here: 
http://www.supersecret.org/images/VGA_write_pipe.png 
http://www.supersecret.org/images/VGA_read_pipe.png

Even the direct mapped modes use banked memory to access more than 64k
if available on the card.