[Coco] clearing memory for other uses

[Robert Gault]

Jason M wrote:
> Yes, exactly, no plans to use anything in basic.
>
> Am i correct in thinking that there is roughly 2k of memory at the top of
> the 4th high-res page that is not used for video when in 320x200x16 mode?
>
> I'm thinking of setting up mmu map 0 and map 1 to both have page 4 in the
> same slot. That way even when I'm not drawing I can expect things to be in
> memory in that high 2k.
>
> BTW, I'm targeting this for a CoCo3 w/ 128K.
>

Jason,

The default Coco3 hi-res graphic screens are mapped from $60000-$67FFF. To get 
that space mapped into your 64k area, you will need 4 MMU blocks.
Since you don't intend to use Basic nor apparently OS-9, you can program the two 
MMU maps $FFA0-$FFA7 and $FFA8-$FFAF any way you desire and have your graphics 
screens anywhere in memory.
Just make sure that you don't map out your program when you switch MMU maps.

If you desire, there is no reason why you could not have the 320x200x16 screen 
in a 4 MMU block at $x1C00-$x7FFF. You can have video memory start pretty much 
anywhere you want. You just need $6400 consecutive bytes for your 320x200x16 screen.

You don't need to keep the graphic screens in memory when you are not drawing on 
them. The location of video memory is fixed by $FF9C-$FF9E regardless of which 
MMU registers are active or what values they contain.

Robert