[Coco] A question for the (Nit)OS9 Developers

[Robert Gault]

jdaggett at gate.net wrote:
> Boisey, Aaron, and anyone else that can explain
>
> I am looking at some of the source code to get a bit of understanding how OS9/NitrOS9
> handles windows. I see in the device descriptors a reserved byte for extended address and a
> word reference to A.W#. When Ilook at the VTIO.defs file I see a reference to an address
> that is the MMU address in the GIME chip.
>
If you boot OS-9 and look at the values assigned to A.W1-A.W15, you will see 
they are $FFA1, ... $FFAF. Term is assigned $FFA0.

> Does OS9 use the same address spaces as the GIME chip internal registers?
>
How could it be otherwise? Software can't change hardware.

> Is OS9 mapping the GIME chip in and out of the memory map to access the variables in
> RAM?
As I understand it, the hardware I/O bytes can't be mapped out. So, $FF00-$FDFF 
are always available.

>
> How does the Column size and Row Size varialble map to the actuall hardware registers? Ie
> like HRES and CRES bits.
Those values represent the actual screen size for a vdg or window. Since these 
parameters are controlled by $FF98 and $FF99, it is not possible to request and 
get a hardware window which the GIME can't create.
However, if the window is an overlay type, then any value for szx and szy which 
fits within the hardware window are legal values.

>
> I have a good part of the GIME coded but untested and have most of the the video control
> registers interface to VGA section done. What I am thinking of doing is to set the background
> size as 800x600 with a single color and allow a DECB window to be configurable by the
> current software using the HRES and CRES bits. I can easily add a couple of registers to
> function as postion. This can lead to a whole host of expansion ideas that I have been
> thinking of. I know that some of the limitation of NitrOS9 is the hardware itself. I guess for any
> hardware to expand, an Idea of where the software can go is a first place in starting any
> improvements.
>
> just some thoughts
>
> james
>

You should study the "OS-9 Windowing System" in the Level II manual and probably 
the Multi-Vue manual to see how windows are created and used.