[Coco] DW3DOS ROM not loading NitrOS9 correctly

[Darren A]

On Wed, Dec 25, 2013 at 8:12 AM, Robert Gault wrote:

>
> Regarding the dw3dos_dsk_cc2.rom image, there is some code in it I've not
> seen in a Coco ROM.
> sta $FFDA
> sta $FFDD
> This code will tell the SAM how much memory is present in the Coco.
> However, I'm under the impression that this info was hardwired with jumpers
> and these two bytes were not used. I've no idea what will happen if you
> POKE these bytes.



Those instructions configure the SAM for 64K dynamic RAM refresh.  This
configuration is normally done by code in the Color Basic ROM which reads
the board's RAM Size jumper setting to determine the type/size of RAM chips
the machine has.

There should be no need for the dw3dos ROM to perform this configuration
unless the Color Basic ROM has been removed and replaced by dw3dos.
 Nevertheless, performing this SAM configuration a second time will not
cause any problem so long as the configuration is appropriate for the
hardware.

Darren