[Coco] DW3DOS ROM not loading NitrOS9 correctly *SOLVED!!*

[Tormod Volden]

On Wed, Dec 25, 2013 at 6:13 PM, Chad H wrote:
> I went back and flashed the 'dw3dos_mb_cc2.rom' thinking it might be
> different, no it showed the same problem so I returned to the original
> 'dw3dos_dsk_cc2.rom'.  This time I re-inserted it into my CoCoEPROMpak and
> REMOVED THE AUTOSTART JUMPER.  It worked!!!   To verify, I replaced the
> jumper and tried again...failure.   In both cases the ROM DOES autostart
> (I've noticed the DECB ROMS and variants seem to do this regardless of the
> jumper setting) but the final part of the bootup with the NitrOS9 startup
> messages never comes up with the AUTOSTART jumpered.  Maybe it's causing
> some sort of reset in the ROM and not allowing it to move forward somehow??
> I'm guessing that the FD-502 controller doesn't have the equivalent of a
> AUTOSTART jumper enabled and so doesn't experience this problem.

The autostart jumper on your EPROM pak is for disabling the
FIRQ-triggered autostart typically used by game cartridges. The FIRQ
handler will eventually jump to $C000.

DOS cartridges on the other hand are started by BASIC looking for a
"DK" marker at $C000, and jumping to the entry point at $C002. The
DWDOS ROM image act like DOS cartridges, using the same marker. If the
FIRQ handler would fire on this one, it would wrongly jump to $C000
but stumble along and run the same code. However the FIRQ is only
enabled after the DOS cartridge has booted which in this case means
NitrOS-9 has been loaded already.

Merry Christmas to all!
Tormod

>
> So, for anyone wanting to put a DW3 DOS (for NitrOS9 autostart) into a EPROM
> pak, remember to remove the AUTOSTART jumper! :)
>
> Again, Merry Christmas to all!
> - Chad