[Coco] [Color Computer] Create NitrOS9 L1 boot disk for Dragon with FD-502?

[Robert Gault]

drag0n1969 wrote:
> I need help creating a NitrOS9 Level 1 boot disk for my unique 
> configuration: Tano Dragon with a Tandy FD-502 disk controller.
> 
> I have replaced the FD-502's EPROM with a special version of Dragon 
> SuperDOS, modified by Phill Harvey Smith to work with the Tandy 
> controller hardware. This works perfectly under basic.
> 
> Creating a NitrOS9 boot disk is a problem, since the Dragon Dos 
> expects the boot sector on track 0 (from sector 3), and not track 34 
> as on the CoCo (though both of them load the boot sector to same 
> memory address at $2600)
> 
> Am I correct that my boot disk should simply be a Dragon NitrOS9 
> boot disk with the modules BOOT and RB1773 from the CoCo (replacing 
> the dragon's BOOT and DDISK)?
> 
Phill should be the expert on this and if he does not see your message 
here, you should e-mail him directly.

Far as I can tell, the Dragon uses the same disk controller as the Coco. 
It is the disk structure that is changed. What you need to know is if 
Dragon NitrOS-9 reserves T0 S1-3 for normal OS-9 use or normal Dragon 
use. If Dragon NitrOS-9 places the boot track at T0 S3-18, then clearly 
you will need a specialized boot module as well as several other modules 
to handle the unique disk structure.

It seems to me that OS-9 on any system ought to use the same disk 
structure. The Dragon should accommodate this with a special DOS command 
expecting the boot track to be at T34. But that's just my opinion :)

> I have tried using MESS to generate this bootdisk – with no success 
> whatsoever.
> 
> I also tried generating a CoCo bootdisk, replacing the VTIO and 
> COVDG – to get a proper Dragon keyboard. Didn't work either…
> 
> I'm starting to think that the BOOT module contains info about both 
> the physical boot sector location, and the controller hardware: thus 
> if I use the Coco boot module it finds the hardware, but looks for 
> the boot module in sector 34 rather than sector 0.
That is correct.

> 
> If this is a correct, I guess the Coco boot module needs to be 
> patched to read sector 0?
That depends on the structure of the Dragon NitrOS-9 disk. Why don't you 
use a raw disk editor to examine the structure of the Dragon NitrOS-9 
disk to see exactly what is located in track 0 and track 34?

> 
> I have also tried to "force" the dragon to boot a CoCo bootdisk, 
> using a small program on the Dragon to read sector 34 from the CoCo 
> boot disk, poke it into address 9728 ($2600)  onwards, and EXEC 
> 9730. Doesn't seem to work either…
That should work excluding other hardware changes between a Coco and a 
Dragon. I don't think you can assume there are not significant hardware 
changes which would prevent Coco NitrOS-9 from running on a Dragon.

> 
> I have been struggling with this for quite a while now, trying 
> numerous combinations. Any help would be greatly appreciated…
>