[Coco] CoCo 3 patch question

[Robert Gault]

Roger Taylor wrote:
> At 02:40 PM 11/25/2008, you wrote:
>> Roger
>>
>> The addresses I quoted are actual addresses of the code in the Disk Basic
>> ROM. In the Coco3 these are copied to RAM. using above that would
>> eliminate the Disk Basic altogether. If that is what you want then go 
>> for it.
> 
> That is exactly what I want because my ROM is not intended to be a DOS.  
> Since the EPROM Pak and floppy controller ROMs don't actually 
> auto-start, Extended BASIC will do it's thing then transfer control to 
> what it thinks is a Disk BASIC ROM because it sees that the first two 
> bytes "DK".
Roger, that is not quite right. Floppy controller ROMs do "auto-start" 
in the sense that Basic looks for DK and if found "runs" the code at 
$C002. This happens on all Coco models.
Normally, the only thing that happens is that the DOS patches Extended 
Basic which includes increasing the number of commands and functions. 
Some DOS like RGBDOS and HDBDOS will also attempt to run a program on a 
hard drive.
What you probably intend is that there will still be new commands or 
functions, and they will need to be patched into Extended Basic. If that 
is not the case, then the code at $C002 could be
  org $C002
  bra $C00C
  org $C00C
  jmp $A0E2.

> 
> The CoCo 3 emulators in M.E.S.S. are crashing the CoCo when my ROM 
> attempts to switch to ROM mode, even if I mask FIRQ and IRQ beforehand.  
> I don't know if this is a M.E.S.S. thing or what will happen on a real 
> CoCo 3.  I could only stay up so late last night.
> 

I agree with Art. There should be no problem with a POKE&HFFDE,0 on a 
Coco3. I can do that with VCC, MESS, and a real Coco3 with no problems 
from a 32 col text screen. RGBDOS will still read the hard drive in ROM 
mode.

Exactly what were you doing to cause the crash?