[Coco] CoCo 3 patch question

[Roger Taylor]

At 04:23 PM 11/25/2008, you wrote:
>On Tue, 25 Nov 2008, Roger Taylor wrote:
>
> > 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.
> >
>
>On a real CoCo 3, if you switch to ROM mode by typing POKE&HFFDE,0, everything
>is fine provided you are in the 32-column mode.  No need to shut off 
>interrupts
>first.  (Of course, Super Extended Basic commands won't work anymore.)  If you
>are in 40/80 column mode, the screen drivers go away;  I think you can still
>type blindly in that situation.
>
>Art


While that may be true, I'm doing everything from a running ROM 
mapped to the Disk BASIC area.  The CoCo powers up, BASIC does it's 
thing, it calls on Extended BASIC, it does it's thing, it calls on 
Disk BASIC if it's there...  it assumes DOS is there if "DK" are the 
first two characters of the ROM.

My ROM does start with "DK" so that BASIC will execute it 
automatically, but it's not a DOS.  So, powering up the CoCo appears 
to jump directly to my ROM program, but behind the scenes 
BASIC/ECB/SECB have set up the BASIC environment and is expecting now 
to jump to the DECB ROM entry (which SECB has already patched in RAM).

 From my ROM, I would assume that switching out of All-RAM mode while 
FIRQ/IRQ is disabled would work, and it should from a real CoCo 3 (I 
hope), but from M.E.S.S., the system crashes.

I'm sure this has something to do with the CoCo 1/2 compatibility bit 
of the GIME, and/or the MMU registers.  Anyway, for now I'm just 
starting my real code at $C900 so it's works fine that way but I lose 
~2K of ROM space.

-- 
Roger Taylor

http://www.wordofthedayonline.com