[Coco] CoCo 3 patch question

[Roger Taylor]

At 06:39 PM 11/25/2008, you wrote:
>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.

Disk ROMs are kick-started from software, not auto-started like a game pak.



>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?

I never said I was doing this from the BASIC prompt.  I don't give 
the command cursor a chance to do it's job.  All along I've said that 
my "pretend Disk ROM" itself is running, printing text to the VDG 
screen, and some of the text is corrupt on a CoCo 3.  We figured out 
why, now I'm trying to switch to ROM mode from within my ROM code 
since the CoCo 3 has patched over my own ROM thinking it's Disk 
BASIC.  From M.E.S.S., it doesn't work without a crash.  I have yet 
to try it from a real 3 or another emulator.

As we know, any ROM can be put in a disk controller or EPROM Pak and 
as long as the first two bytes start with "DK", ECB will jump to 
it.  The appearance is that you've inserted an auto-start program 
pak, but behind the scenes, the BASIC environment has been set up 
(without Disk BASIC yet) and is ready to give the OK prompt *IF* the 
"Disk ROM" doesn't take control.  So on my "embedded system", I don't 
get any BASIC copyright titles or prompts.  I get my own title screen 
and running ML code.


-- 
Roger Taylor

http://www.wordofthedayonline.com