Date   : Mon, 13 Oct 2008 00:01:34 +0100
From   : afra@... (Phill Harvey-Smith)
Subject: *CONFIGURE Q

Michael Firth wrote:
>> I'll check to see what my 2 Masters machines have, I checked and they
>> both have 3.20, however I just knocked up a flash adapter an a piece of
>> stripboard and put the 3.50 from mess on it, installed it into my one of
>> my Masters and it seems to work fine, sooo, it looks like it's an
>> emulator bug which is odd to say the least !
>>
> Sounds like you've saved me a job for tomorrow :-)
> 
> Now I guess the $1,000,000 question is what on earth is happening different
> with *CONFIGURE in MOS 3.5 that breaks two different emulators!

Ok, after much hacking around with the MESS debugger, once I modified 
the bbc master driver to allow it to work, I think I have tracked down 
the problem (at least for MESS), it revolves around the instruction at
$8654 in the terminal rom which is :

       bit     #$40

As emulated this changes the Carry, Overflow & Negative flags which 
would be correct for all addressing modes EXCEPT immediate, acording to 
the instruction sheet in the "New Advanced User Guide", which states 
"When immediate addressing is used (available only on the 65c12) the V 
and N flags are unchanged".

I suspect that BeebEm has exactly the same problem.

Now how to get the MAME team (of which MESS is a derivitive), to allow 
me to fix this could be an up-hill struggle.

I'll see if I can fix it and submit a patch.

Cheers.

Phill.


-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.