Re: [B2-devel] Mac Classic emulation

[Joshua J. <jj...@gm...>]

On Jun 15, 2007, at 1:42 AM, Gwenole Beauchesne wrote:

> Le 14 juin 07 =E0 20:50, Joshua Juran a =E9crit :
>
>> MOVEC is not supported on the 68000, and when it is supported (e.g.
>> 68020) it's privileged.
>
> Yes, that's what surprised me when I caught those instructions. Oh,
> BTW, I have just fixed MOVEC emulation for 68020/68030, though we
> never encountered movec d?,{msp,isp} instructions so far. i.e. that
> turns out to be only a source cleanup. ;-)
>
>> You need the system software to recognize that it's running on a Mac
>> Classic and limit itself to supported instructions.
>
> Actually, I'd expect to reach at least the '?' mark without any
> specified disk but I don't even get that far. Yes, it's a Classic ROM.

Weird.  Does the ROM code have an exception handler for illegal =20
instructions which does something useful, or is it wrongly executing =20
MOVEC in the first place?  I'm going to guess the latter, and =20
speculate that a branch is misfiring.  Is it possible that the =20
emulation incorrectly sets CCR bits, sending us down a 68020 path?

If you can get to the blinking '?', you can hold down Command-Option-=20
X-O at boot to startup from the ROM system disk.  :-)

Josh