>>Come on, it should be REALLY easy hardware- and software-wise to implement
>>a circuit that will reset just the Z380 in order to switch to legacy mode.
>>It's a non-issue.
>
> It's not a hardware matter. It's a software also. What to do with the
>registers...? If the Program Counter is above 64Kb, where will you put
>it? If the SP is above the 64Kb, where you'll put it?
If those are >64kB, then simply execute a real reset instead of a faked one
which sets back all registers.
Do you understand how the switchback works??? I'll explain it again...
Assume there is a BIOS-routine to switch back. This routine saves all
registers in a certain area in the system memory (or only the PC, or saves a
given adress when the routine is called, whatever) (the last option is the
best I think). Then, it signals the MSX-Engine, which sends a reset signal
to the Z380 (bot not to any other device). The Z380 resets, executes the
BIOS from #0000. There is a routine which checks if a certain bit
(switch_back) in the Engine is set. If not, it just resets. If so, a
enhanced to legacy mode switch has been performed. In that case, it gets
back all registers and proceeds from the given PC, or -if an execute adress
is given- leaves all registers corrupted and simply executes from the given
point.
It's really quite easy.
~Grauw
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