Re: 65802 problem

[David.Empson@bbs.actrix.gen.nz]

In article <9301290830.AA12761@apple.com> ST2975@SIUCVMB.SIU.EDU writes:
> I concur with most of what David Empson has described
> regarding the interrupt tables in the upper 16k or ram.
> 
> I can verify that you CAN use ProDOS if the language card is
> enabled and use the emulation and native mode BRK and IRQ vectors
> if they are set up previously and the language card is set up
> to be at least read from before entering native mode.

That's good to hear.  There isn't a problem on the IIgs, since the ROM
is switched in to fetch all interrupt vectors.

> The RESET vector is always read from ROM on the IIe/c/gs.

But not on the ][ or ][+.

> I haven't found use for the COP register (yet).

[COP _instruction_?]  On the IIgs its most common use is for embedded
debugging instructions for the ByteWorks languages (ORCA/C,
ORCA/Pascal, etc.)  The COP's operand byte is used to indicate the
type of breakpoint set on this line (if any).

> I am using ProDOS 1.9 to verify the above.  So far I have had
> no problems with ProDOS stepping on the vectors for native mode
> interrupts.  I would be curious if this will change in the future
> for the IIe/c.

How do you actually deal with the interrupts, though?  The native mode
vectors can't point to the standard IIe/IIc interrupt handler, since
the processor might be in 16-bit mode, or the direct page/stack might be
relocated.  You would have to implement your own interrupt handler,
which at least saved the native environment, switched to emulation
mode, then used the standard interrupt handler to process the interrupt.
-- 
David Empson

Internet: David.Empson@bbs.actrix.gen.nz    EMPSON_D@kosmos.wcc.govt.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand