I would very much welcome support for MC680x. The Hitachi HD6303 clone has an
extended instruction set, so perhaps that could be supported as well. Original
Motorola has 59 illegal or better unused opcodes, while Hitachi has only 26. (I
started a long time ago writing a MC6800 simulator, but never finished.)
Eric
Am Sonntag, 7. Dezember 2025 um 12:42:02 MEZ hat Philipp Klaus Krause
<[email protected]> Folgendes geschrieben:
Am 06.12.25 um 22:31 schrieb Hill, Krista:
> I see that I have some digging to do. I'm using
> the as6801 assembler and aslink linker from the ASxxxx tools and so far,
> so good.
>
> So far I see that uCsim will need some work to support the 6801 cpu and
> devices. It's one step at a time.
Having had a quick look at the architecture, I think SDCC is a good
choice for a compiler targeting it. The instruction set, and adressing
modes look ok, the 16-bit stack pointer and index register will be quite
helpful. It is kind of a typical architecture for an SDCC target - not a
great target for C, but not too bad either.
The main difficulty will likely be the lack of an efficient
stackpointer-relative addressing mode, so stack accesses would have to
use the index register - and there is only one index register, which
also needs to be used for pointer accesses. Thus, you'll probably want
local variables to not be on the stack by default (like for mos6502,
pdk, mcs51, hc08).
IMO, the MC6800 and MC6801 are so similar, that it would make sense to
create ports for both, which would then share register allocation and
most of code generation (like e.g. the z80 port and the z180 port share
code generation). This would also mean that we need assemblers and
simulators for both. In principle, this could later even be extended to
M68HC11 and M68HC12 support, but is probably not be worth the effort,
since GCC already supports that one.
Philipp
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