Megol (golem960.delete@this.gmail.com) on August 12, 2022 3:04 am wrote:
> Brett (ggtgp.delete@this.yahoo.com) on August 11, 2022 3:26 pm wrote:
> > Any 68k manual, each instruction spells out the bits:
> > https://web.njit.edu/~rosensta/classes/architecture/252software/code.pdf
> >
> > There is unused state in the mode bits that can be used to add another 8 data registers transparently for
> > one source.
> FOR A SMALL SUBSET OF OPERATIONS!
> That's the thing - it's not something that's really available as an extension, it's a very lopsided hack.
>
> >Though instead the AMMX extension added 32 bit instructions and used a similar format.
> It also wasted the only reasonable opcode space available for a prefix (11 free bits) to add MMX support.
> At least happy they moved from supporting the mostly useless ColdFire sign extension
> opcodes to use the encoding space as a prefix operation as I had been proposing.
> Of course my prefix ideas were more general.
>
> > ColdFire obsoleted the 2 of the 3 opmode operation size bits for all but MOVE loads/stores. That frees up
> > huge opportunities for expansion. The plan may have been to use these bits to double the register file.
> Not relevant as the 68080 is intended to be compatible with Amiga software.
>
> > Ugly, but not so ugly as x86.
> Debatable. X86 is like two separate architectures with some similarities,
> the 8086-80286 was pretty clean, the 80386 too.
>

I always thought that the 68000 was the less crippled and most forward looking architecture (between x86 and 68k): Everything was 32 bits wide (registers, operations, etc), the address space was flat (non-segmented) and you had a plethora (relatively speaking) of GPRs.

Things appeared to be set up for future success, but then Motorla screwed things up, I suppose.