Anon (no.delete@this.spam.com) on August 11, 2022 11:43 am wrote:
> Megol (golem960.delete@this.gmail.com) on August 11, 2022 9:25 am wrote:
> > Have you actually looked at the 68080 design? The extensions aren't that clean, and for a good reason:
> > there isn't encoding space without adding prefixes or adding a partially incompatible mode.
>
> Where did you find the instruction format?

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. Though instead the AMMX extension added 32 bit instructions and used a similar format.

https://cdn.discordapp.com/attachments/730698753513750539/843620828612526110/VampireProgrammingGuide.pdf#page55

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.

http://bitsavers.org/components/motorola/Coldfire/1995_Coldfire_Family_Programmers_Reference.pdf

Ugly, but not so ugly as x86.