Die space for m68k on FPGA?

[Mrs Beanbag]

How would you encode it in the instruction?

[Mrs Beanbag]

move -(An),Dn
for instance, already updates the address register with the calculated value. So it shouldn't be too much trouble. It's the encoding that worries me, however I have the Motorola reference manual in front of me and it states that IS-I/IS values of 0100 and 1100-1111 are "reserved".

[Mrs Beanbag]

I didn't spot bit #3 of extension word... in the docs it is simply '0'!

"Reserved" means Motorola might use them for something later... I guess they might come back and make a 68080 and then we'd be in trouble!

Although personally I think we're getting ahead of ourselves here... make a fully pipelined 680x0 + accelerator first, and worry about extending the ISA later.