Re: MISC-ShBoom-MuP21-F21

[Roger Ivie <IVIE@xxxxxxxxxx>]

> What do you think about the OISC/SISC/Ultimate RISC projects, where they
> try to have the absolute minimal instruction set. It is known that one single
> (complex) instruction can compute everything, but there are also many 
> disadvantages to do it this way. 

Actually, it is known that a single (simple) instruction can compute
everything. An intriguing example of this that I have seen is a move
machine with 16-bit addresses that moves 8-bit quantites; the PC is also
visible in memory space. It's possible to construct arithmetic on this machine
using clever table lookups. Very very interesting.

> But it is kind of weird to notice that you
> are all talking about Minimal and still have about between 16 and 32
> instructions. I know that those SingleISC actually have more instructions,
> but there are for example also IS with 4 instructions (LOAD, STORE, INC, BRZ).

Another example of a single-instruction machine is one that executes only
subtract and skip on borrow.

Roger Ivie
ivie@cc.usu.edu