Re: [stack] Concatenative Hardware Redux (Another 16 Instruction Set)

On Jan 11, 2008 11:35 AM, William Tanksley, Jr <[email protected]> wrote:
> A fascinating goal, and one which to my knowledge has not been
> attempted together with a high-level instruction set.

I think the distinction between "high-level" and "low-level" is
artificial, and rooted to firmly on the naivete of our predecessors.
If we ignore it, we can come up with something new and interesting.

> > However, to be completely honest, the more I experiment with the
> > instruction set, the more I think that I would prefer to work with a
> > 255-instruction set (ala JVML).
>
> Completely incompatible with the goal of minimal hardware

Not at all, it depends on what you do with these instructions. I
should clarify that I really mean "1-byte" operators. The core
instructions would be few, and many of the bits would be flags.
Consider:

dup
pop
swap
...

and then with a bit flag to represent "dip"

dupd == [dup] dip
popd == [dup] dip
swap == [swap] dip
...

and another bit flag to represent "dup"

ddup = dup dup
dpop = dup pop
dswap = dup swap
...

and another bit flag to represent "swap"

swdup = swap dup
swpop = swap pop
...

Hopefully this illustrates what I have in mind.

> -- and do
> you actually have anything close to 256 opcodes?

It's quite easy to come up with a whole bunch of opcodes.

> Can you imagine
> building all the hardware to support each one and muxing/demuxing them
> together?

Well yes. I don't think it neccessarily has to be complex.

> Wouldn't retreating to 5-bit instructions make more sense
> initially?

The simplicity of the design has less to do with the number of
instructions, than it does with the organization and kind of
instructions. 4-bit instructions is an interesting challenge, because
it is so darn small. 5-bit instructions has already been done and I
believe would be hard to port to other architectures efficiently.
8-bit instructions is easy to port and emulate. I consider emulation
very important, because a practical virtual machine would be run on
many different kinds of chips and software.

- Christopher