[Coco] 16/32 bit 6809 derivative

[Joel Rees]

2017/09/23 15:26 "Gene Heskett" <gheskett at shentel.net>:
>
> On Friday 22 September 2017 23:54:02 Joel Rees wrote:
>
> > A number of people are designing MMUs for their softcore Cocos.
> >
> > I'm wondering if I'm the only one who thinks about designing a CPU
> > that implements the 6809 instruction set in 16-bit accumulators and
> > 32-bit index registers, with a 16-bit instruction set accessed by
> > pre-bytes.
>
> If going to that much trouble Joel,

If only I could.

I keep wishing I had time to write an emulator for such a CPU.That
would likely be my first step.

> how about giving it the 6309 instruction set?

As fun as that may sound, it doesn't seem like a good idea to me. The
6309 instructions would get in the way of making the design a simple
extension of the 6809, and most of the useful functionality would be
present in 16/32 bit versions of the 6809's 8/16 bit instructions.

If I'm going to go to the trouble of warp the machine code layout to
support 6309 instructions, I'd rather warp it a different direction.

It might be useful to add some meaningful features, like microcode
primitives, including full bit primitives for multiplication and division,
caching the stacks, integrating the MMU with the index registers
(properly -- not the half-baked gadgetry of the 8086), true DMA
channels (instead of blind CPU-blocking block moves), that kind of
thing.

6309 support would just get in the way.

> In modern 3.3 volt 1500 mhz silicon, it ought to be
> able to out coco3 a coco3.

Well, yeah. Of course.

> I'd love to see something like that running
> on a 4GB, 4 core rockchip running at 1.5 GHz on a rock64 card. I just
> got 2 of them, and am about to see if I can replace the r-pi-3b running
> my biggest lathe, an 11x36 Sheldon thats about 70 years old. I've not
> yet booted one, just got them yesterday but oral surgery interfered.

Ouch.

> I only need one to run the lathe.

Yeah, if I had the money and time to design this thing, it would make a
good controller for lathes and such.

But for the foreseeable future, the ARM in your rockchip is going to get
you
there a darn sight faster.

(Darn. :-/ )

> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
>  soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> Genes Web page <http://geneslinuxbox.net:6309/gene>

--
Joel Rees

http://defining-computers.blogspot.jp/