[TUHS] 68k prototypes & microcode

[Adam Thornton]

I'm probably Stockholm Syndrommed about 6502.  It's what I grew up on, and
I still like it a great deal.  Admittedly register-starved (well, unless
you consider the zero page a whole page of registers), but...simple, easy
to fit in your head, kinda wonderful.

I'd love a 64-bit 6502-alike (but I'd probably give it more than three
registers).  I mean given how little silicon (or how few FPGA gates) a
reasonable version of that would take, might as well include 65C02 and
65816 cores in there too with some sort of mode-switching instruction.
Wouldn't a 6502ish with 64-bit wordsize and a 64-bit address bus be fun?
Throw in an onboard MMU and FPU too, I suppose, and then you could have a
real system on it.

32-bit SPARC was kind of fun and felt kind of like 6502.  The 6502 wasn't
exactly RISCy...but when working with RISC architectures, understanding the
6502 seemed to be helpful.

I really liked the 68000, but in a different way.  It's a nice, regular,
easy-to-understand instruction set without many surprises, and felt to me
like it had plenty of registers.  Once the 68030 brought the MMU onboard it
was glorious.

Post-370 (which is to say 390/z IBM mainframe architectures) went wild with
microprogrammed crazy baroque very, very special purpose instructions.
Which, I mean, OK, cool, I guess, but not elegant.

I don't really know enough about the DEC architectures.  It is my strong
impression that the PDP-11 is regular, simple to understand, and rather
delightful (like I find the 68000), while VAX gets super-baroque like later
IBM mainframe instruction sets.  Although I've worked with emulated 10s,
11s, and VAXen, I've never really done anything in assembly (sure, you can
argue that C is the best PDP-11 preprocessor there is) on them.

On Thu, Feb 4, 2021 at 3:12 PM Steve Nickolas <usotsuki at buric.co> wrote:

> On Fri, 5 Feb 2021, Dave Horsfall wrote:
>
> > The Z80 was quite nice; I wrote heaps of programs for it, and I even
> found an
> > ANSI C Compiler for it (Hi-Tech as I recall; BDS-C was, well, you could
> > barely call it "C")[*].  I compiled a number of Unix programs...
>
> Well, it *was* "Braindead Software" C.
>
> <snip>
>
> > The x86 architecture is utterly brain-dead; I mean, what's wrong with a
> > linear address space?  I think it was JohnG who said "segment registers
> > are for worms".
>
> The 65816 doesn't have the screwed-up bitshifted segment stuff but it's
> also a segmented architecture and is also braindead.
>
> And I'm a 65C02 fan.
>
> -uso.
>
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