7 Aug
2006
7 Aug
'06
2:12 a.m.
On Sun, 06 Aug 2006 22:41:36 -0400 and Sun, 06 Aug 2006 22:47:23
-0400, Ray Arachelian <ray at arachelian.com> wrote:
Absolutely. The 68000 is an amazing little chip when
you compare
it to
the 6800 and 6502's that it evolved itself from. You can sort of
get a
feel from this from this journal:
It's worth a read to get a feel of the excitement the 68K caused
back in
the day when it was introduced. Some of it is very funny, there's one
issue where the author compares an Intel FPU to the 68000 running
software floating point routines, and guess what, the 68000
actually ran
FASTER! :-)
The excitement was for a good part due to the excellent marketing on
the part of Motorola.
Tony Duell wrote:
In the early '80s we started development of a process controller and
evaluated the 68K as well as the National 32K processor which had
been just released. The NS 32K processor was released with a FP unit
which we required while Moto didn't get around to getting one to
market for another year - the 68K on software just didn't hack it. We
went with the NS 32K and were quite pleased with the beast.
It was a true 32 bit processor witch came in three flavors: 8 bit, 16
bit, and 32 bit external busses - you could move the code from one to
the other with almost no change. The instruction set was extremely
orthogonal and close to those of the VAX sans the three operand
instructions. The only flaw we noted was that the entire machine
state was not saved on interrupt/trap which made a couple of features
useless.
The floating point processor was not a co-processor ala the 68K, but
a external instruction execution module. When the FPU was attached,
the FP instructions became active and you worked between internal
register pairs. IIRC they also made communication processor that
implemented part of the unimplemented instruction set. I played with
my own external processor to implement macro instructions that were
used to optimize execution time.
When Apple was evaluating processors for the Mac, an internal source
told me that NS marketing only made a half*** effort to sell the
part. Unfortunately NS did their normal thing when it came to
processors and shot themselves in the foot (see PACE - both
Studebaker and NS screwed those up) by trying to keep it all to
themselves. Consequently, there was little third party support for
the chip. I believe it to be a better implementation than the 68K.
CRC
That very much depends on the CPU. If the CPU is
many chips (not a
single
package) with microcode in PROMs, there's nothing to stop you
desoldering
said PROMs and reading them out. I've done that, then written a
disassembler for the microode instructions and worked out what was
going on.
True, but you don't find CPU's made of discrete logic these days,
so it
makes it very difficult to get at the microcode.