[TUHS] dmr streams & networking [was: Re: If not Linux, then what?]

[Gregg Levine]

Hello!
That definitely groks with a decidedly thirty year old memory. I
remember going to BUSCON, and getting into an interesting discussion
with the folks behind the M68K just how difficult it could be to run
more modern code (or operating systems). Let's just say it was
peculiar. They wanted to stick with a proprietary OS, and one odd man
there wanted to expand CPM-68K. And still another was looking into
bringing up UNIX on it.

It was fun.
-----
Gregg C Levine gregg.drwho8 at gmail.com
"This signature fought the Time Wars, time and again."

On Fri, Aug 30, 2019 at 10:58 PM Clem cole <clemc at ccc.com> wrote:
>
> Btw. The issue with the 68k was Nick Tredenick’s original Microcode did not save enough information during some of the faults.  Les Crudele once told me, that it turns out he had tried to fix it but there were a series of errors and some short cuts they used to fit it in the store.  They gave up trying to fix it as the part was purely skunkworks and they could not respin it at the time.  After it succeeded and were a real project, the difference between the original and the 10 was Nick redid the microcode but they had made a larger microstore - otherwise basically the same Si.
>
> Sent from my PDP-7 Running UNIX V0 expect things to be almost but not quite.
>
> > On Aug 30, 2019, at 10:46 PM, Clem cole <clemc at ccc.com> wrote:
> >
> > There was most definitely a TLB or as Dave called it ‘The TB’ ***
> > Remember Dave Cane (Masscomp hw lead) was part of the 780, led the 750 and designed the BI before he left dec.  He was a bus and memory specialist
> >
> >
> > *** west coast VS east coast training - calling it a TB vs a TLB.
> >
> > Sent from my PDP-7 Running UNIX V0 expect things to be almost but not quite.
> >
> >>> On Aug 30, 2019, at 9:13 PM, Bakul Shah <bakul at bitblocks.com> wrote:
> >>>
> >>> On Fri, 30 Aug 2019 20:58:13 -0400 Clem Cole <clemc at ccc.com> wrote:
> >>>
> >>> Actually not in lock step.  They were independent.  One was called the
> >>> executor and the other the fixer.  When a fault was detected the executor
> >>> was sent wait stated while the fixer handled the fault and refilled the
> >>> TLB.   Once the TLB was set to instruction was allowed to complete.    Btw
> >>> when the 68010 was released the pals on the board were changed to allow the
> >>> executor to actually take the fault and do something else while the fixer
> >>> replaced the TLB entry
> >>
> >> As I remember, the issue with 68000 was that instructions were
> >> not restartable so in case of accessing memory that didn't
> >> exist, you couldn't take a segfault and do anything useful.
> >> This is why you needed a second processor to deal with an
> >> external MMU. There would have been no TLB unless you actually
> >> added an external TLB -- but an external CAM would've been
> >> very expensive. May be a direct map?
> >>
> >> What we did at Fortune was to utilize a 4 entry external map:
> >> text, data, extra and stack.  When a new function was invoked
> >> it would do a 'probe'. If the probe caused a segfault, stack
> >> was extended in the handler. The probe didn't have to be
> >> restartable. So we didn't need a second 68k. This logic may
> >> have been in the V7 port we started from.