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

[Bakul Shah <bakul@bitblocks.com>]

On Fri, 30 Aug 2019 20:58:13 -0400 Clem Cole <clemc@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.