Happy Birthday VAX 11/780 (influence of)

Ethan Dicks ethan.dicks at gmail.com
Fri Oct 29 13:41:14 CDT 2010

On Fri, Oct 29, 2010 at 2:26 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
> On 2010 Oct 29, at 10:39 AM, Ethan Dicks wrote:
>> That all depends.  Back in the day, what we did was not demand-paged
>> virtual memory (something supported natively on the VAX and the 68010
>> (but not effectively on the 68000)...  (which is part of what
>> distinguishes the 68010 from the 68000 - instruction restart).
> There have been a couple of indications it was the '10 that added the
> instruction restart, but was the implementation in the '10 bug-free?

I know it works well enough in early Sun workstations and the AT&T
Unix PC (3B1/7300), but I have no knowledge of any required
workarounds due to possible bugs.

> I didn't deal with the problem directly, heard about it from some friends
> who were programming around it, and it would have been 1989, so long after
> the 00->10 transition. My recollection about the issue was there was a bug
> under certain conditions that was fixed in the next version, as distinct
> from a 'new feature', but perhaps it was just the way the problem was
> described to me or the way I understood what was being said.

I have no memory of issues with instruction restart on the '10, but I
didn't use that feature of the chip when I was doing embedded product
development 20+ years ago (we only used it for the "loop mode"
1-instruction cache feature that allowed so-called "DBcc loops" to run
~50% faster due to not needing fetch cycles while in the loop).

Could what you remember be something to do with "instruction restart"
vs "instruction continuation"?  (a distinction I was not making, but
now that I've read this -
http://www.easy68k.com/paulrsm/doc/dpbm68k1.htm - perhaps that's a
better way to describe it).


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