68K - test-drb@ccmp.vtda.org

3 Nov 2010

On 2010-11-01 18:00, Ethan Dicks<ethan.dicks at gmail.com> wrote:

...
  On Sat, Oct 30, 2010 at 6:51 AM, Johnny
Billquist<bqt at softjar.se>  wrote:
  >  On 2010-10-30 01:12, Ethan
Dicks<ethan.dicks at gmail.com>  wrote:
> >>  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.
 >
 >  Yes, the 68010 worked fine with demand paging. The 68000 did not.
 >  Neither of them implemented instructions restarts, though. As noted below,
 >  the 68010 did instuction suspension instead.  Yes.  I was previously unaware
of the distinction but did know what
 the 68000 could not do that the 68010 could. 
We were at the same level, then. :-)

...
   >  The
"interesting" workarounds that I've hear of are actually 68000-related...
 >  Using their own designed MMU (there were none from Motorola for the 68000), 
What about the 68451?  (we had one in a prototype product design in
 1984/1985 that never made it to market)

 It wasn't terribly popular, but it did exist. 
Tried to look it up on the net, and I'm unsure if it really was usable 
on the 68K. It would appear that it did hit the market, and if you had a 
68010 in combination with this chip, you could implement virtual memory, 
since you could recover from page faults.
However, there were also third party MMUs competing with the Motorola 
chip, which might explain why it was rather uncommon.
Performance wise, the 68010 in combination with the 68451 appear to not 
have been that impressive.

...
   >  and a
second CPU, Apollo made the primary CPU stall on a page fault, and the
 >  secondady CPU wake up. The secondary CPU could then do a page in...  That
sounds like the design of the Perkin-Elmer workstation I have -
 two 68000s, one for running the OS, one for paging. 
I wouldn't be surprised to learn that SUN did something similar as well...

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol