[Simh] Fixing the FP11's use of MMR1

[Johnny Billquist]

On 2018-11-14 03:07, Johnny Billquist wrote:
> On 2018-11-14 02:58, Paul Koning wrote:
>>
>>
>>> On Nov 13, 2018, at 3:45 PM, Ethan Dicks <ethan.dicks at gmail.com> wrote:
>>>
>>> On Tue, Mar 24, 2015 at 5:07 PM Bob Supnik <bob at supnik.org> wrote:
>>>> This issue, pointed out by Johnny Billquist, has been hanging fire for
>>>> years.
>>>>
>>>> Fixing the FP11's use of MMR1 - implementation proposal
>>>>
>>>> As has been noted, the FP11 does not update MMR1, ever....
>>>
>>> This was very interesting and educational to read, but when does it
>>> matter?  Diagnostics?  Are there any live programs that depend on this
>>> behavior?
>>
>> Interesting question.  FWIW, RSTS does not use MMR1.  It saves it in 
>> crash dumps but never touches it anywhere else.
> 
> I haven't made a proper check in RSX, but at least I know that if you 
> get a memory address error trap in RSX, the contents of the MMU 
> registers are saved on the stack, and the user level program gets them, 
> and then the user level program can do whatever it want with the 
> information, so it is used in the sense that it is provided for 
> applications to potentially make use of.

That said, I should probably go and dig through my old mails to see what 
I did say back then. I'll see if I can dig that out next weekend.

   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