Re: New Vax - future directions :-)

[Johnny Billquist <bqt%update.uu.se@localhost>]

On 2021-07-07 18:42, Anders Magnusson wrote:
> Den 2021-07-07 kl. 17:22, skrev Hans Rosenfeld:
> > > No split I/D space, no FP, any kind of trap exits out to VAX mode, 
> > > anything
> > > that depends how the memory management of the PDP-11 works will have
> > > issues... Even some instructions you might play with are missing (but I
> > > don't think most people would miss them, especially not since we 
> > > don't have
> > > split I/D space anyway).
> > >
> > > Very few 2.11BSD programs would work in this environment... The most 
> > > serious
> > > limitation is the lack of split I/D space.
> > So I guess we have another few feature requests, then... :)
> Maybe add I/D segment registers for PDP-11 compatibility mode?

"Segments"? It's a straight forward page table. The only "odd" thing is 
that the page don't have to actually map the whole part of it. But you 
have a direct mapping from a specific virtual address to a specific 
page. It can't move around, no matter how much you play with the MMU.

> If we go for something with 8k pages in the future XVAX it might fit 
> quite nicely :-)

Yes. Since the PDP-11 pages are 8K it would fit pretty nice. However, 
the fact that the PDP-11 page don't have to fill the whole 8K can maybe 
throw some wrenches in somewhere.

  Johnny

--
Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt%softjar.se@localhost             ||  Reading murder books
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