Port-vax archive

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]

Re: New Vax - future directions :-)

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

Home | Main Index | Thread Index | Old Index