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 17:22, Hans Rosenfeld wrote:
On Wed, Jul 07, 2021 at 04:46:36PM +0200, Johnny Billquist wrote:
I think you are underestimating the limitations of the PDP-11 compatibility
mode of the VAX...

I certainly am. :)

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... :)

This might be extremely hard, since it's a feature that comes from the design of the PDP-11 MMU. The VAX MMU is very different, and don't allow this. (Allow might be the wrong word here - it's just not possible.) (Anyone talked about execute-only protection of memory... The PDP-11 have it. :-) )


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