KA630 guru?

From: Antonio Carlini <a.carlini_at_ntlworld.com>
Date: Sun Aug 1 17:24:42 2004

> Does anyone know the KA630 CPU well enough to say exactly how it is
> this code manages to work? I can't write an emulation of something I
> don't understand, after all. :-)

If only you'd bought either of the VMS Internals books
I've just auctioned on epay :-)

The way VAX/VMS turns on memory management is as follows.
(Yours looks like it's something else, some console
test code, but the same principles should apply).

The code sets up a mapping such that a physical address N,
a system virtual address and a P0 address N (using a part
of the SPT that is also a P0 page table).

So the sequence goes:
[PHYSICAL] something irrelevant
[P0] JMP _at_#10$
[SYSTEM] 10$: next-instruction

Now your numbers are going to be different but in
principle the code must do the same thing. Your
MTPR executes in physical address mode (mapen off)
at address 0x0219. The next instruction will be
0x21c, but by them mapping will be on, so this must be
a virtual address and it will always be a
P0 address (since the preceding physical address
must be less than the 4GB maximum that the VAX architecture

I assume that your "v" command is dumping your
idea of the system and process page tables. Are
you sure that you've correctly emulated the
various registers involved?

The text says that if the code you jump to lives
in PFN n, then the mapping sets up P0LR
with n+2 and P0BR with the SVA that is n longwords
smaller than the SPTE that maps this code.
So my guess is that you've failed somewhere
to accept an attempt to set up the page tables
as expected. I'd work back through the
code and see where it sets those up (this
may be non-trivial) and then verify that you
emulate that stuff properly.

Admittedly I'm assuming that whoever coded up
this test in the KA630 console ROM used the
same mapping technique as VAX/VMS, but I
would have thought it a safe assumption that
insufficient mind-altering drugs exist in
the Universe for someone to sit down and
work out an alternative methode that looks
like the original but is different :-)


Antonio Carlini arcarlini_at_iee.org
Received on Sun Aug 01 2004 - 17:24:42 BST

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