@industrialartifact I have the black VAX hardware books for VAX-11/780 and VAX-11/750 around here (somewhere).
Firmware listings were in the back of those books, and the 11/780 firmware is disconcertingly reminiscent of a 188-bit VLIW single-issue machine.
The VAX XFC instruction was fun, when user-writable control store (UWCS) option was available. Roll your own instructions, running at the same speed as everything else. If you had no UWCS present, XFC trapped to VAX instructions.
Those virtual address mappings fully permit mapping the first page of VAX virtual address space into whatever VAX physical addresses necessary.
It was OpenVMS (née VMS) that chose to set that first memory page no-access.
If you're into this stuff, a copy of DEC Standard 32—the VAX Architecture Standard—has become available in recent years:
http://w.bitsavers.org/pdf/dec/vax/archSpec/EL-00032-00-decStd32_Jan90.pdf
Learn about the virtualized VAX work there and other architectural arcana.
DECSTD032 was restricted access for a very long time.
#VAX #retrocomputing #retrocomputers #retrocomputering #thearchitectureforthe80s #DigitalEquipmentCorporation