Originally, the VAX allowed immediate operands (8F) to be used without
restrictions in address mode instructions, either standalone or indexed.
Starting with MicroVAX II, immediate indexed became reserved. This
remained true for all subsequent chip implementations. The SRM was
ECOed in March, 1985 to make immediate indexed unpredictable.
In MicroVAX II, immediate g-floating operands didn't work correctly. The
problem was found a couple of months after tape-out. While the index
flows could be fixed, and were fixed according to the microcode revision
history:
; 7-May-84 [RMS] Fixed FD problem in index flows (JLR)
the problem in indexed immediate could only be fixed by a significant
hardware change in an area that was already packed full. The VAX
Architecture Team, which had always been very sympathetic to the
VAX chip efforts, proposed a much simpler solution: make immediate
indexed unpredictable. It was useless, in any case.
I'm rather surprised that this wasn't flagged by the 780 diagnostics.
Maybe it was never tested. It was tested in HCORE (the original MicroVAX I
core diagnostic that is failing), but I removed it subsequently:
; 8-may-85 rms removed indexed immediate tests
Bottom line - the simulator is right for the chip VAXes (including, I think,
V11) and wrong for MicroVAX I and probably the 8600, 780, 750, and 730.
# Conflicts:
# VAX/vax_cpu.c
- Recent changes in vax_watch.c changed the input parameter from a
physical address to a register address within the watch chip.
- vax630_sysdev.c called the older wtc_wr() with the new parameter,
but the length argument has been removed.
- The watch chip never starts as valid. Make it valid when the TODR is
attached (i.e. reflecting a connected battery).
- 64 bytes of bus addresses for the watch chip can sometimes be dispatched
to wtc_rd() and wtc_wr(). Make sure that reasonable memory is always
referenced for all potential accesses.
- restore vax8200 to makefile which got lost in a prior merge.
- Force the detection point of a tape structure error to be the logical EOM
on the tape.
- Enable SIGINT abort of a possibly long running validation scan
- Add -L detail record structure option at ATTACH time
- Add extra garbage at end of generated test data files
This change enables the simulator to be shut down cleanly via a
soft-power shutdown command. This is implemented in the real 3B2/400
through the sanity timer, which, if it reaches zero, sets a bus timeout
flag in the CSR and issues an interrupt at IPL 15. The operating
system (System V UNIX) treats this as a shutdown request and enters
runlevel 0.
To use this change in a SIMH startup script, for example to implement a
3B2 simulator as a service, one could add these commands:
# [... simulator setup ...]
BOOT
SET TIMER SHUTDOWN
CONTINUE
EXIT
On catching a SIGTERM, SIGINT, or SIGHUP, the simulator would return to
SCP control, set the soft power shutdown flag, and then continue
simulator execution. After the system is cleanly shut down, the
simulator would then exit back to the operating system.
- Different systems used tape marks in different ways that are now
tolerated (multiple successive ones located on different parts of
the tape, etc.)
- Always validate beginning and end of record length indicators to avoid
moving into invalidly structured tape data
