[Simh] Bug (?) in vax (3900) and pdp11 SIMH 3.9

[Jordi Guillaumes i Pons]

It happens after the simulator has been running for some days. In my case I run it under "screen", but I don't know if that is related to the issue.

Symptom: after hitting "CTRL-E" the simulator seems to enter an endless loop printing the prompt "simh>" until it is killed:

m> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim> sim>     

It does NOT take any input at this stage, and as observed, it prints the prompt without any endline. The CPU usage tops at a 100% (or whatever % is available).

I've seen it happening with the 3900 and the pdp11 simulators (that one running RSTS-11).

I run the simulator under Ubuntu Linux 10.04 LTS, amd64 bits architecture.
                                                     
For reference, this is my vax.ini:

load -r ./ka655x.bin

attach nvr ./vms-nvram.bin

set cpu 64m
set cpu conhalt
set cpu idle
deposit bdr 0
;set console telnet=32923

set rq0 ra92
set rq1 rd54
set rq2 rd54

set rqb enabled
set rqb0 cdrom
set rqb1 cdrom
set rqb2 cdrom
set rqb3 cdrom

attach rq0 ./vms-disk0.dsk
attach rq1 ./vms-disk1.dsk
attach rq2 ./vms-disk2.dsk

attach rqb1 ./vaxdocjun981.iso
attach rqb2 ./vaxdocjun982.iso

set xq mac=AA-00-04-00-3C-1C
attach xq vde:/tmp/vde.ctl
                                                       
set dz disable
set vh enable
set vh lines=8
att vh 32023

att lpt ./vms-printer.txt

set tq disable
set ts enable
set rl disable
set ry enable

Echo Iniciant microVAX 3900
boot cpu



Jordi Guillaumes i Pons
jg at jordi.guillaumes.name
HECnet: BITXOV::JGUILLAUMES