[Simh] Fwd: 4.3BSD Quasijarus0c on the VAX-11/730

[Ethan Dicks]

On Wed, Jul 2, 2014 at 8:38 AM, Christian Gauger-Cosgrove
<captainkirk359 at gmail.com> wrote:
> In other news, I have had some assistance getting Quasijarus up and
> running on the 11/730...
> root device? rb0*         <--- Enter "rb0*" here.
> idc0: lost interrupt       <--- This error repeats infinitely.

So I was able to completely reproduce these results and I've done some
digging into 4.3BSD's idc.c as well as simh's vax730_rb.c... by
disassembling idc.o from the distro files and comparing it to the live
in-memory contents of the running simulation, I've run across
something interesting...

First of all, I was able to confirm the in-memory location of the
variable 'idcdebug' at 0x80063a5c, which lets me turn idc.c's
debugging on and off.  When I did this, I got a surprise - mixed in
with a lot of debugging output was the rest of the startup and a "#"
prompt.  I am able to run commands, look around the disk, etc., only
as long as idcdebug is non-zero.  As soon as I turn it back to 0, the
"lost interrupt" loop returns (but then turning debugging back on does
not seem to unstick it - once stuck, it stays stuck).

Specifically what I did was follow the recipe right up to the "root
device?" prompt, then ^E to gain access to the "sim>" prompt, then
"deposit 80063a5c 1" and "go".  There follows a flurry of debugging
statements ending in "#".

Curiously, "idcdebug" only appears in the printd macro (as
"if(idcdebug)printf"), so there must be some side-effect since the
only direct linkage would be additional reads of the rb730 registers
for some of the printf statements, and the indirect effects are to add
additional cycles between operations (defeating a race condition?)

I can capture the driver debugging output, but most of the output from
a working machine is not useful for debugging - we already have a good
idea of what should be happening when things are going well.

That's all I've got for now, if someone wants to take it and run with it.

-ethan