[Simh] how to move vms backup tapes to the emulator

[Kevin Brunt]

I would have said that using CTRL-E to break out to the simh> prompt 
constitutes 'stoppping the emulator', because while you're "changing 
tapes", the simulated machine isn't executing instructions.

This is rather 'unaesthetic' - it reduces the 'fidelity' of the 
simulation.

What is, perhaps, needed is to turn the structure of SIMH 'upside 
down', with the processing of the event queue as the main loop and the 
command loop and CPU instruction execution being reimplemented as 
events. It then becomes possible to have a separate 'operator 
emulation' window, where tape mounts, and similar activities, can be 
carried out while the emulator is active.

This actually brings the structure of SIMH closer to what Bob Supnik 
described in his recent paper  "SIMH: Forward Into The Past", on the 
SIMH website.

A interesting 'wrinkle' would be to implement the command interface by 
sending TCP/IP packets at it. The command interface would then be a 
separate program, potentially on another machine, and potentially in 
control of multiple simulations. The simulation of an entire 'data 
center' could be envisaged.

Another implication of this 'inversion' is the possibility of multiple 
CPUs. This would entail radical changes to the individual emulations, 
particularly in such areas as the use of global variables, but it would 
make for interesting possibilites, not only such things as 
dual-processor systems, but also some of the more curious things (such 
as the PDP-15/76), and also some of the 'tightly-coupled' multiple 
machine systems, (eg the DEC PCL-11 and the very similar Data General 
Nova 'Multiprocessor Communications Adaptor', both of which did 
word-by-word transfers on a multiplexed bus at close to memory bus 
speed), not to mention multiple-ported disks, which also need close 
coupling.

Kevin

PS 25+ years ago there was a PDP-15/76 running less than 10 feet from 
where I'm sitting now. When it was moved in 1978/79 (to the basement of 
a house where Bertrand Russell had once lived) it was split back into 
its component PDP-15/20 and PDP-11/05, the latter of which may well 
have been the only 'Unichannel-15' to run MiniUNIX.


On Fri, 29 Oct 2004 14:06:38 +0200 (CEST) Andreas Cejna 
<andreas.cejna at gnc.at> wrote:

> Hi Rick,
> 
> you don't need to stop the emulator completely. Hitting CTRL-E on the 
> console window sends you to the simh-console. You can attach and 
> detach files from your tape units there and then continue your 
> emulation with the CONT command. 
> 
> As far as I know simh allows you to emulate 8 tape drives using two 
> controllers. So you are able to access 8 tapes in parallel once you 
> have attached these files to your tape units.
> 
> Do you have access to the tape-unit on the system that runs simh?  
> Another possible way would be to attach the tape-unit directly to 
> simh.
> 
> regards
> Andreas Cejna
> 
> 
> Am Fr 29.10.2004 00:50 schrieb Rick Caldwell <rickc at dallas.oilfield.slb.com>:
> 
> > 
> > I have several vms tapes in backup format that I would like to move to 
> > the Vax emulator.   I'm looking
> > for a smooth way to do this.  From the doc it appears I could read tapes 
> > in tpc format but this would
> > require stopping the emulator to attach the file and restarting the 
> > emulator if I understand how the
> > attach works (at least I think the tape image file is opened when 
> > attached so once the emulation is
> > started the file is attached to the simulated device rather than opening 
> > and closing on allocation
> > and deallocation so you could replace the file with the emulator 
> > running).   It would also seem that
> > I would need to find a way to first convert the tape to tpc format 
> > without a Vax.  As I have several tapes to
> > read and more than 1 user this probably wouldn't work to well.  There 
> > seem to be several utilities in
> > the tools subdirectory of the simh distribution but they don't seem to 
> > do what I would like to do from
> > what documentation there is.
> > 
> > Another thought is to build the vmsbackup.c program on unix/linux and 
> > read the tape and save to disk,
> > then run vmsbackup again to make a on disk saveset which then could be 
> > ftp'ed to the emulator and then
> > backup could then be run in the emulator on the backup saveset.  Most of 
> > this could be scripted but it seems
> > like a lot of steps and a lot of temp disk space so was wondering if 
> > someone had a better solution .
> > 
> > Rick
> > 
> > -- 
> > Have you noticed that a "slight tax increase" costs us at least two
> > hundred dollars a year, but a "substantial tax cut" saves us maybe thirty cents?
> > 
> > rickc at dallas.oilfield.slb.com
> > 
> > _______________________________________________
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> > 
> 
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----------------------
Kevin Brunt
Birkbeck College London