[Simh] VMS 4.6 won't boot from a Massbus disk

[Peter Allan]

Thanks to everyone for their suggestions.

To answer Bob's questions:

1) I am using the vmb.exe image that comes with simh

2) The hang does not occur in SYSBOOT. I can get into SYSBOOT, look at the
parameter values, change them and type CONTINUE. That is when the system
hangs. Yesterday I tried a minimal boot by going into SYSBOOT and typing
SET/STARTUP OPA0:, but that did not help.

4) I will try using the Massbus and RP debugging capability and see what it
tells me.

I am running this on a recently purchased quad-core system that is rather
fast. I have simh set up on a system that is much slower, so I will give
that a try to see if there is a difference.

Cheers

Peter Allan

On 26 January 2011 12:44, Bob Supnik <bsupnik at comcast.net> wrote:

> I agree with Dave Hittner: the hang in booting VMS 4.6 from Massbus is
> either a timing problem, or a bug in replicating some small detail of the
> Massbus controller.
>
> Because booting from an RA81 waits in the same place (but eventually
> succeeds), the "branch to self" loop where the simulator is waiting appears
> to be an idle loop, where VMS is waiting for some sort of event, like a disk
> interrupt. The disk interrupt may have occurred too soon and been lost (a
> problem which occurred in DEC PDP-11 operating systems and in BSD Unix as
> well). Or some detail that was unimportant in VMS 7.x mattered in VMS 4.x,
> such as the handling of attention interrupts versus data transfer
> interrupts.  For an example of the kinds of details that could go wrong, see
> http://simh.trailing-edge.com/docs/massbusmystery.pdf, which documents an
> error in the 7.X driver sources for these disks.
>
> What would be most useful would be a VMS 4.X source set, but up until now,
> no one in the community has found one.  So here are some questions and ideas
> for debugging this problem.
>
> 1. Are you using the VMB (primary boot) image that comes with the 4.X
> series, or the default VMB image that comes with the simulator, which is
> from 7.2? While I don't know of any version skew issues, they could
> certainly exist. Does the same problem occur when booting with a 4.X VMB?
>
> 2. Does the hang occur in SYSBOOT (secondary boot), or in VMS proper? VMS
> runs at high virtual memory (8XXXXXXX), yet the branch to self is in low
> memory. If the hang is in SYSBOOT, the problem is likely to be easier to
> solve, as the environment is simpler. One thing to check: is memory
> management enabled?
>
> 3. Other users have reported success in getting early versions of VMS to
> run. I seem to recall that versions as far back as 1.5 have run
> successfully. Can we get a census of which versions have been successfully
> tested on the 780 booting from Massbus, and what version of VMB they use?
>
> 4. Both the Massbus controller (RH) and the device (RP) have debugging
> capabilities. You can log every register read and write to see how far the
> the controller gets.
>
> 5. As a last resort, zip up your RP disk image and post it to an uploading
> site, like Megaupload, so that others in the community can try their hand at
> the problem. You'll need to include not just the disk image, but
> configuration data, as well as any auxiliary files (such as an earlier VMB,
> if you use one).
>
> /Bob Supnik
>
>
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