[Simh] TE16 CRC Errors

[Larry Baker]

Peter,

My reading of your hardware setup sounds like what was called a "Mixed-MASSBUS" configuration, that is, mixing disks and tapes on the same MASSBUS.  PDP-11 RSX-11M-Plus supported Mixed-MASSBUS.  We dual-ported all our disks and used the MASSBUS that came with our tape drives that way.  I think Mixed-MASSBUS support was unusual.  I do not remember if VMS 3.0 supported Mixed-MASSBUS.  If not, what you are seeing might be the result.

Larry Baker
US Geological Survey
650-329-5608
baker at usgs.gov



> On 7 Nov 2017, at 12:54:40 PM, simh-request at trailing-edge.com wrote:
> 
> ------------------------------
> 
> Message: 4
> Date: Tue, 7 Nov 2017 20:54:31 +0000
> From: Peter Allan <petermallan at gmail.com <mailto:petermallan at gmail.com>>
> To: "simh at trailing-edge.com <mailto:simh at trailing-edge.com>" <simh at trailing-edge.com <mailto:simh at trailing-edge.com>>
> Subject: Re: [Simh] Simh Digest, Vol 166, Issue 12
> Message-ID:
> 	<CAJCrz55fv2uBE5PhmtboUXL5Yzt8CpyiYhn1CyGxgHZHbXEkyw at mail.gmail.com <mailto:CAJCrz55fv2uBE5PhmtboUXL5Yzt8CpyiYhn1CyGxgHZHbXEkyw at mail.gmail.com>>
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> 
> In order to try to understand why I am having trouble reading a simulated
> tape with a simulated TE16 tape drive on a simh VAX 780, I have tried
> several configurations.
> 
> 
> Firstly, a point of clarification. The problem that I came across was in
> finishing the installation of VMS 3.0. This was necessary in order to be
> able to install VMS 1.5 using DSC2, but I have no problem with the
> installation of VMS 1.5 itself. VMS 1.5 is a red herring - the problem is
> with VMS 3.0.
> 
> 
> I had configured a VAX 780 in simh with three RP06 disk drives and two TE16
> tape drives. I was using TE16 tape drives rather than TS11 really just
> because when I was the system manager of a real 780, it had two TE16 tape
> drives.
> 
> 
> All of this has been done on a host system running CentOS 5 (for simh
> 3.8-1) and CentOS 6 (for simh 4.0).
> 
> 
> To remind you of the problem, I started the installation of VMS 3.0 by
> booting stand-alone backup and restoring a saveset from a tape that I
> downloaded from the University of Stuttgart. The first phase went fine and
> when I rebooted the 780, the system asked which device contained the
> installation media so that it could automatically complete the installation
> of VMS. I entered MTA0: and this is where things went wrong. Wilm suggested
> I should trying using a TS11 drive (MSA0) rather than a TE16 drive and this
> did indeed work, but this left me wondering why?
> 
> 
> I have tried to restore a BACKUP saveset from a tape to a disk using
> several configurations. I have tried:
> 
> -          Two difference versions of simh, 3.8-1 and 4.0
> 
> -          Three different versions of VMS, 3.0, 4.6 and 7.3
> 
> -          Different simulated tapes
> 
> -          The two different simulated tape drives, TS11 and TE16
> 
> The results have surprised me.
> 
> 1)      Changing the version of simh makes no difference to the results.
> 
> 2)      I only get a problem in restoring a saveset from tape when running
> VMS 3.0 as the operating system. Everything works fine with VMS 4.6 and 7.3.
> 
> 3)      I have tried different tapes, but if the system is going to fail to
> do a restore operation, it does it with all of the tapes containing BACKUP
> savesets that I tried.
> 
> Following a suggestion from Kevin Handy, I tried to copy the savesets from
> tape to disk, but the copy failed on the VMS 3.0 system when using a TE16
> tape drive.
> 
> 
> My experiments indicate that there is a problem with VMS 3.0 when using
> TE16 tape drives. However, this seems so unlikely, not least because the
> sequence of operations that I have gone through is what hundreds (thousands
> probably) of system managers must have done to install VMS 3.0 on real
> hardware, including my predecessor with “my own” 780.
> 
> 
> This leaves me stumped, but at least I have narrowed the problem down and I
> am able to do the installation of VMS 3.0 (which lets me do the
> installation of 1.5) by using a TS11 drive.
> 
> 
> The only thing I can think of is to wonder if the way that VMS handled TE16
> (i.e. massbus) tape drives changed between VMS 3 and VMS 4 and that somehow
> there is a bug in simh that only rears its head on the earlier version. I
> confess this is a stab in the dark.
> 
> 
> Anyone got a bright idea about this?
> 
> 
> 
> Cheers
> 
> 
> Peter Allan
> 
> 
> 

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