[Simh] TE16 CRC Errors

[Johnny Billquist]

I actually don't think he has a mixed massbus. I don't think you could 
even configure simh for this. Simh have a very simplistic view on 
hardware configurations.
You don't configure massbuses, and put devices on them. You normally 
just configure the devices, and all the bus and controller 
configurations come implicit from that.

So, if you specify a massbus disk, you'll get a corresponding massbus. 
And for tapes, you'll get another one.
Both configured appropriately for that specific type of device you have 
hooked to it.

In RSX land, only M+ supported mixed massbus, as you mention. Not sure 
when/if VMS did. Not sure how much of anything else that might have 
supported it either.

   Johnny

On 2017-11-08 00:57, Larry Baker wrote:
> 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 <mailto:baker at usgs.gov>
> 
> 
> 
>> On 7 Nov 2017, at 12:54:40 PM, simh-request at trailing-edge.com 
>> <mailto: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>>
>> Content-Type: text/plain; charset="utf-8"
>>
>> 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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-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol