[Simh] PSI for TOPS-20

[Timothe Litt]

> Someone please point out if I'm wrong about this.
It's not that simple.  You are, and you aren't.

TOPS-10/20 PSI (X.25) required a DN20; the X.25 gateway software lived 
there.

The KS hardware could not connect directly to the X.25 network. The KDP 
could have done it, but no driver or gateway software was written.  The 
SimH KDP emulation does not support bit-stuffing.

The gateway just made the X.25 connection look like a DECnet circuit, 
albeit it an expensive one.    In the Phase IV DNA, X.25 is a data link 
layer parallel to ethernet and DDCMP.

The gateway in the DN20 was accessed by a standard DECnet logical link 
by the PSI utilities, usually from the local host.

A KS could get to the gateway using DECnet, modulo the routing 
restrictions/hacks of the OS version.

I'm not sure about the VAX implementation - I think the 10/20 PSI (the 
utiltiies, such as x29pad) could talk thru it.  I never tried it.  It 
should have worked.

The NML has entity definitions for X.25 circuits, and any DECnet Phase 
IV or greater NCP can mange one (whatever node it lives on), subject to 
the usual privs.

So yes, the KS can't physically connect to the X.25 network.  But it can 
use a gateway elsewhere.

And it can manage one.  Sometimes.  X.25 Circuits were introduced in 
Phase IV.  The NCP in TOPS-20 on the KS wouldn't have had the command 
tables.  The Phase-IV version did.

This communication may not represent my employer's views,
if any, on the matters discussed.

On 16-Jan-14 19:38, Rich Alderson wrote:
>> From: G. <gerry77 at mail.com>
>> Date: Thu, 16 Jan 2014 14:01:00 +0100
>> On Wed, 15 Jan 2014 23:16:20 -0800, Mark Abene wrote:
>>> By chance, does anyone have a tape image of PSI for TOPS-20 v7?  I want to
>>> get X.25 connectivity going.  Probably a long shot, but doesn't hurt to ask.
>> Both Trailing Edge and Bitsavers have BB-W661A-BM (V1.0 1983) and BB-W661B-BM
>> (V1.1 1984) tape images, but they are for TOPS-20 V5.1 so maybe they do not
>> work with V7. On the other hand, Autopatch tape 23 (V7 indeed) has references
>> to PSI V1.1 so you may just want to give it a try... :)
> Given that this question was raised in a SimH context, I have to point out that
> SimH only emulates a KS-10 processor, which is limited to TOPS-20 v4.1, and
> which does not support the DN20 interface (a PDP-11/40 [or /34?]) which does
> DMA via the DTE20 into KL-10 memory.  Looking at the tape on Trailing Edge, it
> specifies the DN20, so I think that this is a non-starter.
>
> Someone please point out if I'm wrong about this.
>
>                                                                  Rich
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