DEC DMV-11 and DMR-11 point-to-point link questions

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Steve Dyer

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Oct 30, 1986, 3:59:05 PM10/30/86
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A few questions:

is the Q-bus DMV-11 equivalent to the Unibus DMR-11?
- will they interoperate (will a DMV-11 talk to a DMR-11?)
- is the DMV-11 program-compatible with the DMR-11? (i.e.
under Ultrix, will it use the BSD dmc driver?)

How many DMR-11's can be installed on a single VAX?
How many DMV-11's can be installed on a single MicroVAX?
I see no hard-limit in the dmc driver, although
there may be an implicit limit due to resources
like Unibus mapping resisters. Are there power-
consumption issues which would limit their number?
--
---
Steve Dyer
spdcc!dyer
dy...@harvard.harvard.edu

Richard Johnsson

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Nov 6, 1986, 1:21:49 AM11/6/86
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> is the Q-bus DMV-11 equivalent to the Unibus DMR-11?

sort of. They are similar. The DMR is much more general and can go up to
1 megabit per second. The DMV is limited to 56K. For most normal purposes
ther are functionally equivalent.

> will they interoperate (will a DMV-11 talk to a DMR-11?)

Yes. They both speak DDCMP (version 4 I believe). We have many talking to
DMR's in the internal DEC network (all DECnet based). We haven't yet tried
any in Ultrix.

> is the DMV-11 program-compatible with the DMR-11?

Not quite. I don't know the differences, but I have looked at the source for
the DMV driver in Ultrix 2.0 and it says it was derived from the dmc/dmr
driver. It is apparently different enough that putting in a few runtime
conditionals was not reasonable.

> How many DMR-11's can be installed on a single VAX?

Mostly I think it depends on having enough Unibus power. They suck up a lot
of +5 (about the same as a UDA50 which is about 12 amps for the two boards).
I believe the power requirement limits you to four per BA11 box. Locally we
have a VMS 750 in the internal network with 6 DMR's (4 @ 9.6 and 2 @ 56). We
have an Ultrix 750 with 4 DMR's (2 each 9.6 and 56).

> How many DMV-11's can be installed on a single MicroVAX?

Our newly installed DECnet router microvaxen each have 5 DMV's. Corporate
Telecom which runs the internal network approves of running one DEQNA and
5 DMV's @ 56K on a microvax (II of course :-) as a dedicated router.

> I see no hard-limit in the dmc driver...

Actually there's a bug in the Ultrix 1.2 dmc driver (which may have been
propagated from or to elsewhere) which limits it to one:

At line 389 (first executable line of dmcload()) change

unit = (sc - dmc_softc)/ sizeof (struct dmc_softc);
to
unit = (sc - dmc_softc);

Also there are some funnies in the handling of multiple point-to-point links
(and point-to-point links in general) in Ultrix 1.2, BSD 4.2 and at least
early versions of 4.3. I have sent the changes to be included in Ultrix 2.0
but haven't looked lately to see if they're in.


Hope this helps.
--
Richard Johnsson, DEC Western Software Lab, Palo Alto, CA
UUCP: {decvax,ucbvax}!decwrl!johnsson
ARPA: john...@decwrl.dec.com DEC ENet: rhea::johnsson
phone: +1 415 853 6676

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