[HECnet] Connecting an HP Itanium BL860c to HECNET... without ethernet

[Johnny Billquist]

On 2021-12-11 02:25, Paul Koning wrote:
> 
> 
>> On Dec 10, 2021, at 7:08 PM, Thomas DeBellis <tommytimesharing at gmail.com> wrote:
>>
>> Those names almost sound like they want to be familiar, but not quite.  What I recall for a DN20 was that, in terms of communication, MCB only had two speeds.
>>
>> 	• A 'fast' interface could do 56 KBid, synchronous.  I think that part was called a "KMC".  It may have had some sort of embedded microprocessor on it, but I don't recall what kind of operations it performed.
>> 	• A 'slow' interface could do up to 9.6 KBid (I think).  I can't quite remember what it was called.  Maybe a DUP-11?  I might be getting that mixed up with the RSX20F front end, which had single line interfaces that I think were called DL's.
> 
> The only system I know well is RSTS/E.  The only sync comm link it supported were DMC11 and its offshoots DMR11 (same features, modernized design), DMP11 (added multipoint) and DMV11 (like DMP except Qbus).  All except DMV could run up to 1 Mb/s and in fact that speed was achievable.  DMV ran at a max of 56 kbps, I'm not sure why.  That board has a very different design, much smaller.  The DMC/DMR/DMP are all variations on the KMC11 microcontroller, with a directly-connected line card.  There actually were two line cards: one "integral modem", coax connected for up to 3 miles or so distance at speeds in the 56k to 1M range.  The other was a modem card (RS232, RS422, V.35) for up to 56 kbps if the modem could go that fast.  (Perhaps more but I don't know of modems that would do so).
> 
> The KMC you mentioned was a programmable engine which could do DMA and Unibus transactions, so it was paired with sync or async comm devices to offload DDCMP processing.  The idea is that the host would talk to the KMC with a packet API, and the KMC would then talk on its behalf to the actual UART or USRT with byte-oriented transactions to do the real communication.  You'd still have a whole lot of bus activity but no character-level interrupts to the host.  I don't know what speeds were achievable with KMC-DUP or KMC-DZ, the two pairs I know of.   Part of the question is what the most is those character devices could do.  Someone else might have those details.  RSTS never supported KMC for DECnet, though it did for RJ2780 I think.

KMC-DZ would be limited by the DZ, which didn't go above 9600. The same 
is true of the DUP.

RSX supported KMC with both DZ and DUP, as well as DUP or DZ on their own.

   Johnny

-- 
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