From mboxrd@z Thu Jan 1 00:00:00 1970 From: grog at lemis.com (Greg 'groggy' Lehey) Date: Tue, 24 Nov 2020 09:29:52 +1100 Subject: [COFF] DDP-516 hardware (was: 516-TSS Documents) In-Reply-To: <20201123134234.8F52218C096@mercury.lcs.mit.edu> References: <20201123134234.8F52218C096@mercury.lcs.mit.edu> Message-ID: <20201123222952.GF56952@eureka.lemis.com> [Redirecting to COFF] On Monday, 23 November 2020 at 8:42:34 -0500, Noel Chiappa wrote: >> On Mon, Nov 23, 2020 at 12:28 PM Erik E. Fair wrote: > >> The Honeywell DDP-516 was the computer (running specialized software >> written by Bolt, Bernanek & Newman (BBN)) which was the initial model of >> the ARPANET Interface Message Processors (IMP). > > The IMPs had a lot of custom interface hardware; sui generis serial > interlocked host interfaces (so-called 1822), and also the high-speed modem > interfaces. I think there was also a watchdog time, IIRC (this is all from > memory, but the ARPANET papers from JCC cover it all). I worked with a DDP-516 at DFVLR 46 years ago. My understanding was that the standard equipment included two different channel interfaces. One, the DMC (Direct Multiplexer Control, I think) proved to be just what I needed for my program, a relatively simple tape copy program. The input tape was analogue, unbuffered, and couldn't be stopped, so it was imperative to accept all data as it came in from the ADC. But the program didn't work. According to the docco, the DMC should have reset when the transfer was complete (maybe depending on configuration parameters), but it didn't. We called in Honeywell support, who scratched their heads and went away, only to come back later and say that it couldn't be fixed. I worked around the problem in software by continually checking the transfer count and restarting when the count reached 0. So the program worked, but I was left wondering whether this was a design problem or a support failure. Has anybody else worked with this feature? Greg -- Sent from my desktop computer. Finger grog at lemis.com for PGP public key. See complete headers for address and phone numbers. This message is digitally signed. If your Microsoft mail program reports problems, please read http://lemis.com/broken-MUA -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 163 bytes Desc: not available URL: