H316: Add Bob Armstrong's Readme documentation for the IMP tests
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Mark Pizzolato
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H316/tests/00readme.txt
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H316/tests/00readme.txt
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IMP DEMONSTRATION
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-----------------
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This directory contains a version of the IMP firmware, ca 1973, and some simh
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command files to help you run it. These command files define a three IMP
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network consisting of IMP nodes #2, 3 and 4.
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* IMP 2 has a single virtual modem line which connects to IMP 3.
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* IMP 3 has two modem lines, one connects to IMP 2 and the other to IMP 4.
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* IMP 4 has a single modem line, connected to IMP 3.
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A picture is worth a thousand words -
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IMP 2 <-------> IMP 3 <-------> IMP 4
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modem modem
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The interesting thing to notice about this arrangement is that there is no
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path between IMP 2 and IMP 4. Any messages between those two machines must
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pass thru IMP 3. Sounds simple, but for that to work requires all IMPs to
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discover their adjacent nodes, find out the neighbors of their neighbors, build
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routing tables, and then figure out the path to a remote node.
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SETUP
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-----
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Assuming you've already built the H316 simulator with IMP support, open three
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terminal windows and run on instance of H316 in each.
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Window #1 -> H316 imp2.cmd
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Window #2 -> H316 imp3.cmd
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Window #3 -> H316 imp4.cmd
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These command files will configure the hardware, load the IMP firmware,
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set the IMP node numbers, and establish the modem connections. These command
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files DO NOT actually start the simulation, however, so after you've loaded
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all three IMPs, revisit each of the three windows and type "GO".
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Initially you should see a message like this in all three windows
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DBG(737742)> WDT LIGHTS: changed to 177400
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This message refers to the status of the lights on the IMP's display panel -
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177400 means all lights are on. After about 30 seconds (yes, 30 seconds!)
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you'll see this message on IMP 2 and 4
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DBG(19558711)> WDT LIGHTS: changed to 077400
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and these on IMP 3
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DBG(15492720)> WDT LIGHTS: changed to 077400
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DBG(17096499)> WDT LIGHTS: changed to 037400
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This means IMP 2 and 3 have turned off the light corresponding to modem line 1.
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The IMP designers used these lights to indicate problems or errors, so a light
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off means that all is well. IMP 2 and 3 have just told you that their modem
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line #1 is UP. Remember that IMP 3 has two modems, so we see two lights turn
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off there.
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BTW, the time it takes for the IMP lines to come up is controlled by
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intentional delays in the IMP firmware and is driven by the RTC. simh simulates
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the RTC in real, wall clock, time, and the delay you see here is comparable to
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the delay you'd see on real IMP hardware. IT HAS NOTHING TO DO WITH THE SPEED
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OF THE PC RUNNING THE SIMULATION!
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NOW WHAT ?
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----------
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Now that you've got your three IMP network running, what can you do with it?
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Well, the IMPs had a very simple DDT like command language. Typing "0/" will
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display the contents of location 0 -
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0/ 0
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The "C" command was used to "cross patch" the terminal on your IMP to another
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IMP. For example, typing "2C" on IMP 4
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2C
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will connect the console keyboard on IMP 4 to the console printer on IMP 2.
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Anything you type on IMP 4 will now be echoed on IMP 2 - try it... In the
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Olden Days ARPAnet sites would use this facility to communicate, operator to
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operator.
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By adding 100 (octal) to the destination node, you can cross patch to DDT.
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For example, typing "102C" on IMP 4 will cross patch that TTY to DDT, not the
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operator, on IMP 2. This allowed guys at BBN and the NCC to debug IMP problems
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remotely.
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FILES INCLUDED
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--------------
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The files included in this software kit are -
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00readme.txt - this file
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impcode.cmd - simh script to load the IMP firmware
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c-listing-ps.txt - assembly listing of the IMP firmware
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impconfig.cmd - simh script for common IMP configuration
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imp2.cmd - IMP node #2 specific configuration
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imp3.cmd - IMP node #3 specific configuration
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imp4.cmd - IMP node #4 specific configuration
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imploop.cmd - IMP single line loopback test
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imploop4.cmd - IMP 4 line loopback test
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mdmtest1.cmd - simh modem simulation test, part 1
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mdmtest2.cmd - simh modem simulation test, part 2
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testrtc.cmd - simh RTC simulation test
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MORE READING
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------------
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Dave Walden's website,
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http://www.walden-family.com/bbn/
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has a wealth of BBN papers, proposals, reports, journals, and other material.
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There is an entire section devoted to ARPAnet and IMP related content.
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Bob Armstrong
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bob@jfcl.com
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30-Nov-2013
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