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PDP7: GRAPHICS-2 A bit more description on the hardware, and UNIX-7 usage,

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additional thoughts on creating a web interface!!!
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Phil Budne 2016-03-26 14:52:09 -04:00 • committed by Mark Pizzolato
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commit 736bf138b9
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PDP18B/pdp18b_g2tty.c
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@ -35,6 +35,46 @@
realized that the axis was perpendicular to the loading dock 4 floors
below. A 90-degree turn solved the problem.
GRAPHICS-2 was a command list based graphics display system,
and included a light pen, a "button box" and status bits
for a "dataphone" interface to speak to a GECOS system.
The UNIX-7 system driver only uses text display, and reserves 269
words (holding two characters each; the buffer is 273 words, but
three contain display "setup" commands, and the final word in the
buffer must be a display "TRAP" instruction that ends the display
list).
The UNIX system code triggers a refresh every 10 60Hz "ticks" of
the real time clock. This driver attempts to do detect new text
and send it to a user who has TELNETed in.
Thoughts on implementing a web interface:
538 characters redisplaying at 6Hz (every 10 "ticks") gives a
bandwith requirement of only 26Kbit, and most refreshes won't
change the screen and could be suppressed. So it seems like it
would be reasonable to create a web interface.
Make a SIMH TCP server port which implements a tiny HTTP server.
The base URL serves up a skeletal page with (lighted) buttons,
and a "display window".
And either:
1) Use "AJAX": an (invisible) <iframe> on in the HTML served by the
"base URL" keeps a never-ending connection that is sent "script"
tags to alter the "screen" (div) contents, and light push buttons.
Keypresses and buttons could be implemented using "onclick"
actions which trigger a GET (or a POST) on a URLs which
open new (temporary) HTTP connections to SIMH. The key/button
press URL could contain a session UUID which has to match
a value sent in the initial page.
2) Have the "home" page HTML establish a bi-directional WebSocket
connection to Encapsulate all the traffic (screen contents,
button lighting, key & button presses).
The graphics system responds as ten PDP-7 "devices";
UNIX only uses six, and only three of the six are simulated here
(and *JUST* enough of those to figure out the text being displayed),