PDP-11 SPACEWAR running again!

Boris Gimbarzevsky boris at summitclinic.com
Tue May 11 01:00:13 CDT 2021

Thanks Mattis - watching an AR11 making that 
oscilloscope display brings back a lot of 
memories from my PDP-11 programming days.  Had 
heard of spacewar in 1980, but was more 
interested in playing around displaying data on 
screen of a scope.  One of my jobs was to clean 
up electrophysiology data for publication and 
that meant removing noise in signal so had a 
joystick system which could move and click on 
point on screen I wanted deleted.  11/34 was fast 
enough that we had an EE summer student create a 
dot matrix character set so we could put captions 
on our oscilloscope images.  Of course, only way 
of getting hard copies of those was with an oscilloscope Polaroid camera.

Looking at the printouts that you're dealing 
with, I had a hard time making out some of the 
characters.  Can see individual dots in a number 
of the characters and haven't found any OCR in 
past that works well on them.  Had my MSc thesis 
printed on and IBM lineprinter and looks good 
from afar but couldn't get any OCR program to 
digitize it properly.  At least the spacewar code is relatively short!

Boris Gimbarzevsky

>Today I finally got the SPACEWAR version for PDP-11/10 running again on my
>PDP-11/05 with AR11 board. I played a couple of rounds together with my
>daughter. She was better than me. Quite hard game IMHO.
>Bill Seiler and Larry Bryant wrote this version in 1974 and submitted it to
>DECUS. It was believed to have been lost to history. But Bill had saved the
>printouts from the PAL11 assembler. He sent me scans of these printouts as
>pdf files. I then transcribed it into source files and iterated several
>times in SimH to get a clean build and link. I got some help from people
>here doing OCR on some files. But the lines mostly confused the OCR process
>so a lot of errors was introduced. It turned out that it was easier to just
>transcribe the whole lot by hand than finding and correcting errors.
>The AR11 is somewhat different to the AD01 and AA11 that Bill and Larry
>used. AA11 has a 12 bit 2’s complement D/A while the AR11 is only 10 bits
>and not 2’s complement. I did some patches and eventually got everything
>I also connected a couple of analogue joysticks. The fire button is just
>short ciruiting the viper of the potentiometer to the 5V supply lead. The
>screen is a HP1332A vector screen.
>All the transcribed code, AR11 patches and build instructions are available
>on github. https://github.com/MattisLind/SPACEWAR
>It should be possible to adapt it to orher types of A/D and D/A hardware if
>anyone wishes to do so. However the gameplay might be harder when running
>on a faster PDP-11?
>Have fun!

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