[GTALUG] mysterious restarts

[phiscock at ee.ryerson.ca]

>> Who built a computer that cared about AC frequency to drive the real
>> time clock?  Never heard of anyone doing that.
>
> My first computer, a Poly-88 8080 based system, did (I still have it).
> <http://www.polymorphic-computers.com/poly88.html>
>
> The transformer used for the linear power supply was tapped, rectified
> and clamped to feed to an interrupt pin. The interrupt routine would
> increment a counter in RAM which was accessible for real time
> calculations.
>
The Commodore PET and 64 had a 60Hz real-time-interrupt that did a bunch
of housekeeping. You could patch your own routines into it, which was
really handy.

After a particularly nasty bug, that's where I learned about the
importance of semaphores in controlling access to shared resources ;)

-- 
Peter Hiscocks
Syscomp Electronic Design Limited, Toronto
http://www.syscompdesign.com
USB Oscilloscope and Waveform Generator
647-839-0325