Re: Noob question: examine arbitrary memory address? #ELF #memory


I believe random crashing is never really random, we just simply can't see the cause.  So far, my favorite hair pulling trouble shooting story has been the one where someone could not enter 00 into the ELF.  Any other value worked fine.  In the end, it turned out to be 5V was not connected to pin 16 (or 40).  

Sometimes, the things that are supposed to be good can be what causes the problem.  I heard of project fail because the wiring was too neat.  Two students completed an electronic project, one did a very neat job by routing and bundling the wires in a cable harness, the other just took the shortest path between points and let all the wires criss-cross in a messy fashion.  The connections were all correct, the parts were all good, perhaps the design was intolerant but the neatly wired project would not work.  I have a deep respect and admiration for the PCB designers that know how to purposely zig-zag traces to equalize trace lengths required to make Ghz computers work.

A personal story of random failures.  About 30 years ago, a system of controllers would intermittently report a communication glitch about twice a week, usually in the wee hours of the morning.  Communications was via 20mA, active transmit (passive receive), 2400 baud.  There were 2 or 3 clusters of controllers spread throughout the building.  We tried swapping boards between controllers, swapping with new boards.
We asked the manufacturer for help, grounded the metal boxes.  Nothing solved it.  Finally, I had the sense to remove the grounds (opposite to what the manufacturer recommended).  Without grounds, the glitch was GONE.  It turned out that what was thought to be one building, was actually 2 buildings connected by an enclosed walk way.  The ground in the other building was contaminated by some other equipment.  We tried a different ground source, same problem.  Never did find out where the ground contamination came from... the customer that was very irritated at our system became very nice when we could prove it was his building ground that was at fault and wouldn't let us pin point the problem.  Perhaps it could have been the cleaners? Those long cords on vacuums could have had a short between neutral and ground?

So next time someone says "make sure it's grounded" you might want to just try the other way and leave no stone unturned!


From: <> on behalf of Ham Radio <bernard.murphy@...>
Sent: Thursday, September 17, 2020 10:34 PM
To: <>
Subject: Re: [cosmacelf] Noob question: examine arbitrary memory address? #ELF #Memory

Another Noob story (true)...nothing to do with 1802 but here it is anyway.

A whole team of engineers and designers spent weeks trying to figure out why a big telephone switch was crashing randomly.  

They had logic analyzes, digital storage scopes, heat probes, power monitors, etc - all to no avail.

Finally, a manager with grey hair came in the telephone switch room with a small AM transistor radio.  The grey haired manager ran the transistor radio up and down the telephone switch racks for about five minutes.  Finally, he pointed to one card in one rack and said “change that card’.  Sure enough, that card was defective.  The young engineers were dumbfounded !!
Bernie Murphy

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