Z80 embedded system debug session. Two flipping days working out why an NMI wasn't being captured by the kernel interrupt handler in a communications controller I was working on. The NMI handler religiously stopped working after ten minutes. Turned out some chump had bent the CPU _NMI pin in the socket of the device at the manufacturer and it wasn't contacting the socket reliably so when it warmed up it started floating. However, you couldn't see it with visual inspection. I assumed it was my fault and spent hours with the assembler and Z80 and vendor docs trying to work out why it wasn't working. Got miffed, plugged in a logic analyser which caused it to work perfectly.
Eventually I assumed the CPU was duff, gave a finger to the rules which involved not changing the hardware, yanked it and found the inverted pin. Grr!
Bear in mind this was MILSPEC and had gone through QC, soak and thermal testing.
Eventually I assumed the CPU was duff, gave a finger to the rules which involved not changing the hardware, yanked it and found the inverted pin. Grr!
Bear in mind this was MILSPEC and had gone through QC, soak and thermal testing.