[kabouseng]

An embedded CPU would sometimes latch-up when going to sleep. This wasn't seen during development, only reported in the field with very little in the error report, just something like "It stops working, reboot it works again"

Eventually we found the internal JTAG pull up resistances would not be sufficient at certain voltages / temperatures. So it wasn't latchup in the end but the JTAG would halt the processor.

We only found it after days of testing in an oven cycling temperature while stimulating a coil (RF field) close to the device while varying the supply voltage to cause the condition.

All the while the client is not happy that his devices randomly stops working, so we were under quite a bit of pressure.

And of course we only started looking at the hardware after we spent quite a bit of time thinking it was a software bug somewhere.