On our custom board, we have a dedicated hardware reset IC which toggles the nRF51822's nRST line low in response to a magic button press. The nRST line has an external 100k pullup to VDD.
In several months of regularly using this circuit to reset the nRF51, thrice I have seen the chip get into a state where pulling the nRST line low does not reset the chip. Once this occurs, nothing will reset the chip short of disconnecting the power; even manually shorting nRST to ground has no effect. The firmware and everything else continues to run normally, however, since the nRF51 will not reset I cannot reprogram the firmware until I cut the power.
I suspect the problem may be related to pin latchup given the sporadic nature of the issue. There are a few suggestions in the DevZone about adding --pinreset to nrfjprog.exe (here) and installing a bypass capacitor (here), both of which I've added to a test board with no luck.
Short of modifying the electrical design to actually disconnect the power for a reset, is there anything else I can do that might mitigate the problem?
