Hello,
I have a custom board, equiped with a Murata CMWX1ZZABZ, running a firmware based on the LoRa and SigFox libraries provided by ST. Several hundreds, if not thousand, units are currently depoyed. For the most part, everything is fine.
See the attached schematic for reference.
I recently discovered an issue regarding the external reset.
From time to time, it may occur that we need to reset the device using the NRST pin. Again, this was already made on hundreds of units with no problem. However, I've had several cases.
Here is the behaviour :
The device ends up no longer sending LoRa/SigFox frame, for unknown reason. Also for unknown reasons, the watchdog doesn't seem to be triggered ... or it is, the device doesn't restarts properly.
If i try to reset the device via the NRST pin, nothing occurs.
It's also impossible to reprogram/debug the firmware via SWD.
If I disconnect/reconnect the battery, the device restarts properly.
Looking at the oscilloscope, the reset signal is clean and so is the power supply.
My feeling is that the device restarts, but crashes/stucks during its init sequence. Most likelly when init the clock, as it's the very first operation.
However, I have no way to check that: I don't see any changing signal on the gpio.
This is very rare case, and impossible to reproduce as I don't know what's causing the issue.
What could be causing the issue ? How can the chip not be reboot by the NRST pin ?
Thanks.
Vincent
