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Using the External Watchdog Timer

From the "Avionics" page of the PyCubed mainboard schematic.

⚠️
By default, PyCubed ships with the watch dog timer (WDT) DISABLED. Enable the WDT by soldering a 10k 0603 resistor to R42 (labeled "WDT EN" on the board).

Operation

The MAX706RESA "microprocessor supervisor" expects a rising or falling transition on WDI at least once every 1.6 seconds, otherwise it will pull the RESET line LOW (given the circuit configuration above). On PyCubed, this would result in a power reset of the primary flight computer (SAMD).

Software/Firmware

In order to pulse the WDI line at least once every 1.6s without incurring unnecessary processing overhead within CircuitPython, the pulse behavior is established at the C++ level when building CircuitPython for the PyCubed board.

  • pulsing of WDI is enabled in firmware by default.

⚠ CAUTION ⚠

Proper pulsing of WDI is performed at all times once the board is powered except when the microcontroller is in bootloader mode. If you've already enabled the WDT (soldering R42) and need to enter the bootloader (unlikely), you'll need to first remove R42.