I have a Thingy:91 connected to a Garmin LIDAR Lite v4 (built on the nRF52840) via four GPIO cables. The code running on the Garmin reads one GPIO pin to signal a measurement and toggles another one when the measurement is complete. The two devices communicate exactly as expected, but ONLY when the debug cable is still connected to the Garmin.
I've used a voltmeter to verify that the Thingy:91 continues to signal for a new measurement, but after the debug cable is removed, the Garmin sends one more pulse and then stops. When I plug the debug cable back in, JLinkRTTLogger shows that the program has picked up right where it left off. I've tried starting the devices without any debug cables plugged in, but this also causes the Garmin to stop after a single measurement has occurred.
Garmin has not provided a hardware schematic showing how the internal nRF52840 is connected to the LIDAR sensor, and their driver library is pre-compiled. Is there any explanation for why the clock would stop without an external debug probe connected?
