We have several units of a custom carrier board, which we’ve used successfully over the past half year. However recently, we’ve discovered that a few units have started to fail to boot.
Under normal circumstances, the LEDs come on (one flashing, one solid), and the device shows up as “Legacy FMU” in device manager, then boots (custom Ardupilot branch) and changes COM port number and name to “ProfiCNC CUBE F4 FMU”. On at least one board it doesn’t always start up and stays in the mode where the LEDs are on and showing as “Legacy FMU” in device manager. After moving the cube to another custom carrier board or the official ADS-B carrier, it consistently boots.
My question is: Which tests does the Cube run before it finishes its boot sequence? What signals on the carrier board could cause it to stay in what I suppose is the bootloader? Alternatively, is the source code for the bootloader available, so I can see what it does?
Thanks in advance.