[Help!] Cannot connect to the flight stack firmware by USB.

[namasikanam]

Hi, we are trying to reproduce this amazing project. But we strangely stuck after just uploading the firmware. We are students from Tsinghua formal verification group, not very familiar with embedded developing and pixhawk. We really need and appreciate any help!

What we have done

What we try to reproduce is the stand-alone flight without mission computer.

1. Upload the provided factory USB bootloader firmware image of version 4 by JTAG/SWD debugger.
2. Upload the APM firmware to the FMU.
3. Insert a Micro SD card with the provided "px4io.bin" file in the root directory. The PX4IO firmware is upgraded and confirmed as this.
4. Upload the firmware in the galoisinc/smaccmpilot-build docker image.

Description of strange phenomenon

• After uploading the flight stack firmware image, the UI LED turns red (error) for a few seconds, and then turns solid green (armed, GPS). (video)
• If we shake the drone along arbitrary direction, the UI LED will turn red (error). When we stop shaking, the UI LED will turn solid green (armed, GPS).

BTW, do the meanings of the UI LED, which is controlled by the SMACCMPilot firmware, conform this PX4 User Guide?

• Besides, our computer can only detect the drone by USB during the first five seconds when the bootloader is active, after the first five seconds, the USB connection cannot be recognized any more.

Expected behavior

• The USB connection should be recognized after the bootloader.
• The UI LED should probably flutter blue (ready, no GPS) as we upload PX4 Pro Stable Release v1.12 flight stack.

Context

• Drone hardware: Pixhawk 2.4.8
  The board is bought from Taobao (a Chinese online shopping platform).
  In the description of the store, the version of Failsafe System-on-Chip is STM32F103. However, we find it is actually STM32F100 after we open the board.
  • Main System-on-Chip: STM32F427
  • Failsafe System-on-Chip: STM32F100
• Operating system: Ubuntu 20.04

[namasikanam]

Furthermore, we notice that the color of status LEDs are:

	PWR	B/E	ACT
FMU	solid green	solid amber	\
IO	solid green	solid amber	flashing blue

The solid amber of FMU B/E indicates that the firmware of the FMU seems in error. What possible reasons for that?

[namasikanam]

I tried to listen to any logging output from Serial 5, which I assume to be the system console port. But there is nothing when booting.

However, when I booted another firmware, PX4 Flight Stack Stable Release, I can capture the output from Serial 5 (shown below).

Is Serial 5 not the system console port of the SMACCMPilot firmware? If it is, the SMACCMPilot firmware seems to go into the error state even before any logging. How could it happen?