Autopilot fails to boot 1 in 10 times if Siyi A8 is connected

[rmackay9]

If a Siyi A8 is connect as described on the wiki (e.g. using Serial2) to a CubeOrange or CubeOrangePlus (and perhaps any other autopilot) and the two are powered up at the same time, the autopilot will fail to boot about 1/10th the time. This has been reproduced by at least two people using these versions:

• Copter 4.5.1
• Siyi A8 gimbal fw: 0.3.6, camera fw: 0.2.4 (the latest versions)

The issue does not occur if the autopilot and Siyi A8 are powered up at different time. E.g. Siyi before autopilot is OK, Siyi after autopilot is also OK.

The issues occurs whether the standard bootloader that comes with the CubeOrangePlus, or AP's bootloader is used. It also occurs regardless of whether BRD_SER2_RTSCTS = 0 or 2 (the default).

If the USB is then connected to a Windows PC the following error is shown.

The COM port does not appear in the device manager

Mission Planner's COM port list does not show the autopilot (not even the USB bootloader)

One guess is that the A8's serial output is perhaps tricking the autopilot's serial bootloader into think it wants to load a firmware

[rmackay9]

I've captured the startup packets from an A8 with a salea logic analyser here.