Matek F411 Wing, iNav 2.1.0, DJI OcuSync AirModule, FrSky integration

[makattack]

Anyone have experience or perhaps insight into how one might get telemetry over softserial to a DJI OcuSync Air Module? I've got one of these connected up with a Matek F411-Wing, iNav 2.1.0, with a serialRX SBUS connection on one of the UARTs configured successfully, such that I can send RC signals from a FrSky X9D+, connected via a PPM trainer cable to the FrSky Race Edition Goggles.

The F411-Wing only has two UARTs, and the other UART is connected to a GPS receiver.

I was able to get smartport telemetry sent from iNav/F411W to the DJI Air Module and see the telemetry data reflected in the goggles OSD (limited to roll/pitch/battery/GPS/time armed) when I used one of the F411W's UARTs, but cannot get softserial to work for telemetry. I've configured the softserial ST1 pad (PA0 pin) for 19200 baud, and connected that one ST1 pin (TX output only) to the RX input of the Air Modules UART port. I left the TX port floating, and also tried pulling it up with a 1KOhm and 10KOhm resistor to no effect.

Hoping someone might have experience with this. I guess I can always go without telemetry, but it would be nice to have. Maybe my pull up setup is wrong with the wrong resistors? It's supposed to be a 3.3V port, but I have no idea what the draw would be.

 

[makattack]

LATEST UPDATE:

Ok, a bit more trouble-shooting via trial and error, and I've mostly figured it out. First off, in configuring telemetry with the DJI Air Module, it's not using smartport telemetry. It didn't seem to matter what setting I used under telemetry, including disabled. The DJI Air Module UART seems to process MSP (MultiWii Serial Protocol) and at that, only at baud rates of 115,200 bps. Nothing slower, and doesn't seem to auto sense/adjust. I tried different permutations of changing the baud rate with the Air Module connected to UART2 on the F411W flight controller, with powering up everything from scratch and it only works at 115200, which completely rules out softserial compatibility.

Ah well, lesson learned. You will need at least 3 UARTs if you want a GPS enabled, DJI OcuSync long range setup with SBUS control. Since the Air Module and the F411W both support PPM control as well, I thought I could just reconfigure ST1 (the softserial TX port) to be PPM instead. Turns out not to be the case. The PPM output from the Air Module is only used for head tracker control. Well... there are SBUS to PPM converters, so I suppose that's an option. There's also MSP RC control. That's next on the list to try out.

Since this will go on in a flying wing airframe, and is really just to give my friend and I a HD FPV (and long range) wing to experiment with, we'll get it working with some sacrifice in functionality. My friend owns both the DJI RE Goggles and Air Module, while I'm donating my FT Spear for this experiment.