INAV 7.1.2 on SpeedyBee F405 Wing Mini - I can't start Hott telemetry.

[solent710]

I realize that the Hott protocol is no longer very popular, but it is still present in INAV. Unfortunately, despite many attempts, I was unable to start it. The FC hardware is functional because with the S.Port protocol (and a two-transistor inverter + X6R receiver), telemetry works without any problems.

After switching to Hott mode, unfortunately, it does not. UART TX pin is 'high' and it is quite strong 'high' state. My receiver (GR-12L) is not able to pull it down to ground. It tries but voltage doesn't drop much. I even tried with 680 ohms to GND and results were very similar. So it doesn't look like a pin intended for bidirectional communication.

UART4 and UART1 behaves in the same way.

I also tried the 'old way' with half duplex ON and TX/RX 'diode combiner'. I can see receiver scanning for sensors but without even one response from the flight controller.

Maybe I missed something in the Hott telemetry configuration but I'm out of ideas.

[sensei-hacker]

I don't want you to feel like you're being ignored. It's just that most of us don't know much about HOTT. @Scavanger knows it if they are still around.

The F405 serial ports are in some ways less capable than the F3, F7, and H7 ports. The code for running both rx and TX on one pin may not work as easily on the F4. You might test an F7 FC if you have one available.

[solent710]

Thank you very much for your answer. Unfortunately I don't have other FCs. I'll dig into the source code a bit, I'll let you know here if something starts working.

[Scavanger]

I haven't used a Graupner/HOTT Eqiupment for years. But I didn't have the problems back then. Sorry, but I can't help much further.

[solent710]

I have to admit that I caused a false alarm. It is possible to connect the GR-12L receiver and the SpeedyBee F405 wing (I use separate RX and TX connected with a diode). My problem was that the Graupner receiver scans the HoTT bus only for a short while and if it does not detect any sensors, it goes into a standby mode in which it sends packets ignored by INAV (0x80 0x80). Maybe the original sensors respond to these packets but INAV does not.

But at least I learned how to compile INAV and debug with the good old 'printf' :-)

Thank you for all your answers.

[sensei-hacker]

Thanks for the follow up!
That may be useful to someone in the future.

If HOTT was more commonly used I would look into whether we should respond to the 0x80. As things are, other items are higher priority.