crsf_rc: add bind command

[benjinne]

Solved Problem

Ability to bind using the crsf protocol

Fixes #23281

Solution

• based on spectrum bind method in rc_input and bind packet from betaflight source code
• adds capability to the crsf_rc module using cli or vehicle_command

Changelog Entry

For release notes:

crsf_rc: add bind command

Alternatives

Add to rc_input module if needed

Test coverage

• todo test on hardware

I assume vehicle command to bind comes from QGC and we may need to update QGC's UI

[dagar]

FYI this might get weird if other modules (px4io, other rc_input, etc) are running.

[benjinne]

I think in general there's only one rc module running per vehicle. If we expect multiple, then maybe we can handle this with the command parameters

[dagar]

Is there any acknowledgement or mechanism for checking?

[benjinne]

I didn't see any in the betaflight code or ardupilot code. To verify it was successful I think the assumption is you verify the receiver lights blink rapidly signifying it's in bind mode

[benjinne]

@dagar I've tested and verified that this works.
I verified both crsf_rc bind and using the spectrum bind button in QGC works although any spectrum option will work and it's a bit confusing. We'll need to update QGC to have a generic bind for crossfire and ELRS receivers.

[hamishwillee]

The https://mavlink.io/en/messages/common.html#MAV_CMD_START_RX_PAIR message that this hooks into assumes you're going to specify a type of RC. If it is possible to have multiple radios that might pair on a vehicle then you should add ELRS as an option to https://mavlink.io/en/messages/common.html#RC_TYPE and check the command for the type being set.

[hamishwillee]

QGC assumes Spektrum RC because that is the only thing that is supported by the message. Do you plan to update that section of QGC to allow ELRS to to be configured too? If not, how were you expecting this to be called?

Either way, we should document that this can be used and how in https://docs.px4.io/main/en/config/radio.html#additional-radio-setup

[benjinne]

The https://mavlink.io/en/messages/common.html#MAV_CMD_START_RX_PAIR message that this hooks into assumes you're going to specify a type of RC. If it is possible to have multiple radios that might pair on a vehicle then you should add ELRS as an option to https://mavlink.io/en/messages/common.html#RC_TYPE and check the command for the type being set.

Yeah I agree. Right now it accepts any bind message since most vehicles just have one RC receiver, but I can imagine having multiple. Not sure when I'll get around to it

QGC assumes Spektrum RC because that is the only thing that is supported by the message. Do you plan to update that section of QGC to allow ELRS to to be configured too? If not, how were you expecting this to be called?

Either way, we should document that this can be used and how in https://docs.px4.io/main/en/config/radio.html#additional-radio-setup

Either with the command-line or with a QGC button. Currently the spektrum bind button works, but it's a little confusing. I'm also not sure when I'll get around to it