Incoming Mavlink telemetry affects outgoing telemetry rate

[RomanLut]

Mavlink RC command have been implemented recently: #6738 👏

It allows to use single UART for RC and telemetry ✔️

Unfortunately RC_CHANNELS_OVERRIDE can not be sent with rate comparable to SBUS because incoming telemetry messages affect outgoing telemetry rate ❌

At 50 Hz, outgoing telemetry is not emited at all.

telemetry\mavlink.h:

#define TELEMETRY_MAVLINK_MAXRATE       50
#define TELEMETRY_MAVLINK_DELAY         ((1000 * 1000) / TELEMETRY_MAVLINK_MAXRATE)


    // If we did serve data on incoming request - skip next scheduled messages batch to avoid link clogging
    if (processMAVLinkIncomingTelemetry()) {
        incomingRequestServed = true;
    }

    if ((currentTimeUs - lastMavlinkMessage) >= TELEMETRY_MAVLINK_DELAY) {
        // Only process scheduled data if we didn't serve any incoming request this cycle
        if (!incomingRequestServed) {
            processMAVLinkTelemetry(currentTimeUs);
        }
        lastMavlinkMessage = currentTimeUs;
        incomingRequestServed = false;
    }

I gues code above was added to support half-duplex links.

I would like to fix this and do a PR, but first I would like to discuss how to handle this problem.

I see the following solutions:

1. Remove incomingRequestServed flag completely.
2. Add a setting mavlink_half_duplex default true. If set to false, incomingRequestServed will be disabled.
3. let RC_CHANNELS_OVERRIDE not affect incomingRequestServed flag.

Which solution would be appropriate?

[RomanLut]

Ok I rephrase: which pull request will be accepted? 😃

[payor-ma]

Based on a quick search of github the mavlink_maxrate seems to come from cleanflight and has been carried on since then. Seems like a bit of a hack that worked in the context of it being used for mostly unidirectional telemetry and not being fully utilised in cleanflight.

[RomanLut]

Ok, there is "Receiver protocol half-duplex" box in configuratior:

It can be used to set mavlink protocol half/full duplex if RC protocol is "Mavlink".