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The TX backpack sends every CRSF telemetry frame as a unicast to its own UID address and expects an 802.11 ACK from a peer carrying that MAC (a bound VRX backpack). If no such peer is present (VRX switched off, telemetry consumed by a passive listener such as a ground station) or the peer is out of range, the WiFi stack retransmits every frame several times. While those retries run, esp_now_send() fails for the frames arriving from the TX module, and the return value is not checked, so most of the stream is dropped silently: with an iNav flight controller at 500 Hz only about a third of the GPS frames reached a listener, even at 1 m. The retries also occupy 2.4 GHz right next to the ELRS TX module for nothing. Register a send callback and count unacknowledged unicasts to the UID address. After 8 failures in a row, telemetry frames are sent as broadcast, which goes out exactly once without ACK or retry. Every 128 frames one unicast is tried, so a peer coming back in range switches delivery back to unicast. Bound VRX backpacks that acknowledge see no change at all; they filter on the sender MAC, so they also receive the broadcast frames. All other MSP traffic stays unicast.
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Fork-internal test PR to run the CI workflows for the upstream pull request ExpressLRS#245. Not for merging.