CRSFDude — Session Retro

What slowed us down

Trial-and-error on half-duplex pin switching

~15 iterations of GPIO matrix / uart_set_line_inverse / open-drain combos. Each required flash + test + radio restart. Should have searched the internet earlier for existing implementations (mLRS, ESP32 forums). Had to be nudged twice to do web searches.

Lesson: Search for working reference implementations before trying to figure out low-level hardware behavior from scratch.

Misdiagnosing the radio freeze

Many iterations assuming it was a pin release problem. It was actually a protocol problem (missing Device Ping handshake). Only found it after cloning EdgeTX and reading the source.

Lesson: When behavior is “works once then stops forever”, think protocol state machine, not just hardware.

Not reading the CRSF spec first

The inverted signal is documented. The half-duplex timing is documented. Could have skipped the auto-detect detour by reading the spec up front.

How to go faster next time

Point at reference code early. Best unblocking moves were cloning EdgeTX and linking the mLRS wiki. Reading existing code beats guessing hardware behavior.
Full hardware setup up front. “Single wire, half-duplex, JR bay, ESP32-C3” from the start would have skipped several dead ends (two-pin attempts, wrong TX pin assumptions).
Push for web searches sooner. Both times it was suggested, it unblocked us (mLRS implementation, ESP32 forum).
Establish test protocol early. “Restart radio between tests” wasn’t obvious at first. A few times we thought code was broken but the radio was just stuck from a previous attempt.

What went well

Auto-detect baud scanner was great for initial signal discovery
Incremental approach (RX first → TX → telemetry) kept momentum
Live testing + pasting serial output made diagnosis fast and clear
Reading the EdgeTX source was the breakthrough — wouldn’t have found the handshake any other way
End result is genuinely useful: standalone ESP32-C3 CRSF module library with half-duplex TX and EdgeTX handshake support