Spektrum SRXL2 ESC: enable the driver and fix protocol decoding

[RobertoD91]

Spektrum SRXL2 Smart ESC support

Drives a Spektrum Smart ESC (Avian/Firma) directly from a UART TX pad over the single-wire half-duplex SRXL2 bus, replacing PWM and carrying ESC telemetry (RPM, voltage, current, FET temperature) back to the FC. The FC implements the SRXL2 bus-master role (device ID 0x21) per the official SpektrumRC/SRXL2 state machine.

Bench-validated on MATEKF405SE + Spektrum Smart ESC: handshake completes, motor responds to throttle, ESC answers telemetry polls.

Full documentation: docs/SRXL2_ESC.md (wiring, configuration, protocol details, debug_mode = SRXL2 reference, development notes).

What's included

• src/main/drivers/srxl2_esc.c/h: SRXL2 master driver — official handshake sequence (50ms addressed polls → ESC reply → final 0xFF broadcast handshake), 100Hz control frames, telemetry polling every 10th frame, 300µs half-duplex turnaround guard, DEBUG_SRXL2 counters.
• PWM_TYPE_SRXL2 motor protocol (no hardware timer), FUNCTION_SRXL2_ESC serial function (bit 28), USE_SRXL2_ESC gate (targets >512KB flash).
• ESC sensor integration for telemetry consumers (e.g. vbat_meter_type = ESC).

Issues found and fixed along the way

1. CRC16-CCITT byte order on RX validation (big-endian on wire, no swap on compare).
2. Current telemetry already in centiamps — removed wrong ×10 scaling.
3. Half-duplex: SERIAL_BIDIR (open-drain + pull-up, Betaflight-proven). SERIAL_BIDIR_PP floats the line between frames — reverted.
4. Handshake state machine: the ESC's unprompted destId 0 handshake is a request to answer, not a confirmation; the final 0xFF broadcast is required for the ESC to enter Running.
5. baudSupported = 0: advertising 400k (as the original code did) makes the ESC switch baud on the broadcast handshake and drop off the bus.
6. Throttle channel band: Spektrum channel values span ±150% travel (32768 = center); raw 0 decodes as an invalid −150% throttle and the ESC keeps beeping. Now mapped to the standard ±100% band 0x2AA0..0xD554.
7. Build fixes for non-DSHOT targets (pwmCompleteMotorUpdate guard) and fork CI (check-pg-versions.sh, log.c VLA folding, osd.c STATIC_ASSERT float literal on Apple clang).

Known limitations / follow-ups

• Single ESC (motor 0); no motor-pole RPM scaling.
• Telemetry display path under investigation (frames arrive and are parsed; consumer wiring being verified).
• ESC reverse channel transmitted but fixed to "forward" — reversible-ESC integration is future work.

Companion configurator PR: RobertoD91/inav-configurator#5

🤖 Generated with Claude Code

https://claude.ai/code/session_01GroYFi23gHDgj43xrTAVaY

[github-actions]

Test firmware build ready — commit f6509e6

Download firmware for PR #2

243 targets built. Find your board's .hex file by name on that page (e.g. MATEKF405SE.hex). Files are individually downloadable — no GitHub login required.

Development build for testing only. Use Full Chip Erase when flashing.