sl-firmware
accf7fdf39
Protocol choice: implemented from spec (CRSFforArduino needs Arduino
framework; Betaflight extraction has deep scheduler dependencies).
Protocol verified against Betaflight src/main/rx/crsf.c + CRSF spec.
crsf.c:
- UART4 PA0=TX/PA1=RX (GPIO_AF8_UART4), 420000 baud 8N1, oversampling×8
APB1=54MHz → BRR=0x101 → 418604 baud (0.33% error, within spec)
- DMA1 Stream2 Channel4, circular 64-byte buffer, IDLE interrupt
DMA half/complete callbacks drain buffer; IDLE fires at frame boundary
- CRC8 DVB-S2 (polynomial 0xD5) validated on every frame
- Parser state machine: SYNC(0xC8)→LEN→DATA with length sanity check
- 11-bit channel unpack for all 16 channels from 22-byte payload
- RC channels frame (0x16): unpacks 16ch, updates last_rx_ms + armed
- Link stats frame (0x14): captures RSSI dBm, LQ%, SNR dB
crsf.h: added rssi_dbm, link_quality, snr fields to CRSFState
config.h: CRSF_ARM_THRESHOLD=1750, CRSF_STEER_MAX=400, CRSF_FAILSAFE_MS=300
main.c:
- crsf_init() called after motor_driver_init()
- RC failsafe: disarm if (now - last_rx_ms) > CRSF_FAILSAFE_MS, but only
after RC was first seen (last_rx_ms != 0) — USB-only mode unaffected
- RC arm: CH5 rising edge → safety_arm_start(); falling edge → disarm
Same ARMING_HOLD_MS interlock as USB arm command
- RC steer: CH1 → crsf_to_range() → ±CRSF_STEER_MAX → motor_driver steer
- RSSI/LQ: appended to JSON when safety_rc_alive() ("rssi","lq" fields)
ui/index.html: hidden RC RSSI row revealed on first packet with rssi/lq
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>