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saltylab-firmware/docs/SAUL-TEE-SYSTEM-REFERENCE.md
sl-firmware 5ef1f7e365 docs: full SAUL-TEE ESP32-S3 spec — pins, CAN, UART, RC mapping 
Complete hardware reference from hal@Orin spec (2026-04-04):
- docs/SAUL-TEE-SYSTEM-REFERENCE.md: authoritative pin/protocol/CAN reference
  ESP32-S3 BALANCE: QMI8658 SPI(IO38-42), GC9A01 LCD, SN65HVD230 CAN(IO43/44),
  inter-board UART(IO17/18)
  ESP32-S3 IO: Crossfire UART0(IO43/44), ELRS UART2(IO16/17), BTS7960(IO1-8),
  I2C(IO11/12), WS2812(IO13), buzzer/headlight/fan, arming btn, kill-sw, UART(IO18/21)
- Inter-board binary protocol: [0xAA][LEN][TYPE][PAYLOAD][CRC8] @ 460800 baud
- CAN: VESC L=68, R=56; Orin cmds 0x300-0x303; telemetry 0x400-0x401 @ 10Hz
- RC: CH5=ARM, CH6=ESTOP, CH7=speed-limit; CRSF loss >100ms = motors cut
- CLAUDE.md, TEAM.md, docs/AGENTS.md, docs/SALTYLAB.md updated with full spec

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
2026-04-04 08:25:24 -04:00

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SAUL-TEE System Reference — SaltyLab ESP32 Architecture

Authoritative source of truth for hardware, pins, protocols, and CAN assignments. Spec from hal@Orin, 2026-04-04.

Overview

Board Role MCU USB chip
ESP32-S3 BALANCE PID balance loop, CAN→VESCs, LCD display ESP32-S3 CH343 USB-serial
ESP32-S3 IO RC input, motor drivers, sensors, LEDs, peripherals ESP32-S3 JTAG USB (native)

Robot form factor: 4-wheel wagon — 870 × 510 × 550 mm, ~23 kg Power: 36 V LiPo, DC-DC → 5 V and 12 V rails Orin connection: CANable2 USB → 500 kbps CAN (same bus as VESCs)

ESP32-S3 BALANCE

Board

Waveshare ESP32-S3 Touch LCD 1.28

  • GC9A01 round 240×240 LCD
  • CST816S capacitive touch
  • QMI8658 6-axis IMU (accel + gyro, SPI)
  • CH343 USB-to-serial chip

Pin Assignments

Function GPIO Notes
QMI8658 IMU (SPI)
SCK IO39
MOSI IO38
MISO IO40
CS IO41
INT1 IO42 data-ready interrupt
GC9A01 LCD (shares SPI bus)
CS IO12
DC IO11
RST IO10
BL IO9 PWM backlight
CST816S Touch (I2C)
SDA IO4
SCL IO5
INT IO6
RST IO7
CAN — SN65HVD230 transceiver 500 kbps
TX IO43 → SN65HVD230 TXD
RX IO44 ← SN65HVD230 RXD
Inter-board UART (to IO board) 460800 baud
TX IO17
RX IO18

Responsibilities

  • Read QMI8658 @ 1 kHz (SPI, INT1-driven)
  • Complementary filter → pitch angle
  • PID balance loop (configurable Kp / Ki / Kd)
  • Send VESC speed commands via CAN (ID 68 = left, ID 56 = right)
  • Receive Orin velocity+mode commands via CAN (0x300–0x303)
  • Receive IO board status (arming, RC, faults) via UART protocol
  • Drive GC9A01 LCD: pitch, speed, battery %, error state
  • Enforce tilt cutoff at ±25°; IWDG 50 ms timeout
  • Publish telemetry on CAN 0x400–0x401 at 10 Hz

ESP32-S3 IO

Board

Bare ESP32-S3 devkit (JTAG USB)

Pin Assignments

Function GPIO Notes
TBS Crossfire RC — UART0 (primary)
RX IO44 CRSF frames from Crossfire RX
TX IO43 telemetry to Crossfire TX
ELRS failover — UART2 active if CRSF absent >100 ms
RX IO16
TX IO17
BTS7960 Motor Driver — Left
RPWM IO1 forward PWM
LPWM IO2 reverse PWM
R_EN IO3 right enable
L_EN IO4 left enable
BTS7960 Motor Driver — Right
RPWM IO5
LPWM IO6
R_EN IO7
L_EN IO8
I2C bus
SDA IO11
SCL IO12
NFC (PN532 or similar) I2C
Barometer (BMP280/BMP388) I2C
ToF (VL53L0X/VL53L1X) I2C
WS2812B LEDs
Data IO13
Outputs
Horn / buzzer IO14 PWM tone
Headlight IO15 PWM or digital
Fan IO16 (if ELRS not fitted on UART2)
Inputs
Arming button IO9 active-low, hold 3 s to arm
Kill switch sense IO10 hardware estop detect
Inter-board UART (to BALANCE board) 460800 baud
TX IO18
RX IO21

Responsibilities

  • Parse CRSF frames (TBS Crossfire, primary)
  • Parse ELRS frames (failover, activates if no CRSF for >100 ms)
  • Drive BTS7960 left/right PWM motor drivers
  • Read NFC, barometer, ToF via I2C
  • Drive WS2812B LEDs (armed/fault/idle patterns)
  • Control horn, headlight, fan, buzzer
  • Manage arming: hold button 3 s while upright → send ARM to BALANCE
  • Monitor kill switch input → immediate motor off + FAULT frame
  • Forward RC + sensor data to BALANCE via binary UART protocol
  • Report faults and RC-loss upstream

Inter-Board Binary Protocol (UART @ 460800 baud)

[0xAA][LEN][TYPE][PAYLOAD × LEN bytes][CRC8]
  • 0xAA — start byte
  • LEN — payload length in bytes (uint8)
  • TYPE — message type (uint8)
  • CRC8 — CRC-8/MAXIM over TYPE + PAYLOAD bytes

IO → BALANCE Messages

TYPE Name Payload Description
0x01 RC_CMD int16 throttle, int16 steer, uint8 flags flags: bit0=armed, bit1=kill
0x02 SENSOR uint16 tof_mm, int16 baro_delta_pa, uint8 nfc_present
0x03 FAULT uint8 fault_flags bit0=rc_loss, bit1=motor_fault, bit2=estop

BALANCE → IO Messages

TYPE Name Payload Description
0x10 STATE int16 pitch_x100, int16 pid_out, uint8 error_state
0x11 LED_CMD uint8 pattern, uint8 r, uint8 g, uint8 b
0x12 BUZZER uint8 tone_id, uint16 duration_ms

CAN Bus — 500 kbps

Node Assignments

Node CAN ID Role
VESC Left motor 68 Receives speed/duty via VESC CAN protocol
VESC Right motor 56 Receives speed/duty via VESC CAN protocol
ESP32-S3 BALANCE — Sends VESC commands; publishes telemetry
Jetson Orin (CANable2) — Sends velocity commands; receives telemetry

Frame Table

CAN ID Direction Description Rate
0x300 Orin → BALANCE Velocity cmd: int16 speed_mmps, int16 steer_mrad 20 Hz
0x301 Orin → BALANCE PID tuning: float Kp, float Ki, float Kd (3×4B IEEE-754) on demand
0x302 Orin → BALANCE Mode: uint8 (0=off, 1=balance, 2=manual, 3=estop) on demand
0x303 Orin → BALANCE Config: uint16 tilt_limit_x100, uint16 max_speed_mmps on demand
0x400 BALANCE → Orin Telemetry A: int16 pitch_x100, int16 pid_out, int16 speed_mmps, uint8 state 10 Hz
0x401 BALANCE → Orin Telemetry B: int16 vesc_l_rpm, int16 vesc_r_rpm, uint16 battery_mv, uint8 faults 10 Hz

RC Channel Mapping (TBS Crossfire / ELRS CRSF)

CH Function Range (µs) Notes
1 Steer (Roll) 988–2012 ±100% → ±max steer
2 Throttle (Pitch) 988–2012 forward / back speed
3 Spare 988–2012
4 Spare 988–2012
5 ARM switch <1500=disarm, >1500=arm SB on TX
6 ESTOP <1500=normal, >1500=kill SC on TX — checked first every loop
7 Speed limit 988–2012 maps to 10–100% speed cap
8 Spare

RC loss: No valid CRSF frame >100 ms → IO sends FAULT(rc_loss) → BALANCE cuts motors.

Safety Invariants

  1. Motors NEVER spin on power-on — 3 s button hold required while upright
  2. Tilt cutoff ±25° — immediate motor zero, manual re-arm required
  3. IWDG 50 ms — firmware hang → motors cut
  4. ESTOP RC channel checked first in every loop iteration
  5. Orin CAN timeout 500 ms → revert to RC-only mode
  6. Speed hard cap — start at 10%, increase in 10% increments only after stable tethered testing
  7. Never untethered until stable for 5+ continuous minutes tethered

USB Debug Commands (both boards, serial console)

help                     list commands
status                   print pitch, PID state, CAN stats, UART stats
pid <Kp> <Ki> <Kd>      set PID gains
arm                      arm (if upright and safe)
disarm                   disarm immediately
estop                    emergency stop (requires re-arm)
tilt_limit <deg>         set tilt cutoff angle (default 25)
speed_limit <pct>        set speed cap percentage (default 10)
can_stats                CAN bus counters (tx/rx/errors/busoff)
uart_stats               inter-board UART frame counters
reboot                   soft reboot