STM32 Switch Table for SZEmission

The switch table is the "brain" of the car, used for controlling most functions like lights, wiper, and brake. It processes the inputs from the switches, steering wheel and pedal then compiles them into it's state and sends that out over the CAN bus. It can also send motor control commands when the override switch is turned off.

Features

1. State Broadcasting: Sends a CAN message every 50ms about its own state (switch positions, throttle position)
2. Wiper Control: Controls the wiper converter and servo with PWM
3. Throttle Input: Reads and filters the analog potentiometer on the throttle pedal
4. Motor Control: Optionally sends motor control CAN messages

Test hardware

Nucleo C092RC Development Board

• Microcontroller: STM32C092RCTx (LQFP64)
• Clock: Internal HSI oscillator running at 48MHz
• CAN Interface: FDCAN1 using the on-board CAN transceiver
• Programmer/Debugger: Nucleo built-in ST-Link

Communication Protocols

This controller uses 4 types of IO to achieve its functionality:

• CAN bus for communicating with the various components of the car
• GPIO to read switch positions and control some outputs
• ADC (Analog to Digital conversion) to read the throttle pedal potentiometer
• PWM for controlling the wiper servo motor

Pin Configuration

CAN Bus

Signal	Pin	Direction
FDCAN1_RX	PC2	Input
FDCAN1_TX	PC3	Output

GPIO Inputs (Switches)

Function	Name	Pin	Type
Switch used to enable lights	SW_LIGHTS	PC8	Digital Input
Wiper on/off	SW_WIPER	PC6	Digital Input
Hazard signal	SW_HAZARD	PC13	Digital Input
Autonomous mode switch	SW_AUTO	PC11	Digital Input
Motor control override	SW_MC_OW	PC7	Digital Input
Headlight switch	SW_HEADLIGHT	PC0	Digital Input
Shell relay input	IN_SHELL_RELAY	PC1	Digital Input
Brake pedal input	IN_BRAKE	PC12	Digital Input

GPIO Outputs

Function	Name	Pin	Type
Wiper converter enable	OUT_WIPER_CONVERTER	PD3	Digital Output

ADC Input

Function	Name	Pin
Throttle Potentiometer	ADC1_IN0	PA0

PWM Output

Function	Timer	Channel	Pin
Wiper Servo Control	TIM2	CH1	PA5

CAN Bus Messages

Received Messages

ID	ID Type	Name	Purpose
0x185	Standard	Sync State	No idea
0x190	Standard	Steering Wheel	State of buttons and position of switches on the steering wheel
0x123	Standard	RPM Measurement	RPM data from the posigion sensor

Steering Wheel State (0x190) Bit Fields

Byte 0 (STW_STATE_A):
  Bit 0: ACC (Cruise Control Activate)
  Bit 1: DRIVE (Drive Mode)
  Bit 2: REVERSE (Reverse Mode)
  Bit 3: LAP (Lap timing signal)
  Bit 4: TS_L (Traction Control Left)
  Bit 5: TS_R (Traction Control Right)
  Bit 6: FUNCTION1 (Reserved)
  Bit 7: FUNCTION2 (Reserved)

Bytes 1-3: Position of the 3 switches on the steering wheel (STW_STATE_B/C/D)

Transmitted Messages

ID	Type	Purpose	Data Format	Rate
0x129	Standard	VCU State	Bytes 0-1: VCU_STATE_A/B, Bytes 2-5: Throttle % (fixed-point)	20Hz
0xA51	Extended	Motor Control	Bytes 0-3: Throttle reference (fixed-point, signed)	20Hz

VCU State (0x129) Bit Fields

Byte 0 (VCU_STATE_A):
  Bit 0: HEADLIGHT
  Bit 1: HAZARD
  Bit 2: AUTO
  Bit 3: BRAKE
  Bit 4: LIGHTS_ENABLE
  Bit 5: MC_OW (Motor Control Override)
  Bit 6: WIPER
  Bit 7: Reserved

Byte 1 (VCU_STATE_B):
  Bit 0: RELAY_NO
  Bit 1: RELAY_NC
  Bits 2-7: Reserved

Code Structure

This code is designed to minimize the amount of user code in generated files. The main working logic is in user.c and user.h.

Directory Breakdown

sw_table_stm32/
├── sw_table_stm32.ioc            # STM32CubeIDE pin/peripheral configuration
├── sw_table_stm32.pdf            # Auto-generated hardware pinout diagram
├── Core/
│   ├── Inc/
│   │   ├── main.h               # Generated header (pin definitions)
│   │   └── user.h               # User-defined functions and structures
│   ├── Src/
│   │   ├── main.c               # Main entry point and initialization
│   │   └── user.c               # User-defined functions (motor control, CAN, GPIO)

Key Files

• main.c: System initialization, timer setup, interrupt handlers and main loop entry point
• user.c: Core application logic including CAN communication, GPIO control, and throttle processing
• user.h: Data structures, function declarations, and most importantly declarations for constants

Timer Configuration

• TIM1: Base timer for interval management (1ms period)
  • Used for CAN message intervals (20Hz)
  • Used for wiper control intervals (750ms)
• TIM2: PWM timer for wiper servo control (50Hz clock)

Development Guidelines

• Use fixed-point math instead of floating-point (no FPU)
• Keep ISRs short: Set flags and do the actual processing in main loop

Power Optimization

See TODO.md for a detailed power optimization roadmap. Key strategies:

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Authors

Created by SZEnergy Team for Shell Eco Marathon

• Váradi Marcell (varma02@GitHub)