STM32 Traffic Light Controller (FSM Based)

A robust, register-level traffic light control system implemented on the STM32F446RE (Nucleo-64). This project demonstrates a Non-blocking Finite State Machine (FSM) approach to handle car and pedestrian traffic synchronization with real-time button interrupts and rate-limiting logic.

Features

• Non-blocking Logic: Uses a global timer reference instead of delay() functions, allowing the MCU to remain responsive.
• Finite State Machine (FSM): Clean state transitions (Red -> Yellow -> Green) for both car and pedestrian lanes.
• Interrupt-Driven Button: Pedestrian requests are handled via EXTI (External Interrupt) for immediate response.
• Smart Rate Limiting: "Anti-vandal" logic ensures the pedestrian button only triggers a phase change once every 60 seconds.
• Register-Level Programming: Core peripherals (GPIO, RCC, TIM2, SYSCFG) are configured directly via registers for maximum performance and educational depth.

---

🛠 Hardware Configuration

Component	MCU Pin	Logic	Function
Car Red LED	PA10	High = ON	Stop signal for cars
Car Yellow LED	PB5	High = ON	Warning signal for cars
Car Green LED	PB4	High = ON	Go signal for cars
Pedestrian Red LED	PC0	High = ON	Stop signal for pedestrians
Pedestrian Green LED	PC1	High = ON	Go signal for pedestrians
Pedestrian Button	PB0	Pull-up	Active Low (Interrupt)

---

⏱ Timing Logic

The system operates on a Global Time Reference principle. Instead of halting the processor, we calculate the time elapsed since a state started.

State	Car Signal	Pedestrian Signal	Duration
CAR_RED_LIGHT	Red	Green (Blinks at end)	10 Seconds
CAR_YELLOW_LIGHT	Yellow	Red	4 Seconds
CAR_GREEN_LIGHT	Green	Red	20 Seconds

---

💻 Code Structure

File	Purpose
clock.c / .h	Timer 2 configuration (Hardware 1Hz tick)
gpio.c / .h	Pin definitions and EXTI Interrupt Handler
rcc.c / .h	System clock configuration (84MHz)
main.c	Main loop with FSM transition logic

---