This project toggles an onboard LED connected to GPIOA Pin 5 of an STM32 microcontroller by directly accessing memory-mapped registers using macros. It avoids using HAL or CMSIS libraries and focuses purely on register-level embedded C.

• LED Connection:
  • Port: GPIOA(Port A)
  • Pin: 5

• Purpose: Starting base address for peripheral registers in STM32.
• UL: Stands for Unsigned Long to ensure it's treated as a 32-bit constant.

• Purpose: Offset to AHB1 peripheral block from PERIPH_BASE.

• Usage: Base address for AHB1 peripherals like GPIO, RCC, etc.

• GPIOA offset from AHB1 base.

• Usage: Base address for GPIOA registers.

• RCC (Reset and Clock Control) offset from AHB1 base.

• Base address for RCC control registers.

• Offset of the AHB1 peripheral clock enable register.

• Points to RCC register enabling AHB1 clocks (like GPIOA).

• Points to GPIOA’s mode register (MODER).

• Offset of Output Data Register (ODR) in GPIO.

• Used to set or clear GPIO output pins like PA5.

• Enables GPIOA clock in RCC register.

• Bitmask for setting Pin 5 of GPIOA.

• Bitmask for clearing Pin 5 of GPIOA.

void delay(volatile unsigned int time)

• A simple software delay using nested loops.
• Not accurate for real-time use.

This project demonstrates:

• Enabling GPIOA via RCC.
• Setting PA5 as output.
• Writing 1 and 0 to PA5 using ODR for LED on/off.
• Using only low-level register macros without any libraries.