Embedded-C-Practice

Bare-metal Embedded C examples covering the fundamentals of microcontroller firmware development — register-level peripheral configuration, bit manipulation, and communication protocols. Written without HAL or framework abstractions to demonstrate understanding of what happens underneath.

Target hardware is STM32F4 (Nucleo-64), but the patterns apply to any ARM Cortex-M MCU.

---

Files

bit_manipulation.c

Core bit operation macros and functions used throughout embedded firmware — set, clear, toggle, read individual bits and multi-bit register fields. Includes practical examples simulating GPIO ODR register operations and STM32 MODER field writes, plus utility functions (power-of-2 check, Brian Kernighan's set-bit count, XOR swap) that come up in embedded interviews and real firmware work.

bare_metal_stm32.c

Direct register-level peripheral configuration on STM32F411 with no HAL, no CubeMX. Covers:

• Enabling peripheral clocks via RCC_AHB1ENR and RCC_APB1ENR
• GPIO mode, output type, speed, and pull configuration via MODER/OTYPER/OSPEEDR/PUPDR
• Atomic GPIO set/reset using BSRR
• USART2 init at 115200 baud with alternate function pin config
• GPIO input with pull-up for button reading This is what HAL_GPIO_Init() and HAL_UART_Init() generate under the hood.

uart_basics.c

UART communication patterns in bare-metal C:

• Polling TX with TXE flag — blocking single-byte and string transmit
• Polling RX with RXNE flag — blocking receive and line buffering
• ISR-driven RX with a power-of-2 ring buffer — correct pattern for production firmware where the main loop must not block
• Integer-to-string formatting for UART debug output without printf (avoids ~8KB of C stdlib overhead on small MCUs)
• USART2 IRQ handler with overrun error handling

---

Why no HAL?

HAL (Hardware Abstraction Layer) is useful for production code and portability. But understanding the registers underneath is what makes debugging possible when HAL behaves unexpectedly — which it does, especially around DMA, timing, and interrupt configuration. These examples exist to build that register-level understanding.

---

Tools

STM32F411RE ARM Cortex-M4 Embedded C GCC ARM STM32CubeIDE Keil ST-Link UART GPIO Bare-metal