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STM32F446xx Bare Metal Driver Development

🚀 Bare-metal driver development for STM32F446RE without using HAL libraries. This project focuses on low-level register programming, driver abstraction, interrupt handling, and embedded system design.

📊 Current Status

  • Version: v0.4.0

  • Status:

    • ✅ GPIO Driver Complete
    • ✅ SPI Driver Complete (Polling + Interrupt APIs)
    • ✅ I2C Driver Complete (Polling + Interrupt APIs)
    • ✅ USART/UART Driver Complete (Polling + Interrupt APIs)

  • Next Target: TIM Driver

📌 Overview

This repository contains a custom driver framework built completely from scratch for the STM32F446RE MCU.

The main goal of this project is to:

  • Understand STM32 peripherals at register level
  • Build reusable and scalable embedded drivers
  • Learn industrial-style driver architecture
  • Develop strong debugging and low-level programming skills

No HAL or external abstraction libraries are used.

🧩 Features (Version-wise)

✅ v0.1.0 - GPIO Driver

GPIO Features

  • Peripheral Clock Control APIs
  • GPIO Initialization APIs
  • Input / Output Mode Configuration
  • Push-Pull / Open-Drain Configuration
  • Speed Configuration
  • Pull-up / Pull-down Configuration
  • GPIO Read/Write APIs
  • Interrupt-Based GPIO Handling (EXTI)
  • IRQ Priority Configuration
  • Multiple GPIO Test Applications

✅ v0.2.0 - SPI Driver

SPI Core Features

  • SPI Peripheral Initialization
  • Master / Slave Mode
  • Full Duplex / Half Duplex / Simplex RX Only
  • Clock Polarity (CPOL)
  • Clock Phase (CPHA)
  • Software Slave Management (SSM)
  • Hardware NSS Output Management (SSOE)
  • Configurable Baud Rate Prescaler
  • 8-bit and 16-bit Data Frame Support

SPI Polling APIs

  • Blocking Transmit API
  • Blocking Receive API
  • Full-Duplex Transmit/Receive API
  • Busy Flag Handling
  • Proper TXE/RXNE Synchronization

SPI Interrupt APIs

  • Interrupt-Based Transmission
  • Interrupt-Based Reception
  • TXE Interrupt Handling
  • RXNE Interrupt Handling
  • Overrun (OVR) Error Interrupt Handling
  • IRQ Enable/Disable APIs
  • NVIC Priority Configuration APIs
  • Application Callback Mechanism

SPI Driver Improvements

  • Proper Volatile Register Access
  • Explicit 8-bit and 16-bit Register Access Handling
  • Even-Length Validation for 16-bit Transfers
  • Safe Interrupt Close/Reset Handling
  • OVR Flag Clearing Sequence
  • Improved Register-Level Documentation

✅ v0.3.0 - I2C Driver

I2C Core Features

  • I2C Peripheral Initialization
  • Peripheral Clock Management
  • Peripheral Enable/Disable Control
  • Standard Mode (100 kHz) Support
  • Fast Mode (400 kHz) Support
  • Fast Mode Duty Cycle Configuration
  • Own Address Configuration
  • ACK Enable/Disable Control
  • START Condition Generation
  • STOP Condition Generation
  • Address Phase Management
  • APB1 Clock-Based Timing Calculation
  • CCR Calculation
  • TRISE Calculation

I2C Polling APIs

  • Master Transmit (Blocking)
  • Master Receive (Blocking)
  • Single-Byte Reception Handling
  • Multi-Byte Reception Handling
  • ACK/NACK Management
  • Repeated START Support
  • Address Flag Handling
  • TXE/RXNE Polling
  • BTF Synchronization
  • Communication Completion Handling

I2C Interrupt APIs

  • Master Transmit (Interrupt Mode)
  • Master Receive (Interrupt Mode)
  • Event Interrupt Handling
  • Error Interrupt Handling
  • TXE Interrupt Processing
  • RXNE Interrupt Processing
  • SB Event Handling
  • ADDR Event Handling
  • BTF Event Handling
  • STOPF Event Handling

I2C Error Handling

  • Bus Error (BERR)
  • Arbitration Lost (ARLO)
  • Acknowledge Failure (AF)
  • Overrun/Underrun (OVR)
  • Timeout Detection
  • Application Error Callback Notification

I2C Slave Features

  • Slave Transmit Support
  • Slave Receive Support
  • Slave Event Callback Mechanism
  • Data Request Callback
  • Data Receive Callback
  • STOP Detection Callback

I2C Driver Improvements

  • STM32-Compliant ADDR Flag Clearing
  • Proper Single-Byte Receive Sequence
  • Correct ACK/NACK Timing Control
  • Repeated START Transaction Support
  • Interrupt-Based State Machine
  • Safe Transmission/Reception Close Handling
  • Application Callback Architecture
  • Enhanced Documentation and Register-Level Comments

✅ v0.4.0 - USART / UART Driver

USART Core Features

  • USART Peripheral Initialization
  • Peripheral Clock Management
  • Peripheral Enable/Disable Control
  • Baud Rate Configuration
  • APB1/APB2 Clock Based Baud Rate Calculation
  • Oversampling by 8 Support
  • Oversampling by 16 Support
  • TX Only / RX Only / TX-RX Modes
  • Configurable Stop Bits
  • 8-bit Word Length Support
  • 9-bit Word Length Support
  • Even Parity Support
  • Odd Parity Support
  • CTS Flow Control
  • RTS Flow Control
  • CTS/RTS Combined Flow Control

USART Polling APIs

  • Blocking Transmission API
  • Blocking Reception API
  • TXE Flag Synchronization
  • RXNE Flag Synchronization
  • Transmission Complete (TC) Handling
  • 8-bit Data Transfers
  • 9-bit Data Transfers
  • Parity-Aware Data Handling

USART Interrupt APIs

  • Interrupt-Based Transmission
  • Interrupt-Based Reception
  • TXE Interrupt Handling
  • TC Interrupt Handling
  • RXNE Interrupt Handling
  • IRQ Enable/Disable APIs
  • NVIC Priority Configuration APIs
  • Application Callback Mechanism
  • Non-Blocking Communication Support

USART Event Handling

  • Transmission Complete Event
  • Reception Complete Event
  • CTS Event Detection
  • IDLE Line Detection Event

USART Error Handling

  • Overrun Error (ORE)
  • Framing Error (FE)
  • Noise Error (NF)
  • Error Callback Notification

USART Driver Improvements

  • Accurate BRR Register Calculation
  • APB1/APB2 Aware Baud Generation
  • Support for Oversampling by 8 and 16
  • Proper 8-bit and 9-bit Data Access
  • Safe Interrupt State Management
  • Automatic Interrupt Disable on Completion
  • RXNE Flush Utility for Stale Data Handling
  • Enhanced Register-Level Documentation

🏗️ Project Structure

.
├── drivers/        → Peripheral drivers (GPIO, SPI, I2C, USART, TIM, etc.)
├── bsp/            → Board Support Package (Nucleo-F446RE)
├── applications/   → Application layer code
├── devices/        → External device drivers
├── mcu/            → MCU-specific headers
├── Startup/        → Startup assembly code
├── test/           → Driver test programs

🎯 Goals

  • Understand STM32 registers deeply
  • Build reusable driver architecture
  • Avoid HAL and write everything from scratch
  • Improve interrupt-driven peripheral handling
  • Learn industrial embedded driver design

Prepare drivers for:

  • GPIO
  • SPI
  • I2C
  • USART
  • TIM
  • PWM
  • ADC
  • CAN
  • DMA
  • RTOS Integration
  • Bootloader Development

🔖 Versioning

This project follows Semantic Versioning:

MAJOR.MINOR.PATCH
Version Description
v0.1.0 GPIO Driver Complete
v0.2.0 SPI Driver Added
v0.3.0 I2C Driver Added
v0.4.0 USART/UART Driver Added
v1.0.0 Stable Driver Framework (Future Goal)

🚀 Future Work

  • GPIO Driver
  • SPI Driver
  • I2C Driver
  • USART/UART Driver
  • SPI Driver Refactor (Industrial-Grade IT/DMA Architecture)
  • Timer Driver
  • PWM Driver
  • ADC Driver
  • DMA Support
  • RTOS Integration (FreeRTOS)
  • Bootloader Development

🧪 Testing

Test applications are available under:

test/

Test Directory

test
├── 001_led_toggle_pp_od_gpio.c
├── 002_inbuilt_led_button_gpio.c
├── 003_external_led_button_gpio.c
├── 004_button_interrupt_gpio.c
├── 005_interrupt_delay_halt_test_gpio.c
├── 006_spi_tx_testing.c
├── 007_spi_master_tx_rx_fd.c
├── 008_spi_slave_rx_tx_fd.c
├── 009_spi_master_tx_rx_fd_it.c
├── 010_spi_slave_rx_tx_fd_it.c
├── 011_i2c_master_tx_testing.c
├── 012_i2c_master_rx_testing.c
├── 013_i2c_master_rx_testing_it.c
├── 014_i2c_slave_tx_string.c
├── 015_i2c_slave_tx_string2.c
├── 016_uart_tx.c
├── 017_uart_case_exchange.c
├── AHT10_I2C.c
├── rtc_app.c 
├── gpio_app_keyboard_test.c
└── RFID-RC522_SPI.c

GPIO Tests

Test File Description
001_led_toggle_pp_od_gpio.c Push-Pull and Open-Drain output validation
002_inbuilt_led_button_gpio.c On-board button and LED interaction
003_external_led_button_gpio.c External button and LED interfacing
004_button_interrupt_gpio.c GPIO interrupt handling using EXTI
005_interrupt_delay_halt_test_gpio.c Interrupt latency and blocking behavior study
gpio_app_keyboard_test.c Matrix keyboard GPIO application testing

SPI Tests

Test File Description
006_spi_tx_testing.c Basic SPI transmission testing
007_spi_master_tx_rx_fd.c Full-duplex master communication
008_spi_slave_rx_tx_fd.c Full-duplex slave communication
009_spi_master_tx_rx_fd_it.c Interrupt-driven master communication
010_spi_slave_rx_tx_fd_it.c Interrupt-driven slave communication
RFID-RC522_SPI.c RFID-RC522 module interfacing using SPI

I2C Tests

Test File Description
011_i2c_master_tx_testing.c Master transmit operation validation
012_i2c_master_rx_testing.c Master receive operation validation
013_i2c_master_rx_testing_it.c Interrupt-driven master receive testing
014_i2c_slave_tx_string.c Slave transmit functionality
015_i2c_slave_tx_string2.c Advanced slave transmit testing
AHT10_I2C.c Real sensor interfacing using AHT10 temperature and humidity sensor
rtc_app.c Real time clock interfacing using DS1307, bsp, device driver added

USART and UART Tests

Test File Description
016_uart_tx.c polling transmit operation validation
017_uart_case_exchange.c interrupt receive operation validation

Validation Coverage

GPIO

  • Input and Output Modes
  • Push-Pull Configuration
  • Open-Drain Configuration
  • External Interrupt Handling
  • Button Debouncing Experiments
  • GPIO-Based Keyboard Interface

SPI

  • Polling-Based Communication
  • Interrupt-Based Communication
  • Master Mode Operation
  • Slave Mode Operation
  • Full-Duplex Data Transfer
  • External Device Communication (RC522 RFID)

I2C

  • Master Transmit Operations
  • Master Receive Operations
  • Interrupt-Based Reception
  • Slave Transmit Operations
  • ACK/NACK Handling
  • START and Repeated START Sequences
  • Real Sensor Communication (AHT10)
  • Real Time Clock (DS1307)
  • Multi-Byte Data Transfers
  • Event and Error Interrupt Validation

USART

  • Polling Transmission
  • Polling Reception
  • Interrupt-Based Communication
  • TXE/TC/RXNE Event Handling
  • Parity Handling
  • Error Event Validation

🛠️ Build & Run

Toolchain

  • ARM GCC

IDE

  • STM32CubeIDE
  • Makefile-Based Builds Possible

Steps

  1. Import project into STM32CubeIDE
  2. Build the project
  3. Flash to STM32F446RE board
  4. Run test applications from test/

⚙️ Hardware Used

  • STM32F446RE (Nucleo Board)

📚 Learning Focus

  • Embedded C Programming
  • Register-Level MCU Control
  • Pointer and Memory Manipulation
  • Peripheral Driver Abstraction
  • Interrupt Handling
  • Embedded Debugging
  • Bare-Metal Architecture Design
  • Hardware Register Access Patterns

🧠 Key Concepts Practiced

  • Memory-Mapped I/O
  • Volatile Register Access
  • Pointer Casting
  • Register Bit Manipulation
  • Interrupt-Driven Communication
  • Peripheral State Management
  • SPI Communication Protocol
  • I2C Communication Protocol
  • USART Communication Protocol
  • ACK/NACK Handling
  • Hardware/Software Synchronization
  • Embedded API Design

👨‍💻 Author

Shree Chandan Samal

⭐ Notes

This is a learning-driven project focused on understanding embedded systems deeply through practical driver development.

The codebase will continuously evolve as new peripherals, improved architectures, advanced debugging techniques, and industrial-grade embedded concepts are explored.

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Custom Bare Metal Driver layer for NUCLEO-F446XX

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gpio i2c stm32 stm spi uart usart baremetal nucleo-f446re

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Releases 2

v0.4.0 - USART/UART Driver Complete Latest
Jun 13, 2026
+ 1 release

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