MCAL Overview

Supported STM32 families: F4 · G4 · H5 · U5
Not supported: H7, L4

Standardized software interface to STM32 internal peripherals, built for modularity, portability, and testability.

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Overview

The Microcontroller Abstraction Layer (MCAL) sits directly on top of the hardware registers and provides a clean, unified API for accessing STM32 internal peripherals. Higher-level software components interact with hardware through this layer — without any knowledge of low-level register details.

MCAL is part of the BSP (Board Support Package) and leverages CMSIS and STM32 LL (Low-Layer) drivers for register-level access.

Key design goal: one peripheral, one interface. For example, the I2C driver can internally manage DMA without requiring the user to configure the DMA module separately — all dependency handling is encapsulated within the driver itself.

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Architecture

┌─────────────────────────────────────┐
│         Application Layer           │
├─────────────────────────────────────┤
│              MCAL                   │
│  (Gpio, Usart, Rcc, I2C, SPI, ...)  │
├─────────────────────────────────────┤
│   RAL — Register Abstraction Layer  │
│     (CMSIS + STM32 LL Drivers)      │
├─────────────────────────────────────┤
│         STM32 Hardware              │
└─────────────────────────────────────┘

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Supported Peripherals

Peripheral	Description
GPIO	General-Purpose Input/Output
USART / UART	Serial communication
SPI	Serial Peripheral Interface
I2C	Inter-Integrated Circuit (with optional DMA)
Timers	General-purpose and advanced timers
ADC / DAC	Analog-to-Digital / Digital-to-Analog conversion
NVIC / EXTI	Interrupt controller and external interrupts
RCC	Clock and reset control
Flash	Flash memory access
PWR	Power and system configuration

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Repository Structure

Each peripheral has its own dedicated folder containing:

File	Purpose
<Peripheral>.c	Driver implementation
<Peripheral>.h	Public API declarations
<Peripheral>_Port.h	Hardware-specific port configuration
<Peripheral>_Types.h	Type definitions and enumerations

Mcal/
├── Gpio/
│   ├── Gpio.c
│   ├── Gpio.h
│   ├── Gpio_Port.h
│   └── Gpio_Types.h
├── Usart/
│   ├── Usart.c
│   ├── Usart.h
│   ├── Usart_Port.h
│   └── Usart_Types.h
├── Rcc/
│   ├── Rcc.c
│   ├── Rcc.h
│   ├── Rcc_Port.h
│   └── Rcc_Types.h
├── I2c/
├── Spi/
├── Adc/
└── ...

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Dependencies

Dependency	Purpose
CMSIS	Core interface to ARM Cortex-M processor and system peripherals
STM32 LL Drivers	Lightweight, low-overhead register access without HAL abstraction

Both are included from the STM32Cube Firmware Package and integrated in the BSP under the RAL layer.

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Initialization Flow

The recommended startup sequence:

1. NVIC  — Interrupt controller setup
2. RCC   — System clock and voltage configuration
3. GPIO  — Pin multiplexing and output configuration
4. USART / SPI / I2C / ... — Peripheral initialization
5. DMA / Timers / SysTick  — Optional, as needed

This sequence can be executed as part of the system startup or triggered on demand by the application.

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Design Guidelines

• All hardware-specific code is encapsulated within MCAL — no register access outside this layer
• Consistent naming convention: <Module>_<Action> (e.g., Gpio_Init, Usart_Send, Rcc_SetClock)
• Macros and inline functions are used where performance is critical
• No hardcoded register values — CMSIS/LL macros are used throughout
• Each peripheral driver is self-contained and manages its own internal dependencies (e.g., DMA)
• All public APIs are documented

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Usage Example

GPIO Initialization

static gpioHal_PinConfig_t gpioHal_GpioConfiguration[GPIOHAL_IO_CNT] =
{
    {
        .GpioId = GPIOHAL_IO_USR_BTN,
        .ConfigStruct = {
            .PortId        = GPIO_PORT_C,
            .PinId         = GPIO_PIN_13,
            .PinMode       = GPIO_PIN_MODE_INPUT,
            .PinPull       = GPIO_PIN_PULL_NONE,
            .PinSpeed      = GPIO_PIN_SPEED_LOW,
            .PinOutType    = GPIO_PIN_OUTPUT_PUSHPULL,
            .PinAltFunction = GPIO_ALT_FUNC_CNT,
            .PinActiveLevel = GPIO_PIN_LEVEL_HIGH
        }
    }
};

void GpioHal_Init(void)
{
    for (uint16_t i = 0u; i < GPIOHAL_IO_CNT; i++)
    {
        Gpio_Init(&gpioHal_GpioConfiguration[i].ConfigStruct);
    }
}

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Future Enhancements

• Integration testing framework
• Unit test coverage for each peripheral driver
• Support for additional STM32 families

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License

This project is licensed under the Creative Commons Attribution–NonCommercial 4.0 International (CC BY-NC 4.0).

You are free to use, modify, and share this work for non-commercial purposes, provided appropriate credit is given.

See LICENSE.md for full terms or visit creativecommons.org/licenses/by-nc/4.0.

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Authors

• Mr.Nobody — embedbits.com

Contributions are welcome! Please open a pull request.

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Family support

	F4	G4	H5	U5
Core	✅	✅	—	✅
RCC	✅	✅	✅	✅
GPIO	✅	✅	✅	✅
EXTI	✅	✅	✅	✅
NVIC	✅	✅	✅	✅
TIM	✅	✅	✅	✅
USART	✅	✅	✅	✅
I2C	✅	—	✅	—
SPI	✅	—	—	—
ADC	✅	—	✅	—
DAC	✅	—	—	—
CRC	✅	—	—	✅
RNG	✅	—	—	✅
IWDG	✅	—	✅	—
DMA	✅	✅	—	—
GPDMA	—	—	✅	✅
DMA2D	✅	—	—	—