🧠 Getting Started with STM32G031xx.h — Masks & Structs

🎯 Learning Objectives

By the end of this lesson, students will:

Understand the purpose of the STM32G031xx.h header file
Learn how peripheral registers are accessed using data structures
Use bit masks to manipulate register values
Write simple code to control GPIO using register-level programming

Part1: 📘 What Is STM32G031xx.h?

This header file is part of the CMSIS (Cortex Microcontroller Software Interface Standard) and provides:

Definitions for peripheral base addresses
Bit masks for register fields
Memory-mapped structs for hardware registers

Example snippet from the file:

#define GPIOA_BASE (0x50000000UL)
#define GPIOA ((GPIO_TypeDef *) GPIOA_BASE)

🧱 Part 2: Understanding Data Structures and Registers

Peripheral registers are grouped into structs. For example, GPIO_TypeDef might look like:

typedef struct {
  volatile uint32_t MODER;   // GPIO port mode register
  volatile uint32_t OTYPER;  // GPIO port output type register
  volatile uint32_t OSPEEDR; // GPIO port output speed register
  volatile uint32_t PUPDR;   // GPIO port pull-up/pull-down register
  volatile uint32_t IDR;     // GPIO port input data register
  volatile uint32_t ODR;     // GPIO port output data register
} GPIO_TypeDef;

Let’s say we want to modify the MODER register for GPIOA

Each port, in this case GPIOA, has 16-PINs (GPIA15..GPIOA00)
To configure the MODER register, we need 2-bits per Port PIN as there are 4 possible configurations:
Then the MODER register has 16x2 = 32bits (b31..b00) to configure it according to the following table:
The 32-bits of the MODER register as distributed as follows:
Let’s say we want to configure GPIOA0 as an output, that means we need to write 10b on b1 and b0 of the MODER register.

GPIOA->MODER = 0x00000001; // Set PA0 as output

0x00000001 = 00000000 000000000 000000000 000000001 in binary
If we wanted to configure GPIOA10 as an output, that means we need to write 10b on b21 and b00 of the MODER register.

GPIOA->MODER = 0x00200000; // Set PA0 as output

0x00000001 = 00000000 000100000 000000000 000000000 in binary

🎭 Part 3: Using Bit Masks

The vendor provide us with convinient masks to avoid having to write raw numbers in hex or binary
Extract from the header file (STM32G031xx.h)

#define GPIO_MODER_MODE0_Msk (0x3U << 0)  // Mask for PA0 mode bits
#define GPIO_MODER_MODE0_Output (0x1U << 0)

GPIOA->MODER &= ~GPIO_MODER_MODE0_Msk;       // Clear PA0 mode bits
GPIOA->MODER |= GPIO_MODER_MODE0_Output;     // Set PA0 as output

🎯 Part 4: Sumary - Write Into the Registers using Masks

Clear the BITS using the *xxx_Msk
Write the proper BITS using the corresponding mask for the BITS

🧩 Part 5: Challenge for Students

Configure GPIOA12 as output using the BIT masks from the library
Configure GPIOA15 as analog mode using the BIT masks from the library
Verify it is working by using the debugger