Analysis of Less Common Library Functions for STM32 GPIO

1.

void GPIO_DeInit(GPIO_TypeDef* GPIOx);

First, let’s take a look at this function. We can see that the parameter of this function is a GPIO group parameter (GPIOB, GPIOC, GPIOA, etc.),Now, let’s enter the definition of this function in the standard peripheral library.

void GPIO_DeInit(GPIO_TypeDef* GPIOx){  /* Check the parameters */  assert_param(IS_GPIO_ALL_PERIPH(GPIOx));  if (GPIOx == GPIOA)  {    RCC_AHB1PeriphResetCmd(RCC_AHB1Periph_GPIOA, ENABLE);    RCC_AHB1PeriphResetCmd(RCC_AHB1Periph_GPIOA, DISABLE);  }  else if (GPIOx == GPIOB)  {    RCC_AHB1PeriphResetCmd(RCC_AHB1Periph_GPIOB, ENABLE);    RCC_AHB1PeriphResetCmd(RCC_AHB1Periph_GPIOB, DISABLE);  }  else if (GPIOx == GPIOC)  {    RCC_AHB1PeriphResetCmd(RCC_AHB1Periph_GPIOC, ENABLE);    RCC_AHB1PeriphResetCmd(RCC_AHB1Periph_GPIOC, DISABLE);  }  。。。。  。。。。  。。。。    }

Function Description:

The purpose of this function is:

To reset the specified GPIO port (such as GPIOA, GPIOB…) to its power-on default state.

In other words:

  • Clear all previous configurations of the port (input/output mode, pull-up/pull-down, multiplexing function, output value, etc.);

  • Reset its register values back tothe reset default values (Reset Value)..

This is equivalent to “clearing this GPIO before reinitializing it”.

Key Point: Use RCC peripheral reset function to clear configurations

In STM32, all peripherals (including GPIO) are connected to RCC (Clock Controller). RCC has a very important function:

It can “soft reset” any peripheral by setting the reset bit.

For example:

  • <span><span>RCC_AHB1PeriphResetCmd(RCC_AHB1Periph_GPIOA, ENABLE)</span></span> means:Put GPIOA into reset state;

  • Then execute<span><span>RCC_AHB1PeriphResetCmd(RCC_AHB1Periph_GPIOA, DISABLE)</span></span> means:Exit reset state.

This “reset-release” operation will clear the GPIOA registers, restoring them to factory default values.

Therefore, this function is rarely used.

2.

void GPIO_StructInit(GPIO_InitTypeDef*GPIO_InitStruct);

The parameter is a pointer to a structure. Next, we go to the standard peripheral library to see the definition of this function.

void GPIO_StructInit(GPIO_InitTypeDef* GPIO_InitStruct){  /* Reset GPIO init structure parameters values */  GPIO_InitStruct-&gt;GPIO_Pin  = GPIO_Pin_All;  GPIO_InitStruct-&gt;GPIO_Mode = GPIO_Mode_IN;  GPIO_InitStruct-&gt;GPIO_Speed = GPIO_Speed_2MHz;  GPIO_InitStruct-&gt;GPIO_OType = GPIO_OType_PP;  GPIO_InitStruct-&gt;GPIO_PuPd = GPIO_PuPd_NOPULL;}

<span><span>GPIO_InitStruct->GPIO_Pin = GPIO_Pin_All;</span></span>

This means:

By default, selectall pins (Pin0~Pin15)..

In other words, the default structure assumes “I want to configure all pins of the entire port”, but in practice, you can modify it before use, for example:

GPIO_InitStruct.GPIO_Pin = GPIO_Pin_5; // Only configure PA5 pin

<span><span>GPIO_InitStruct->GPIO_Mode = GPIO_Mode_IN;</span></span>

The default mode is:

Input mode (Input Mode).

The GPIO modes in STM32 mainly include the following:

Mode Meaning
<span>GPIO_Mode_IN</span> Input mode
<span>GPIO_Mode_OUT</span> Push-pull output
<span>GPIO_Mode_AF</span> Multiplexing function (e.g., USART, SPI)
<span>GPIO_Mode_AN</span> Analog input (for ADC)

The default is input mode forsafety reasons (to prevent accidental output causing short circuits or interference).

<span><span>GPIO_InitStruct->GPIO_Speed = GPIO_Speed_2MHz;</span></span>

Set the default pin output speed to:

2MHz (low-speed mode)

This corresponds to the switching speed of the GPIO output signal. Different speeds correspond to different power consumption and interference levels:

Parameter Speed Characteristics
<span>GPIO_Speed_2MHz</span> Low speed Low power, low interference (default)
<span>GPIO_Speed_25MHz</span> Medium speed Balanced for general peripheral use
<span>GPIO_Speed_50MHz</span> High speed Suitable for high-speed communication ports (SPI, etc.)
<span>GPIO_Speed_100MHz</span> Ultra-high speed Used for clock or high-speed peripheral lines

<span><span>GPIO_InitStruct->GPIO_OType = GPIO_OType_PP;</span></span>

Set the output type to:

Push-pull output (Push-Pull)

The characteristics of push-pull output are:

  • Can actively output high or low levels;

  • Strong driving capability.

The other type isopen-drain output (Open-Drain), used in situations like I²C bus where multiple devices share the line.

<span><span>GPIO_InitStruct->GPIO_PuPd = GPIO_PuPd_NOPULL;</span></span>

Set pull-up/pull-down to:

No pull-up or pull-down (No Pull-up or Pull-down)

The input pins of STM32 are in a “high-impedance state”. If no pull-up or pull-down is set, the level mayfloat unpredictably (floating)..

The options are as follows:

Parameter Function
<span>GPIO_PuPd_NOPULL</span> No internal pull-up/pull-down
<span>GPIO_PuPd_UP</span> Pull-up
<span>GPIO_PuPd_DOWN</span> Pull-down

Example Usage Scenarios

In practical applications, it is usually used like this:

GPIO_InitTypeDef GPIO_InitStructure;/* First call the structure initialization function to fill in default values */GPIO_StructInit(&amp;GPIO_InitStructure);/* Then modify some fields as needed */GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5;GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;/* Finally apply to the specific port */GPIO_Init(GPIOA, &amp;GPIO_InitStructure);

This can avoid forgetting to initialize certain fields in the structure, reducing program errors.

3.

void GPIO_PinLockConfig(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin);
void GPIO_PinLockConfig(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin){  __IO uint32_t tmp = 0x00010000;  /* Check the parameters */  assert_param(IS_GPIO_ALL_PERIPH(GPIOx));  assert_param(IS_GPIO_PIN(GPIO_Pin));  tmp |= GPIO_Pin;  /* Set LCKK bit */  GPIOx-&gt;LCKR = tmp;  /* Reset LCKK bit */  GPIOx-&gt;LCKR =  GPIO_Pin;  /* Set LCKK bit */  GPIOx-&gt;LCKR = tmp;  /* Read LCKK bit*/  tmp = GPIOx-&gt;LCKR;  /* Read LCKK bit*/  tmp = GPIOx-&gt;LCKR;

Background Principle — GPIO Lock Mechanism

Each GPIO port in STM32 has a dedicated register: GPIOx_LCKR (Lock Register)

The function is: Once locked, the configuration of this pin’s mode, pull-up/pull-down, output type, speed, etc., will be frozen. Even if you later call <span>GPIO_Init()</span> or directly write to the register, youcannot modify! You must reset the MCU to unlock it again.

So this function is used to lock a specified GPIO pin, and it is rarely used.

4.

void GPIO_PinAFConfig(GPIO_TypeDef* GPIOx, uint16_t GPIO_PinSource, uint8_t GPIO_AF);

1. Function Overview

<span>GPIO_PinAFConfig()</span> is used to selectthe peripheral multiplexing function for a GPIO pin.

In simple terms, STM32 pins are very “versatile”; a pin can serve as a regular IO or be connected to various peripherals. For example:

Pin Optional Functions
PA9 Regular output / USART1_TX / TIM1_CH2 / …
PB6 GPIO / I2C1_SCL / TIM4_CH1 / USART1_TX / …

<span>GPIO_PinAFConfig()</span> tells the chip:

“Hey, PA9, you are no longer a GPIO; you are now USART1_TX!”

2. Function Prototype Analysis

void GPIO_PinAFConfig(GPIO_TypeDef* GPIOx, uint16_t GPIO_PinSource, uint8_t GPIO_AF);
Parameter Description
<span>GPIOx</span> The port to be configured (e.g., GPIOA, GPIOB…)
<span>GPIO_PinSource</span> Pin number (0~15, corresponding to Pin0~Pin15)
<span>GPIO_AF</span> The selected multiplexing function number (AF0 ~ AF15)

3. STM32 Multiplexing Function Structure Diagram

The function of each pin is controlled by registers:

GPIOx_AFRL register  → Controls Pin0~Pin7
GPIOx_AFRH register  → Controls Pin8~Pin15

Each pin occupies 4 bits to select the AF function number:

AF Value Peripheral Function (varies slightly by model)
AF0 System functions (e.g., MCO, RTC, SWD)
AF1 TIM1 / TIM2
AF2 TIM3 / TIM4 / TIM5
AF3 TIM8 / TIM9 / TIM10 / TIM11
AF4 I2C1 / I2C2 / I2C3
AF5 SPI1 / SPI2
AF6 SPI3 / I2S
AF7 USART1 / USART2
AF8 USART6 / UART4 / UART5
AF9 CAN1 / CAN2 / TIM12 / TIM13 / TIM14
AF10 OTG_FS / OTG_HS
AF11 Ethernet
AF12 FSMC / SDIO / OTG_HS
AF13 DCMI
AF14 Undefined
AF15 EVENTOUT

Complete Multiplexing Configuration Process

Assuming we want to use PA9 as USART1_TX:

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);   // Enable GPIO clock
GPIO_InitTypeDef GPIO_InitStructure;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;            // Change mode to multiplexing function
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
GPIO_Init(GPIOA, &amp;GPIO_InitStructure);
GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF7_USART1); // Configure AF mapping

Both steps are essential:

  1. <span>GPIO_Mode_AF</span> — Switch the pin to multiplexing mode;

  2. <span>GPIO_PinAFConfig()</span> — Tell it who to multiplex to.

Related posts

  1. Arduino Basic Experiment 6: Voltmeter Experiment
  2. STM32 Series Tutorial (7): Understanding GPIO Interrupt Mechanism
  3. Getting Started with Python: Mastering print, input, and Operators in 30 Minutes
  4. Traps in STM32 Clock System Design
  5. STM32F1 Series – IWDG (Independent Watchdog)
  6. The New Era of Laparoscopic Surgical Robots
  7. Using Streamable HTTP for Real-Time AI Tool Interaction with MCP
  8. RISC-V Processor and FPGA Reusing JTAG
  9. What is the H20 Chip? Who Will Buy It? [Financial Explanation]
  10. Patent Drafting: A Single Word Difference Leads to a 510,000 Yuan Compensation Demand Withdrawn in 12 Days
  11. Network Programming in C: Basics of Socket Programming
  12. Mastering Data Exchange with Python’s JSON Four Musketeers!
  13. Common Causes of Microcontroller Crashes and Solutions
  14. Design and Implementation of a Solar Tracking System Based on the 51 Microcontroller
  15. AI Robotic Dog Transforms into a ‘Safety Sentinel’
  16. Teaching Plan for Python Level 1 and After-Class Exercises
  17. Discussing C Programming – Address Manipulation and Byte Control in C Language
  18. How Should Interface Testing Engineers Learn HTTP/HTTPS Protocols? (Part 19)
  19. What Development Tools Are Available for STM32 Edge AI?

Leave a Comment