STM32 self-study notes - multiplexing and remapping

Port multiplexing

What is port multiplexing: 
STM32 has many built-in peripherals, and the external pins of these peripherals are multiplexed with GPIO. In other words, if a GPIO can be multiplexed as a function pin of a built-in peripheral, then when this GPIO is used as a built-in peripheral, it is called multiplexing. 
How to use: 
1. Enable GPIO clock 
2. Enable the clock of the multiplexed function 
3. Set the GPIO port data according to the data manual, 
eg.

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);//①IO clock enableRCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);//②Peripheral clock enable//③Initialize IO to the corresponding modeGPIO_InitStructure.GPIO_Pin = GPIO_Pin_9; //PA.9//Multiplexed push-pull outputGPIO_InitStructure.GPIO_Speed ​​= GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP; 
GPIO_Init(GPIOA, &GPIO_InitStructure);

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10; //PA10 PA.10 floating input GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING; //Floating input GPIO_Init(GPIOA, &GPIO_InitStructure); 12345678910111213

Port Remapping

What is port remapping: 
Each built-in peripheral has several input and output pins. Generally, the output ports of these pins are fixed. In order to allow design engineers to better arrange the direction and function of the pins, the concept of peripheral pin remapping is introduced in STM32. That is, in addition to the default port, the pin of a peripheral can also be mapped to other ports by setting the remapping register. In order to optimize the number of peripheral IO functions of different device packages, some multiplexed functions can be remapped to other pins. Many built-in peripheral input and output pins in STM32 have the function of remapping. 
How to use: 
1. Enable the remapped IO port 
2. Enable the functional peripheral clock 
3. Enable the AFIO clock 
4. Set the GPIO port data according to the data manual 
5.. Enable remapping 
eg.

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);//①IO clock enableRCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);//②Peripheral clock enableRCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO, ENABLE);③Multiplexing clock enable//④Initialize IO to the corresponding modeGPIO_InitStructure.GPIO_Pin = GPIO_Pin_9; //PA.9//Multiplexing push-pull outputGPIO_InitStructure.GPIO_Speed ​​= GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP; 
GPIO_Init(GPIOA, &GPIO_InitStructure);

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10; //PA10 PA.10 floating input GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING; //Floating input GPIO_Init(GPIOA, &GPIO_InitStructure);  

GPIO_PinRemapConfig(GPIO_Remap_USART1, ENABLE); //Enable remapping 1234567891011121314151617

question

When to turn on the AFIO clock: 
Before reading and writing registers AFIO_MAPR, AFIO_EXTICRX and AFIO_EVCR, the AFIO clock should be turned on first. 
AFIO_MAPR: Configure multiplexing function remapping 
AFIO_EXTICRX: Configure external interrupt line mapping 
AFIO_EVCR: Configure EVENTOUT event output

What is a partial remap? What is a full remap? 

Partial remaps have some pins overlapped with no remaps.

Why is it designed this way: 
1. Save the number of IO ports 
2. Convenient for PCB to reduce cross-interference of signals 
3. Achieve the purpose of time-sharing multiplexing