STM32 USART serial port configuration

Concept 
In the STM32 reference manual, the serial port is described as a universal synchronous asynchronous receiver and transmitter (USART), which provides a flexible method for full-duplex data exchange with external devices using the industry standard NRZ asynchronous serial data format. (Okay, I don't quite understand it, so I'll just post the official definition for now, and you can figure it out yourself) 
Configuration steps

1. Turn on the clock (RCC configuration). 
   Since the TX, RX and AFIO of UART are all hung on the APB2 bridge, the firmware library function RCC_APB2PeriphClockCmd() is used for initialization. UARTx needs to be discussed separately. If it is UART1, it is hung on the APB2 bridge, so RCC_APB2PeriphClockCmd() is used for initialization. The rest of UART2~5 are hung on APB1.

2. GPIO configuration 
   The properties of GPIO are included in the structure GPIO_InitTypeDef, where for the TX pin, the GPIO_Mode field is set to GPIO_Mode_AF_PP (multiplexed push-pull output), and the GPIO_Speed ​​switching rate is set to GPIO_Speed_50MHz; for the RX pin, the GPIO_Mode field is set to GPIO_Mode_IN_FLOATING (floating input), and the switching rate does not need to be set. Finally, enable the IO port through GPIO_Init().

3. When NVIC configures 
   STM32, even if there is only one interrupt, it still needs to configure the priority level, which is used to enable the trigger channel of a certain interrupt. STM32 interrupts have at most two levels, namely preemption priority (main priority) and sub-priority (slave priority), and the length of the entire priority setting parameter is 4 bits, so it is necessary to first divide the preemption priority bit and sub-priority bit, which is implemented through NVIC_PriorityGroupConfig();

   The interrupt priority NVIC property of a specific device is contained in the structure NVIC_InitTypeDef, where the field NVIC_IRQChannel contains the interrupt vector of the device, which is saved in the startup code; the field NVIC_IRQChannelPreemptionPriority is the primary priority NVIC_IRQChannelSubPriority is the secondary priority, and the value range should be determined according to the bit division; the last NVIC_IRQChannelCmd field is whether it is enabled, which is generally set to ENABLE. Finally, NVIC_Init() is used to enable this interrupt vector.

4. The USART configuration 
   is determined by the structure USART_InitTypeDef. The fields in UART mode are as follows:

   USART_BaudRate: Baud rate (data bits that can be transmitted per second), the default value is 9600.

   USART_WordLength: word length

   USART_StopBits: Stop bits

   USART_Parity: Check mode (parity check)

   USART_HardwareFlowControl: Hardware flow control

   USART_Mode: Single/duplex, i.e., transmit/receive status.

   Finally, set it up through USART_Init().

5. Code Summary

void uart_init(u32 bound){

    GPIO_InitTypeDef GPIO_InitStructure;
    USART_InitTypeDef USART_InitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1|RCC_APB2Periph_GPIOA, ENABLE); //Enable USART1 and GPIOA clocks
    USART_DeInit(USART1); //Reset serial port 1 (set all parameters to default values)

    //USART1_TX (send data) PA.9 pin
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9; 
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP; //Multiplex push-pull output
    GPIO_Init(GPIOA, &GPIO_InitStructure); //初始化PA.9

    //USART1_RX (receive data) PA.10 pin
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING; //Floating input
    GPIO_Init(GPIOA, &GPIO_InitStructure);  //初始化PA.10

   //NVIC interrupt vector configuration 
    NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=3 ; //Set the preemption priority to 3
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 3; //The sub-priority is set to 3. The priority is determined according to the importance of different interrupts.
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; //IRQ channel enable
    NVIC_Init(&NVIC_InitStructure); //Initialize NVIC registers according to the parameters set above

   //USART initialization settings
    USART_InitStructure.USART_BaudRate = bound; //Baud rate is 9600;
    USART_InitStructure.USART_WordLength = USART_WordLength_8b; //Word length is 8 bits
    USART_InitStructure.USART_StopBits = USART_StopBits_1; //1 stop bit
    USART_InitStructure.USART_Parity = USART_Parity_No; //No parity bit
    USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None; //No hardware data flow control
    USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx; //Transmit and receive mode

    USART_Init(USART1, &USART_InitStructure); //Serial port initialization
    USART_ITConfig(USART1, USART_IT_RXNE, ENABLE); //Interrupt enable
    USART_Cmd(USART1, ENABLE); //Serial port enable}123456789101112131415161718192021222324252627282930313233343536373839

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