STM32 learning: USART interrupt mode

 Earlier we have learned about the query method of serial communication. Now let's introduce the interrupt method.

   Step 1: Initialize GPIO

GPIO_InitTypeDef GPIO_InitStructure;

 /* Configure USART1 Tx (PA.09) as alternate function push-pull */

 GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;

 GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

 GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;

 GPIO_Init(GPIOA, &GPIO_InitStructure);

 /* Configure USART1 Rx (PA.10) as input floating */

 GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;

 GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;

GPIO_Init(GPIOA, &GPIO_InitStructure);

Step 2: Turn on the clock

/* Enable USART1, GPIOA, GPIOD and AFIO clocks */

 RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1 | RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOD

                         | RCC_APB2Periph_AFIO, ENABLE);

It is noted here that it is also possible not to set RCC_APB2Periph_AFIO, that is, the multiplexing function is not used here.

These two steps are the same as the query method.

Step 3: Initialize USART1

USART_InitStructure.USART_BaudRate = 115200;

 USART_InitStructure.USART_WordLength = USART_WordLength_8b;

 USART_InitStructure.USART_StopBits = USART_StopBits_2;

 USART_InitStructure.USART_Parity = USART_Parity_No; //Communication error occurs when setting odd parity

 USART_InitStructure.USART_HardwareFlowControl=USART_HardwareFlowControl_None;

 USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;

 /* Configure the USART1 */

 USART_Init(USART1, &USART_InitStructure);

 /* Enable the USART Transmoit interrupt: this interrupt is generated when the

     USART1 transmit data register is empty */ 

 USART_ITConfig(USART1, USART_IT_TXE, ENABLE);

 /* Enable the USART Receive interrupt: this interrupt is generated when the

     USART1 receive data register is not empty */

 USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);

 /* Enable USART1 */

 USART_Cmd(USART1, ENABLE);

Here we need to enable the peripheral interrupt of USART1, such as USART_ITConfig(USART1, USART_IT_TXE, ENABLE); this is to enable the transmit interrupt, but an interrupt can be generated when the transmit register is empty.

Step 4: Write the interrupt function

uint8_t TxBuffer[] = "\n\rUSART Hyperterminal Interrupts Example: USART-Hyperterminal\

 communication using Interrupt\n\r";

uint8_t RxBuffer[RxBufferSize];

uint8_t NbrOfDataToTransfer = TxBufferSize;

uint8_t NbrOfDataToRead = RxBufferSize;

uint8_t TxCounter = 0;

uint16_t RxCounter = 0;

void USART1_IRQHandler(void)

{

 if(USART_GetITStatus(USART1, USART_IT_RXNE) != RESET)

 {

    /* Read one byte from the receive data register */

    RxBuffer[RxCounter++] = (USART_ReceiveData(USART1) & 0x7F);

    if(RxCounter == NbrOfDataToRead)

    {

      /* Disable the USART Receive interrupt */

      USART_ITConfig(USART1, USART_IT_RXNE, DISABLE);

    }

 }

 if(USART_GetITStatus(USART1, USART_IT_TXE) != RESET)

 {  

    /* Write one byte to the transmit data register */

      USART_SendData(USART1, TxBuffer[TxCounter++]);

    if(TxCounter == NbrOfDataToTransfer)

    {

      /* Disable the USART1 Transmit interrupt */

      USART_ITConfig(USART1, USART_IT_TXE, DISABLE);

    }

 }

}

This is the end of the procedure.

We will have a question, main() only includes the initialization of the first three steps and an infinite loop, so how is the interrupt triggered? The structure of main() is as follows:

int main(void)

{

 /* System Clocks Configuration */

 RCC_Configuration();

 /* NVIC configuration */

 NVIC_Configuration();

 /* Configure the GPIO ports */

 GPIO_Configuration();

 USART_Configuration();

 while (1)

 {

 }

}

It turns out that the reset value of the status register USART_SR is 0x00C0H, that is, the reset value of the seventh bit TXE and the sixth bit TC is 1, and TXE=1 indicates that the transmit data register is empty, and TC=1 indicates that the transmission is completed. In the USART settings, there is

USART_ITConfig(USART1, USART_IT_TXE, ENABLE);

 USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);

These two sentences enable interrupts, that is, when TXE=1, an interrupt will be entered, so the program can enter the interrupt after initialization and execute

if(USART_GetITStatus(USART1, USART_IT_TXE) != RESET)

 {  

    /* Write one byte to the transmit data register */

      USART_SendData(USART1, TxBuffer[TxCounter++]);

    if(TxCounter == NbrOfDataToTransfer)

    {

      /* Disable the USART1 Transmit interrupt */

      USART_ITConfig(USART1, USART_IT_TXE, DISABLE);

    }

 }