STM32LL library - USART interrupt to receive variable length information

The Universal Synchronous Asynchronous Receiver (USART) is both a serial port and can be connected with the serial port assistant on the computer, which is an important way to debug the microcontroller.Two-way communication requires at least 2 pins: receive data input (RX) and transmit data output (TX).

First, configure the basic parameters of using the serial port in STM32CubeMX, enable the serial port interrupt, and set the library to be used as the LL library:

After the basic code is automatically generated, add the following code to enable the receive buffer Rx non-empty interrupt and idle interrupt:

 LL_USART_EnableIT_RXNE(USART2);LL_USART_EnableIT_IDLE(USART2);

RXNE is the reception buffer Rx non-empty flag, set to 1 to indicate that data (1 byte) has been received, and an interrupt is generated; IDLE is an idle flag, set to 1 to indicate that the current data is received (1 frame of data), and an interrupt is generated.Receive variable length messages:

char data[20];uint8_t Rflag = 0;uint8_t Rnum = 0;// We store the received data in the string array data[], Rnum indicates the data length, Rflag indicates the receiving status, = 1 means the reception is completevoid USART2_IRQHandler(void){/* USER CODE BEGIN USART2_IRQn 0 */// Idle interrupt, indicating that all data of 1 frame has been receivedif(LL_USART_IsActiveFlag_IDLE(USART2)){// clear interrupt flagLL_USART_ClearFlag_IDLE(USART2);data[Rnum] = '\0';Rflag = 1;Rnum = 0;}// Rx non-null interrupt, indicating that a byte was received// Read Rx to automatically clear the interrupt flagif(LL_USART_IsActiveFlag_RXNE(USART2)){// If the length of the array is greater than the set maximum length of data, stop receiving directlyif(Rnum > 18){data[19] = '\0';Rflag = 1; // stop receiveRnum = 0; // wait for the next data}if(Rflag == 0){data[Rnum] = LL_USART_ReceiveData8(USART2);Rnum++;}}WRITE_REG(USART2->RQR, USART_RQR_RXFRQ);/* USER CODE END USART2_IRQn 0 *//* USER CODE BEGIN USART2_IRQn 1 *//* USER CODE END USART2_IRQn 1 */}

The relevant LL library functions are defined as follows:

/* Legacy define */#define LL_USART_EnableIT_RXNE LL_USART_EnableIT_RXNE_RXFNE/*** @brief Enable RX Not Empty and RX FIFO Not Empty Interrupt* @note Macro IS_UART_FIFO_INSTANCE(USARTx) can be used to check whether or not* FIFO mode feature is supported by the USARTx instance.* @rmtoll CR1 RXNEIE_RXFNEIE LL_USART_EnableIT_RXNE_RXFNE* @param USARTx USART Instance* @retval None*/__STATIC_INLINE void LL_USART_EnableIT_RXNE_RXFNE(USART_TypeDef *USARTx){SET_BIT(USARTx->CR1, USART_CR1_RXNEIE_RXFNEIE);}/*** @brief Enable IDLE Interrupt* @rmtoll CR1 IDLEIE LL_USART_EnableIT_IDLE* @param USARTx USART Instance* @retval None*/__STATIC_INLINE void LL_USART_EnableIT_IDLE(USART_TypeDef *USARTx){SET_BIT(USARTx->CR1, USART_CR1_IDLEIE);}/*** @brief Read Receiver Data register (Receive Data value, 8 bits)* @rmtoll RDR RDR LL_USART_ReceiveData8* @param USARTx USART Instance* @retval Value between Min_Data=0x00 and Max_Data=0xFF*/__STATIC_INLINE uint8_t LL_USART_ReceiveData8(USART_TypeDef *USARTx){return (uint8_t)(READ_BIT(USARTx->RDR, USART_RDR_RDR) & 0xFFU);}