STM32 serial port DMA variable length reception

STM32 serial port DMA variable length reception
When configuring the serial port, open the serial port interrupt, open the receiving and sending DMA

main.c

Front

/* USER CODE BEGIN 0 */
#define BUFFERSIZE 255//可以接收的最大字符个数
uint8_t ReceiveBuff[BUFFERSIZE]; //接收缓冲区
uint8_t Rx_len;//接收完成中断标志，接收到字符长度
extern DMA_HandleTypeDef hdma_usart1_rx