Introduction - If you have any usage issues, please Google them yourself
//DMA serial send / receive
Function Description: / / can be sent through the serial port DMA keys, two keys are sent to different things,
/ / key definition can be viewed in key.c, sending the length can be modified in function
/ / serial port to receive through the variable length can modify RX_DATA_LENTH, serial port to receive through USART_SendData function to send back