What should I do if the stm32 serial port is lost?

"STM32 serial port transmission must first detect the status, otherwise the first byte cannot be sent. After the transmission is completed, it must detect whether the transmission status is completed. Otherwise, the transmission is unsuccessful. When using stm32f10x to debug serial communication, an error occurs, and the hardware reset is restarted. After that, the test data is sent 0x01 0x02 0x03 0x04. The data received by the receiver is: 0x02 0x03 0x04, the first data is lost. The data is sent to another value, such as 0x06 0x0ff, then 0x0ff is received, 0x06 is lost. The error remains.

Troubleshooting process: 1, initially suspected to be the receiver error, I use the computer serial port, run the serial port auxiliary debugging tool to receive, after switching to other software, found that the fault remains, and the computer software is always open, unlike computer software related. 2, using single-step debugging, single-step operation of each send command, are normal. Can receive 0x01 0x02 0x03 0x04 data. Indirect exclusion of problems other than computer software, but other errors. 3. Although the single-step debugging operation is normal, the error remains after continuous operation. Now I can't touch the clue. The single step is normal. It seems that there is no error in programming. What is the fault? The test procedure is as follows

USART_SendData(USART2, 0x01); //A while(USART_GetFlagStatus(USART2, USART_FLAG_TC) == RESET); //B USART_SendData(USART2, 0x02); //C while(USART_GetFlagStatus(USART2, USART_FLAG_TC) == RESET); USART_SendData (USART2, 0x03); while(USART_GetFlagStatus(USART2, USART_FLAG_TC) == RESET); USART_SendData(USART2, 0x04); while(USART_GetFlagStatus(USART2, USART_FLAG_TC) == RESET);

4. Guess, perhaps because of a special reason, the second data covers the first data, making the first data lost. Assume that when the B instruction is executed, the USART's TC status bit == SET, then the C instruction will be executed immediately, and data coverage may occur. So, before the A command, add the following command: USART_ClearFlag (USART2, USART_FLAG_TC);

5. After adding the previous instruction, run and the error disappears. Explain the previous hypothesis, which should be established.

6. Check the stm32f10x reference manual and find a sentence like this: TC: Send Complete This bit is set by the hardware when the transmission of a frame containing data is completed. If the TCIE in USART_CR1 is 1, an interrupt is generated. This bit is cleared by the software sequence (first read USART_SR and then written to USART_DR). The TC bit can also be cleared by writing a 0, which is recommended only in multi-cache communication.

0: The transmission has not been completed; 1: The transmission is completed.

7. Note this sentence: This bit is cleared by the software sequence (read USART_SR first, then USART_DR). In other words, you must first read USART_SR and then write USART_DR to clear the TC status bit. After the hardware reset, the first data sent by the serial port does not have the read SR operation, and the write DR is directly written, that is, the TC is not cleared. Explain that the guess in step 4 is correct.

8, then, should be added to the USART_ClearFlag (USART2, USART_FLAG_TC); in front of the command A to USART_GetFlagStatus (USART2, USART_FLAG_TC);, should also eliminate the error. After the test, it is confirmed that this is the case. Before sending the first data, read USART_SR first, then the first data loss will not occur.

9. Summary: After the hardware reset, before the serial port sends the first data, first read the USART_SR, then it can ensure that the first data is sent without coverage. Of course, there are other methods, such as clearing the TC status bit first, or adding a small delay after the write USART_DR, so that the data is sent, it should also indirectly eliminate this error.