STM32 library function USART_SendData problem and solution

1. Problems and Phenomena

There is no problem in using USART_SendData() function to send single characters non-continuously; when sending characters continuously (no delay between two characters), the sending buffer will overflow. If the amount of data sent is very small, the serial port will only send the last character. When the amount of data sent is large, the sent data will be lost inexplicably.

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2. Reasons

This API function is imperfect. There is no statement in the function body to determine whether a character has been sent. Instead, the data is directly placed in the send buffer. When sending data continuously, due to the speed limit of the send shift register (related to the communication baud rate), the data in the send buffer overflows. The old data has not been sent out in time, and the new data overwrites the old data in the send buffer.

3. Solution

I won't talk about the method of waiting for a period of time after sending. The waiting time is uncertain, which is the worst option. The following two solutions are provided:

Solution 1. Check the status bit after each character is sent

USART_SendData(USART1, RxBuffer[TxCounter]);

while(USART_GetFlagStatus(USARTx, USART_FLAG_TXE) == RESET){} //Wait for the send buffer to be empty before sending the next character

Solution 2. Modify the library function

Modify the USART_SendData() function and add the USART_FLAG_TXE status detection statement of the send buffer to ensure that one character is completely sent before sending the next character.

Implementation method: Check the status register every time a character is sent to ensure that the data has been sent. The specific steps are as follows.

Function definition body before modification

Modified function definition body

Some people may think, why not handle this problem in advance in the library function, and throw the solution to the user. Personally, I think the reason why ST does this is: use the send interrupt function.

STM32 library function USART_SendData problem and solution | Xiao Xie's blog http://blog.xieyc.com/stm32-lib-function-usart-send-data-problem-and-solution/