Single chip microcomputer serial port data processing (1) -- serial port interrupt sending data

Real time is very important in embedded development , Optimize MCU Serial port transmission processing method can improve the real-time performance of embedded system . Study on the Internet and experiment in person （ be based on STM32 Single chip microcomputer ） after , I will introduce optimization in two parts MCU Method of sending and receiving data through serial port , Resources will be listed in the second blog . For the first time, the optimization of serial port sending data is introduced .

Sending method 1 ：

Mode 1 is adopted “ Death etc. ” The way to send data , That is to say while Wait for the position bit of the word sending completion flag in the loop .

void usartsend(void)
{
    while(USART_GetFlagStatus(USART1, USART_FLAG_TC) == RESET); // Wait until the last byte is sent  
    USART1->DR=txbuf[cnt]; // The bytes to be sent are stored in the serial port data register  
}

void sendcmd(void)
{
    for(cnt=0;cnt<100;cnt++)// send out 100 Bytes 
    {
        usartsend();// Call the byte sending function 
    }
}

In this way while A lot of time is consumed in the loop , and sendcmd Call... Over and over again in the function usartsend Functions are also time-consuming . The baud rate I used in the experiment is 115200, In theory, send 100 Byte data takes about 8.68ms, The time spent in hardware simulation is about 9.45ms. Here 9.54ms Inside ,MCU In addition to sending bytes and while There are no other tasks to deal with besides waiting , Seriously affect the real-time performance of the system .

Sending mode 2 ：

Mode 2: send data by interrupt . To send data , Enable the transmission buffer of the serial port to be disconnected in the air , stay ISR Determine whether there is data to send , If there is , Then the bytes to be sent are stored in the serial port data register . When all data is sent, the transmission buffer of the serial port is forbidden to be disconnected in the air .

void usartsend(void)
{
    USART_ITConfig(USART1,USART_IT_TXE,ENABLE);// Enable the transmission buffer of the serial port to be disconnected in the air 
}

void USART1_IRQHandler(void) // A serial port 1 Of ISR              
{
    if(USART_GetITStatus(USART1,USART_IT_TXE)==SET)
    {
        USART1->DR=txbuf[cnt];
        cnt++;
        if(cnt>=100)
        {
            USART_ITConfig(USART1, USART_IT_TXE, DISABLE);// Data sent , It is forbidden to interrupt the sending buffer of the serial port in the air 
        }
    }
} 

This way is mainly ISR Elapsed time . use 115200 Baud rate experiment , send out 100 Byte data takes about 8.51ms. It takes less time than the theoretical time （8.68ms） The reason may be that the program reached the breakpoint I set before the last byte was sent .

The second method takes less time than the first method . What is more noteworthy is that the second method costs 8.51ms It's piecemeal , The program won't wait 8.51ms, in the meantime MCU Can handle other tasks , The real-time performance of the system is high . The first method is to wait for the program to die 9.54ms,MCU No other tasks can be processed during this period , Real time performance is seriously affected .