STM32 serial port sending configuration process

Serial port byte sending process:

Program the M bit of USARTx_CR1 to define the word length.

Program the STOP bit in USARTx_CR2 to define the number of stop bits.

Program the USARTx_BRR register to determine the baud rate.

Enable the UE bit of USARTx_CR1 to enable USARTx.

If multi-buffer communication is performed, configure the DMA enable (DMAT) of USARTx_CR3.

Enabling the TE bit of USARTx_CR1 enables the transmitter.

Write the data to be sent to the transmit data register TDR.

After writing the last data to the TDR register, wait for the TC position of the status register USARTx_ISR to be set to 1 and the transmission is completed.

Configuration steps 1-6: Configure word length, stop bit, parity bit, baud rate, etc.:

HAL_StatusTypeDef HAL_USART_Init(USART_HandleTypeDef * huart); 

The identifier HAL_USART_ENABLE will be referenced inside this function to enable the corresponding serial port.

The routine is as follows:

void uart_init(u32 bound)

{   

    //UART initialization settings

    UART1_Handler.Instance=USART1; //USART1

    UART1_Handler.Init.BaudRate=bound; //Baud rate

    UART1_Handler.Init.WordLength=UART_WORDLENGTH_8B; //Word length 8 bits

    UART1_Handler.Init.StopBits=UART_STOPBITS_1; //One stop bit

    UART1_Handler.Init.Parity=UART_PARITY_NONE; //No parity bit

    UART1_Handler.Init.HwFlowCtl=UART_HWCONTROL_NONE; //No hardware flow control

    UART1_Handler.Init.Mode=UART_MODE_TX_RX; //Transmit and receive mode

    HAL_UART_Init(&UART1_Handler);                      //HAL_UART_Init()会使能UART1

    HAL_UART_Receive_IT(&UART1_Handler, (u8 *)aRxBuffer, RXBUFFERSIZE);//This function will enable the receive interrupt;

}

Step 7-8 Send data and wait for sending to complete

HAL_StatusTypeDef HAL_USART_Transmit(USART_HandleTypeDef * huart,uint8_t *pTxdata,uint16_t Size,uint32_t Timeout);

First of all, we need to mention the __weak keyword: 

A function with the __weak modifier in front of it is called a weak function. For a weak function, the user can redefine a function with the same name in the user file, and the compiler will eventually choose the user-defined function when compiling. If the user does not define it, the content of the function is the content of the weak function definition. 

Benefits of the __weak keyword: 
1. For a pre-defined process, we only want to modify a part of the code related to the user in the process. At this time, we can use a weak function to define an empty function, and then let the user define the function. The advantage of this is that we will not make any changes to the existing program flow. 
2. The __weak keyword is widely used in the HAL library to modify peripheral callback functions. 
3. The peripheral callback function is used by users to write MCU-related programs, which greatly improves the versatility and portability of the program.

The serial port handle is as follows:

We can see that there is a serial port parameter initialization structure in the serial port handle, the specific content is as follows:

Next, we will describe the overall configuration process of the serial port sending program (HAL library):

1. Initialize serial port related parameters and enable serial port: HAL_USRT_Init(); 
2. Configure serial port related IO ports and multiplex configuration: 
call HAL_GPIO_Init() in HAL_UART_MspInit; 
3. Send data and wait for data transmission to be completed: 
HAL_UART_Transmit();