STM32 Development Board—-STM32MP157

First, find the content of UART3 on the stm32mp157 schematic diagram of the baseboard.

Then determine the pins used by SART3 from the core board. It can be seen that USART3_TX and USART3_RX use the PB10 and PB12 pins respectively.

2. Software design

Select the serial port to be configured in Connectivity. In this section, the experiment uses USART3.

Select Assign to Cortex-M4 core and select Asynchronous mode in Mode. The serial port can be configured in Parameter Settings. The default settings are: baud rate 115200, 8 data bits, 1 stop bit, no parity bit. This is also the most commonly used configuration in serial ports. You can modify the serial port parameters according to your needs. In addition to these basic parameter configurations, there are some more advanced configuration parameters. This chapter only explains the most commonly used configurations.

The way to enable the USART interrupt is very simple, just check the interrupt enable of USART3 in the NVIC.

The USART3_TX and USART3_RX pins on the development board use PB10 and PB12 respectively. After configuring the serial port parameters, you need to select the pin where USART3 is located and set it to serial port mode.Set the PB10 pin to USART3_TX mode.

Set PB12 pin to USART3_RX mode

In the previous steps we have assigned USART3 to Cortex-M4, there is no need to reconfigure the pins to the M4 core here.

Enable HSE clock

Set the clock of the Cortex-M4 to 209Mhz

At the same time, you can also choose to adjust the clock of USART3

3. structure related to USART initialization.

The initialization settings of USART3 have been completed here, and the project code can be generated. Before we enter the code and see how USART3 is initialized and works, let’s first understand the structure related to USART initialization.

3.1 UART_HandleTypeDef structure

  The serial port uses the UART_HandleTypeDef structure to describe a serial port device. Some members are as follows:

1) Instance pointer: used to point to the base address of the serial port register used by the user;

2) Init serial port initialization structure: It is used to configure the communication parameters of the serial port, such as baud rate, serial port data bits, stop bits and so on. For detailed parameter description, please see the analysis of the initialization structure below;

3) AdvancedInit serial port advanced function configuration structure: It is used to configure the advanced functions of the serial port, such as automatic baud rate, MSB first and so on. This chapter is temporarily unavailable, so it will not be explained in detail;

4) PTXBuffPtr, TXXferSize, TXXferCount: are the address pointer of the data to be sent, the size of the data to be sent and the number of data to be sent;

5) PRXBuffPtr, RXXferSize, RXXferCount: are the address pointer to the stored data, the size of the received data, and the number of received data;

6) Mask: The serial port accepts the mask of the register, which is used to store the parity bit of the data, which is related to the Parity parameter in the initialization structure;

7) hdmatx, hdmarx structure: configure the DMA specific parameters of the serial port to send and receive data;

8) Lock: serial port object resource lock. This structure is mainly responsible for allocating lock resources. You can choose HAL_UNLOCKED or HAL_LOCKED as two parameters. If the value of gState is equal to HAL_UART_STATE_RESET, it is considered that the serial port is not initialized. At this time, the lock resource is allocated, and the HAL_UART_MspInit function is called to initialize the GPIO and clock of the serial port. This part of the code is used to implement the function of the bottom layer configuration of the serial port.

9) EState, RXState: The structure of the serial port’s sending state, the working state and the structure of the serial port’s receiving state, respectively. HAL_UART_StateTypeDef is an enumeration type that lists the state values ​​of the serial port in the working process. Some values ​​are only applicable to EState, such as HAL_UART_STATE_BUSY;

10) ErrorCode: Serial port error operation information. It is mainly used to store the error information of serial port operation.

11) RXISR: function pointer, usually used to handle serial port receive interrupts

12) TXISR: Function pointer, usually used to handle serial port send interrupts.

3.2 UART_InitTypeDefstructure

This structure is used to configure the communication mode of the serial port. It is embedded in the UART_HandleTypeDef structure and is defined as follows

1) BaudRate: Baud rate setting. Generally set to 2400, 9600, 19200, 115200. The standard library function will calculate the USARTDIV value according to the set value, see Equation 20-1, and set the USART_BRR register value.

2) WordLength: data frame word length, optional 8 bits or 9 bits. It sets the value of the M bit of the USART_CR1 register. If parity control is not enabled, 8 data bits are generally used; if parity is enabled, it is generally set to 9 data bits.

3) StopBits: stop bit setting, optional 0.5, 1, 1.5 and 2 stop bits, it sets the value of the STOP[1:0] bits of the USART_CR2 register, generally we choose 1 stop bit.

4) Parity: Parity control selection, optional USART_Parity_No (no parity), USART_Parity_Even (even parity) and USART_Parity_Odd (odd parity), which sets the value of the PCE bit and the PS bit of the USART_CR1 register.

5) Mode: USART mode selection, there are USART_Mode_Rx and USART_Mode_Tx, allowing to use logical OR operation to select two, it sets the RE bit and TE bit of the USART_CR1 register.

6) HwFlowCtl: Hardware flow control selection, only valid in hardware flow control mode, options are: enable RTS, enable CTS, enable both RTS and CTS, and disable hardware flow.

7) OverSampling: Oversampling selection, choose 8 times oversampling or 16 oversampling.

8) OneBitSampling: One sampling bit method is enabled. Either the three sample bit method or the one sample bit method can be selected.

9) ClockPrescaler: serial port clock frequency division factor. By default, no frequency division is selected.

3.3 MX_USART3_UART_Init serial port initialization function

After understanding the two structures described above, you can enter the MX_USART3_UART_Init serial port initialization function

The content in the MX_USART3_UART_Init function is also relatively simple. Some basic configurations are performed on USART3, and HAL_UART_Init is called to initialize huart3. The function of the HAL_UART_Init function is similar to that of the HAL_GPIO_Init function that we have explained directly. They all initialize some low-level registers. Interested readers can follow the ideas of our direct explanation of the HAL_GPIO_Init function to track how the serial port registers are initialized. Another point to note is that the HAL_UART_MspInit function is called in HAL_UART_Init to initialize the GPIO pins and clock. The HAL_UART_MspInit function is also generated by STM32CubeIDE for us. The detailed code is as follows:

The functions of the HAL_UART_MspInit function can be divided into setting the serial port clock, pin functions and interrupts. The configuration of the relative serial port is more low-level.

3.4 Serial transceiver function

Among the transceiver functions of the HAL library, the following two groups of transceiver functions are often used:

parameter

huart : UART_HandleTypeDef type structure pointer, which contains the base address of the serial port.

PData : The first address of sending (or receiving) data.

Size : The size of the sent (or received) data.

Timeout : The function timeout period.

return value

Success: HAL_OK

Failure: HAL_BUSY is returned when the serial port is occupied, HAL_TIMEOUT is returned when Timeout is exceeded, and HAL_ERROR is returned when the pData or Size parameter is incorrect.

When the two serial port transceiver functions are called, the function will send in a blocking manner, and when the sending is not completed when the timeout period expires, the sending function will exit.

parameter

huart : UART_HandleTypeDef type structure pointer, which contains the base address of the serial port.

pData : The first address of sending (or receiving) data.

Size : The size of the sent (or received) data.

return value

Success: HAL_OK

Failure: Return HAL_BUSY when the serial port is occupied, and return HAL_ERROR when the pData or Size parameter is incorrect.

When using the interrupted serial port transceiver function, two functions are mainly completed.

Enable the corresponding serial port receive or transmit interrupt.

Assign value to RxISR function pointer or TxISR function pointer in UART_HandleTypeDef.

After completing the interrupt sending and receiving, turn off the receiving or sending interrupt enable, and assign the RxISR function pointer or TxISR function pointer in UART_HandleTypeDef to NULL;

If you need more program code, please contact us.