UART with Polling

1. Introduction

UART in polling mode transmit data and receive data untill the data is transmitted and received respectively or timeout. This is the simplest way to use UART. But it is not efficient as it blocks the CPU for doing other job.

2. CubeMX Configuration

• Open CubeMX and generate basic code with:

  • microcontroller: stm32f407vgt6 or board: STM32F407VG-DISC1

  • project name: uart_polling

  • Toolchain/IDE: Makefile

• Move to STM32CubeMX Pinout and Congiguration. From Categories, select Connectivity > USART2. Change mode to Asynchronous mode.

• Generate code and open the project.

3. Code to Send and Receive Data using UART Polling

• Navigate to Core > Src and open main.c.

• Include header file.

  SWVUSB

  /* USER CODE BEGIN Includes */
  #include <stdio.h>
  /* USER CODE END Includes */
  

• Overwrite definition of _write as:

  SWVUSB

  /* USER CODE BEGIN 0 */
  int _write(int file, char *data, int len)
  {
    for (int i = 0; i < len; ++i)
    {
      ITM_SendChar(data[i]);
    }
    return len;
  }
  /* USER CODE END 0 */
  

• Add code for sender as well as receiver.

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  #define SENDER // comment this line to make for receiver
  
  #ifdef SENDER
    char msg[] = "Hello World\n";
  #endif
  
    while (1)
    {
  #ifdef SENDER
      HAL_UART_Transmit(&huart2, (uint8_t *)msg, sizeof(msg), 1000);
      HAL_Delay(1000);
  #else
      char c;
      HAL_UART_Receive(&huart2, (uint8_t *)&c, sizeof(c), 0); // 0 means if no data is available, it will return immediately
      printf("%c", c);
  #endif
      /* USER CODE END WHILE */
  
      /* USER CODE BEGIN 3 */
    }
    /* USER CODE END 3 */
  

• Build and flash sender code to sending controller.

• Comment #define SENDER. Build and flash the receiver code to receiving controller.

4. Connection

• Connect TX pin of sender to RX pin of receiver.

• Connect GND of both controllers together.

References

References are from STM32 HAL Driver documentation.

HAL_StatusTypeDef HAL_UART_Transmit(UART_HandleTypeDef *huart, const uint8_t *pData, uint16_t Size, uint32_t Timeout)

Sends an amount of data in blocking mode.

Note: When UART parity is not enabled (PCE = 0), and Word Length is configured to 9 bits (M1-M0 = 01), the sent data is handled as a set of u16. In this case, Size must indicate the number of u16 provided through pData.

Parameters:

• huart (UART_HandleTypeDef*) – Pointer to a UART_HandleTypeDef structure that contains the configuration information for the specified UART module.

• pData (const uint8_t*) – Pointer to data buffer (u8 or u16 data elements).

• Size (uint16_t) – Amount of data elements (u8 or u16) to be sent.

• Timeout (uint32_t) – Timeout duration.

Returns:

HAL status.

Return type:

HAL_StatusTypeDef

HAL_StatusTypeDef HAL_UART_Receive(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout)

Receives an amount of data in blocking mode.

Note:

When UART parity is not enabled (PCE = 0), and Word Length is configured to 9 bits (M1-M0 = 01), the received data is handled as a set of u16. In this case, Size must indicate the number of u16 available through pData.

Parameters:

• huart – Pointer to a UART_HandleTypeDef structure that contains the configuration information for the specified UART module.

• pData – Pointer to the data buffer (u8 or u16 data elements).

• Size – Amount of data elements (u8 or u16) to be received.

• Timeout – Timeout duration.

Returns:

HAL status.

Return type:

HAL_StatusTypeDef