Microsecond Tick

1. Introduction

Microsecond timing is used generally for sampling, pulse generation, frequency counter, precise calculation and many more. Using CPU clock, it may be diffucult to get microsecond ticks or it may not be precise. Timers can be do this job easily and precisely.

2. CubeMX Configuration

• Open CubeMX and generate basic code with:

  • microcontroller: stm32f407vgt6 or board: STM32F407VG-DISC1

  • project name: microtick

  • Toolchain/IDE: Makefile

• Go to Pinout and Congiguration > Timers > TIM1. Select Internal Clock for Clock Source.

Tip

It is better to keep ARR value to maximum i.e. 65535 for 32-bit.

• Generate Code.

3. Code to Get Microsecond Tick

• 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 */
  

• Create variable to store timer period ellapsed count.

  /* USER CODE BEGIN PV */
  uint32_t htim1PeriodEllapsedCount = 0;
  /* USER CODE END PV */
  

• When timer period ellapse, HAL_TIM_PeriodElapsedCallback is fired. Increment the htim1PeriodEllapsedCount in this callback. Also add function to get microtick.

  /* USER CODE BEGIN 0 */
  // ...
  // ...
  
  void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
  {
    if (htim->Instance == htim1.Instance)
    {
      htim1PeriodEllapsedCount++;
    }
  }
  
  uint64_t GetMicros()
  {
    return (uint64_t)htim1PeriodEllapsedCount * htim1.Instance->ARR + (uint64_t)htim1.Instance->CNT;
  }
  /* USER CODE END 0 */
  

• Start the timer in interrupt mode inside main().

  /* USER CODE BEGIN 2 */
  HAL_TIM_Base_Start_IT(&htim1);
  /* USER CODE END 2 */
  

• Now, you can use GetMicros() to get microsecond tick.

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    printf("Micros: %lu\n", GetMicros());
    HAL_Delay(100);
  }
  /* USER CODE END WHILE */
  

• Build and flash the code.

4. Observe Output

Open STM32CubeProgrammer and see output on SWV. If you used USB, see on terminal or serial monitor.