STM32 create a microsecond timer

Question

I'm relatively new to stm32 stuff and I want to get data from some rotary encoder, and I'm using interrupts to do so, I'm using a USB cable to send data from MCU (STM32F103C8T6) to my PC device and I want to send the exact time in microseconds when a rotation happened (my encoder has 20 steps so by moving 18 degrees it will send signal). For example :

500 (time in microseconds)
800
900
1500
...

I'm trying to use timer peripherals in order to achieve that, but no luck. is there any standard way to to do this? Thanks in advance.

My approach was to create an interrupt with timer every 1 microsecond and increase a variable in it. It didn't work right away. My code:

/**
 ******************************************************************************
 * File Name          : main.c
 * Date               : 08/09/2020 20:48:01
 * Description        : Main program body
 ******************************************************************************
 *
 * COPYRIGHT(c) 2020 STMicroelectronics
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *   1. Redistributions of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 *   2. Redistributions in binary form must reproduce the above copyright notice,
 *      this list of conditions and the following disclaimer in the documentation
 *      and/or other materials provided with the distribution.
 *   3. Neither the name of STMicroelectronics nor the names of its contributors
 *      may be used to endorse or promote products derived from this software
 *      without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 ******************************************************************************
 */

/* Includes ------------------------------------------------------------------*/
#include "stm32f1xx_hal.h"

#include "usb_device.h"

/* USER CODE BEGIN Includes */

/* USER CODE END Includes */

/* Private variables ---------------------------------------------------------*/
TIM_HandleTypeDef htim2;

/* USER CODE BEGIN PV */

/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_TIM2_Init(void);

/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

/* USER CODE BEGIN 0 */

/* USER CODE END 0 */

uint32_t c = 0;

int main(void) {

  /* USER CODE BEGIN 1 */

  /* USER CODE END 1 */

  /* MCU Configuration----------------------------------------------------------*/

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();

  /* Configure the system clock */
  SystemClock_Config();

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_TIM2_Init();
  MX_USB_DEVICE_Init();

  /* USER CODE BEGIN 2 */

  /* USER CODE END 2 */
  HAL_TIM_Base_Start_IT( & htim2);
  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  char d[50];
  HAL_Delay(1000);
  while (1) {
    HAL_Delay(1000);
    sprintf(d, "%d \r\n", c);
    CDC_Transmit_FS(d, strlen(d));
  }
  /* USER CODE END 3 */

}

/** System Clock Configuration
 */
void SystemClock_Config(void) {

  RCC_OscInitTypeDef RCC_OscInitStruct;
  RCC_ClkInitTypeDef RCC_ClkInitStruct;
  RCC_PeriphCLKInitTypeDef PeriphClkInit;

  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL6;
  HAL_RCC_OscConfig( & RCC_OscInitStruct);

  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_SYSCLK | RCC_CLOCKTYPE_PCLK1;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
  HAL_RCC_ClockConfig( & RCC_ClkInitStruct, FLASH_LATENCY_1);

  PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USB;
  PeriphClkInit.UsbClockSelection = RCC_USBPLLCLK_DIV1;
  HAL_RCCEx_PeriphCLKConfig( & PeriphClkInit);

}

/* TIM2 init function */
void MX_TIM2_Init(void) {

  TIM_ClockConfigTypeDef sClockSourceConfig;
  TIM_MasterConfigTypeDef sMasterConfig;

  htim2.Instance = TIM2;
  htim2.Init.Prescaler = 48000;
  htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
  // just for test if it can count every 1sec as 1000,000 microsecond
  htim2.Init.Period = 1000;
  htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  HAL_TIM_Base_Init( & htim2);

  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
  HAL_TIM_ConfigClockSource( & htim2, & sClockSourceConfig);

  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
  HAL_TIMEx_MasterConfigSynchronization( & htim2, & sMasterConfig);

}

/** Configure pins as 
 * Analog 
 * Input 
 * Output
 * EVENT_OUT
 * EXTI
 */
void MX_GPIO_Init(void) {

  GPIO_InitTypeDef GPIO_InitStruct;

  /* GPIO Ports Clock Enable */
  __GPIOC_CLK_ENABLE();
  __GPIOD_CLK_ENABLE();
  __GPIOA_CLK_ENABLE();

  /*Configure GPIO pin : PC13 */
  GPIO_InitStruct.Pin = GPIO_PIN_13;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Speed = GPIO_SPEED_LOW;
  HAL_GPIO_Init(GPIOC, & GPIO_InitStruct);

  /*Configure GPIO pin : PA0 */
  GPIO_InitStruct.Pin = GPIO_PIN_0;
  GPIO_InitStruct.Mode = GPIO_MODE_IT_RISING_FALLING;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(GPIOA, & GPIO_InitStruct);

  /*Configure GPIO pins : PA1 PA2 */
  GPIO_InitStruct.Pin = GPIO_PIN_1 | GPIO_PIN_2;
  GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(GPIOA, & GPIO_InitStruct);

  /* EXTI interrupt init*/
  HAL_NVIC_SetPriority(EXTI0_IRQn, 0, 0);
  HAL_NVIC_EnableIRQ(EXTI0_IRQn);

}

int i;
uint8_t bc = 0, bp = 0, ac = 0, ap = 0;
char str[50];
/* USER CODE BEGIN 4 */
/* its encoder code */
void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin) {
  ac = HAL_GPIO_ReadPin(GPIOA, GPIO_PIN_0);
  bc = HAL_GPIO_ReadPin(GPIOA, GPIO_PIN_1);
  if (bc == 0 && bp == 1) {
    if (ac == 0 && ap == 1)
      i = -1;
    else
      i = 1;
    sprintf(str, "%d", i * HAL_GetTick());
    CDC_Transmit_FS(str, strlen(str));
  }
  bp = bc;
  ap = ac;

}

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef * htim) {
  c++;
}

/* USER CODE END 4 */

#ifdef USE_FULL_ASSERT

/**
 * @brief Reports the name of the source file and the source line number
 * where the assert_param error has occurred.
 * @param file: pointer to the source file name
 * @param line: assert_param error line source number
 * @retval None
 */
void assert_failed(uint8_t * file, uint32_t line) {
  /* USER CODE BEGIN 6 */
  /* User can add his own implementation to report the file name and line number,
    ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
  /* USER CODE END 6 */

}

#endif

/**
 * @}
 */

/**
 * @}
 */

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

Answer 1

It's not practical to generate interrupts at 1MHz. I don't have enough information about your application but I can suggest reading timer counter value instead of proceeding a high frequency interrupt.

Configure any of your timers to generate interrupts at 1kHz(PSC = Timer clock(in MHz) - 1, ARR = 999). In timer ISR count milliseconds. When your rotation event triggers you can directly read TIMx_CNT(there is a macro in hal library to read timer counter value) to get microsecond digit.

Answer 2

If you basically need a microsecond counter, then the below code implements what commenters have proposed: SYSTICK is used to increment a counter every millisecond. If you call GetMicros(), the internal SYSTICK counter is read as well to compute the microseconds part.

Note that a GetMicros() is called from regular code and GetMicrosISR() from interrupt handlers.

The code is derived from code in one of the STM32 Arduino cores, which is probably derived from some other code...

The microseconds counter will wrap around after about 70 minutes. It shouldn't be too difficult to extend it to a longer data type.

some.h

extern volatile uint32_t UptimeMillis;

static inline uint32_t GetMicros()
{
    uint32_t ms;
    uint32_t st;

    do
    {
        ms = UptimeMillis;
        st = SysTick->VAL;
        asm volatile("nop");
        asm volatile("nop");
    } while (ms != UptimeMillis);

    return ms * 1000 - st / ((SysTick->LOAD + 1) / 1000);
}

static inline uint32_t GetMicrosFromISR()
{
    uint32_t st = SysTick->VAL;
    uint32_t pending = SCB->ICSR & SCB_ICSR_PENDSTSET_Msk;
    uint32_t ms = UptimeMillis;

    if (pending == 0)
        ms++;

    return ms * 1000 - st / ((SysTick->LOAD + 1) / 1000);
}

some.cpp

volatile uint32_t UptimeMillis;


extern "C" void SysTick_Handler()
{
    UptimeMillis++;
    HAL_IncTick();
}

Answer 3

The answer given by Codo (from the Arduino core) actually behaved glitchy for me.

• I am running on 6 MHz and therefore SysTick->LOAD is 5999 in my case.
• I was calling GetMicrosFromISR() from higher priority ISR.
• Now I heightened Systick priority to 0 but that gave the same results described below.

Note: when Systick is handled on a higher priority as the calling code, GetMicros() can be used instead of GetMicrosISR()

SysTick->VAL counts down in a range of SysTick->LOAD and is substracted from the milliseconds->microseconds offset. (the counting down is compensated by the subtraction) Due to that logic, GetMicros() is starting with "negative" values (upper 3 bytes 0xFF) for the first second. This happens as long ms is low and until SysTick->VAL is low enough to not underflow the calculation.

Next to that I am getting a glitch that on 3 subsequent calls to GetMicros() the middle call sometimes returns a lower value as the first one. This can also be caused by this subtraction, but I am not completely able to pinpoint/reproduce this outside of my normal code. Also the time intervals I got were 100-200 us off which is a big deal if you need to check on 400 us 10% deviations.

I found that the following works more stable:

    range = (SysTick->LOAD + 1);
    return (ms * 1000) + ((range - st) / (range / 1000));

This converts the counter in a scaled up counting value which is added to the milliseconds. This will start nicely from 0 and count up to 0xFFFFFFFF and will overflow every 80+ hours.

For completeness, the systick part from my generic-hal.h:

/* HAL Time functions --------------------------------------------------------*/
#if defined(HAL_IncTick)
#define GetMillis() HAL_GetTick()
#define Delay_ms(t) HAL_Delay(t)
#else
void SysTick_Handler_custom(void);
uint32_t GetMillis(void);
void Delay_ms(uint32_t wait_ms);
#endif

uint32_t GetMicros(void);
uint32_t GetMicrosISR(void);

And generic-hal.c:

/* HAL Time functions --------------------------------------------------------*/
#if !defined(HAL_IncTick)
volatile uint32_t ticks_ms = 0;

void SysTick_Handler_custom(void)
{
    ticks_ms++;
}

uint32_t GetMillis(void)
{
    return ticks_ms;
}

void Delay_ms(uint32_t wait_ms)
{
    uint32_t start = GetMillis();
    do {
    } while ((GetMillis() - start) < wait_ms);
}
#endif // !defined(HAL_IncTick)

// SysTick does not decrement on microseconds, due to lack of prescaler and limited divider.
// Scale is adjusted in the return formula.
// The unmodified example for this code can be found on:
// https://electronics.stackexchange.com/questions/521020/stm32-create-a-microsecond-timer
uint32_t GetMicros(void)
{
    uint32_t ms;
    uint32_t st;
    uint32_t range;

    do  // Retreive SysTick->VAL, retry on a ms transition because that will reload SysTick
    {
        ms = GetMillis();
        st = SysTick->VAL;
        asm volatile("nop");
        asm volatile("nop");
    } while (ms != GetMillis());

    range = (SysTick->LOAD + 1);
    return (ms * 1000) + ((range - st) / (range / 1000));
}

uint32_t GetMicrosISR(void)
{
    uint32_t st = SysTick->VAL;
    uint32_t pending = SCB->ICSR & SCB_ICSR_PENDSTSET_Msk;
    uint32_t ms = GetMillis();

    if (pending == 0)
        ms++;

    uint32_t range = (SysTick->LOAD + 1);
    return (ms * 1000) + ((range - st) / (range / 1000));
}