Nano second Precision using a hardware timer on STM32L4S5ZI

[SJant.1]

Hi,

I am working with STM32L4S5ZI MCU and I have a custom board with the same.

I am evaluating the hardware timer and as part of my project I need time in nano seconds for some time constrained work. Right now I am using Timer3 and below is my sample code with which I am able to get the counter value between a start and stop of the timer.

Can I derive the time with nano second precision using these timers on the chip? And I need to do this specifically with a timer and not using any other means like a DWT.

Please let me know if there is a way to do this. Thanks a lot.

int i =1;
regValue = TIM3->CNT; 
printf("Timer value %d\n", regValue);
HAL_TIM_Base_Start(&htim3);
 
printf("Timer cycle %d\n", i);
i++; 
 
HAL_TIM_Base_Stop(&htim3);
regValue = TIM3->CNT;
printf("Timer value %d\n\n", regValue);

[Uwe Bonnes]

Timer resolution is limited by the timer clock Maximum clock is 120 MHz, so you get 8.33 ms resolution.

[SJant.1]

Hi Uwe Bonnes,

Thank you for your response. I figured out the max clock as 120MHz just after posting the above question.

As per your response, the resolution for a 120MHz clock should be 8.33ns rather than 8.33ms right?

Thanks!

[Uwe Bonnes]

Off by one typing...

[Javier1]

If what you want to do is measure the time in nanoseconds in between events (for example width of a digital pulse)

you should take a look at the INPUT CAPTURE funcionality

and maybe use the timer with 0 preescaler and max clock speed

[SJant.1]

Just to confirm what you mean by "Off by one typing" is that you pressed m instead of n right? :)

[SJant.1]

Just wanted to add to the question,

so the max Period that can be set to TIM3 is 65535 since it is a 16bit timer. So once the period is completed I can see that the counter restarts from 0.

Now how can I keep track of the number of times that the period got completed so that at the final calculation I can calculate the entire time?

Sharing something on this would be really helpful. Thanks!

[Uwe Bonnes]

Use Timer overflow interrupt and count overflows. Be carefully when combining overflow count and timer count to a number > 16 Bit!

[SJant.1]

That sounds good.

order to use the interrupts, I should start and stop the timer with interruption right?

HAL_TIMx_BaseStart_IT()

HAL_TIMx_BaseStop_IT()

[SJant.1]

Hi Uwe,

Checkout my below test code, with this I dont see that the callback function

void HAL_GetTimerOverflow_Count(struct __TIM_HandleTypeDef *);
 
int main(void)
{
  /* USER CODE BEGIN 1 */
  uint32_t regValue;
  uint8_t cycles;
 
  /* USER CODE END 1 */
 
  /* MCU Configuration--------------------------------------------------------*/
 
  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();
 
  /* USER CODE BEGIN Init */
 
  /* USER CODE END Init */
 
  /* Configure the system clock */
  SystemClock_Config();
 
  /* USER CODE BEGIN SysInit */
 
  /* USER CODE END SysInit */
  MX_GPIO_Init();
  MX_TIM3_Init();
  HAL_TIM_Base_Start_IT(&htim3);
  TIM3->DIER = TIM_DIER_UIE_Msk;
  
  while (1)
  {
    
    regValue = TIM3->CNT ;
    printf("Timer value %d\n", regValue);
    for(int i=0; i<100000; i++);
    if(overflowCount_g > 0) {
      HAL_TIM_Base_Stop_IT(&htim3);
      regValue = TIM3->CNT;
      HAL_CalculateTime(regValue);
    }
   // printf("Timer value %d\n\n", regValue);
  }
  /* USER CODE END 3 */
}
 
void HAL_GetTimerOverflow_Count(struct __TIM_HandleTypeDef *htim)
{
  overflowCount_g += 1;
} 

is executed but I can see that the counter finished counting till 65535 and started recounting. I have enabled the Update Interrupt in the DIER register. In the call back function I am incrementing a global variable and checking the value to be more than 0 in while loop. But if I put a breakpoint in callback function, I never see that breakpoint being hit.

I have also set the USE_HAL_TIM_REGISTER_CALLBACKS in stm32l4xx_hal_conf.

Is there anything wrong in what I am doing?

Please let me know what do you think

Thanks