STM32f103c8t6 how to comfigure TIM3 for a period of 5ms

[Keita]

Hi community,

I am trying to port a project from old library maple leaf or older built for Arduino to to STM32cubeIDE

this function I couldn't find any ref to it, my guess it that is sets the period to 5ms

Timer3.setPeriod(1000 / 200);

browsing some threads in the community I found this formula for calculating the period

TIM Update = TIM Clock / (X * Y) Prescaler = X - 1 Period = Y - 1

according to it I put Presclaer X-1 = 59999 and Period to 5999

  htim3.Instance = TIM3;
  htim3.Init.Prescaler = 59999;
  htim3.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim3.Init.Period = 5999;
  htim3.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  htim3.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;

Actually the entire code compiles but in the debug session TIM3 never starts, can any knowledgeable person help me to configure this timer for 5ms. thank you in advance.

Note: complete newby here I just started learning about electronics and mcu...

[TDK · Accepted solution]

Your understanding is correct, but not sure the math checks out.

Let's say your timer clock is 72 MHz and you want an update period of 5ms (so 200 Hz update frequency).

Your need a prescaler and period to combine to (72 MHz / 200 Hz) = 360000. One particular set that will satisfy this is PSC (prescaler) = 5 and ARR (period) = 59999.

If instead you have PSC=5999, then the update frequency is 0.2 Hz, or once every 5 seconds.

> in the debug session TIM3 never starts

What does "starts" mean here? Are you watching TIM3->CNT, or are you expecting some code to be called or some event to happen such as an LED blinking?

[Karl Yamashita]

Without you posting more code, don't know if you even started the timer?

[Keita]

Thanks I found the culprit

initialization happens in the TimBase class

void TimBase::init(void){
	if (_Instance == TIM1) {
		if(is_init[0]){
			return;
		}
		is_init[2] = true; //the culprit TIM1 init() call sets TIM3 FLAG
		MX_TIM1_Init();
		return;
	}else if (_Instance == TIM3) {
		if(is_init[2]){
			return;
		}
		is_init[2] = true;
		MX_TIM3_Init();
		return;
	}
}

that's one of issues solved, according to my setting can you tell me if I got it right? the timer3 runs for 5ms.

[Karl Yamashita]

The code shows your are calling MX_TIM1_Init() or MX_TIM3_Init(), but I still don't see code that starts the timer?

HAL_TIM_Base_Start_IT?

[TDK]

		if(is_init[0]){
			return;
		}
		is_init[2] = true; //the culprit TIM1 init() call sets TIM3 FLAG
...
		if(is_init[2]){
			return;
		}
		is_init[2] = true;

Well this seems bogus.

[Keita]

This method does the init as per MXcube configfor TIM3 wich fails

MX_TIM1_Init

As per HAL_TIM_Base_Start_IT() it is called inside the member method start() in the main.cpp

  tim3.start();
  adc1.start();

Like I said the issue with starting TIM3 was related to the init() needed by my own code where the flag for TIM1 was setting init[2] instead of init[0] so the code sets over when calling init() for TIM3 why the start method fails.

the current issue is more related to the period as I explained.

[Keita]

sorry for late replay. I am now trying to solve another technical issue :) regarding the modulation of the analog signal inside the PWM. kind of a hassle I am trying to make a lazer sound spot with transducers array TC40T :p I know not the best component but that's what can use for now. Thank you again

[David Littell]

Is there an actual question anywhere in there?  :thinking_face: