Timer Configuration for specific duration

[dbgarasiya]

Hello ,

I want to configure a timer which start and runs for specific duration and stops automatically

and when again i want to start that timer i could be able to start timer and agian stops automatically

duration is fixed all time

Dipak Garasiya

[berendi]

Enable the timer in RCC. This is dependent on the MCU series, check the reference manual to see which register in RCC has the APB enable bit for the timer.

Set the prescaler (if needed) in PSC, and set the UG bit in EGR.

TIMx->PSC = prescaler - 1; TIMx->EGR = TIM_EGR_UG;

Set the auto reload register (ARR) to the required timer period - 1

TIMx->ARR = period - 1;

Start the timer by setting the counter enable (CEN) and one pulse mode (OPM) bits in CR1.

TIMx->CR1 = TIM_CR1_CEN|TIM_CR1_OPM;

If the timer period is elapsed, (TIMx->CR1 & TIM_CR1_CEN) will be automatically cleared, the timer stops, and you can repeat the line above to start it again.

[dbgarasiya]

If I want to set timer of 5 sec , how to calculate prescaler and period

my system clock is 16MHZ

[berendi]

You need the peripheral clock frequency of the timer, not the system clock. You have already found out in the previous step which APB bus the timer is connected to, so note the frequency of that APB bus.

The frequency is the number of cycles in one second. For a timeout of 5 seconds, the required number of cycles is five times the frequency.

Most timers have 16 bit counters (check the timer main features in the reference manual), and the required number of cycles is likely greater than 2^16, so you have to factorize it into a product of two numbers, both less than 2^16. Then use one of them as the prescaler, the other one as the period.

[dbgarasiya]

Thanks @berendi​ 

I have tried your code but i am not getting clearing register. like i am posting my code with this post

i have test to set pin high for some time to test using timer

RCC->APB1ENR |= (1<<1); // Enable clock for TIM3

TIM3->PSC = 999;    // Int clk divided by 1000(999+1)

TIM3->EGR = TIM_EGR_UG; // Forcing to generate a update

TIM3->ARR = 7999; // Counts from 0 to 7999

TIM3->CR1 = TIM_CR1_CEN|TIM_CR1_OPM;

while ( (TIM3->CR1 & TIM_CR1_CEN) != 0)

{

HAL_GPIO_WritePin(GPIOH, GPIO_PIN_6,GPIO_PIN_SET);

}

Best Regards

Dipak Garasiya

[berendi]

How do you know that CEN does not get cleared? What do TIM3 registers contain when you let it run for a while and stop it? Does it exit the loop?

[dbgarasiya]

I have checked by debugging code , while loop never exits. and stops code there

i have attached my debugging sceenshot where you will get TIM3 register value at timer of entering while loop

Best Regards

Dipak Garasiya

[berendi]

I can't see the screenshot.

Check the timer registers. Do PSC, ARR and CR1 contain the values you've set? Is the counter changing?

[waclawek.jan]

What's *after* the while loop?

Put some code there, e.g. another write to a GPIO pin.

JW

[dbgarasiya]

Sorr for inconvience , i have just attached sceenshot with this post

[dbgarasiya]

I have solved out this problem , actually when i have write some code , like making another gpio write as @Community member​  have suggested, i solved issue

Thanks for support @Community member​  and @berendi​ 

[berendi]

Looks like the debugger got confused because there was no code after the while loop. This happens with gdb.

Add an

asm("nop");

instruction when you are not sure the debugger has something to put a breakpoint on.

[dbgarasiya]

which interrupt is generated when TIM_CR1_CEN becomes zero ?

[berendi]

It's called Update Interrupt, and it's generated every time the counter reaches the limit (even if the timer is not in one-shot mode).

Look the name of the interrupt up in the interrupt and exception vector table in the reference manual. Some timers have one global interrupt, others have separate vectors for different events.

Enable the update interrupt both in the NVIC and in the timer DIER register.