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dbgarasiya
dbgarasiya
Senior
January 18, 2020
Solved

how to set long delay with use of timer(like up to 5 minute,)

  • January 18, 2020
  • 26 replies
  • 13086 views

part number: STM32F779BI

I am using clock frequency 108 MHz ( not system clock , system clock is 216 MHZ)

I don't want to use loop

if not possible what is the maximum value i could set using timer

This topic has been closed for replies.
Best answer by turboscrew

Ahh, not 10 ms period, but 10 ms ticks that the timer counts.

You need to divide the clock by 1080000. That won't fit into a 16-bit prescaler. you need to prescale the APB bus timer clock too. The down side is that all timers on the same APB bus are slowed down. 54000 fits in a 16-bit prescaler, so you need to divide the bus timer clock by 20. I don't have the reference manual for that chip at hand to check what you can do with the bus clocks.

If you have a timer with 32-bit prescaler, you write (1080000-1) into the prescaler (supposing that the bus clock to that timer is 108MHz too).

Then you probably have 32-bit counter (and ARR) too. The maximum is then 42949672,95 seconds = ~ 1.3 years.

The other way could be the earlier 10 ms timer and a software counter. The timer interrupts at ARR (=10000-1) and the interrupt adds 1 to a global variable.

26 replies

Tesla DeLorean
Tesla DeLorean
Guru
January 18, 2020

TIM2 and TIM5 are 32-bit with 16-bit prescaler, should be able to get quite a span with those.​

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dbgarasiya
dbgarasiyaAuthor
Senior
January 18, 2020

Thanks a lot , i have done

dbgarasiya
dbgarasiyaAuthor
Senior
January 18, 2020

I Have done using timer2 and timer5 ,but just want to know is it possible another method to generate delay with using another timers (except TIM2 & TIM5)

i know that other timers are 16 bit , so maximum value could be 65536 ,so if any other way i could configure then please suggest

Thanking in advance

berendi
berendi
Principal
January 18, 2020

The real time clock has two programmable alarms that can be set one month in advance.

Using one timer as a prescaler for another. Setting both PSC and ARR in the master timer sufficiently high, the slave might tick once every second or at even longer intervals. The maximum time interval that can be set using two 16 bit timers is thus 2^64 divided by the timer clock frequency.

turboscrew
turboscrew
Senior III
January 19, 2020

You can also cascade timers such that one timer works as a slave to an other timer such that the slave counts events from its master - like update events.

That slave can then used as a master to a third timer...

dbgarasiya
dbgarasiyaAuthor
Senior
January 20, 2020

I want to use TIM3 as slave and TIM2 as master

RCC->APB1ENR |= (1<<0);   // Enable clok for timer 2

TIM2->CR2 |= TIM_CR2_MMS_1;

TIM2->PSC = 54000;         // will give me timer2 as 1 ms clock clycle

TIM2->EGR = TIM_EGR_UG;

TIM2->SMCR |= TIM_SMCR_ETPS_0;  

TIM3->SMCR |= TIM_SMCR_TS_0;  

TIM3->SMCR |= TIM_SMCR_SMS_0 | TIM_SMCR_SMS_1 |TIM_SMCR_SMS_2;  

TIM3->EGR = TIM_EGR_UG;

TIM2->CR1 = TIM_CR1_CEN;

TIM3->CR1 = TIM_CR1_CEN;

while(1)

{

//read both timers

}

My problem is I am getting timer 2 proper value but i am getting timer 3 count always zero

I am attaching you my clock configuration with this post

berendi
berendi
Principal
January 20, 2020

Is the clock of TIM3 enabled in RCC too?

dbgarasiya
dbgarasiyaAuthor
Senior
January 20, 2020

no

is it required

will TIM2 won't triger this ?

berendi
berendi
Principal
January 20, 2020

RCC clock is required even to read/write the registers. Are the other registers of TIM3 set as expected, or are they all 0s?

The master clock drives the slave counter, everything else is powered by the RCC clock.

dbgarasiya
dbgarasiyaAuthor
Senior
January 20, 2020

ok, I will configure , and let you know

dbgarasiya
dbgarasiyaAuthor
Senior
January 20, 2020

I have updated my code, but still not working,

RCC->APB1ENR |= (1<<0);   // Enable clok for timer 2

RCC->APB1ENR |= (1<<1);   // Enable clok for timer 3

TIM2->PSC = uwPrescalerValue;

TIM3->PSC = uwPrescalerValue;

TIM2->EGR = TIM_EGR_UG;

TIM3->EGR = TIM_EGR_UG;

TIM2->CR2 |= TIM_CR2_MMS_1;

TIM2->SMCR |= TIM_SMCR_ETPS_0;  // done

TIM3->SMCR |= TIM_SMCR_TS_0; // done

TIM3->SMCR |= TIM_SMCR_SMS_0 | TIM_SMCR_SMS_1 |TIM_SMCR_SMS_2; // done

TIM2->CR1 = TIM_CR1_CEN;

TIM3->CR1 = TIM_CR1_CEN;

waclawek.jan
waclawek.jan
Super User
January 20, 2020

Be more specific with "not working".

Read out and check the content of both TIMs' registers.

JW

dbgarasiya
dbgarasiyaAuthor
Senior
January 20, 2020

0690X00000BwC8lQAF.pngI am attaching you two screenshot , which is at break point before entering in while loop, where i finally read timer count , all configuratin done before this step

for both timers

berendi
berendi
Principal
January 20, 2020

You can see the prescaler and period (ARR) values for TIM2. Using these and the APB clock value, you can calculate the period of TIM2. Now multiply this period with the prescaler of TIM3. That's when the counter of TIM3 will be incremented by 1.

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