Delay function with timer

[raducara]

Posted on February 22, 2013 at 09:12

Hi, 

I am trying to make a simple delay function using a timer but i get weird results .Here is some of the code void TIMERS_init(){   TIM3->PSC = 23999; // f timer = fclk / 24000 => 1kHz TIM3->ARR = 0xFFFF; TIM3->CR1 = TIM_CR1_CEN; DBGMCU->CR = DBGMCU_CR_DBG_TIM3_STOP;}void Delay_ms(uint16_t ms){ TIM3->CNT = 0; while (TIM3->CNT < ms){}}

while(1){

GPIOC->ODR ^= GPIO_ODR_ODR8; Delay_ms(500); //delay 0.5 sec GPIOC->ODR ^= GPIO_ODR_ODR8; Delay_ms(500); //delay 0.5 sec}The while in main is to test that the blue LED blinks at 2 Hz .I am using keil 4 . In debug if i run step by step works fine , but in continuously run the LED is half bright (probably is on and off at a high frequency) . I can't understand why because the prescalar remains set .

[Tesla DeLorean]

Posted on February 22, 2013 at 09:35

On a VL-Discovery board? Or something else?

Did you enable the TIM3 clocks? What frequency do you see on a scope? Post sufficiently complete examples if you want support.

[raducara]

Posted on February 22, 2013 at 11:17

STM32-discovery with 32F100 uc .

Yes , i enabled the timer clk . I don't have a scope . ________________ Attachments : Source_Code.rar : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006HznG&d=%2Fa%2F0X0000000bSo%2Fh4gOY5ZIGYHyrBe2m.y.Wpc3kVJPeaQah9GXtNCJMaw&asPdf=false

[raducara]

Posted on February 22, 2013 at 12:27

void Delay_ms(uint16_t ms){

TIM3->ARR = ms; TIM3->CNT = 0; while((TIM3->SR & TIM_SR_UIF)==0){}  TIM3->SR &= ~TIM_SR_UIF;}I did some changes and works fine now , but i can't understand why it didn't work the previous version .

[Tesla DeLorean]

Posted on February 22, 2013 at 19:24

void Delay_ms(uint16_t ms)
{
uint16_t start = TIM3->CNT; // assumes struct is volatile
while((TIM3->CNT - start) < ms);
}

Arguably a better solution would be to meter in micro seconds, and have a smaller prescaler.

[zhoupn138]

Posted on March 01, 2013 at 21:18

This delay function needs to take care of the case when there is an overflow in the counter, i.e., TIM3->CNT wraps around.

[Tesla DeLorean]

Posted on March 01, 2013 at 22:09

This delay function needs to take care of the case when there is an overflow in the counter, i.e., TIM3->CNT wraps around.

Actually it does. It might have issues if you exceed the scope (ie >65.535 Seconds), but is otherwise sound.