WHILE LOOP PROBLEM FOR MICRO SECONDS WITH TIMER ??

[Ramazan Gülcan]

Posted on June 16, 2018 at 22:25

Hi friends,

The while loop does not work in the following function. Why could it be?

For STM32F407VG;

void US_BEKLE(uint16_t us)

{

uint16_t baslangic = (uint16_t)__HAL_TIM_GET_COUNTER(&htim1);

while(((uint16_t)__HAL_TIM_GET_COUNTER(&htim1)) - baslangic < us);

}

htim1.Instance = TIM1;

htim1.Init.Prescaler = 167;

htim1.Init.CounterMode = TIM_COUNTERMODE_UP;

htim1.Init.Period = 65000;

htim1.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;

htim1.Init.RepetitionCounter = 0;

#microsecond-timer #while-loop

[Tilen MAJERLE]

Posted on June 16, 2018 at 22:29

Hello,

please clarify 'it doesn't work'. Please check some of these questions:

1. Is the timer running?
2. Do you use optimizations and while loop was optimized out?
3. Is your delay longer or shorter than expected?

Best regards,

Tilen

[Ramazan Gülcan]

Posted on June 16, 2018 at 22:40

hi,

timer is running.

I do not use optimization.

I want to run the delay time for 20 us as an example.

[Tesla DeLorean]

Posted on June 16, 2018 at 23:37

For the math to work you want

htim1.Init.Period = 65535;

try this

void US_BEKLE(uint16_t us)

{

uint16_t baslangic = (uint16_t)__HAL_TIM_GET_COUNTER(&htim1);

while( (uint16_t)(__HAL_TIM_GET_COUNTER(&htim1) - baslangic) < us);

}

[Ramazan Gülcan]

Posted on June 17, 2018 at 00:21

htim1.Init.Period = 65535;

unfortunately did not work

[henry.dick]

Posted on June 17, 2018 at 00:47

'

Why could it be?'

look up integer promotion. the simplest yet most complex aspect of C.

[T J]

Posted on June 17, 2018 at 02:59

this is a similar issue to

Turvey.Clive.002

mention of HAL_timeout.

change the order of calculation, (but this is not a good solution)

void US_BEKLE(uint16_t us)

{

uint16_t endTime = (uint16_t)TIM1->CNT + us

while( (uint16_t)(TIM1->CNT ) != endTime); // must be exact, so can fail, if the timer is tooo fast.

}

the problem there is that you may miss a count, just when you need it.. depending on the clocking rate.

I suggest that you use the output compare function of the timer, to be sure that you have a hit.

void US_BEKLE(uint16_t us)

{

uint16_t endTime = (uint16_t)TIM1->CNT + us

// set OutputCompare to endTime

htim->Instance->CCR1 =endTime;

// wait for OC flag;

while( ! htim->Instance->SR & TIM_SR_CC1IF)

;

}