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

[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 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.

[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.

[Ramazan Gülcan]

Posted on June 17, 2018 at 00:21

htim1.Init.Period = 65535;

unfortunately did not work

[Ramazan Gülcan]

Posted on June 17, 2018 at 00:32

I think it's a problem because the subtraction process is not an absolute value. 

for example; 

us=500

baslangic=65500

current get timer = 300 (autoreload overflow after from 65535  - > +1 CNT = 0 ) 

substract = 300 - 65500 = -65200

because -65200 < 500 while loop is constantly going on

As a solution, the absolute value must be applied, or the timer module must be reset each time.

[Tesla DeLorean]

Posted on June 17, 2018 at 00:43

That's not how unsigned 16-bit math works. Also for the wrapping to work properly the Period needs to be 0xFFFF (65535)

336 < 500

Perhaps the HAL function is masking the volatile nature of the peripheral register, assuming optimization involved.

void US_BEKLE(uint16_t us)

{uint16_t baslangic = (uint16_t)TIM1->CNT;

while( (uint16_t)(TIM1->CNT - baslangic) < us);

}

And your complaint is that it isn't exiting the loop?

What tool chain is involved here?

[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)

;

}

[Ramazan Gülcan · Accepted solution]

Posted on June 17, 2018 at 14:07

I solved the problem. As I said, there was a problem when the subtraction was negative. It worked smoothly in the following manner.

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) && (baslangic - ((uint16_t) __HAL_TIM_GET_COUNTER(&htim1))  <  (65535 - us)) );

}

Thanks