Need a counter to count in micro seconds

[RRajb.1]

Hi All,

I am using STM32F74xxx.

I need to count micro seconds. currently we are using HAL_GetTick(), function but it gives the time in ms.

After I searched on google I found some ways to get micro seconds count, and I tried it but no luck.

can any one help me here?

This is what I tried to use but my board gets rebooted.

void DWT_Init(void)

{

 if (!(CoreDebug->DEMCR & CoreDebug_DEMCR_TRCENA_Msk))

 {

  CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;

  DWT->CYCCNT = 0;

  DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;

 }

}

uint32_t DWT_Get(void)

{

 return DWT->CYCCNT;

}

uint8_t DWT_Compare(int32_t tp)

{

 return (((int32_t)DWT_Get() - tp) < 0);

}

void DWT_Delay(uint32_t us) // microseconds

{

 int8_t correction_factor = 8;

 int32_t tp = DWT_Get() + us * ((SystemCoreClock/1000000) / correction_factor);

 while (DWT_Compare(tp));

}

/**

 * @brief Initializes DWT_Clock_Cycle_Count for DWT_Delay_us function

 * @return Error DWT counter

 *     1: clock cycle counter not started

 *     0: clock cycle counter works

 */

uint32_t DWT_Delay_Init(void) {

 /* Disable TRC */

 CoreDebug->DEMCR &= ~CoreDebug_DEMCR_TRCENA_Msk; // ~0x01000000;

 /* Enable TRC */

 CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk; // 0x01000000;

 /* Disable clock cycle counter */

 DWT->CTRL &= ~DWT_CTRL_CYCCNTENA_Msk; //~0x00000001;

 /* Enable clock cycle counter */

 DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk; //0x00000001;

 /* Reset the clock cycle counter value */

 DWT->CYCCNT = 0;

   /* 3 NO OPERATION instructions */

   __ASM volatile ("NOP");

   __ASM volatile ("NOP");

 __ASM volatile ("NOP");

 /* Check if clock cycle counter has started */

   if(DWT->CYCCNT)

   {

    return 0; /*clock cycle counter started*/

   }

   else

 {

  return 1; /*clock cycle counter not started*/

 }

}

main()

{

DWT_Init();

uint32_t count = 0;

while(1)

{

DWT_Delay(2000000);

printf("count = %lu\r\n",count++);

}

}

Is there any other way to get microseconds count at run time? currently all my timers are in use.

[KnarfB]

You need to speak a magic word first:

CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
DWT->LAR = 0xC5ACCE55;
DWT->CYCCNT = 0;
DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;

Next, stick to uint32_t when comparing differences, this will handle overflows correctly because the diff is silently modulus 2^32.

uint32_t tick = DWT->CYCCNT;
...
uint32_t tock = DWT->CYCCNT;
...
if( tock - tick > delay )

[RRajb.1]

Thanks KnarfB for the quick response,

I think I am able to access DWT registers now, but I am still not getting how to use it for getting count at real time?

Is it correct what I am planning to do?

this is for just basic understanding.

uint32_t curr_tick = 0;

main()

{

    curr_tick = DWT->CYCCNT;   

 //some task

if((DWT->CYCCNT - curr_tick) >= 1000000)

{

printf("after 1 sec\r\n");

}  

}

[KnarfB]

Yes. If you need a delay_us function you wait in a while loop until the condition is met. This is busy waiting though, the while loop eats up the whole processor.

[Tesla DeLorean]

Might be simpler just to configure TIM2 or TIM5 as 32-bit timers, of maximal length, prescaled down to 1 MHz