DWT_Library not working for STM32F767

[VPras]

Hi,

I'm using DWT library to generate us_delay.

#include "stm32f7xx_hal.h"          // change to whatever MCU you use
#include "dwt_delay.h"
 
/**
 * Initialization routine.
 * You might need to enable access to DWT registers on Cortex-M7
 *   DWT->LAR = 0xC5ACCE55
 */
void DWT_Init(void)
{
    if (!(CoreDebug->DEMCR & CoreDebug_DEMCR_TRCENA_Msk)) {
    	DWT->LAR = 0xC5ACCE55;
        CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
        DWT->CYCCNT = 0;
        DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
    }
}
 
#if DWT_DELAY_NEWBIE
/**
 * If you are a newbie and see magic in DWT_Delay, consider this more
 * illustrative function, where you explicitly determine a counter
 * value when delay should stop while keeping things in bounds of uint32.
*/
void DWT_Delay(uint32_t us) // microseconds
{
    uint32_t startTick  = DWT->CYCCNT,
             targetTick = DWT->CYCCNT + us * (SystemCoreClock/1000000);
 
    // Must check if target tick is out of bounds and overflowed
    if (targetTick > startTick) {
        // Not overflowed
        while (DWT->CYCCNT < targetTick);
    } else {
        // Overflowed
        while (DWT->CYCCNT > startTick || DWT->CYCCNT < targetTick);
    }
}
#else
/**
 * Delay routine itself.
 * Time is in microseconds (1/1000000th of a second), not to be
 * confused with millisecond (1/1000th).
 *
 * No need to check an overflow. Let it just tick :)
 *
 * @param uint32_t us  Number of microseconds to delay for
 */
void DWT_Delay(uint32_t us) // microseconds
{
    uint32_t startTick = DWT->CYCCNT,
             delayTicks = us * (SystemCoreClock/1000000);
 
    while (DWT->CYCCNT - startTick < delayTicks);
}
 
#endif

I'm trying to integrate the DS18B20 Temperature sensor,where i need microsecond delay .

I feel initialization of DWT is not happening?

any idea to solve the issue?

[Tesla DeLorean]

//******************************************************************************
 
volatile unsigned int *DWT_CYCCNT   = (volatile unsigned int *)0xE0001004; //address of the register
volatile unsigned int *DWT_CONTROL  = (volatile unsigned int *)0xE0001000; //address of the register
volatile unsigned int *DWT_LAR      = (volatile unsigned int *)0xE0001FB0; //address of the register
volatile unsigned int *SCB_DEMCR    = (volatile unsigned int *)0xE000EDFC; //address of the register
 
//******************************************************************************
 
void EnableTiming(void)
{
  *DWT_LAR = 0xC5ACCE55; // unlock
  *SCB_DEMCR |= 0x01000000;
  *DWT_LAR = 0xC5ACCE55; // unlock
  *DWT_CYCCNT = 0; // reset the counter
  *DWT_CONTROL |= 1 ; // enable the counter
}
 
//******************************************************************************
 
void HAL_Delay_us(uint32_t tick) // SystemCoreClock / 1000000 = 1us
{
  unsigned int start, current;
 
  start = *DWT_CYCCNT;
 
  do
  {
    current = *DWT_CYCCNT;
  } while((current - start) < tick);
}
 
//******************************************************************************

[VPras]

Hi Clive ,

I'm toggling the GPIO pin for 50us using above function given by you.but i'm not getting the exact delay .

Please let me know how to fix this???

[Piranha]

Don't You see that Clive's code actually waits clock ticks not microseconds?

[Tesla DeLorean]

That, and one might have to compensate for cycles eaten entering/exiting.

I would tend to use precomputed constants so as not to repeat the math.

Also your wave-form doesn't look 50/50, so clearly doing something else there that you need to adjust/compensate for.

Hard to understand what exactly you're doing when you fail to provide code.

[VPras]

got it working thanks

[JMJV]

Could you please share

[JMJV]

Hi VPras, Could you kindly share your code or share which was the error?