What is accurate way of generete microsecond delay function without systick timer ?

[hazall]

Here is my code, but its not working correctly

 
void DelayMicros(uint32_t micros) {
	
	   uint32_t multiplier;
     multiplier = SystemCoreClock / 4000000;
 
    micros = micros * multiplier - 10;
    /* 4 cycles for one loop */
    while (micros--);
}
 

[RomainR.]

Hello @hazall (Community Member)

Using a GP Timer:

https://community.st.com/s/question/0D50X0000A7UdMjSQK/how-to-correctly-set-up-a-micro-second-timer

Using DWT (only for STM32 with ARM M3/M4/M7/M33 cpu)

https://community.st.com/s/question/0D50X0000BGkxmCSQR/stm32l462-delay-in-a-microsecondus

Regards,

romain.

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[TDK]

You can't count on the loop taking 4 ticks per cycle. The compiler can optimize it out entirely. You can define the loop variable as volatile, in which case the compiler can't optimize it out, but you still cannot guarantee 4 ticks/cycle in general. Using a timer seems best, there are usually more than enough to go around.

[Piranha]

A busy loop delay can be accurate only when written with assembly. And even then an interrupt can happen and f*ck up the accuracy severely.

[Tesla DeLorean]

Use a TIM clocking faster, in free run, without interrupts and check the CNT register, delta that and compare.

[S.Ma]

As said, debug cycle counter seems nice for microseconf delays.

On cortex M0 STM32, I use a LPTIM for it. Can generate an interrupt if later on the core "sleeps' to save a bit more power.