How can I get minimum nanosecond delay with a Nucleo F446RE using a Cortex M4 180 Mhz?

[YSall.1]

Hi everyone,

I am using a nucleo F446RE using a Cortex M4 180 Mhz, and I have a problem when I try to get nano second delays.

void delay (uint16_t delay)
 
{
 
	__HAL_TIM_SET_COUNTER(&htim1,0);
 
	while(__HAL_TIM_GET_COUNTER(&htim1)<delay);
 
 
 
}

In the main, while(1):

HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_1);
 
	 delay(1);

I used this function to set the delay according to the clock. I set up the APB2 clock corresponding to the timer 1 at 100 MHz, logically the function delay(1) would get me a delay of 10 ns, but the problem is that I only have a minimum value of 530 ns delay.

What would be a better method to get a minimum delay without using assembly language?

[Uwe Bonnes]

You will not get reproducable delays. Flash prefetch for the called function, stack setup inside the called function, bus contention and code alignment will lead to substantial variance.

[MM..1]

Try change delay func to inline

[YSall.1]

I tried but there is no effect

[YSall.1]

Even without a function called, for exemple using this inside the while doesn't get me results, the minimum I got was 460 ns:

timer_val=__HAL_TIM_GET_COUNTER(&htim1);
 
while (1)
{
if (__HAL_TIM_GET_COUNTER(&htim1)-timer_val>=1)
	  {
		HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_1);
		timer_val=__HAL_TIM_GET_COUNTER(&htim1);
	  }
}

So the best way to obtain what I want is in assembly ?

[Uwe Bonnes]

Multiple pin operations will prolong that operation in a much more controlled way. However the jump at the end of the loop will eat up a hard controllable number of cycles.

while(1) {
SetPin(pin);
SetPin(pin);
SetPin(pin);
ClearPin(pin);
ClearPin(pin);
}

[YSall.1]

Thank for your response but there is a deeper problem as I tried to see the resolution of the while loop using a LL-Driver instruction to get a more optimised way, but the minimum of the while loop is 344 ns (I saw it on a 100MHz Oscilloscope), I used this code:

LL_GPIO_TogglePin(GPIOA, LL_GPIO_PIN_1);

So how can I increase the while loop frequency?

[YSall.1]

To precise that there is a net performance between LL and HAL as for HAL instruction I got around 500ns

[waclawek.jan]

Enable compiler optimization.

JW

[Bob S]

And disable interrupts. Any interrupt occurring during your tight loop (including SysTick) will ruin your tightly coded delays.