Can someone explain how to read these line ?

[ChristenTen]

Hello everyone !

I'm new here and i wanted to know how these lines say please??

I wanted to have microsecond delay for my ultrasonic sensor.

Thanks for all your help!

void usDelay(uint32_t uSec)
{
	if(uSec < 2) uSec = 2;
	usTIM->ARR = uSec - 1; 	
	usTIM->EGR = 1; 			
	usTIM->SR &= ~1; 		
	usTIM->CR1 |= 1; 		
	while((usTIM->SR&0x0001) != 1);
	usTIM->SR &= ~(0x0001);
}

[waclawek.jan]

First, read the timer chapter in reference manual.

 void usDelay(uint32_t uSec)
 {
 	if(uSec < 2) uSec = 2; // sanitize input value, minimum possible duration using this method is 2usec
 	usTIM->ARR = uSec - 1; 	 // counter counts up to 0 to ARR inclusive
 	usTIM->EGR = 1; 	// generate update, this ensures ARR value is copied to the "active" register even its shadowing is on
 	usTIM->SR &= ~1; 	// clear bit 0 i.e. update flag in status register - this is incorrectly written, it should be = rather than &=
 	usTIM->CR1 |= 1; 		// start counter
 	while((usTIM->SR&0x0001) != 1); // wait until update
 	usTIM->SR &= ~(0x0001); // clear update again, again incorrectly (and here, it's better to stop the counter first)
 }

> I wanted to have microsecond delay for my ultrasonic sensor.

There's more to that, e.g. you have to switch on optimization.

JW

[turboscrew]

I don't think these:

usTIM->SR &= ~1;

are wrong. At least timer 1 has a reserved bit in the status register. It shouldn't be written "1".

Then it's better not to alter the other bits.

[waclawek.jan]

https://community.st.com/s/feed/0D50X00009bLSAZSA4

(formatting and videos did not survive migration from jive)

JW