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Not executing while condition

Associate II


float init_sensor(void){

	uint32_t numTicks;
	float distance;

	RCC->AHB1ENR		|= (1U<<1);
	GPIOB->MODER		&=~	(1U<<19);		//  pin 9 as output
	GPIOB->MODER		|=	(1U<<18);		//  pin 9 as output
	GPIOB->MODER		&=~	(1U<<16);		//  pin 8 as input
	GPIOB->MODER		&=~	(1U<<17);		//  pin 8 as input
	GPIOA->MODER		|=	(1U<<10);
	GPIOA->MODER		&=~	(1U<<11);
	RCC->CFGR			|= (1U<<4);
	RCC->CFGR			|= (1U<<5);
	RCC->CFGR			&=~ (1U<<6);
	RCC->CFGR			|= (1U<<7);

		//generate 10uS pulse and 250uS delay
		GPIOB->ODR			|= (1U<<9);
		GPIOB->ODR			&=~ (1U<<9);
		while((GPIOB->IDR) & (1U<<8)){
		distance = (numTicks)/58;
	return distance;



I wrote this code,

and the code get stuck in the while GPIOB condition and I don't know why..

it's also happens when I tried similar condition to check UIF timer flag.

I checked it with my oscilloscope and pin8 generate pulses so numTick should be increment, I don't know why the code not processed.


Edit: the problem is the IDR not updating value although the pin get signals from the sensor.

any ideas?


First of all, when posting code, please use the </> button, that makes it more readable.

Next, although it's really nice that you are using registers and not HAL functions, it will help you and us if you not use (1U<<9) for register settings, but the bit defines from the STM32xyz.h file. Believe me, in a few weeks you will probably not remember what bit x of register y means.

Now about your code:

1) Setup: try to set mode of input pin to input MODER.xy = 00, now it's set to analog

2) Then you set pin 9 to 1, then to 0, then you wait in the while loop that pin 8 gets 1.

Even assuming that pin 8 and 9 are connected, this leads to getting stuck in the while loop, because pin 8 = 0, so pin 9 = 0


Associate II

thank you for the answer.

I don't realize you proper.

are you saying that the problem is pin configuration? that's why the while condition not working?

I'm pretty sure the pins configuration is ok because I copied this code from a working project.




I'm not sure what "analog mode" = 11 is, I guess input without Schmitt-trigger.

Maybe try 00.

Anyway, I made a mistake and didn't read your while loop properly.

Right now you set pin 9 = 0, then the next while(pin 8 == 1) numTicks++; never increments numTicks because pin 8 = 0.

What do you actually want to do?

And again, are pin 8 & pin 9 connected?

Associate II

I'm trying to generate pulse for ultra-sonic distance sensor(HC-SR04) and it works. its  calculate distance by counting the pulse width time. 

in my case pin 9 should send a pulse from the stm32 and pin 8 ( input)  should get his "1" from the sensor - and according to my oscilloscope it's working but for some reason the code not increasing numTicks variable although there is a "1" in pin8.


Whats coming in , pin8 ? (show scope screen)


Maybe your code is working , but no timeout there. So if it "miss" the pulse, it will wait forever.

I would just do some limit here:

	while((GPIOB->IDR) & (1U<<8)
            if (numTicks > 10000000) break;  // max. possible distance
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yes pin 8 is input.

I added 2 lines to check : 



while(!((GPIOB->IDR) & GPIO_IDR_ID8)){


and the variable check is increase which means the problem is the IDR don't get "1" value at all..

Wait until the input becomes 1 BEFORE you start counting the time. Your code has many other problems but this is the starting point.

Associate II

that what I did in the while..

the while says "wait until input "1" and then count numTicks"