I am using stm32l011K4U3 microcontroller on a custom made pcb. I am trying to use EXTI on PC14 pin (which is also oscillator input pin). The interrupt is triggering continuously even though there is no raising or falling edge on the pin.

[PPULA.1]

I am unable to clear the EXTI pending register it always stays high and probably that is what is causing interrupt to trigger again and again. I am attaching snippets of code .Please Help me figure out the issue .

#include "stm32l0xx.h"                  // Device header
#include "RTE_Components.h"             // Component selection
 
volatile int HPA,HPB,HPC,interrupt,interrupt1;
 
void clock_init(void);
void gpio_init(void);
void exti_interrupt_init(void);
 
 
int main(void){
	clock_init();
	gpio_init();
 exti_interrupt_init();
	__enable_irq();
 
	while(1){
	//NOTHING TO DO
	}
 
}
 
void clock_init(void){
 
	RCC->APB1ENR|=RCC_APB1ENR_PWREN; //PWR clock enable
	PWR->CR=0x800;										//set vcore to 1.8V	
	
	while((PWR->CSR & PWR_CSR_VOSF));		// wait till core voltage is setelled
	
	RCC->CR &=~(1<<RCC_CR_PLLON_Pos);	//disable pll
	
	RCC->CSR&=~(1<<RCC_CSR_LSEON_Pos);	//TURN OFF LSE
	RCC->CR&=~(1<<RCC_CR_HSEON_Pos);		//TURN OFF HSE
	
	RCC->CR |= 1<<RCC_CR_HSION_Pos;			//enable internal HSI16 MHz oscillator
	RCC->CFGR|=RCC_CFGR_PLLDIV2 | RCC_CFGR_SW_PLL | RCC_CFGR_PLLMUL4;//select pll as system clock, pllvco=hsi*6=16*6=96Mhz, core freq=pllvc0/plldiv=96Mhz/3=32Mhz
	
	RCC->CR|=RCC_CR_PLLON;	//enable pll
	while(!(RCC->CR & RCC_CR_PLLRDY));		// wait till pll is on
	
	//RCC->APB1ENR|=RCC_APB1ENR_TIM2EN | RCC_APB1ENR_I2C1EN |RCC_APB1ENR_LPTIM1EN |RCC_APB1ENR_USART2EN ;	//ENABLE clock for timer 2,i2c1
	RCC->APB2ENR=RCC_APB2ENR_SYSCFGEN;	//ENABLE clock for SYSCFGEN
	}
	
	
	void gpio_init(void){
 
	RCC->IOPENR |= 0b111;   //clk for portA,B,C
	
	
	/*hall sensor pins*/
 
	GPIOC->MODER &=~((0b11)<<28);	//PC14(HPC) AS INPUT	
	
 
	
}
 
void exti_interrupt_init(void){
 
	SYSCFG->EXTICR[3]|=SYSCFG_EXTICR1_EXTI3_PC;
	EXTI->IMR|=1<<EXTI_IMR_IM14_Pos;	//INTERRUPT UNMASK ON 14
	EXTI->RTSR|=1<<EXTI_RTSR_RT14_Pos;	//ENABLE RISING INTERRUPT
	EXTI->FTSR|=1<<EXTI_FTSR_FT14_Pos;//ENABLE FALLING INTERRUPT
	NVIC_EnableIRQ(EXTI4_15_IRQn);	//ENABLE IRQ4-15
 
 
}
 
 
 
 
void EXTI4_15_IRQHandler(void){
	interrupt++;	//	KEEP TRACK OF NUMBER OF INTERRUPTS
	if (EXTI->PR & (1<<14)) {                       // CLEAR PENDING INTERRUPT !!!!!!!! HERE IS THE ISSURE IT NEVER GETS CLEARED 
    EXTI->PR = (1<<14);
	}
	HPC=(GPIOC->IDR & 0x8000);	//PC15
	HPB=(GPIOA->IDR & 0x0001);	//PA0
	HPA=(GPIOC->IDR & 0x4000);	//PC14
}
 
 

[waclawek.jan · Accepted solution]

Try to read out all the relevant registers' content (GPIOC, EXTI, SYSCFG), to check whether they are set as you expect them.

> SYSCFG->EXTICR[3]|=SYSCFG_EXTICR1_EXTI3_PC;

Are you sure?

JW

[PPULA.1]

Thank you for the reply . SYSCFG->EXTICR[3]|=SYSCFG_EXTICR1_EXTI3_PC; is to select the source input for the EXTIx external interrupt which in my case is PORTC . I checked this in the register window too .

I have checked the register contents and they seem to change as I expect . Only issue is the PC14 EXTI pending register which is always set high even though I am trying to clear it in the interrupt as soon as I enter it .

I have tried a different pin ,namely PC15 as external interrupt and I see that it is triggering as expected . PC14,PC15 both have same interrupt handler EXTI4_15_IRQHandler.

I was thinking may be this has got something to do with the nature of the pin PC14 which is a clock input for the mcu and I am probably missing setting to do . Any help would be great . Thank you

[waclawek.jan]

SYSCFG->EXTICR[3]|=SYSCFG_EXTICR1_EXTI3_PC; 

On which address is this register, and what is its value?

JW

[PPULA.1]

Thanks a lot . My understanding of SYSCFG_EXTICR1_EXTI3_PC was wrong . It was not enabling exti for PC14 . Thank you very much