#include "mbed.h"

volatile uint32_t systick=0;

extern "C" void RIT_IRQHandler()
{
    //update counter
    systick++;
    
    //clear flag
    LPC_RIT->RICTRL |= (1<<0);
}

int main(void)
{
    //initialize timer
    LPC_SC->PCONP |= (1<<16);             //power up RIT clock
    LPC_SC->PCLKSEL1 |= (3<<26);          //run RIT clock by 12MHz (prescale by 8)
    LPC_RIT->RICOUNTER = 0;               //set counter to zero
    LPC_RIT->RICOMPVAL = 12000000;        //interrupt tick every second
    LPC_RIT->RICTRL |= (1<<1) | (1<<3);   //enable timer clear on match

    //enable interrupt
    NVIC_EnableIRQ(RIT_IRQn);

    while(1) {
      wait(5.0);
      printf("%d\r\n", systick);
    }
}

So I have this code (smaller part of my program) <<code>> #include "mbed.h" volatile uint32_t systick=0; extern "C" void RIT_IRQHandler() { //update counter systick++; //clear flag LPC_RIT->RICTRL |= (1<<0); } int main(void) { //initialize timer LPC_SC->PCONP |= (1<<16); //power up RIT clock LPC_SC->PCLKSEL1 |= (3<<26); //run RIT clock by 12MHz (prescale by 8) LPC_RIT->RICOUNTER = 0; //set counter to zero LPC_RIT->RICOMPVAL = 12000000; //interrupt tick every second LPC_RIT->RICTRL |= (1<<1) | (1<<3); //enable timer clear on match //enable interrupt NVIC_EnableIRQ(RIT_IRQn); while(1) { wait(5.0); printf("%d\r\n", systick); } } <</code>> interrupt works fine, only problem is, systick is incremented twice. 1st printf - systick=10 2st printf - systick=20 etc... I don't see any reason why my program is behaving as such

extern "C" void RIT_IRQHandler()
{
    //clear flag
    LPC_RIT->RICTRL |= (1<<0);

    //update counter
    systick++;
}

Hi, Try this in your interrupt handler: <<code>> extern "C" void RIT_IRQHandler() { //clear flag LPC_RIT->RICTRL |= (1<<0); //update counter systick++; } <</code>>

wow, it works. thanks but i don't get why it behaves like that