Can't access variable in IRQ Handler

[bitFrost]

Hi,

I'm getting familiar with my nRF52 DK (PCA 10040).

I stumbled on something when I was doing an application that toggles LED1 on every TIMER0 event (200ms). Here is my code

#include "stdint.h"
#include "nrf52.h"

//volatile uint32_t varA;	<POS A>

void initSystem (void) {	
    NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
    NRF_CLOCK->TASKS_HFCLKSTART = 1;	
    while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) { }

    NRF_TIMER0->MODE		= 0;
    NRF_TIMER0->BITMODE		= 3;
    NRF_TIMER0->PRESCALER	= 5;
    NRF_TIMER0->CC[0]		= 100000;		// TIMER0_IRQn event each 200ms

    NRF_TIMER0->INTENSET	= (1<<16);

    NRF_TIMER0->TASKS_CLEAR = 1;
    NRF_TIMER0->SHORTS		= 1;
    NRF_TIMER0->TASKS_START = 1;

    NVIC_SetPriority(TIMER0_IRQn, 7);
    NVIC_ClearPendingIRQ(TIMER0_IRQn);
    NVIC_EnableIRQ(TIMER0_IRQn);
}

int main (void) {		
    NRF_P0->DIRSET = (1<<17);
    NRF_P0->OUTSET = (1<<17);

    initSystem();

    while (1) { }
}

void TIMER0_IRQHandler (void) {	
    volatile uint32_t varA;		// <POS B>

    varA = NRF_P0->OUTSET & (1<<17);

    if (varA)
	    NRF_P0->OUTCLR = (1<<17);
    else
	    NRF_P0->OUTSET = (1<<17);	

    NRF_TIMER0->EVENTS_COMPARE[0] = 0;
}

Everything is great. But if I move the declaration of the varA to the top (i.e. in my opinion declaring it as a global variable) it does not work. I don't get a compile or link error. The LED just won't toggle.

Why can't I access global variables inside my IRQ Handler??

NOTE: I'm only using CMSIS: Core and Device startup

[butch]

BTW, the var is not really volatile, only the IO regs, since you only write and read the var from one thread (the IRQ handler.) But I suppose you declared it volatile to insure it was not optimized away. The Nordic definitions should declare the IO regs as volatile to insure reads and writes are not optimized away. But you already said you have tested without optimizing.