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]

Don't you need to configure P0.17 as an output since it resets to an input with buffer disconnected?

[bitFrost]

I'm sorry. There is of course some code not shown in this example. Like UARTE initialization and pin configuration.

[FormerMember]

It should normally not be any problem to use global variables in an interrupt context. When defining 'temp' as a global variable, does it change anything if it is declared as static volatile?

[butch]

If you still have a problem, it might help to post all of the exact code that doesn't work. You have only posted the code (and only part of it) that does work. The problem could be something as simple as a typo. Few readers will try to debug code they can't see. Some readers won't mind reading a lot of code, but sometimes it helps to reduce the code to a minimum that demonstrates the problem. Also, have you tried without optimization?

[bitFrost]

@butch Now you have the complete code in a simplified example.