Interrupt works on for one button but not the other?

[mbeals 74]

I'm in the process of figuring out how interrupts and timers work on this board, so I wrote a short program to adjust the brightness of the blue led by clicking on either button.  The left button trips the interrupt just fine and does what it is supposed to....but the right button will not, even though it is configured identically.  I even tried a simpler version of the code in which would only interrupt pin 0 or pin 4, and even then it will not interrupt on pin 0.  I also tried clearing both interrupts right before entering the main loop, and it didn't help.

 

It has to be something stupid simple, but I can't see it.  The code is below

#include "inc/hw_types.h"
#include "inc/hw_memmap.h"
#include "inc/hw_ints.h"

#include "driverlib/sysctl.h"
#include "driverlib/gpio.h"
#include "driverlib/timer.h"
#include "driverlib/pin_map.h"
#include "driverlib/interrupt.h"

volatile unsigned long ulPeriod = 1000;
volatile unsigned long dutyCycle = 250;

int main(void) {
    // 40 MHz system clock
    SysCtlClockSet(SYSCTL_SYSDIV_5|SYSCTL_USE_PLL|SYSCTL_XTAL_16MHZ|SYSCTL_OSC_MAIN);

    /*Pwm the blue LED*/

    // Configure PF2 as T1CCP0
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
    GPIOPinConfigure(GPIO_PF2_T1CCP0);
    GPIOPinTypeTimer(GPIO_PORTF_BASE, GPIO_PIN_2);


    // Configure timer
    SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER1);
    TimerConfigure(TIMER1_BASE, TIMER_CFG_SPLIT_PAIR|TIMER_CFG_A_PWM);
    TimerLoadSet(TIMER1_BASE, TIMER_A, ulPeriod -1);
    TimerMatchSet(TIMER1_BASE, TIMER_A, dutyCycle); // PWM
    TimerEnable(TIMER1_BASE, TIMER_A);


    /* Configure buttons for input */
    GPIOPinTypeGPIOInput(GPIO_PORTF_BASE, GPIO_PIN_0|GPIO_PIN_4);

    GPIOPadConfigSet(GPIO_PORTF_BASE,GPIO_PIN_0|GPIO_PIN_4,GPIO_STRENGTH_2MA,GPIO_PIN_TYPE_STD_WPU);

    GPIOIntTypeSet(GPIO_PORTF_BASE, GPIO_PIN_0|GPIO_PIN_4, GPIO_FALLING_EDGE);

    GPIOPinIntEnable(GPIO_PORTF_BASE, GPIO_PIN_0|GPIO_PIN_4);


    /* Configure interrupt for buttons */
    IntEnable(INT_GPIOF);
    IntMasterEnable();



    while(1){}
}

void IntGPIOF(void)
{
	if (GPIOPinIntStatus(GPIO_PORTF_BASE, GPIO_PIN_0) & GPIO_PIN_0)
	{
		GPIOPinIntClear(GPIO_PORTF_BASE, GPIO_PIN_0);
	    TimerMatchSet(TIMER1_BASE, TIMER_A, dutyCycle+=100);
		if(dutyCycle >= ulPeriod - 1) dutyCycle = 0;

	}else{
	    GPIOPinIntClear(GPIO_PORTF_BASE, GPIO_PIN_4);
	    TimerMatchSet(TIMER1_BASE, TIMER_A, dutyCycle-=100);
	    if(dutyCycle < 100 ) dutyCycle = ulPeriod - 1;
	}
}

[igor 163]

Port F pin 0 has special function (NMI), so you have to do a special incantation to program it as an input.

 

See drivers/buttons.h in stellarisware for an example

    HWREG(GPIO_PORTF_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY_DD;
    HWREG(GPIO_PORTF_BASE + GPIO_O_CR) |= 0x01;
    HWREG(GPIO_PORTF_BASE + GPIO_O_LOCK) = 0;

[mbeals 74]

Thanks.  Worked perfectly.

 

What exactly does NMI do in this context (what utility is there in binding it to this pin to begin with)?  

[igor 163]

I would guess the reason for putting a push button on the non-maskable interrupt input is sort of like the programmer's button on the Apple II.

It gives a way to get the processor back to some known code (if it wanders off into never never land), of course you have to write the handler.

Note that the same button is also wired to the !Wake input - again making it into a kind of wake up and pay attention button (but not as drastic as reset).

(The special incantation means your errant code is highly unlikely to change the programming of that pin.)

 

Also, there are a limited number of pins, and a lot of functions, so things get overlaid.

 

They should do a better job at documenting it though.  The launchpad manual should have a warning under user switches and buttons, pointing out

the need for a special incantation to program PF0.

 

(Of course there are a number of things the launchpad manual should cover more clearly, like PD7 wiring should be mentioned under USB).