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embeddedmicrocontrollerinterruptlpc

NXP LPC17xx pending interrupts

I am facing a weird problem with the external interrupts of the LPC17xx series.

I have an external button set to external interrupt 1, falling edge with both an internal as an external pull-up resistor (p2.11):

PinCfg.Funcnum = 1;
PinCfg.OpenDrain = 0;
PinCfg.Pinmode = PINSEL_PINMODE_PULLUP;
PinCfg.Pinnum = 11;
PinCfg.Portnum = 2;
PINSEL_ConfigPin(&PinCfg);
GPIO_SetDir(2,((uint32_t)1<<11),0);

And:

EXTICfg.EXTI_Line = EXTI_EINT1;
EXTICfg.EXTI_Mode = EXTI_MODE_EDGE_SENSITIVE;
EXTICfg.EXTI_polarity = EXTI_POLARITY_LOW_ACTIVE_OR_FALLING_EDGE;
EXTI_Config(&EXTICfg);
EXTI_ClearEXTIFlag(EXTI_EINT1);

And:

NVIC_SetPriority(EINT1_IRQn,1);
NVIC_EnableIRQ(EINT1_IRQn);

This is a part of the ISR (including 200ms button debouncing timer):

void EINT1_IRQHandler(void)
{
    EXTI_ClearEXTIFlag(1);

    uint32_t tim1Cnt = LPC_TIM1->TC;

    if (tim1Cnt > ButtDebounceUs)
    {
        LPC_TIM1->TC = 0x00000000;

        // Do work here
    }
}

The "Do work here" section could take some time (e.g. more than 200ms in some cases). This is intended and no problem for the further execution of the program.

The problem is that when the ISR is entered first and I press the button a second time while the ISR is executing (this has to be done fast) a pending interrupt is set and causes the ISR to execute again if it has ended for the first time. This is normal behaviour I guess, since EXTI_ClearEXTIFlag(1) does not clear any pending interrupts in the NVIC. So I added NVIC_ClearPendingIRQ(EINT1_IRQn) to clear the new pending interrupts on several locations in the ISR code to be sure the pending interrupt(s) is/are cleared. Strangely enough this does not work at all.

Some my question is, how can I read the pending interrupts via JTAG/debugger (memory address?). And what is going on here? Can someone explain this behaviour and maybe has a clue how to fix it?

Thanks!

Solution

  • when the ISR is entered first and I press the button a second time [...]

    This triggers the EINT1 Flag again, but after you cleared it first. Thats why

    NVIC_ClearPendingIRQ(EINT1_IRQn) to clear the new pending interrupt

    does not work, as EINT1 still signals the interrupt line. You need to call

    EXTI_ClearEXTIFlag(1);

    again after the "work" to clear this flag.