NRF51422 - GPIOTE PORT events stop being generated - why?

[Martin Ling]

I am encountering a problem with GPIOTE PORT events on the NRF51422 in a custom design. The chip occasionally seems to be able to get into a state in which the registers are set up correctly for a PORT event and interrupt to be generated, but despite this no event occurs.

I have a pin which is connected to a push switch and external pullup resistor, which normally triggers various visible actions on the system. The symptom of the problem is that the system stops responding to the button.

If I hold the switch down when the problem is occuring and then halt the CPU, I can see in the debugger that:

• PIN_CNF is set to input, connected, no pull, standard drive, sense low.
• The IN register for the pin shows the input level as low.
• The GPIOTE INTENSET register shows the PORT enable bit set.
• EVENTS_PORT is zero.

If I set a breakpoint at the GPIOTE interrupt, then:

• With the system working normally, the breakpoint is hit when the button is pressed and shows the registers in the state above, except that EVENTS_PORT reads 1, indicating the event has occured.

• When the problem is occuring, the breakpoint is not hit, and if I halt the CPU I see the registers in the same state as above with EVENTS_PORT reading zero.

I can reproduce this problem on two copies of the board.

What could be preventing this event from being generated?

[Vito]

Here's a version of mine with some optimization:

void GPIOTE_IRQHandler(void)
{		
uint8_t i;
uint32_t pins_state = NRF_GPIO->IN;	//save current input state
uint32_t triggered_pins = 0ul;			//save pins that actually generated IRQ
uint8_t sense[NO_OF_PINS];					//save sense configuration

//clear event
NRF_GPIOTE->EVENTS_PORT = 0ul;

// Backup and then disable all SENSE settings to ensure that DETECT signal is deasserted.
// Check if pin value and sense agree and store it in triggered_pins
for (i = 0; i < NO_OF_PINS; i++)
{
	//store sense value of each pin
	sense[i] = (uint8_t) ( (NRF_GPIO->PIN_CNF[i] & GPIO_PIN_CNF_SENSE_Msk) >> GPIO_PIN_CNF_SENSE_Pos) );	
	NRF_GPIO->PIN_CNF[i] &= ~GPIO_PIN_CNF_SENSE_Msk;		//disable sense field in pincnf
	if ( (sense[i] == GPIO_PIN_CNF_SENSE_High) && ((pins_state & (1ul << i)) != 0) )	//sense high, pin high
	{
		triggered_pins |= (1u << i);		//flag current pin caused IRQ
		sense[i] = GPIO_PIN_CNF_SENSE_Low;	//flip sense value (IRQ won't be recalled until pin changes value again
	} else if ( (sense[i] == GPIO_PIN_CNF_SENSE_Low) && ((pins_state & (1ul << i)) == 0) )							//sense low, pin low
	{
		triggered_pins |= (1u << i);		//flag current pin caused IRQ
		sense[i] = GPIO_PIN_CNF_SENSE_High;	//flip sense value
	}
}

//***
// here check if bits in triggered_pins are one of the ISRs you need, and compare it with pins_state for the transition you need
// call related ISRs
// i.e.
// if ( triggered_pins & pins_state & (1ul << IRQpin) ) {dosmth} <- for lowtohi
// if ( triggered_pins & ~pins_state & (1ul << IRQpin) ){dosmth} <- for hitolow
//***

// now restore modified sense values in PIN_CNF
for (i = 0; i < NO_OF_PINS; i++)
 {
	NRF_GPIO->PIN_CNF[i] |= (sense[i] << GPIO_PIN_CNF_SENSE_Pos);
 }

}