GPIOTE Interrupt

[Jose Xavier]

I'm learning about GPIOTE and PPI and looking at an example I come to the following code but now it act incorrectly. So as you can see I'm enabling the interrupt for GPIOTE channel 0:

NRF_GPIOTE->INTENSET = GPIOTE_INTENSET_IN0_Msk;

But when the IRQHandler is called this is what I get:

I expected CC[1] to be 0 but instead it is the value when the signal go HITOLOW!

Here is the signal I'm capturing:

CC[0] is cursor #3 (LOWTOHIGH) and CC[1] is cursor #4 (HIGHTOLOW). Timer starts to count at #2!

void GPIOTE_IRQHandler(void)
{
    
		curr_cc1 = NRF_TIMER1->CC[1];	
		curr_cc0 = NRF_TIMER1->CC[0];  

    // Clear the event causing the interrupt.
    NRF_GPIOTE->EVENTS_IN[0] = 0;  
		NRF_GPIOTE->EVENTS_IN[1] = 0;
	
		NRF_TIMER1->TASKS_STOP = 1;
}

/** @brief Function for initializing the GPIO Tasks/Events peripheral.
*/
static void gpiote_init(void)
{
    NVIC_EnableIRQ(GPIOTE_IRQn);

    nrf_gpio_cfg_sense_input(ECHO, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_SENSE_LOW);

    // Enable interrupt on input 1 event.
    NRF_GPIOTE->INTENSET = GPIOTE_INTENSET_IN0_Msk;

    // Configure GPIOTE channel 0 to generate event on input pin low-to-high transition.
    nrf_gpiote_event_config(0, ECHO, NRF_GPIOTE_POLARITY_LOTOHI);
	
		// Configure GPIOTE channel 1 to generate event on input pin high-to-low transition.
    // Note that we can connect multiple GPIOTE events to a single input pin.
    nrf_gpiote_event_config(1, ECHO, NRF_GPIOTE_POLARITY_HITOLO);
	
}

/** @brief Function for initializing the PPI peripheral.
*/
static void ppi_init(void)
{
    // Configure PPI channel 0 to capture Timer 1 value into  the CC[0] register.
    // This is achieved when GPIOTE detects Low-to-High transition on pin INPUT_PIN_NUMBER.
    NRF_PPI->CH[0].EEP = (uint32_t)&NRF_GPIOTE->EVENTS_IN[0];
    NRF_PPI->CH[0].TEP = (uint32_t)&NRF_TIMER1->TASKS_CAPTURE[0];

    // Configure PPI channel 1 to capture Timer 1 value into CC[1] register.
    // This is achieved when GPIOTE detects High-to-Low transition on pin INPUT_PIN_NUMBER.
    NRF_PPI->CH[1].EEP = (uint32_t)&NRF_GPIOTE->EVENTS_IN[1];
    NRF_PPI->CH[1].TEP = (uint32_t)&NRF_TIMER1->TASKS_CAPTURE[1];

    // Enable only PPI channels 0 and 1.
    NRF_PPI->CHEN = (PPI_CHEN_CH0_Enabled << PPI_CHEN_CH0_Pos)
                  | (PPI_CHEN_CH1_Enabled << PPI_CHEN_CH1_Pos);
}

[yd]

It looks like the values are being read after the GPIOTE task 1 has completed. Make sure you don't put any breakpoints in the GPIOTE_IRQHandler before reading the values of CC[0] / CC[1]. Check below for breakpoint positioning.

From the documentation of GPIOTE abstraction:

The GPIOTE users are responsible for configuring all their corresponding pins, except the SENSE field, which should be initialized to GPIO_PIN_CNF_SENSE_Disabled.

Although you are not using the abstraction, it might have to do something with Sense Low. I don't configure the sense field in my project, so I am not sure about this.

Try changing:

nrf_gpio_cfg_sense_input(ECHO, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_SENSE_LOW);

To:

nrf_gpio_cfg_input(ECHO, NRF_GPIO_PIN_NOPULL);

Enable Interrupts on GPIOTE after you have cleared the pending flags like this:

NVIC_DisableIRQ(GPIOTE_IRQn);
NVIC_ClearPendingIRQ(GPIOTE_IRQn);

NRF_GPIOTE->INTENSET = 0x00000001;// enable interrupts for config[n] pins, n = 0 in this case so bitmask is 0x01

NVIC_SetPriority(GPIOTE_IRQn, 3); //optional: set priority of interrupt
NVIC_EnableIRQ(GPIOTE_IRQn);

Try to separate GPIOTE events in GPIOTE_IRQHandler and put breakpoints after reading CC values:

if(NRF_GPIOTE->EVENTS_IN[0] == 1)
{
	curr_cc0 = NRF_TIMER1->CC[0];
	curr_cc1 = NRF_TIMER1->CC[1]; //keep this if you need it
	NRF_GPIOTE->EVENTS_IN[0] = 0;  //this is where you should set breakpoint to make sure CC[0] and cc[1] don't change while you are in breakpoint
}

if(NRF_GPIOTE->EVENTS_IN[1] == 1) //will run only if you intenset event 1
{
	curr_cc0 = NRF_TIMER1->CC[0]; //keep this if you need it
	curr_cc1 = NRF_TIMER1->CC[1];
	NRF_GPIOTE->EVENTS_IN[1] = 0;  //this is where you should set breakpoint to make sure CC[0] and cc[1] don't change while you are in breakpoint
}