measuring input GPIO pin frequency with soft device running

[adriand]

Hello,

is it possible to measure frequency from 1Hz up to 400kHz (50% duty cycle) on gpio pin having soft device enabled with Peripheral functionality? The measurement will be invoked on demand by the connected central device. I will use nRF51822, rev. 3, S110 or S130, SDK 8 or 9.

If this is not possible, please tell me if following scenario would be ok:

• invoke measurement
• disable soft device (disconnection from central)
• manage measurement (what's the best way: which timer?, PPI? GPIOTE?)
• enable soft device

Thank you!

btw, what is the maximum frequency that can be measure on gpio pin?

[adriand]

@Aryan, It's been a long time, however now I've already got time to deal with this frequency meter. Your advice works perfectly! After datasheet and forum reading I came up with the final code using all of these peripherals according to your scheme. PPI rulez :-) It also works with Soft Device enabled. I share my code below (not yet so beautiful..) so maybe someone would save his time on a similiar problem.

#define FREQ_MEASURE_PIN 6

static void timer_init()
{
	NRF_TIMER1->TASKS_STOP = 1;
	NRF_TIMER1->MODE = TIMER_MODE_MODE_Timer;
	NRF_TIMER1->PRESCALER = 8;	// Fhck / 2^8 
	NRF_TIMER1->CC[0] = 62500;	// 62500 - 1s
	
	NRF_TIMER1->BITMODE = (TIMER_BITMODE_BITMODE_16Bit << TIMER_BITMODE_BITMODE_Pos);	
	
	NRF_TIMER1->TASKS_CLEAR = 1;
	NRF_TIMER1->INTENSET = (TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos);
	
	NRF_TIMER1->EVENTS_COMPARE[0] = 0;
}

static void counter_init()
{
	NRF_TIMER2->TASKS_STOP = 1;	
	NRF_TIMER2->MODE = TIMER_MODE_MODE_Counter;
	NRF_TIMER2->BITMODE = (TIMER_BITMODE_BITMODE_24Bit << TIMER_BITMODE_BITMODE_Pos);
	NRF_TIMER2->TASKS_CLEAR = 1;
	NRF_TIMER2->EVENTS_COMPARE[0] = 0;
}

static void gpiote_init(uint32_t pin)
{
	NRF_GPIOTE->CONFIG[0] 	= 	0x01 << 0; 								// MODE: Event
	NRF_GPIOTE->CONFIG[0] 	|= 	pin << 8;								// Pin number
	NRF_GPIOTE->CONFIG[0] 	|= 	NRF_GPIOTE_POLARITY_LOTOHI	<< 16;		// Event rising edge 	
}

static void ppi_timer_stop_counter_init()
{
	NRF_PPI->CHEN |= 1 << 0;
	*(&(NRF_PPI->CH0_EEP)) = (uint32_t)&NRF_TIMER1->EVENTS_COMPARE[0];
	*(&(NRF_PPI->CH0_TEP)) = (uint32_t)&NRF_TIMER2->TASKS_STOP;
	NRF_PPI->CHENSET |= 1 << 0;
}

static void ppi_gpiote_counter_init()
{
	NRF_PPI->CHEN |= 1 << 1;
	*(&(NRF_PPI->CH1_EEP)) = (uint32_t)&NRF_GPIOTE->EVENTS_IN[0];
	*(&(NRF_PPI->CH1_TEP)) = (uint32_t)&NRF_TIMER2->TASKS_COUNT;
	NRF_PPI->CHENSET |= 1 << 1;
}

int main()
{
    // Soft Device initialization..

   	NVIC_EnableIRQ(TIMER1_IRQn);
    NVIC_SetPriority(TIMER1_IRQn, NRF_APP_PRIORITY_LOW);	

    nrf_gpio_cfg_input(FREQ_MEASURE_PIN, NRF_GPIO_PIN_NOPULL);

	counter_init();
	timer_init();
	gpiote_init(FREQ_MEASURE_PIN);
	ppi_gpiote_counter_init();
	ppi_timer_stop_counter_init();

	NRF_TIMER1->TASKS_START = 1;
	NRF_TIMER2->TASKS_START = 1;
	
	for(;;) {
		// power manage //
	}
}

void TIMER1_IRQHandler(void) 
{
	if (NRF_TIMER1->EVENTS_COMPARE[0] != 0)
	{
		NRF_TIMER1->EVENTS_COMPARE[0] = 0;
		NRF_TIMER2->TASKS_CAPTURE[0] = 1;
				
		LOG_INFO("cc: %dHz", NRF_TIMER2->CC[0]);
      	
		NRF_TIMER1->TASKS_CLEAR = 1;
		NRF_TIMER2->TASKS_CLEAR = 1;	
						
		NRF_TIMER2->TASKS_START = 1;			
    }
}

Thanks!

[Susheel Nuguru]

Good to know, thanks for coming back here to update me.

[Inspectron]

I try to use the same code, but I will never get into TIMER1_IRQHandler. What can be a reason, that i dont get into the TIMER1IRQHandler? Or is there a newer example to measure frequency on a Pin? I'm working with SDK 11.0

[Susheel Nuguru]

Hi Inspectron, Check if there are any hardfaults or other conflicts with modules used here somewhere else in your code, this code should work perfectly when used alone.

[Inspectron]

I tested the same code without SD. And then it works. I dont need the SD so this is good for me.

[Inspectron]

Oh I undestand. And what accuracy did you get? On the logic analyzer I have 665 Hz and the Nordic chip measures 657 Hz.