measuring input GPIO pin frequency with soft device running

RE: measuring input GPIO pin frequency with soft device running

thenagi — Sun, 12 Dec 2021 05:35:08 GMT

Followed same stratergy , same code for a similar requriment if frequency measurement. Able to get frequency count in gpio. But when we left it for a long run of 48 hours, we observed a one side always decreasing frequency. Screenshot of counter shared. We know both external source frequency and hfclk will have some temperature component. But instead of periodic ups and down it just kept on decreasing one way. We are yet to found a reasonable explanation fir this. External frequency is tested with with another probe and result in a fix frequency slightly going up and down with ambient temperature in a day cycle. Any pointer regarding this is highly appreciated.

48hour frequency reading

drive.google.com/.../view

RE: measuring input GPIO pin frequency with soft device running

Susheel Nuguru — Thu, 19 May 2016 06:41:38 GMT

commented on your post

RE: measuring input GPIO pin frequency with soft device running

Tim — Wed, 18 May 2016 22:14:15 GMT

I'm using Simblee in a product. It uses the nRF51822 and I think softdevice 110. I'm using TIMER1 for critical timing of GPIO pin pulse from 0-1 second in width. I discovered impact of BLE on TIMER1 function even when used only with PPI and GPIOTE. Please see this post and comment if you can offer any insight. Much appreciated. -Thanks.

RE: measuring input GPIO pin frequency with soft device running

adriand — Tue, 12 Apr 2016 10:01:51 GMT

Aryan, probably I wasn't sure if the timer/counter is still counting after clear, this is redundant I see.

RE: measuring input GPIO pin frequency with soft device running

Susheel Nuguru — Tue, 12 Apr 2016 09:40:23 GMT

Hi, I think above implementation should have been very accurate with/Without softdevice enabled.

adriand, in the timer1 interrupt handler, why did you start NRF_TIMER2->TASKS_START = 1; ??

RE: measuring input GPIO pin frequency with soft device running

adriand — Tue, 12 Apr 2016 08:22:21 GMT

accuracy wasn't so important to me, I just wanted to know if I have 1500Hz or 1800Hz.. so I didn't analyze it very accurately. Maybe try to measure your signal for a bit longer time than 1 second if you can. And don't forget to divide counted value by the the time [seconds] you'll try.

RE: measuring input GPIO pin frequency with soft device running

Inspectron — Tue, 12 Apr 2016 08:15:39 GMT

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

RE: measuring input GPIO pin frequency with soft device running

Inspectron — Tue, 12 Apr 2016 07:53:56 GMT

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

RE: measuring input GPIO pin frequency with soft device running

Susheel Nuguru — Tue, 12 Apr 2016 07:23:22 GMT

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.

RE: measuring input GPIO pin frequency with soft device running

Inspectron — Mon, 11 Apr 2016 14:34:38 GMT

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

RE: measuring input GPIO pin frequency with soft device running

azizg — Fri, 18 Mar 2016 15:40:00 GMT

Hi, i would like to also measure frequency on a pin by this method. But i have not a regular square signal to measure. Namely it is not a symmetrical signal. And it's amplitude is bigger than 5V. Can anybody help to me, to design the input circuit? And how i should define the input pin to not damage it?

Thanks a lot aziz

RE: measuring input GPIO pin frequency with soft device running

Susheel Nuguru — Mon, 26 Oct 2015 10:59:28 GMT

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

RE: measuring input GPIO pin frequency with soft device running

adriand — Sun, 25 Oct 2015 22:47:34 GMT

@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!

RE: measuring input GPIO pin frequency with soft device running

Susheel Nuguru — Thu, 03 Sep 2015 13:23:31 GMT

your welcome, please let me know if it worked after you implement it. I can help you if there are any problems you face. I have changed the title for this thread to reflect the contents, i hope it is ok.

RE: measuring input GPIO pin frequency with soft device running

adriand — Thu, 03 Sep 2015 13:18:23 GMT

@Aryan - thank you for the great explanation! I will try your method as soon as I get the sensor. Thx!

RE: measuring input GPIO pin frequency with soft device running

Susheel Nuguru — Thu, 03 Sep 2015 08:54:06 GMT

at the end of the day you will get a very good understanding of all these peripherals :) Good luck and let me know how it goes.

RE: measuring input GPIO pin frequency with soft device running

Susheel Nuguru — Thu, 03 Sep 2015 08:50:16 GMT

ah I see. It is doable Configure Timer1 in timer mode to generate an event in X seconds. This event should be converted to TASK_STOP using a PPI Configure other peripherals as below but do not enable the last block timer 2 yet.

When you want to start the measurements, START the timer1 and timer2.

After X number of seconds, Timer2 counter will have counted the number of rising edges of the pin in X seconds. get the value into timer CC[n] by triggering a CAPTURE[n] task on timer 2.

Divide Timer2->CC[n] by X and you have your frequency. This should work even with softdevice as we are not using any interrupts.

RE: measuring input GPIO pin frequency with soft device running

adriand — Thu, 03 Sep 2015 08:06:13 GMT

@Aryan - thank you for the answer, however, no no, I don't want to generate clock on pin. I want to measure frequency of a square wave. I need to connect Light-to-Frequency converter to the nRF51822. This converter gives square wave (50% duty) (toggling its output pin) depending on the light intensity. Its output frequency has range from several Hz up to 400kHz.

RE: measuring input GPIO pin frequency with soft device running

Susheel Nuguru — Thu, 03 Sep 2015 07:52:24 GMT

What do you mean by manage measurements on gpio pin, I presume that you want to generate clock on the gpio pin.

Check this older thread. You can generate a 4MHZ stable clock on GPIO using the modules gpiote, ppi and Timer2 and this should work with or without softdevice enabled and with and without and BLE activity as we do not use any interrupts to generate this clock.