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?

[Susheel Nuguru]

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.

[adriand]

@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.

[Susheel Nuguru]

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.

[Susheel Nuguru]

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.

[adriand]

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