Simplest way to continuously toggle a GPIO pin for a fixed amount of time then stop?

[Mike Yeung]

Experienced developer new to embedded C programming here, so please forgive me if I'm missing something obvious. I already went through the GPIOTE example from the nRF52 SDK (v15) and this app timer tutorial.

I want to continuously (say, every 100ms) toggle a GPIO pin between high and low but stop that loop after 20 seconds. I also want to be able to start and stop (don't need the ability to resume) this 20-second sequence on demand.

It looks like either a GPIOTE task or a repeating app timer could handle the continuous toggling for me, but I'm not sure how best to stop it after 20 seconds. Could I start a GPIOTE task to perform the repeated GPIO toggling inside a single-shot 20-second timer then start/stop that timer whenever I please? Given that both GPIOTE tasks and the app timer use the LFCLK, I want to make sure that they will not conflict with one another.

Any high-level example code you could share would be much appreciated. Thanks!

[twihtronics]

I think you might be better off creating a 100ms timer and inside the timer increment a variable and compare it is 200 which should equate to 20000ms or 20 sec.

timer_handler

if counter < 200 then nrf_gpio_pin_toggle() and counter++ else stop timer

[ovrebekk]

Hi 

Unless you need extremely consistent timing I agree with Mike: You can just use an app_timer to toggle the LED, and update a counter inside the callback to stop the app_timer after the set period. 

The app_timer callbacks can be delayed by the SoftDevice (up to some hundred microseconds), so if this is an issue it is a better option to set up a dedicated TIMER or RTC module, and use PPI and GPIOTE to update the pin whenever the TIMER/RTC reaches a preset compare value. 

Best regards
Torbjørn 

[Jaewook]

Thank you for your inputs!.

I found useful information below :

• https://infocenter.nordicsemi.com/index.jsp?topic=%2Fug_nrf5340_pdk%2FUG%2Fnrf5340_PDK%2Fhw_nfc_if.html 

NFC uses two pins, W1 (NFC1) and AA1 (NFC2), to connect the antenna. These pins are shared with GPIOs (P0.02 and P0.03) and the PROTECT field in the NFCPINS register in UICR defines the usage of these pins and their protection level against abnormal voltages. The content of the NFCPINS register is reloaded at every reset.

In Zephyr, GPIO0_2 & 3 were set to NFC pins as default and so you should set  CONFIG_NFCT_PINS_AS_GPIOS to y to disable NFC.

As I used the configuration, it worked as normal GPIO pins.    Resolved.

[ovrebekk]

Hi 

I am not sure how your issue relates to the original case, but it is good to hear that you found a solution

Regards
Torbjørn