Why doesn't Timer interrupt operate at the interval which is configured in code?

[Yusuke]

I want to execute timer interrupt at a certain interval, like 1sec or 5 sec.

I measured an actual interval of voltage change with oscilloscope, but the actual interval is different from the interval configured in code.

Does anyone know this reason?

(configured) -> (actual)
1 sec -> 0.74 5sec
2 sec -> 1.49 sec
3 sec -> 2.24 sec
5 sec -> 4.25 sec
10 sec -> 7.46 sec

#include <nrf9160.h>
#include <zephyr.h>
#include <misc/printk.h>
#include <device.h>
#include <gpio.h>

#define TIEMR_INTERVAL_SEC 1 // 1,2,3,5,10 sec were tested

struct device *gpio_0_dev;
struct k_timer my_timer;
uint8_t toggle = 1;

void my_expiry_function(struct k_timer *timer_id){
        ++toggle;
        gpio_pin_write(gpio_0_dev, 16, toggle % 2);
}

void main(void)
{
        printk("------------\r\nHello, World!\r\n");
        k_timer_init(&my_timer, my_expiry_function, NULL);

	gpio_0_dev = device_get_binding("GPIO_0");
        gpio_pin_configure(gpio_0_dev, 16, GPIO_DIR_OUT);
        gpio_pin_write(gpio_0_dev, 16, toggle);
        k_timer_start(&my_timer, K_SECONDS(TIEMR_INTERVAL_SEC), K_SECONDS(TIEMR_INTERVAL_SEC));
        
        while(1){
                 k_cpu_idle();
        }
}

[Bjørn Kvaale]

Sorry for the delayed response. Have you taken this code from a specific example (if yes, where is the code location?) or have you written it yourself?

[Yusuke]

Thank you for your reply! This is what I did.

1. I copied secure_boot example and change the folder name as well as some file names.
secure_boot(folder) -> timer_interrupt
secure_boot.emProject -> timer_interrupt.emProject
secure_boot.emSession -> timer_interrupt.emSession

2. implement the code above by myself.

[Bjørn Kvaale]

There is a timer example here that may help you. You could either try copying some of the code into your secure_boot implementation or download the user's branch of the nrf folder (will most likely require the master branch of nrfxlib, mcuboot & zephyr). You could create a new ncs folder called ncs_master & then clone Rallare's nrf branch, along with the master branches of the other three folders mentioned.

[Yusuke]

Hi, Bjørn

I've already checked the timer example. It's a timer delay example, not timer interrupt example.

In my case, an interrupt interval is long, like 1 sec, so It's better to use kernel timers instead (RTC based)

Please read my previous post here

https://devzone.nordicsemi.com/f/nordic-q-a/45200/how-to-implement-timer-interrupt-in-nrf9160

[Bjørn Kvaale]

This may be related to this bug reported here.

[Yusuke]

I see. So nRF9160 may have the same issue in low frequency timer as nRF51 has. Ok, I will wait for next update.