nrf52 timer example, over 5 minutes event handler.

[JW]

When I test the timer example with nrf52832 DK, it so nice to 4 minutes.

uint32_t time_ms = 240000;

But when I set the time interval over 5 minutes, then the event handler run more rapidly.

So, what should I do for long time period?

[Jørgen Holmefjord]

Hi JW,

By default, the timer runs at 16 MHz and the maximum bit width of the timer is 32-bit. This corresponds to a maximum timer value of:

(2^32)-1 = 4294967295

The reason why you see event handler more rapidly with 5 minutes, is that nrf_drv_timer_ms_to_ticks use the configured frequency and the time_ms parameter to generate the number of ticks, and return this in a 32 bit variable:

5*60*16000000 = 4800000000

This overflows the 32 bit variable, giving you a tick count of 505032705 = ~31.5 seconds.

You need to change the frequency of the timer to make it run run slower. This is done by changing the timer configuration:

timer_cfg.frequency = NRF_TIMER_FREQ_8MHz;

You can set it to any of the frequencies documented here.

Best regards,

Jørgen

[Jørgen Holmefjord]

I see there is a 32 bit multiplication inside the function, resulting in the return value being wrong. If you change line 618 in nrf_timer.h from return ((time_ms * 16000UL) >> prescaler); to return ((time_ms * 16000ULL) >> prescaler);, you should get correct behavior.