nrf52 timer example, over 5 minutes event handler.

RE: nrf52 timer example, over 5 minutes event handler.

Jørgen Holmefjord — Fri, 21 Jul 2017 13:36:16 GMT

It should not affect other projects, as this only changes the multiplication result from 32 to 64 bits. The ASSERT in the nrf_timer_ms_to_ticks() should have fired when you called the function with time_ms = 300000, but this does not seems to have happened. I'm not sure why, but I have reported this issue internally.

If you want to keep the ASSERT and make sure all inputs are valid, you can use this function:

__STATIC_INLINE uint32_t nrf_timer_ms_to_ticks(uint32_t time_ms,
                                               nrf_timer_frequency_t frequency)
{
    // The "frequency" parameter here is actually the prescaler value, and the
    // timer runs at the following frequency: f = 16000 kHz / 2^prescaler.
    uint32_t prescaler = (uint32_t)frequency;
    uint64_t ticks = ((time_ms * 16000ULL) >> prescaler);
    ASSERT(ticks <= UINT32_MAX);
    return (uint32_t)ticks;
}

You can configure the timer frequency all the way down to 31250 Hz, which should give you a maximum of ~2290.6 minutes. If you want to run timers longer, you can use the RTC. The RTC can be configured to run for up to ~582.5 hours before overflowing. RTC is also lower power than the TIMER.

RE: nrf52 timer example, over 5 minutes event handler.

JW — Fri, 21 Jul 2017 13:33:04 GMT

It works!! Thank you so much! But actually 'nrf_timer.h' is referred by every Keil projects. So..isn't there any problem with 16000ULL in other case? In my opinion, it might be okay because the difference between UL and ULL is just size.

RE: nrf52 timer example, over 5 minutes event handler.

Jørgen Holmefjord — Fri, 21 Jul 2017 11:31:45 GMT

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.

RE: nrf52 timer example, over 5 minutes event handler.

JW — Fri, 21 Jul 2017 11:06:52 GMT

Well, but when I set the time interval 5 minutes with time_ms = 300000 after change frequency to 8MHz, the event handler also run every 30 seconds.

RE: nrf52 timer example, over 5 minutes event handler.

Jørgen Holmefjord — Fri, 21 Jul 2017 10:53:41 GMT

Your observations are correct, this change will not affect the time between event handler calls. What it will change is the output from nrf_drv_timer_ms_to_ticks(), the variable time_ticks. With time_ms = 1000 and frequency set to 16 MHz, the returned value will be 16 000 000. With time_ms = 1000 and frequency set to 8 MHz, it will return 8 000 000. Reducing the frequency will reduce the resolution of the timer, but it will increase the time the timer can run before overflowing.

RE: nrf52 timer example, over 5 minutes event handler.

JW — Fri, 21 Jul 2017 10:13:29 GMT

Hello Jørgen,

Thank you for answering my question. I can understand the timer configuration by your explanation.

But when I changed the frequency on 'nrf_drv_config.h'

from 16MHz

#define TIMER0_ENABLED 1

#if (TIMER0_ENABLED == 1)
#define TIMER0_CONFIG_FREQUENCY    NRF_TIMER_FREQ_16MHz
#define TIMER0_CONFIG_MODE         TIMER_MODE_MODE_Timer
#define TIMER0_CONFIG_BIT_WIDTH    TIMER_BITMODE_BITMODE_32Bit
#define TIMER0_CONFIG_IRQ_PRIORITY APP_IRQ_PRIORITY_LOW

#define TIMER0_INSTANCE_INDEX      0
#endif

to 8MHz

#define TIMER0_CONFIG_FREQUENCY    NRF_TIMER_FREQ_8MHz

and set the timer interval 1 second

uint32_t time_ms = 1000;

nothing changed.

The timer event handler run every 1 second at both configuration.

RE: nrf52 timer example, over 5 minutes event handler.

Jørgen Holmefjord — Fri, 21 Jul 2017 07:17:27 GMT

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