Clocks, timers, RTC, why?

RE: Clocks, timers, RTC, why?

awneil — Mon, 29 Jul 2019 10:07:27 GMT

[quote userid="13415" url="~/f/nordic-q-a/12731/clocks-timers-rtc-why/48339"]In the industry RTC always refers to a "Real-time clock"[/quote]

Actually, that's not true - there are other manufacturers who also use "RTC" to mean "Real-time counter".

Doesn't make it right, of course!

RE: Clocks, timers, RTC, why?

awneil — Mon, 29 Jul 2019 10:04:26 GMT

Report broken links here:

https://devzone.nordicsemi.com/nordic/backstage/f/backstage-forum/46958/broken-links-since-moving-back-to-infocentre-from-doclib

However, the links would point to 3-year-old versions of the resources - so out-of-date now.

Probably easiest to just go straight to the current Product Specification and SDK documentation ...

RE: Clocks, timers, RTC, why?

Heiner — Mon, 29 Jul 2019 09:13:04 GMT

Hi Tesc,

unfortunately the links you posted are no longer working. Could you be so kind and update them?

Thank you.

RE: Clocks, timers, RTC, why?

Jarmo — Tue, 24 Jan 2017 13:11:37 GMT

Thanks! I just noted the prescaler thing, too.

RE: Clocks, timers, RTC, why?

tesc — Tue, 24 Jan 2017 11:51:00 GMT

For RTC, the rate at which the counter ticks is configured using the 12 bit PRESCALER register.

The timer ticks every PRESCALER + 1 tick of the LFCLK (@32768 Hz). With the maximum PRESCALER setting of 4095, the RTC gets a period of 125 ms and overflows after 582.542 hours.

I have fixed the broken link to the documentation for "RTC -- Real-time counter" in the answer above.

RE: Clocks, timers, RTC, why?

Jarmo — Tue, 24 Jan 2017 09:08:08 GMT

There's also typically 32-bit second counters without calendar, and they are also called "Real Time Clocks". Actually, I prefer this type of counter to days/months etc. calendar because it is pretty easy to convert seconds counter (e.g. Epoch Time) into days/months etc, but more complicated to do it vice versa. And in a program code you will eventually need second counter, mostly.

But the reason I ended up here into an old discussion is that nRF5 RTC seems to be only 24 bit and thus wraps over after 512 seconds (@32768 Hz). Thats way too little. Now I am trying to find out a solution for the system to deep sleep e.g. an hour without losing the "real time".

RE: Clocks, timers, RTC, why?

jcondon — Mon, 02 May 2016 20:44:53 GMT

Btw, I think it was a mistake to call the "Real-time counter" an RTC. In the industry RTC always refers to a "Real-time clock" which keeps track of days/months w/ an internal calendar. The RTC is really a low-freq counter... a totally different thing.

RE: Clocks, timers, RTC, why?

tesc — Wed, 23 Mar 2016 15:15:52 GMT

The main difference between TIMER and RTC (Real-time counter) is that:

TIMER uses the high-frequency clock source (HFCLK, 16 MHz), which means better resolution (62.5 ns) and higher power consumption (typ. 5 or 70 uA depending on HFCLK source).
RTC uses the low-frequency clock source (LFCLK, 32 KHz), which means less resolution (~30 us) and lower power consumption (typ. 0.1 uA).

For the details, see chapters 24 (TIMER -- Timer/counter) and 25 (RTC -- Real-time counter) of the nRF52832 Product Specification.

For RTC there is also a library in the SDK: Timer library

Based on what you write about your application I would suggest using RTC.

CLOCK_ENABLED is for enabling the clock driver in the SDK. This is not a timer. Rather it is a driver for handling the low and high frequency clock sources.