onboard external Real Time Clock on nrf52840

[Ubaid_M]

Hello ,

Does nrf52840dk has an onboard external Real Time Clock ..? If yes, I couldn't find it's specifications anywhere in the documentation. Please help with the links.

Can I get any sample programs link to interface any external RTC like ds1307 or ds3231 etc,. over i2c with nrf52840dk..?

Using nCS.

Thanks,

[runsiv]

Hi

Our devices has a Real time Counter not a Real time clock. 

I would recommend having a look at the DS3231 sample in Zephyr

Regards

Runar

[Ubaid_M]

Hello runsiv 

runsiv said:

Our devices has a Real time Counter not a Real time clock. 

Ok

I wanted to understand the characteristics of Real time Counter and how accurate it is, If i keep the nordic board running for one whole year, will the time be accurate or will there be a few seconds difference as compared to external RTC modules like ds3231..?

[runsiv]

Hi 

The timer accuracy is directly linked to the crystal tolerance, typically you can find that a specific crystal have an initial tolerance, a temperature tolerance, and an aging tolerance. These 3 parameters from the crystal spec should give you the information you want, there is no additional "inaccuracy" added internally. 

in short it depends on the crystal used as the RTC source. 

Regards

Runar

[Ubaid_M]

Ok Thanks runsiv 

Based on this Real Time Counter, can the firmware maintain calendar time..?
Is there any calendar module in nCS for maintaining calendar time.

Can you give me a link to the sample program for calendar time from RTC..?

Thanks,

[runsiv]

Hi 

You can have a look at this case. Just remember by default it would not keep the time if the device is reset. If you want to I would look into the following: 

Using  Settings in Zephyr to write something to the reserved flash page before shutting the core and read from the stored value when waking up. You can still use the read value to add on top of the RTC value to get an essence of tracking the time from the start.

Regards

Runar

[Ubaid_M]

Thanks, That clears it up for me.

One last thing, these terms like set_alarm, maxim_ds3231_get_syncpoint etc appear new to me.
Please point me to documentation where I can read the implementation of RTC & maxim_ds3231 

[runsiv]

I would have a look at the zephyr driver

Regards

Runar