RealTimeClock accuracy

[ken mccullagh]

Does anyone know the accuracy of the RealTimeClock on the conduit? Specificially looking to find the maximum drift per year, and which RTC chip is in place?
Thanks
Ken

[John Klug]

If ntpd is running, it will periodically update the real time clock (hardware clock). Also, shutdown (/etc/init.d/hwclock.sh stop) will update the real time clock with the system clock.

There is also the script /etc/network/if-up.d/ntpdate-sync script that can be configured through /etc/default/ntpdate to update the hardware clock, if it can reach an ntpserver, when a network is brought up.

hwclock –systohc will set the hardware clock to UTC, based on the system clock.

[ken mccullagh]

Thanks John,
in the event that the gateway is unplugged for a period of time, how much drift is expected in the RTC, in the event that there is no connectivity when it is rebooted?
Ken

[ken mccullagh]

So can no-one tell me the accuracy of the RTC?

[Tim Barr]

The RTC is the internal RTC on the AT91SAM9G25 processor. The 32 kHz crystal tolerance is 20 ppm. So the error could be as much as 2 seconds a day.

[ken mccullagh]

Thanks Tim
I was hoping for a physical RTC onboard, given that there’s an onboard battery – what does that power if it’s not an RTC?
Cheers
Ken

[John Klug]

The battery (if present) powers the SAM9G25 Real Time Clock.

See page 124, section 14:

http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-11032-32-bit-ARM926EJ-S-Microcontroller-SAM9G25_Datasheet.pdf

• This reply was modified 6 years ago by John Klug.

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