You can even get a Zigbee module combined with an RTC, and optional even PoE if you want.
https://www.tindie.com/products/electrolama/zoe-rtc-zigbee-radio-and-rtc-for-raspberry-pi/ https://www.tindie.com/products/electrolama/zoe-poe-zigbee-radio-rtc-poe-for-raspberry-pi/ Am Sun, Jan 10, 2021 at 01:14:13AM +0800 schrieb Archimedes Gaviola: > Hi, > > As Mark have said, you can buy an RTC. For how many months right now my > standalone (not connected to the internet) Raspberry Pi 4B has been very > stable with time using DS3231 module > https://shopee.ph/DS3231-Mini-RTC-Module-i.18252381.315148783. Sharing to > you as well https://marc.info/?t=159819358900001&r=1&w=2. > > Thanks and best regards, > Archimedes > > On Sun, Jan 10, 2021 at 12:37 AM Mark Kettenis <mark.kette...@xs4all.nl> > wrote: > > > > Date: Sat, 09 Jan 2021 17:24:59 +0100 > > > From: "Filippo Valsorda" <fili...@ml.filippo.io> > > > > > > (Emailing the arm@ list because this is a common issue on arm platforms, > > > although not arm specific. Let me know if I should redirect.) > > > > > > I run a simple OpenBSD firewall on a RPi 4, which doesn't have a > > > real-time clock. When the power goes out, the firewall boots faster > > > than its upstream, so it doesn't have network connectivity in the first > > > seconds. > > > > > > This interacts poorly with ntpd's settime logic: ntpd will only use > > > settime in securelevel 0 (see auto_preconditions() in ntpd.c), and will > > > only try reaching the Internet twice, with a 1s pause, upon starting. > > > > > > The result is that the firewall boots, gives up on settime, and ends up > > > stuck forever with a clock weeks old, enough to break the system, and > > > too far for ntp to catch up. > > > > > > I'm not sure what the right solution is. I think I would want ntpd to > > > wait until it has network connectivity at boot, but I'm not sure if this > > > is something I should hack myself or maybe there's space for an ntpd CLI > > > option. > > > > > > Opinions? > > > > Add an RTC to the Pi4. They can be bought for a few euros and can be > > enabled by adding the appropriate device tree overlay to the > > config.txt file on the firmware partition of your boot disk. > > > >
