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Going in circles without a real-time clock

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Re: Going in circles without a real-time clock

#51

Post by silasdavis »

pynne wrote: post #44
silasdavis wrote: post #30

Tangential: I have a pi 4 running openwrt and a wireguard interface that is routed over the WiFi access point. If you connect to this network it's as if you are connecting in another country. I have outbound traffic only going over wireguard. If wireguard is down then no internet (to avoid any leakage). However if pi loses power the clock resets, wireguard can't handshake with that much clock skew, NTP can't connect…

Yeah you got it. Set the listening interface to eth0 or whatever the wan interface is. Might need to get full ntpd instead of the busy box version. The Interface option here: https://www.ntp.org/documentation/4.2.8-series/miscopt/ I’m actually setting up a router with a rpi4 right now, only using Fedora IoT instead of OpenWrt. It’s a bit more assembly required lol

I need to have a play with it, but the problem is i deliberately have a 'kill switch' style setup to stop any requests accidentally going not over wireguard (for reasons) so I assume I'll need to do some other firewall type thing. Maybe something something tagging.

Re: Going in circles without a real-time clock

#53

Post by Joel_Mckay »

teruakohatu wrote: post #49
hcfman wrote: post #41

Earlier quoted context omitted.

Having said that, I've never personally seen my stratum #1 Pi loose sync due to weather and I run about 4 of em here. I also use a cheap 7 euro ublox 7m. So long as you position it or an antennae with a reasonable view of the sky that shouldn't happen I reckon. Why all the complex solutions when it's so easy and cheap now to install a stratum #1 time server, even a Pi 3 will suffice. It works on a Pi Zero, but then y…

Any advice for a cheap USB GPS for a stratum #1 time server? EDIT: Any any advice on how essential PPS is?

The PPS can be good (pi kernel support is stable), but one needs to be careful as some modules PPS signal has a great deal of instability.

Some U-Blox modules support the additional ground based navigation signal and cellular beacons. This is recommended in addition to the 3 satellite networks classes, but note some modules will not work with some antennas (get the unified hardware with built in antenna/lna if unsure about RF notes).

Best regards, =)

Re: Going in circles without a real-time clock

#54

Post by mikepurvis »

mapreduce wrote: post #34
CaliforniaKarl wrote: post #26

I know I’ve brought this up before, but I can’t remember exactly where. It would be nice if DHCP could provide the current time as one of the pieces of information it provides with a lease. If you’re already trusting it for your IP address, you might as well trust it with the current UTC time: The current 64-bit timestamp would be enough to get timestamp-sensitive things working.

> If you’re already trusting it for your IP address, you might as well trust it with the current UTC time I don't follow! How does trusting DHCP with IP address automatically mean I should trust it with the current UTC time? Time requires higher degree of trust than IP. I may not care what my IP address looks like but I might care a lot about what the current UTC time is and I might want this to come from a more trus…

DHCP servers can command your dns config and hostname too. It's not a total mitm story since the certs are still on the machine itself but it's definitely more than just a local IP address.

Re: Going in circles without a real-time clock

#55

Post by M95D »

michaelt wrote: post #50
M95D wrote: post #8

RTC module for Raspberry is ~ $1.

Right, it's only $1. Plus the time to learn a few modprobe commands. Perhaps run a few commands echoing numbers to random sysfs files. Perhaps learn WTF a 'Device Tree Overlay' is - a concept that's completely absent on x86 systems. You see, this is an 'I2C' device, so it doesn't plug and play like USB and PCIe devices do. It is much simpler, and hence for some reason more difficult. Perhaps your device tree overlay…

If the user has issues with all of that, then RPi is not the rigth tool for them.

Re: Going in circles without a real-time clock

#56

Post by hcfman »

teruakohatu wrote: post #49
hcfman wrote: post #41

Earlier quoted context omitted.

Having said that, I've never personally seen my stratum #1 Pi loose sync due to weather and I run about 4 of em here. I also use a cheap 7 euro ublox 7m. So long as you position it or an antennae with a reasonable view of the sky that shouldn't happen I reckon. Why all the complex solutions when it's so easy and cheap now to install a stratum #1 time server, even a Pi 3 will suffice. It works on a Pi Zero, but then y…

Any advice for a cheap USB GPS for a stratum #1 time server? EDIT: Any any advice on how essential PPS is?

I have good results with cheap ublox 6m's and 7m's from aliexpress. For some reason the 8m's I got were poor in sensitivity.

Adafruit ones also work great, but are a lot mor expensive, I do have several though.

PPS is criticial to proper timing. However... I was using the time synched systems for sound localization. But as they only cost around 7 euros on aliexpress, why not.

Re: Going in circles without a real-time clock

#57

Post by riobard »

Hrnrurj wrote: post #31
riobard wrote: post #14

Speaking of RTC battery, I've recently come to the realization that I have to make sure that BIOS battery is not absolutely dead in always-on PC boxes. Background: I use an x86 box as home router. I've changed the configuration in the BIOS that it should automatically boot up on power. However if the BIOS battery is dead, the config will be lost and it will revert to default settings, which is not to boot on power. B…

Voltage check on battery is part of regular PC maintenance. Like cleaning dust, checking all fans are spinning, capacitors are not getting bigger, checking for weird sounds in PSU, overnight memtest... You should do it every year or two...

Cannot do that if it acts as the always-on router…

Re: Going in circles without a real-time clock

#58

Post by hcfman »

Joel_Mckay wrote: post #53
teruakohatu wrote: post #49

Earlier quoted context omitted.

Any advice for a cheap USB GPS for a stratum #1 time server? EDIT: Any any advice on how essential PPS is?

The PPS can be good (pi kernel support is stable), but one needs to be careful as some modules PPS signal has a great deal of instability. Some U-Blox modules support the additional ground based navigation signal and cellular beacons. This is recommended in addition to the 3 satellite networks classes, but note some modules will not work with some antennas (get the unified hardware with built in antenna/lna if unsure…

If you have good sky visibility, then I don't need an antenna. Though this often tends to mean putting a Pi outside. I'm also using just the first Antenna I find actually.

Re: Going in circles without a real-time clock

#59

Post by [deleted] »

CaliforniaKarl wrote: post #26

I know I’ve brought this up before, but I can’t remember exactly where. It would be nice if DHCP could provide the current time as one of the pieces of information it provides with a lease. If you’re already trusting it for your IP address, you might as well trust it with the current UTC time: The current 64-bit timestamp would be enough to get timestamp-sensitive things working.

[deleted]

Re: Going in circles without a real-time clock

#60

Post by riobard »

guenthert wrote: post #43
riobard wrote: post #14

Speaking of RTC battery, I've recently come to the realization that I have to make sure that BIOS battery is not absolutely dead in always-on PC boxes. Background: I use an x86 box as home router. I've changed the configuration in the BIOS that it should automatically boot up on power. However if the BIOS battery is dead, the config will be lost and it will revert to default settings, which is not to boot on power. B…

> But there is no way to know how much juice is left in the BIOS battery, True, but its voltage can be used as an estimate. Most PC MB still around monitor the supply voltages, some also of the battery feeding the RTC. If you have the (Debian) package 'lm-sensors' installed, look for sensors[ ]: Vbat: +2.91 V (min = +2.70 V, max = +3.63 V) ALARM in /var/log/syslog.

Ran `sensors` and it only shows CPU core temps. I guess my MB does not report RTC battery voltage?
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