• dhork@lemmy.worldEnglish
    21·
    14 hours ago

    Don’t assume your phone has the correct time anymore. It usually does, but my current Android phone has been off for some reason.

    You can tell by going to NIST’s time website at https://time.gov/ . It will not only tell you the current time, but also how far off your web browser’s time is from NIST’s. And my phone is currently just over 1 s off.

    I think they may have misconfigured the phone’s NTP service. NTP has a “poll interval” which configures how often a client asks for time, which is in powers of 2. The maximum interval is 2^17, which is 131072 seconds, or about 36 hrs and 25 mins. My guess is that the phone may go a whole day and a half before synchronizing again.

      • dhork@lemmy.worldEnglish
        1·
        13 hours ago

        I havent found a place to configure NTP on my Android phone. Even if there was, I don’t think it’s the server that’s the problem, I think it’s the poll interval.

    • tal@lemmy.todayEnglish
      2·
      14 hours ago

      I think they may have misconfigured the phone’s NTP service.

      I believe that phones can get time from the cell tower or GPS, and both are probably more-accurate than NTP, since they don’t have to try to compensate for network latency.

      • pHr34kY@lemmy.world
        2·
        3 hours ago

        NTP is accurate within a few milliseconds. GPS is accurate within a few microseconds. However, you need to hook into the PPS (pulse per second) on the GPS signal to get proper accuracy. Think of it like a super-precise drummer keeping beat. NTP servers typically use GPS as a primary time source.

        Source: I operate a stratum-1 time server in the NTP pool.

      • dhork@lemmy.worldEnglish
        3·
        13 hours ago

        I have a GPS app on my phone, and when I run it, I can see the difference between the GPS time and phone time quite clearly

        • tal@lemmy.todayEnglish
          2·
          10 hours ago

          searches

          For Android:

          https://source.android.com/docs/core/connect/time

          From Android 12, device manufacturers can change the core/res/res/values/config.xml configuration file to specify which time origins to include in automatic time detection, and the priority in which time_detector considers these origins.

          For devices running Android 11 or lower, origin priority is hardcoded to [“telephony”, “network”], meaning that telephony suggestions are prioritized above network suggestions.

          The default AOSP configuration is as follows:

          <!-- Specifies priority of automatic time sources. Suggestions from higher entries in the list
     take precedence over lower ones.
     See com.android.server.timedetector.TimeDetectorStrategy for available sources. -->
<string-array name="config_autoTimeSourcesPriority">
    <item>network</item>
    <item>telephony</item>
</string-array>

          In Android 12, network and telephony suggestions are configured as origins to use by default. Network time suggestions are prioritized above telephony time suggestions. Device manufacturers can change the order of the origins to revert to the behavior in Android 11 or lower, where telephony is given a higher priority.

          By default, if the highest priority valid suggestion matches the device’s current system clock time to within a couple of seconds, the device time won’t be changed. This is to avoid creating work for installed apps that listen to the ACTION_TIME_CHANGED intent.

          The allowed origin values are:

          • Network
          • Telephony
          • GNSS
          • External

          “Network” will presumably be NTP, “Telephony” the cell tower time, “GNSS” GPS, and I dunno what “External” is — maybe there’s some way to have a USB-connected time device or something.

          • dhork@lemmy.worldEnglish
            3·
            10 hours ago

            This is all good stuff, maybe at some point I will get back into some Android development and make an app that exposes some of the underlying NTP configuration. Really, I just want to see the ntpd (or chrony) config file (if it exists) and tweak it.

            I did some searching of my own today, and found this guy’s blog

            https://jitinsharma.com/posts/adventures-in-android-timekeeping/

            And he seems to think the poll interval is 16, or 18 hours. I don’t know why these poll intervals are so long. I bet even 2^10 (17 mins) would work much better across all phones, and not really consume that much bandwidth.

            And also, if the phone has access to time from the cell network, why can’t it use that more often?

            This is the first phone I have had that is regularly more than a second off, and it bugs me…