mikkeli
75 lines
3.6 KiB
Markdown
75 lines
3.6 KiB
Markdown
---
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type: report
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date: 2026-10-08
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---
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# Time Sync and Timezone
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## Result
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| Item | State |
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|------|-------|
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| Network time | **chrony** (since 2026-10-09; was `systemd-timesyncd`), primary `ntp.nict.jp` (stratum 1) + JP pool + Ubuntu pools, over whichever uplink holds the default route |
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| Timezone | `Asia/Tokyo` (was `Asia/Yakutsk`: same +09:00 and no DST either, but the wrong place) |
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| Clock across power-off | **Not kept.** The RTC has no backup battery (see below) |
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| GPS time | chrony refclock `GPS` (gpsd SHM 0), fallback only; used when offline with a fix |
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| Boot clock without network | `fake-hwclock` restores the last saved time (replaces timesyncd's saved timestamp) |
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## RTC loses time when powered off
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On the 2026-10-08 cold boot, the kernel set the system clock from `rtc0` (`nvvrs-pseq-rtc`, `hctosys=1`) to **June 4**.
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Then the clock was corrected in two steps:
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1. ~12 s: timesyncd stepped forward to its last saved timestamp (`/var/lib/systemd/timesync/clock`). This is close, but behind by however long the board was off.
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2. ~43 s: first NTP sync corrected the rest. The kernel then writes the synced time back to the RTC, which only lasts until the next power-off.
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Until step 2, timestamps are wrong, and with no uplink (in the car, out of coverage) they stay wrong. The fix is hardware:
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an RTC backup battery (see [BOM](../../BOM.md#rtc-backup-battery)). `rtc1` (`tegra_rtc`) isn't used for boot time and reads 1970.
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## Configuration
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```
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sudo timedatectl set-timezone Asia/Tokyo
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```
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`/etc/systemd/timesyncd.conf.d/10-servers.conf` (superseded on 2026-10-09 by chrony, below; timesyncd is no longer installed):
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```
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# Japan-local primary (NICT, national time standard), global pool as backup.
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[Time]
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NTP=ntp.nict.jp
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FallbackNTP=ntp.ubuntu.com 0.jp.pool.ntp.org 1.jp.pool.ntp.org 2.jp.pool.ntp.org
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```
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`sudo systemctl restart systemd-timesyncd`, then check with `timedatectl timesync-status` (server, stratum, offset).
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## Chrony with GPS fallback (2026-10-09)
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Replaced `systemd-timesyncd` (removed by the `chrony` package) so GPS can serve as an offline time source.
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```
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sudo apt install chrony fake-hwclock
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```
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`/etc/chrony/conf.d/10-yukart.conf`:
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```
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server ntp.nict.jp iburst prefer
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pool 2.jp.pool.ntp.org iburst maxsources 2
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refclock SHM 0 refid GPS precision 1e-1 offset 0.0 delay 0.5 poll 3
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```
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- **NTP stays primary.** The GPS refclock's generous `precision`/`delay` give it a large root distance, so any reachable NTP server wins.
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It steers the clock only offline with a fix. NMEA over USB has no PPS, so GPS time is good to ~tens of ms, plenty for log timestamps.
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- **`offset 0.0` is a placeholder.** Tune it once NTP and a GNSS fix are both available: `chronyc sourcestats` shows the GPS offset
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against NTP.
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- **`makestep 1 -1`** in `/etc/chrony/chrony.conf` (was `1 3`): step the clock whenever it's > 1 s off, not only in the first three
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updates, because with no RTC battery a stale clock may only meet its first source (a late GPS fix) well into an offline drive.
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chrony's config format has no inline comments; the explanation sits on its own line above.
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- **`fake-hwclock`** saves the time hourly and at shutdown and restores it at boot, so an offline boot starts near the last shutdown
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instead of the RTC's reset date. This replaces what timesyncd's `/var/lib/systemd/timesync/clock` did.
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- gpsd must run with **`-n`** to feed SHM without a client. See the SIM7600 report: a stray gpsd started by a `gpsdctl` udev hook ran
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without it, now fixed.
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Check: `chronyc -n sources` (`^*` = selected NTP server, `#` = GPS refclock), `chronyc tracking`.
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At setup: synced to `ntp-a3.nict.go.jp` (stratum 1); `GPS` listed with no samples (antenna detached indoors).
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