mikkeli
1d405a6b91
timesyncd now uses ntp.nict.jp (stratum 1), with the JP pool and Ubuntu as fallback, over whichever uplink holds the default route. Timezone moves from Asia/Yakutsk to Asia/Tokyo: same offset, right place. Records that the RTC loses time at power-off (the cold boot came up at June 4 until NTP synced), and the planned chrony + gpsd setup once GNSS has a fix. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
52 lines
2.1 KiB
Markdown
52 lines
2.1 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 | `systemd-timesyncd`, primary `ntp.nict.jp` (stratum 1), synced over whichever uplink holds the default route (Ethernet / WiFi / LTE) |
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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 | Not yet. Waiting on a GNSS fix (see [SIM7600 report](SIM7600-SETUP.md)) |
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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`:
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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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## Later: GPS as a time source
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timesyncd only speaks NTP. Once GNSS has a fix, replace it with `chrony`, configured with:
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- the same NTP servers as above, which remain the default whenever any uplink exists, and
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- a gpsd refclock (`refclock SHM 0`), which takes over when offline.
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NMEA over the USB serial port carries no PPS signal, so GPS time alone is only good to tens of milliseconds. That is plenty for log timestamps.
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