---
type: report
date: 2026-10-08
---
# Time Sync and Timezone

## Result

| Item | State |
|------|-------|
| 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 |
| Timezone | `Asia/Tokyo` (was `Asia/Yakutsk`: same +09:00 and no DST either, but the wrong place) |
| Clock across power-off | **Not kept.** The RTC has no backup battery (see below) |
| GPS time | chrony refclock `GPS` (gpsd SHM 0), fallback only; used when offline with a fix |
| Boot clock without network | `fake-hwclock` restores the last saved time (replaces timesyncd's saved timestamp) |

## RTC loses time when powered off

On the 2026-10-08 cold boot, the kernel set the system clock from `rtc0` (`nvvrs-pseq-rtc`, `hctosys=1`) to **June 4**.
Then the clock was corrected in two steps:

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.
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.

Until step 2, timestamps are wrong, and with no uplink (in the car, out of coverage) they stay wrong. The fix is hardware:
an RTC backup battery (see [BOM](../../BOM.md#rtc-backup-battery)). `rtc1` (`tegra_rtc`) isn't used for boot time and reads 1970.

## Configuration

```
sudo timedatectl set-timezone Asia/Tokyo
```

`/etc/systemd/timesyncd.conf.d/10-servers.conf`:

```
# Japan-local primary (NICT, national time standard), global pool as backup.
[Time]
NTP=ntp.nict.jp
FallbackNTP=ntp.ubuntu.com 0.jp.pool.ntp.org 1.jp.pool.ntp.org 2.jp.pool.ntp.org
```

`sudo systemctl restart systemd-timesyncd`, then check with `timedatectl timesync-status` (server, stratum, offset).

## Chrony with GPS fallback (2026-10-09)

Replaced `systemd-timesyncd` (removed by the `chrony` package) so GPS can serve as an offline time source.

```
sudo apt install chrony fake-hwclock
```

`/etc/chrony/conf.d/10-yukart.conf`:

```
server ntp.nict.jp iburst prefer
pool 2.jp.pool.ntp.org iburst maxsources 2
refclock SHM 0 refid GPS precision 1e-1 offset 0.0 delay 0.5 poll 3
```

- **NTP stays primary.** The GPS refclock's generous `precision`/`delay` give it a large root distance, so any reachable NTP server wins.
  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.
- **`offset 0.0` is a placeholder.** Tune it once NTP and a GNSS fix are both available: `chronyc sourcestats` shows the GPS offset
  against NTP.
- **`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
  updates, because with no RTC battery a stale clock may only meet its first source (a late GPS fix) well into an offline drive.
  chrony's config format has no inline comments; the explanation sits on its own line above.
- **`fake-hwclock`** saves the time hourly and at shutdown and restores it at boot, so an offline boot starts near the last shutdown
  instead of the RTC's reset date. This replaces what timesyncd's `/var/lib/systemd/timesync/clock` did.
- 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
  without it, now fixed.

Check: `chronyc -n sources` (`^*` = selected NTP server, `#` = GPS refclock), `chronyc tracking`.
At setup: synced to `ntp-a3.nict.go.jp` (stratum 1); `GPS` listed with no samples (antenna detached indoors).