orin-nano-env-setup/docs/impl/reports/TIME-SYNC.md

type, date

type	date
report	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). 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/etc/systemd/timesyncd.conf.d/10-servers.conf (superseded on 2026-10-09 by chrony, below; timesyncd is no longer installed):

# 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).