Watchdog

Source: openspec/changes/rock64-ab-image/specs/watchdog/spec.md

Requirements

Current status: implementation hooks are present, but the Rock64 runtime watchdog is intentionally disabled during development. The scenarios below define the current release behavior and the deferred target settings.

ADDED: Hardware watchdog target is deferred

The RK3328 hardware watchdog (dw_wdt) target is documented, but systemd manager watchdog settings are not enabled in the current release.

Scenario: Watchdog triggers on hang

Given the current Rock64 image boots
Then AtomicNix leaves RuntimeWatchdogSec unset
And the deferred target remains RuntimeWatchdogSec=30s

ADDED: Reboot watchdog

A separate reboot watchdog (RebootWatchdogSec) remains deferred until Rock64 boot reliability validation approves active watchdog enforcement.

Scenario: Reboot hang recovery

Given the current Rock64 image boots
Then AtomicNix leaves RebootWatchdogSec unset
And the deferred target remains RebootWatchdogSec=10min

ADDED: Configurable timeouts

The watchdog timeouts are set in modules/watchdog.nix:

systemd.settings.Manager = {
  # RuntimeWatchdogSec = "30s";
  # RebootWatchdogSec = "10min";
};

Runtime: 30 seconds – aggressive enough to catch hangs quickly, long enough to avoid false triggers during normal operation
Reboot: 10 minutes – generous because clean shutdown may need time to stop containers

ADDED: Watchdog interacts with boot-count rollback

A watchdog reboot is indistinguishable from any other abnormal reboot from U-Boot’s perspective. Each watchdog-triggered reboot:

Decrements the boot counter for the current slot
If the counter reaches 0, the slot is skipped
The previous working slot boots instead

This means a systemd hang on a newly updated slot will trigger automatic rollback within 3 watchdog cycles (approximately 90 seconds total).

Scenario: Watchdog-triggered rollback

Given slot B was just installed
And slot B causes a systemd hang on every boot
Then the watchdog reboots 3 times (30s each)
And BOOT_B_LEFT decrements from 3 to 0
And U-Boot falls back to slot A

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