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4.5.18. Watchdog Test

4.5.18.1. Test Principle

The X5 integrates a hardware watchdog (watchdog@34250000, driver dw_wdt). After the WDT is started, its internal counter counts down continuously. A kick (keepalive) must be received before the timeout expires to reload the counter; otherwise an SoC system reset is triggered.

Typical behavior:

  • Kernel auto-feed (default): The kernel watchdogd thread kicks the WDT periodically. /sys/class/watchdog/watchdog0/state is inactive, and no userspace program is required.

  • Userspace takeover: After a process opens /dev/watchdog0 and writes to it, the kernel stops auto-feeding and that process must keep feeding the watchdog.

  • Disable watchdog: When nowayout=0, the watchdog can be stopped via Magic Close; a reboot is required to enable it again.

  Kernel / Userspace                DesignWare WDT     No kick before timeout
 ┌─────────────┐  Periodic kick    ┌──────────────┐                             ┌────────────┐
 │ Feed source │ ────────────────> │ Counter down │   ──────────────────────>   │  SoC reset │
 └─────────────┘                   └──────────────┘                             └────────────┘

4.5.18.2. Preparation

Script Usage

watchdog_test.sh supports the -h option to display help information:

# ./watchdog_test.sh --help

usage: ./watchdog_test.sh <command>

commands:
  info      show hardware watchdog information
  timeout   show configured watchdog timeout (seconds)
  feeder    show whether kernel or userspace is feeding
  timeleft  show remaining timeout (seconds)
  feed      feed watchdog N times: feed <count> [-i interval_sec]
  disable   stop watchdog (requires nowayout=0)

examples:
  ./watchdog_test.sh info
  ./watchdog_test.sh feeder
  ./watchdog_test.sh feed 1
  ./watchdog_test.sh feed 6 -i 2

Parameter description:

  • info: Show basic hardware watchdog information

  • timeout: Show the configured timeout (seconds)

  • feeder: Determine whether the kernel or userspace is feeding the watchdog

  • timeleft: Show the remaining timeout (seconds)

  • feed: Feed the watchdog <count> times [-i interval_sec]; default interval is 1 second

  • disable: Stop the watchdog; a reboot is required to enable it again

  • -h / --help: Show help

4.5.18.3. Test Steps

Check Default Timeout

# ./watchdog_test.sh timeout

Watchdog timeout: 10 sec

Check Feeding Source

# ./watchdog_test.sh  feeder

========================================
Watchdog Feeding Source
========================================
Sysfs state : inactive
Sampling timeleft (1s x 7, kernel feeds about every 5s):
  [1] timeleft=9s
  [2] timeleft=8s
  [3] timeleft=7s
  [4] timeleft=6s
  [5] timeleft=10s
  [6] timeleft=9s
  [7] timeleft=8s
Timeleft seq : 9 8 7 6 10 9 8
Feed source : kernel  # kernel is feeding the watchdog
Reason      : state=inactive, timeleft increased during sampling
              (kernel watchdog worker kicked the hardware WDT)
========================================
root@buildroot:/app/platform_samples/chip_base_test/14_watchdog_test

Check Remaining Timeout

# ./watchdog_test.sh timeleft

Watchdog timeleft: 9 sec (timeout=10 sec)

Feed Test

  • Feed once

# ./watchdog_test.sh  feed 1

Feeding watchdog on /dev/watchdog0: 1 time(s), interval=1s
  [1/1] keepalive ok, timeleft=10s
[  647.681517] watchdog: watchdog0: watchdog did not stop!
Feed done (1 times)
Note: userspace took over (state may become active);
      kernel auto-feed pauses until reboot or disable

  • Feed multiple times with a 5-second interval

# ./watchdog_test.sh feed 10  -i 5

Feeding watchdog on /dev/watchdog0: 10 time(s), interval=5s
  [1/10] keepalive ok, timeleft=10s
  [2/10] keepalive ok, timeleft=10s
  [3/10] keepalive ok, timeleft=10s
  [4/10] keepalive ok, timeleft=10s
  [5/10] keepalive ok, timeleft=10s
  [6/10] keepalive ok, timeleft=10s
  [7/10] keepalive ok, timeleft=10s
  [8/10] keepalive ok, timeleft=10s
  [9/10] keepalive ok, timeleft=10s
  [10/10] keepalive ok, timeleft=10s
[  329.019018] watchdog: watchdog0: watchdog did not stop!
Feed done (10 times)
Note: userspace took over (state may become active);
      kernel auto-feed pauses until reboot or disable

Note: Once userspace feeds the watchdog, kernel auto-feed pauses. If you feed only N times and then exit without further feeding, the system will reset on timeout.

Disable Watchdog

# ./watchdog_test.sh disable

Stopping watchdog via magic close on /dev/watchdog0 ...
State after disable: inactive
Timeleft after disable: 0 sec
Watchdog disable command sent (magic close 'V')
Note: reboot or re-probe driver to re-enable if needed

Note: A reboot is required to enable the watchdog again after it is disabled.

4.5.18.4. Test Metrics

  • The watchdog is a Synopsys DesignWare hardware WDT with driver dw_wdt; the device node /dev/watchdog0 is available.

  • Under /sys/class/watchdog/watchdog0, attributes such as timeleft, timeout, identity, and state are present.