12. Watchdog Usage

12.1. Introduce

Watchdog is actually a timer. After starting, it will start timing. The system or software needs to communicate with the watchdog (commonly known as dog feeding) within a specified time to reset timing, constantly repeat that, to ensure the system and software is working.

If the dog is not fed within the specified time and the watchdog times out, that means the system or application is trapped in a loop or stuck. At this time, the watchdog sends a reset signal to reset the CPU and get rid of the stuck.

iCore-3568JQ has a internal watchdog and a external watchdog. The model of the external watchdog is PC9202.

12.2. Internal watchdog

The internal watchdog is /dev/watchdog, here’s how to use it:

# Write anything (Except capital letter 'V') into it to enable watchdog, and needs to feed it within every 45s
echo 1 > /dev/watchdog

# Write capital letter V to close it
echo V > /dev/watchdog

You can also write a programe to control watchdog:

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <syslog.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

void main() {
	unsigned char food = 0;
	int fd_watchdog = open("/dev/watchdog", O_WRONLY);

	if(fd_watchdog < 0) {
		printf("FAILED to open /dev/watchdog, errno: %d, %s\n", errno, strerror(errno));
		syslog(LOG_WARNING, "FAILED to open /dev/watchdog, errno: %d, %s", errno, strerror(errno));

	// default timeout is 45s
	// feed the watchdog once
	ssize_t eaten = write(fd_watchdog, &food, 1);
	if(eaten != 1) {
		printf("FAILED feeding watchdog\n");
		syslog(LOG_WARNING, "FAILED feeding watchdog");

	// close the watchdog
	food = 'V';
	write(fd_watchdog, &food, 1);

Notice: Internal watchdog will start timing right after you using open function

Reference documentation: SDK/RKDocs(docs in linux)/common/watchdog

12.3. External watchdog

The external watchdog is /dev/wdt_crl, here’s how to use it:

# Write different numbers to enable it and set timeout
# The numbers 0, 1, 2, 3 represent 0.64s, 2.56s, 10.24s and 40.96s respectively

# Enable watchdog and set 10.24s as timeout, needs to feed it within every 10.24s, or write other numbers to change timeout
echo 2 > /dev/wdt_crl

External watchdog can also be controled by programe, just like the internal one, only needs to change the device name and food.


  1. External watchdog will not start timing after opening it until you write numbers into it

  2. External watchdog only accept number 0, 1, 2, 3

  3. Now iCore-3568JQ v1.0 version, external watchdog cannot be closed in software way after it is enabled, you need to cut the power

  4. So if you want to update firmware after external watchdog enabled, please press recovery button, disconnect power and reconnect to enter loader mode, using reboot loader command will be reset by watchdog