Watchdog Usage

Introduction

Watchdog is actually a timer that will start counting once the board
is powered up. System or software needs to repeatedly communicate with
it and reset the countdown during a specific period to detect and
recover from malfunctions.This process is typically called feeding.

If watchdog is not fed in time or there is any timeouts,  system or
application being trapped in a cycle or being stuck occur. At this
time, watchdog will send a signal to reset the SOC in order to pull
the system or application out of the current situation.

AIBOX-9075 development board includes a watchdog. This section will
show you how to manage it.

Usage

If there is a hardware watchdog, a wdt_XXX device file should be
generated under /dev/.

   ls /dev/wdt_*

It will be /dev/wdt_core or /dev/wdt_base

Enabling and feeding the dog is accomplished by writing the device
file.

   echo e > /dev/wdt_core
   echo 1 > /dev/wdt_core

   # echo different value means
   echo 0: set timeout 0.64s
   echo 1: set timeout 2.56s
   echo 2: set timeout 10.24s
   echo 3: set timeout 40.96s
   echo e: enable wdt
   echo d: disable wdt

You can also control the watchdog through the program. The demo code
is as follows:

   #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 = '2';
       int fd_watchdog = open("/dev/wdt_core", O_WRONLY);

       if(fd_watchdog < 0) {
           printf("FAILED to open /dev/wdt_core, errno: %d, %s\n", errno, strerror(errno));
           syslog(LOG_WARNING, "FAILED to open /dev/wdt_core, errno: %d, %s", errno, strerror(errno));
           exit(1);
       }

       while (1) {
           // feed the watchdog
           ssize_t eaten = write(fd_watchdog, &food, 1);
           if(eaten != 1) {
               printf("FAILED feeding watchdog\n");
               syslog(LOG_WARNING, "FAILED feeding watchdog");
               exit(1);
           }
           sleep(8);
       }

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