If you have a watchdog on your system and a driver that uses
/dev/watchdog, all you have to do is kill the process that is feeding it; if there is no such process, then you can
touch /dev/watchdog once to turn it on, and if you don't touch it again, it will reset.
You also might be interested in resetting the device using the "magic sysrq" way. If you have a kernel with the
CONFIG_MAGIC_SYSRQ feature compiled in, then you can
echo 1 > /proc/sys/kernel/sysrq to enable it, then
echo b > /proc/sysrq-trigger to reboot. When you do this, it reboots immediately, without unmounting or or syncing filesystems.