I implement softare watchdog on my system. But It not work well.
I use timer 0 interrupt and some counter for set time out. And call address 0x0000. It work at only first time no more interrupt again. sourec ininterrupt is here.

if ( --pcaWatchDog == 0x00 )
{
TR0 = 0;
ET0 = 0;
EA = 0;
((void(code *)(void))0x0000)();
}
thank you