Lpc2000

>  Watchdog testing is tricky.  I've found that if I erase the 2138 and set 
a break in the MM_WATCHDOG_ISR() it works ONCE. Then, I must erase or re-flash the part with watchdog dis. before trying again, otherwise it will
always hit the watchdog ISR as soon as the watchdog is enabled.  Also, test in flash only, not in ram.  Do NOT load test code with watchdog time-out too quick or it becomes hard to talk to the part again.  Example, write test code to watchdog_hit() for about 5-10 sec. before trying to test a wathdog time-out.  This gives you the 5-10 sec. after each crash to try to re-flash the part with code that doesn't enable the watchdog. WATCHDOG_DEBUG does hit break point but only ONCE, THEN step 2,
STEP 1) test your code
STEP 2) load code with-out watchdog en.
STEP 3) goto step 1
Don't ship with WATCHDOG_DEBUG defined ,MM_WATCHDOG_ISR() OR after watchdog time-out it locks instead of resets (while(1);)
IAR lpc2138 code (12Mhz xtal):
//watchdog.h
#define WATCHDOG
//#define WATCHDOG_DEBUG

void watchdog_init(void);
void watchdog_hit(void);
//watchdog.c

#include "EWARM_version_420_430.h"
#include <iolpc2138.h>
#include <stdio.h>
#include <inarm.h>

#include "watchdog.h"

void watchdog_init(void)
{
  //WDTC = 0x004fffff; //4 sec //no pll
  //WDTC = 0x27FFFF; //2 sec //without pll
  WDTC = 0x9FFFFC; //2 sec //with pll 60Mhz

  WDFEED = 0xAA;
  WDFEED = 0x55;
  WDMOD_bit.WDEN = 1;
#if !defined(WATCHDOG_DEBUG)
  WDMOD_bit.WDRESET = 1;
#endif
  WDFEED = 0xAA;
  WDFEED = 0x55;
}

void watchdog_hit(void)
{
  WDFEED = 0xAA;
  WDFEED = 0x55;
}
//main.c
#include "Timer0_IntOnMR0.h"
#include "rtc.h"
#include "watchdog.h"
unsigned int us_Ticks;
#define InitPORT()	IO1DIR  = 0xFF0000; \
			IO1CLR  = 0xFF0000
#define TogglePORTbit0()  IO1PIN ^= 0x00800000
#define TogglePORTbit1()  IO1PIN ^= 0x00100000
void main(void)
{
  int i;
...
//12-22-05 add watchdog
#ifdef WATCHDOG
  watchdog_init();
#ifdef WATCHDOG_DEBUG
  VICIntSelect &= ~(1<<VIC_WDT); // watchdog intrpt is an IRQ (VIC_WDT = 0)
  VICVectAddr8 = (unsigned int)&MM_WATCHDOG_ISR; // Install ISR in VIC addr 
  VICVectCntl8 = 0x20 | VIC_WDT;    // IRQ type, watchdog int enabled
  VICIntEnable |= (1<<VIC_WDT);    // Turn on watchdog Interrupt
#endif
#endif
...
  __enable_interrupt();                        // Global interrupt enable
  InitPORT();
...
  i = 1;
  while(TRUE)                                  // Foreground "task"
  {
    if(bl_TimerFlag)
    {
      TogglePORTbit1();
      if(i < 20){
      //if(i){
        i++;
        watchdog_hit(); //10 sec. of this, then 2 sec. then TIME-OUT
        TogglePORTbit0();
      }
      bl_TimerFlag = FALSE; // Clear flag set by isr
      if( IOPIN0 & (1<<PIN0_4) )               // Is P0.4 High?
        IOCLR0 |= (1<<PIN0_4);                 // Yes, make it low
      else
        IOSET0 |= (1<<PIN0_4);                 // No, set pin high
    }
    read_rtc();

  } // end foreground loop
}   // end main()
#pragma vector=0x18
__irq __arm void IRQ_ISR_Handler (void)
{
  void (*interrupt_function)(void);
  unsigned int vector;
  static unsigned int us_count;
  us_count++;
  vector = VICVectAddr;                   // Get interrupt vector.
  interrupt_function = (void(*)())vector; // Call MM_.._ISR thru pointer
  (*interrupt_function)();            // Call vectored interrupt function
  VICVectAddr = 0;                      // Clear interrupt in VIC
}
void MM_WATCHDOG_ISR()
{
  IO1PIN = 0;
  while(1)
    ;
}