Watchdog is a very necessary module for embedded system. Someone said that embedded system operates without watchdog enabled just like the car without air bag. You should always enabled watchdog as possible as you can.
The PIC32MZ Watchdog Timer (WDT), when enabled, operates from the internal Low-Power RC (LPRC) Oscillator clock source which is 32.768 KHz. The WDT can be used to detect system software malfunctions by resetting the device if the WDT is not cleared periodically in software. The WDT can be configured in Windowed mode or non-Windowed mode. Various WDT time-out periods can be selected using the WDT postscaler. The WDT can also be used to wake the device from Sleep or Idle mode.
At the moment, I implement the primary function of the WDT is to reset the processor in the event of a software malfunction. I enable WDT with Non-Windowed mode, and the WDT will increment until it overflows or "times out". A WDT time-out will force a device Reset, except during Sleep or Idle modes. To prevent a WDT time-out Reset, my application always periodically clear the WDT by writing a key word 0x5743 to the WDTCLEKEY (WDTCON<31:16>) through a single 16-bit write (for some other devices, or by setting the WDTCLR (WDTCON<0>).
The WDT is enabled or disabled by the device configuration bits or controlled through software by writing to the WDTCON register. In my application I just set the device configuration bits like below.
#pragma config WDTPS = PS32 // Watchdog Timer Postscaler (1:32) #pragma config WDTSPGM = STOP // Watchdog Timer Stop During Flash Programming (WDT stops during Flash programming) #pragma config WINDIS = NORMAL // Watchdog Timer Window Mode (Watchdog Timer is in non-Window mode) #pragma config FWDTEN = OFF // Watchdog Timer Enable (WDT Disabled) #pragma config FWDTWINSZ = WINSZ_25 // Watchdog Timer Window Size (Window size is 25%)
The setting as above, the postscaler of Watchdog Timer is 32. It determines the period of Watchdog Timer overflow is 32ms. The FWDTEN Configuration bit is clear, so I need enable Watchdog Timer by software, and I also need a function to clear Watchdog and call this function periodically in the main loop. Below is my implementation of them.
void Wdt_Init(void) { WDTCONSET = 0x8000; } void Wdt_Refresh(void) { unsigned short *pWdtClear = (unsigned short *)0xBF800800 + 1; *pWdtClear = 0x5743; }