SSV - CP/386LN

CP/386LN WATCHDOG TIMER

The CP/386LN offers non-stop operation for critical embedded PC applications such as medical instruments, security systems, test equipment, and communication devices with an watchdog timer. A watchdog timer is used to restart the CP/386LN in case normal operation is interrupted by unexpected events such as software or hardware failures and power brownouts. The CP/386LN watchdog timer is supported by the EMBEDDED SYSTEM BIOS ESB386EX with 3 functions:

BIOS Int. 15h, AX= 0C301h START WATCHDOG TIMER

BIOS Int. 15h, AX= 0C302h TRIGGER WATCHDOG TIMER

BIOS Int. 15h, AX= 0C300h STOP WATCHDOG TIMER

If an application program starts the watchdog timer, the watchdog timer must periodically be retriggered by the application program. When a timeout condition occurs, the CP/386LN watchdog timer restarts the system by generating a hardware reset. The timeout value can be set with BIOS Interrupt 15h / AX= 0C301h (START WATCHDOG TIMER). The function needs the timeout value in 80x86 register BX. The integer value 382 is an timeout from 1 sec., 382 * 2 is 2 sec., 382 * 3 is 3 sec. watchdog timeout and so on. The following C sourcecode shows an example for an watchdog timeout from 5 sec. This code was written in Borland Turbo C for DOS.

/****************************************************************************/
/*  Programm: WATCHDOG.C                                                    */
/*  Version.: 1.00							    */
/*  Date....: 14.04.1996 KDW			                            */
/*  LUPD....: 14.04.1996 KDW                                                */
/*                                                                          */
/*  Watchdog Timer demo program for 386EX CPU with SSV EMBEDDED SYSTEM BIOS */
/*  (ESB386EX). This BIOS supports the INTEL 386EX internal  WATCHDOG  with */
/*  BIOS interrupt 15h. This program shows  the 3 main functions: 1.) START */
/*  WATCHDOG;  2.) (RE)TRIGGER WATCHDOG and 3.) STOP WATCHDOG.              */
/****************************************************************************/

	/************/
	/* Includes */
	/************/

#include ‹stdio.h›
#include ‹dos.h›
#include ‹bios.h›

	/***********************/
	/* FunctionPrototyping */
	/***********************/

unsigned char  main (void);                     /* main................ */
void           StartWatchdog (void);            /* START WATCHDOG...... */
void           TriggerWatchdog (void);          /* (RE)TRIGGER WATCHDOG */
void           StopWatchdog (void);             /* STOP WATCHDOG....... */

/****************************************************************************/
/* Function: main --  Trigger Watchdog if the user press a key ...          */
/****************************************************************************/

unsigned char main (void)
{
   /************/
   /* Variable */
   /************/

   int LoopFlag, c;

   /**************************************************************/
   /* Start Watchdog and enter loop. Wait for key's in this loop */
   /**************************************************************/

   clrscr ();
   LoopFlag= 1;
   StartWatchdog ();                            /* Start Watchdog.... */
   printf ("**** START WATCHDOG TIMER. ****\n");
   printf ("-------------------------------\n");
   while (LoopFlag) {

      /************************************************************/
      /* ... Wait for Key, Display ScanCode & KeyCode and trigger */
      /* Watchdog. Stop Watchdog and exit program if ESC.         */
      /************************************************************/

      c= bioskey (0);
      TriggerWatchdog ();
      cprintf ("TRIGGER WD. Key SC/KC 0x%02X/0x%02X\n\r", (c >> 8) & 0xff, c & 0xff);

      /*******************************/
      /* ... Checks for ESC key here */
      /*******************************/

      if ((c & 0xff) == 0x1b) LoopFlag= 0;
   }
   StopWatchdog ();                             /* Stop Watchdog.... */
   printf ("-------------------------------\n");
   printf ("***** STOP WATCHDOG TIMER *****\n");
   return (1); 					/* Exit Program here */
}

/****************************************************************************/
/* Function: StartWatchdog -- Start Watchdog Timer with 5 sec. Timeout      */
/****************************************************************************/

void StartWatchdog (void) {

   union REGS inregs, outregs;			/* 80x86 Registers */

   /********************************************************/
   /* ... uses ESB386EX Int. 15h / AX= 0C301h, BX= timeout */
   /********************************************************/

   inregs.x.ax= 0xc301;
   inregs.x.bx= 382*5;				/* TimeOut = 5 Sec. */
   int86 (0x15, &inregs, &outregs);
}

/****************************************************************************/
/* Function: TriggerWatchdog -- (Re)Trigger Watchdog                        */
/****************************************************************************/

void TriggerWatchdog (void) {

   union REGS inregs, outregs;			/* 80x86 Registers */

   /*******************************************/
   /* ... uses ESB386EX Int. 15h / AX= 0C302h */
   /*******************************************/

   inregs.x.ax= 0xc302;
   int86 (0x15, &inregs, &outregs);
}

/****************************************************************************/
/* Function: StopWatchdog -- Stop Watchdog                                  */
/****************************************************************************/

void StopWatchdog (void) {

   union REGS inregs, outregs;			/* 80x86 Registers */

   /*******************************************/
   /* ... uses ESB386EX Int. 15h / AX= 0C300h */
   /*******************************************/

   inregs.x.ax= 0xc300;
   int86 (0x15, &inregs, &outregs);
}
/****************************************************************************/