Listing 2—Event.plm 

EventScheduler: Do;
   /* _________________________________________________
                                                      
        Event Scheduler                               
        Development started : 16/07/95                
        Last Updated        : 31/08/95                
        S/W Designed and Developed by Ramakrishnan.K.V
     _________________________________________________*/
   
   Declare FunctionReference Literally  'word   ';
   Declare true              Literally  '0ffh';
   Declare FREE              Literally  '0ffffh';
   Declare PoolSize          Literally  '20';/* maximum timer pool available */
   Declare IntNo             Literally  '10'; /* int. level, used for syntax */
   Declare Dummy             Word; /* dummy used to assign return values */
   declare data$seg$ptr      pointer; /* to separate offset and base */ 
   declare data$seg$addr     structure(offset  word ,
                                       base    word)
                                       at (@data$seg$ptr);
   /*______________________________________________________ */
   /* Data structure used for event scheduler */
   Declare CurrentToken     Byte;
   Declare   Pool(PoolSize)Structure(
             AssignedToken  Word,             /* AssignedToken are made true */
             CounterValue   Word,             /* max count is loaded         */
             ActionTask     FunctionReference /* to execute when TC  reached */
             );

    /* Interrupt  related variables.  Initialized  according to the hardware
      configuration of  system  by  the  user  while  initializing  timer  &
      interrupt  controller.  (Refer  procedure done init$80186  to use this
      with a 80186 based system.  */

   Declare EoiPort         word public; /* eoi port address of PIC      */
   Declare EoiValue        word public; /* eoi value to be given on eoi */
   Declare TIMER$INTLEVEL  byte public; /* interrupt vector number      */ 
   
   /*______________________________________________________________
     The  following 3 functions are local
       a) Despatching - EventScheduler interrupt service routine
       b) rq$set$interrupt - for Interrupt vector setting
       c) Search - search for a given token and return its index in timer pool
     ______________________________________________________________*/
   
   Despatching : Procedure interrupt IntNo;
   
    /* This function is an interrupt program.  Invoked by the timer at every
      slot-time.  This  will  execute  all  the  ActionTasks  which  require
      service at this timer event.  And also update timer pools.  */

       Declare   i  Byte;
       Declare   ActionTaskPtr FunctionReference;
       Do i = 0 to PoolSize-1;
          If Pool(i).AssignedToken<>FREE then
          Do;
             If Pool(i).AssignedToken >PoolSize then
             Do; /* it is a task pool */
                  Pool(i).CounterValue = Pool(i).CounterValue - 1;
                  If Pool(i).CounterValue = 0 then
                  Do;
                    ActionTaskPtr  =   Pool(i).ActionTask; /* take the ActionTask */
                    Call ActionTaskPtr;
                    Pool(i).AssignedToken = FREE;
                  End;
             End;
             Else
             Do; /* it is a timer pool */
                  Pool(i).CounterValue = Pool(i).CounterValue + 1;
             End;
          End;
       End;
       outword(EoiPort) = EoiValue; 
   End Despatching;
   /*_______________________________________________________________*/
   
   rq$set$interrupt:  Procedure( level,
                                 interrupt$task$flag,
                                 interrupt$handler,
                                 interrupt$handler$ds,
                                 except$ptr );
      /* Function to set interrupt vector.*/
      Declare level                   Word,
              interrupt$task$flag     Byte,
              interrupt$handler       POINTER,
              interrupt$handler$ds    Word,
              except$ptr              POINTER;
      Declare exception   based except$ptr Word;
      Declare  INT$addr      structure(offset  Word ,
                                       base    Word)
                                       at (@interrupt$handler);
      Declare ptr$loc pointer,
               vct$addr      structure(offset  Word ,
                                       base    Word)
                                       at (@ptr$loc),
               w  based ptr$loc(2) Word;
      If level > 255 then
      Do;
         exception = 1;
         Return;
      End;
      vct$addr.offset = level * 4;
      vct$addr.base   = 0;
      w(0) = int$addr.offset;
      w(1) = int$addr.base;
      exception = 0;
   End rq$set$interrupt;
   /*_______________________________________________________________*/
   
   Search:Procedure(Token) Word;
    /*  this Procedure will search  the given token and  Return the index at
      which the match is found.  Else Return 0FFFFH; */
         Declare i     Word;
         Declare Token Word;
         i = 0;
         Do While(((Pool(i).AssignedToken)<>Token) and (i= Count then
         Do;/* Requested delay elapsed */
              Dummy = StopTimer(TimerToken);/*free timer*/
              Return;
         End;
      End;
   End RequestDelay;
   
   /*_______________________________________________________________*/
   
   SubmitTask:Procedure(MaxWaitTime,FunctionPtr)byte reentrant Public;

    /* function to execute a  function  after  given  delay  (MaxWaitTime  *
      slot-time ) is occurred */

   Declare   MaxWaitTime         Word,
             FunctionPtr   FunctionReference;
   Declare   i      Word;
   
         disable;
         /* search for the Pool  */
         i = Search(FREE);
         If(i 0ffffh then
            Do;/* Do not wait indefinitely */
                If ElapsedTime(TimerToken) >= WaitTime then
                Do;/* condition not satisfied */
                       Dummy = StopTimer(TimerToken);/*free timer*/
                       Return(0ffffh);  /* with in the specified time */
                End;
            End;
       End;
   End StopWatch;
   /*_______________________________________________________________*/
   
   StartTimer:Procedure Word Public;
   Declare i Word;
       /* Search For the Free Timer Pool*/
         disable;
         i = Search(FREE);
         If(iFREE then
          Do;
             If Pool(i).AssignedToken >PoolSize then
             Do; /* it is a task pool */
                  Pool(i).CounterValue = Pool(i).CounterValue - 1;
                  If Pool(i).CounterValue = 0 then
                  Do;
                    ActionTaskPtr  =   Pool(i).ActionTask; /* take the ActionTask */
                    Call ActionTaskPtr;
                    Pool(i).AssignedToken = FREE;
                  End;
             End;
             Else
             Do; /* it is a timer pool */
                  Pool(i).CounterValue = Pool(i).CounterValue + 1;
             End;
          End;
       End;
       outword(EoiPort) = EoiValue; 
   End Despatching;
   /*_______________________________________________________________*/
   
   rq$set$interrupt:  Procedure( level,
                                 interrupt$task$flag,
                                 interrupt$handler,
                                 interrupt$handler$ds,
                                 except$ptr );
      /* Function to set interrupt vector.*/
      Declare level                   Word,
              interrupt$task$flag     Byte,
              interrupt$handler       POINTER,
              interrupt$handler$ds    Word,
              except$ptr              POINTER;
      Declare exception   based except$ptr Word;
      Declare  INT$addr      structure(offset  Word ,
                                       base    Word)
                                       at (@interrupt$handler);
      Declare ptr$loc pointer,
               vct$addr      structure(offset  Word ,
                                       base    Word)
                                       at (@ptr$loc),
               w  based ptr$loc(2) Word;
      If level > 255 then
      Do;
         exception = 1;
         Return;
      End;
      vct$addr.offset = level * 4;
      vct$addr.base   = 0;
      w(0) = int$addr.offset;
      w(1) = int$addr.base;
      exception = 0;
   End rq$set$interrupt;
   /*_______________________________________________________________*/
   
   Search:Procedure(Token) Word;
    /*  this Procedure will search  the given token and  Return the index at
      which the match is found.  Else Return 0FFFFH; */
         Declare i     Word;
         Declare Token Word;
         i = 0;
         Do While(((Pool(i).AssignedToken)<>Token) and (i= Count then
         Do;/* Requested delay elapsed */
              Dummy = StopTimer(TimerToken);/*free timer*/
              Return;
         End;
      End;
   End RequestDelay;
   
   /*_______________________________________________________________*/
   
   SubmitTask:Procedure(MaxWaitTime,FunctionPtr)byte reentrant Public;

    /* function to execute a  function  after  given  delay  (MaxWaitTime  *
      slot-time ) is occurred */

   Declare   MaxWaitTime         Word,
             FunctionPtr   FunctionReference;
   Declare   i      Word;
   
         disable;
         /* search for the Pool  */
         i = Search(FREE);
         If(i 0ffffh then
            Do;/* Do not wait indefinitely */
                If ElapsedTime(TimerToken) >= WaitTime then
                Do;/* condition not satisfied */
                       Dummy = StopTimer(TimerToken);/*free timer*/
                       Return(0ffffh);  /* with in the specified time */
                End;
            End;
       End;
   End StopWatch;
   /*_______________________________________________________________*/
   
   StartTimer:Procedure Word Public;
   Declare i Word;
       /* Search For the Free Timer Pool*/
         disable;
         i = Search(FREE);
         If(i<PoolSize)then
         Do;
            Pool(i).CounterValue   = 0;
            Pool(i).AssignedToken  = i;
         End;
         enable;
         Return i; /* fail or token */
   End StartTimer;
   /*_______________________________________________________________*/
   
   StopTimer:Procedure(Token) Word Public;
      Declare   Token  Word;
      Declare Count Word;

    /*  Search For the Timer Pool for given token.  Since for timer pool the
      token is the pool index.  Directly use it.*/

         disable;
         If(Token%lt;PoolSize)then
         Do;
            Pool(Token).AssignedToken  = 0ffffh;
            Count = Pool(Token).CounterValue;
         End;
         Else Count = 0ffffh;
         enable;
         Return Count;
   End StopTimer;
   /*_______________________________________________________________*/
   
   RestartTimer:Procedure(Token) Public;
     Declare   Token  Word;

    /*  Search For the Timer Pool for given token.  Since for timer pool the
      token is the pool index.  Directly use it.*/

         If(Token<PoolSize)then Pool(Token).CounterValue = 0;
   End RestartTimer;
   /*_______________________________________________________________*/
   
   ElapsedTime:Procedure(Token) Word Public;
     Declare   Token  Word;

    /*  Search For the Timer Pool for given token.  Since for timer pool the
      token is the pool index.  Directly use it.  */

         If(Token<PoolSize)then Return Pool(Token).CounterValue;
         Return 0ffffh; /* fail return max value */
   End ElapsedTime;
End EventScheduler;