0_05_11g.c

外国人写的时间触发的调度器源码

/*------------------------------------------------------------------*-

   0_05_11g.C (v1.00) 

  ------------------------------------------------------------------

   *** THIS IS A SCHEDULER FOR THE STANDARD 8051 ***

   *** Uses T0 for timing, 16-bit, manual reload ***

   *** With 11.059 MHz crystal -> 5ms tick interval ***
   --- (see 'reload' function for details) ---


   COPYRIGHT
   ---------

   This code is from the book:

   PATTERNS FOR TIME-TRIGGERED EMBEDDED SYSTEMS by Michael J. Pont 
   [Pearson Education, 2001; ISBN: 0-201-33138-1].

   This code is copyright (c) 2001 by Michael J. Pont.
 
   See book for copyright details and other information.

-*------------------------------------------------------------------*/

#include "Main.h"
#include "0_05_11g.h"

// ------ Public variable declarations -----------------------------

// The array of tasks (see Sch51.C)
extern sTask SCH_tasks_G[SCH_MAX_TASKS];

// Used to display the error code
// See Main.H for details of error codes
// See Port.H for details of the error port
extern tByte Error_code_G;

// ------ Private function prototypes ------------------------------

static void SCH_Manual_Timer0_Reload(void);

/*------------------------------------------------------------------*-

  SCH_Init_T0()

  Scheduler initialisation function.  Prepares scheduler
  data structures and sets up timer interrupts at required rate.
  You must call this function before using the scheduler.  

-*------------------------------------------------------------------*/
void SCH_Init_T0(void) 
   {
   tByte i;

   for (i = 0; i < SCH_MAX_TASKS; i++) 
      {
      SCH_Delete_Task(i);
      }

   // Reset the global error variable
   // - SCH_Delete_Task() will generate an error code, 
   //   (because the task array is empty)
   Error_code_G = 0;

   // Using Timer 0, 16-bit manual reload
   TMOD &= 0xF0; // Clear all T0 bits (T1 left unchanged)
   TMOD |= 0x01; // Set required T0 bits (T1 left unchanged) 

   // Sets up timer reload values
   SCH_Manual_Timer0_Reload();

   //  Interrupt Timer 0 enabled
   ET0  = 1;
   }

/*------------------------------------------------------------------*-

  SCH_Start()

  Starts the scheduler, by enabling interrupts.

  NOTE: Usually called after all regular tasks are added,
  to keep the tasks synchronised.

  NOTE: ONLY THE SCHEDULER INTERRUPT SHOULD BE ENABLED!!! 
 
-*------------------------------------------------------------------*/
void SCH_Start(void) 
   {
   EA = 1;
   }

/*------------------------------------------------------------------*-

  SCH_Update

  This is the scheduler ISR.  It is called at a rate 
  determined by the timer settings in SCH_Init_T0().
  This version is triggered by Timer 0 interrupts.

-*------------------------------------------------------------------*/
void SCH_Update(void) interrupt INTERRUPT_Timer_0_Overflow 
   {
   tByte Index;

   // Reload the timer
   SCH_Manual_Timer0_Reload();

   // NOTE: calculations are in *TICKS* (not milliseconds)
   for (Index = 0; Index < SCH_MAX_TASKS; Index++)
      {
      // Check if there is a task at this location
      if (SCH_tasks_G[Index].pTask)
         {
         if (SCH_tasks_G[Index].Delay == 0)
            {
            // The task is due to run
            SCH_tasks_G[Index].RunMe += 1;  // Inc. the 'Run Me' flag

            if (SCH_tasks_G[Index].Period)
               {
               // Schedule periodic tasks to run again
               SCH_tasks_G[Index].Delay = SCH_tasks_G[Index].Period;
               }
            }
         else
            {
            // Not yet ready to run: just decrement the delay 
            SCH_tasks_G[Index].Delay -= 1;
            }
         }         
      }
   } 

/*------------------------------------------------------------------*-

  SCH_Manual_Timer0_Reload()

  This scheduler uses a (manually reloaded) 16-bit timer.
  The manual reload means that all timings are approximate. 
  THIS SCHEDULER IS NOT SUITABLE FOR APPLICATIONS WHERE
  ACCURATE TIMING IS REQUIRED!!!
  
  Timer reload is carried out in this function. 
 
-*------------------------------------------------------------------*/
void SCH_Manual_Timer0_Reload()
   {
   // Stop Timer 0
   TR0 = 0;

   // Crystal is assumed to be 11.059 MHz
   // Assume 12 osc cycles per timer increment
   // -> timer resolution is 0.0000010850694 seconds (1.085 祍)
   //
   // The required Timer 0 overflow is 0.005 seconds (5 ms)
   // - this takes 4608 timer ticks
   //
   // Reload value is 65536 - 4608 = 60928 (dec) = 0xEE00
   TH0  = 0xEE;
   TL0  = 0x00;

   //  Start Timer 0
   TR0  = 1;
   }

/*------------------------------------------------------------------*-
  ---- END OF FILE -------------------------------------------------
-*------------------------------------------------------------------*/