timer.c

schduler for AVR mcu

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

   *** THIS IS A SCHEDULER FOR STANDARD 8051 / 8052 ***

   *** Uses T2 for timing, 16-bit auto reload ***
   *** 12 MHz oscillator -> 1 ms (precise) tick interval ***


   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.
 
   --- Modefied by  sylva zhu to apply for  AVR Microcontroller .
   --- Ver 1.0  Sept 25th , 2006 .

-*------------------------------------------------------------------
*/
#include  <iom32.h>
#include  <inavr.h>
#include  <comp_a90.h>
//
#include  "Timer.H"
#include  "Main.H"
#include  "Scheduler.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 unsigned char Error_code_G;

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

  SCH_Init()

  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(void) 
{
   unsigned char 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;  

   // Now set up Timer 2
    TCCR2 =(1<<CS20);     // select precaler: 32.768 kHz / 1 = 7.8 mS between each overflow
                          // Set TCNT2=223 , 1mS per time tick
    ASSR = (1<<AS2);       // select asynchronous operation of Timer2
    //TCNT2 = 0;             // clear TCNT2
    TCNT2 = 223 ;         // Preset value 
    //
    // wait for TCN2UB and TCR2UB to be cleared
    // while((ASSR & 0x01) | (ASSR & 0x04)); 
    while( (ASSR&(1<<TCN2UB)) || (ASSR&(1<<TCR2UB)) );
    TIFR  |= (1<<TOV2);      // clear interrupt-flags
    TIMSK |= (1<<TOIE2);     // enable Timer2 overflow interrupt
}
/*
------------------------------------------------------------------*-

  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;
  __enable_interrupt();
}

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

  SCH_Update()

  This is the scheduler ISR.  It is called at a rate 
  determined by the timer settings in the 'init' function.

  This version is triggered by Timer 2 interrupts:
  timer is automatically reloaded.

-*------------------------------------------------------------------
*/
#pragma vector=TIMER2_OVF_vect
__interrupt void SCH_Update(void)
{
   unsigned char Index;
   // reload by manual .
   TCNT2 = 223 ;         // Preset value  , for 1mS time tick .
   //
   // 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 'RunMe' flag

             if (SCH_tasks_G[Index].Period)
                {
                 // Schedule regular 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;
            }
        }         
    }
}   
/*
------------------------------------------------------------------*-
  ---- END OF FILE -------------------------------------------------
-*------------------------------------------------------------------
*/