simple_eos.c

Embedded C 这本书的范例光碟程式

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

   Simple_EOS.C (v1.00)

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

   Main file for Simple Embedded Operating System (sEOS) for 8051.

   *** This version uses T0 (easily adapted for T1) ***

   Demonstration version with dummy task X(). 


   COPYRIGHT
   ---------

   This code is associated with the book:

   EMBEDDED C by Michael J. Pont 
   [Pearson Education, 2002: ISBN: 0-201-79523-X].

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

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

#include "Main.H"
#include "Simple_EOS.H"

// Header for dummy task 
#include "X.H"

// ------ Private variable definitions -----------------------------
static tByte Reload_08H;
static tByte Reload_08L;

// ------ Private function prototypes ------------------------------
static void sEOS_Manual_Timer0_Reload(void);


/*------------------------------------------------------------------*-
  
  sEOS_ISR()

  Invoked periodically by Timer 0 overflow: 
  see sEOS_Init_Timer0() for timing details.

-*------------------------------------------------------------------*/
void sEOS_ISR() interrupt INTERRUPT_Timer_0_Overflow
   {
   // Flag cleared automatically but must reload the timer
   sEOS_Manual_Timer0_Reload();
   //===== USER CODE - Begin =======================================

   // Call dummy task here
   X();

   //===== USER CODE - End =========================================
   }

/*------------------------------------------------------------------*-
  
  sEOS_Init_Timer0()

  Sets up Timer 0 to drive the simple EOS.

  Parameter gives tick interval in MILLISECONDS.

  Max tick interval is ~60ms (12 MHz oscillator).

  Note: Precise tick intervals are only possible with certain 
  oscillator / tick interval combinations.  If timing is important,
  you should check the timing calculations manually. 

-*------------------------------------------------------------------*/
void sEOS_Init_Timer0(const tByte TICK_MS)
   {
   tLong Inc;
   tWord Reload_16;

   // 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) 

   // Number of timer increments required (max 65536)
   Inc = ((tLong)TICK_MS * (OSC_FREQ/1000)) / (tLong)OSC_PER_INST;   

   // 16-bit reload value
   Reload_16 = (tWord) (65536UL - Inc);

   // 8-bit reload values (High & Low)
   Reload_08H = (tByte)(Reload_16 / 256);
   Reload_08L = (tByte)(Reload_16 % 256);

   // Used for manually checking timing (in simulator)
   //P2 = Reload_08H;
   //P3 = Reload_08L;

   TL0  = Reload_08L; 
   TH0  = Reload_08H;

   // Timer 0 interrupt is enabled, and ISR will be called 
   // whenever the timer overflows.
   ET0 = 1;

   // Start Timer 0 running
   TR0 = 1;     

   // Globally enable interrupts
   EA = 1;            
   }

/*------------------------------------------------------------------*-
  
  sEOS_Manual_Timer0_Reload()

  This OS uses a (manually reloaded) 16-bit timer.
  The manual reload means that all timings are approximate. 

  THIS OS IS NOT SUITABLE FOR APPLICATIONS WHERE
  ACCURATE TIMING IS REQUIRED!!!

  Timer reload is carried out in this function. 

-*------------------------------------------------------------------*/
void sEOS_Manual_Timer0_Reload()
   {
   // Stop Timer 0
   TR0 = 0;

   // See 'init' function for calculations
   TL0  = Reload_08L; 
   TH0  = Reload_08H;

   //  Start Timer 0
   TR0  = 1;
   }

/*------------------------------------------------------------------*-
  
  sEOS_Go_To_Sleep()

  This operating system enters 'idle mode' between clock ticks
  to save power.  The next clock tick will return the processor
  to the normal operating state.

  *** ADAPT AS REQUIRED FOR YOUR HARDWARE ***

-*------------------------------------------------------------------*/
void sEOS_Go_To_Sleep(void)
   {
   PCON |= 0x01;    // Enter idle mode (generic 8051 version)
   }

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