/* PROGRAM NAME: CLOCK.C */
/* PROGRAM TO DEMOSTRATE THE USE OF INTERRUPTS USING SMALL C.         */
/* PROGRAM WRITTEN FOR MOTOROLA 68HC11 BOARD RUNNING BUFFALO MONITOR. */
/* PROGRAM SIZE: 4200 BYTES                                           */
/*  NOTE: fprintf() uses 3500 bytes of those 4200 bytes- instead use  */
/*        fputs() (about 120 bytes) and itoa() (about 100 bytes)      */
/*        if memory is tight.                                         */
/*    ENSURE THERE ARE AT AT LEAST 0x80 BYTES OF STACK SPACE!!!!      */

/* Define where things should reside... */
#code    0xC0f0
#data    0xC000
#include <startup.c>

/* Define where register bank is mapped... */
#define  REG_BASE 0x1000

#include <68hc11.h>
#include <stdio.h>

/* Link in the following libraries (nearly all needed by fprintf() )*/
#include <fopen.c>
#include <fputs.c>
#include <fputc.c>
#include <itoa.c>
#include <atoi.c>
#include <is.c>
#include <fprintf.c>
#include <itoab.c>
#include <reverse.c>
#include <strlen.c>

/* Link in the device driver for the Motorola 68HC11 EVB */
#include <EVB_out.c>

FILE            stdout;
unsigned int    sys_clk;
char            buf[10];

/* Make the message live in ROM, so it's there on power up!! */
rom char        message[]="ELAPSED TIME: %u minutes and %u seconds.\n";

/* Define the ISR routine... */
/* Called whenever the system timer overflows (about every 0.5 seconds) */

interrupt toi(){

 sys_clk++;
 /* Reset the timer overflow interrupt flag so it can happen again */
 bit_set(0x1025,0x80);

}

main() {

/* Set the PreScale bits before the time protect timer expires */
    
#asm
   LDX  #$1024
   LDAB #$03
   STAB 0,X
   LDS  #$DFFF
#endasm

    /* change the Timer Overflow Interrupt Vector to point to our routine */
    poke(0xD1,toi);

    /* Clear the Timer Overflow Flag */
    bit_set(REG_BASE+TFLG2,0x80);

    /*  Enable the Timer Overflow Interrupt */
    bit_set(REG_BASE+TMSK2,0x80);

    /* Enable interrupts */
    e_int();

    sys_clk=0;
    stdout=fopen(EVB_out);
    fprintf(stdout,"Starting system timer...\n");

    while (1) {
        unsigned int temp;
        temp=sys_clk;
        while (temp/2==sys_clk/2);
            fprintf(stdout, message, sys_clk/120, (sys_clk/2) % 60);
    }
}