Keil-PING-PONG

#include<REGX52.H>
#define F_CLK 18432000
#define F_INT 1000
typedef unsigned char byte;

byte xdata LED_PREK _at_ 0x8000;
byte xdata ZUTA _at_ 0x8002;
byte xdata ZELENA _at_ 0x8001;
byte xdata PLAVA _at_ 0x8003;
byte i=0;
byte j=0;
byte LEDS=0x01;
byte prek;
byte clear=0xff;

unsigned long sys_time = 0;

void timer2_ISR() interrupt 5
{
    sys_time++;
    TF2 = EXF2 = 0;
}

 unsigned long millis()
{
    unsigned long tmp;

    EA = 0;             //zabrana prekida
    tmp = sys_time;     //ocitavanje vremena
    EA = 1;             //dozvola prekida

    return tmp;
}
void delay_ms(unsigned long d)
{
    unsigned long t0 = millis();

    while(millis() - t0 < d);
}
void boja(byte x,byte y)
{
    switch((~x)&0x03)
    {
        case 0:
        {
            LED_PREK=y;
            ZUTA=clear;
            ZELENA=clear;
            PLAVA=clear;
        }
            break;
       case 1:
       {
            ZUTA=y;
            LED_PREK=clear;
            ZELENA=clear;
            PLAVA=clear;
        }
            break;
        case 2:
        {
            ZELENA=y;
            LED_PREK=clear;
            ZUTA=clear;
            PLAVA=clear;
        }
            break;
        case 3:
        {
            PLAVA=y;
            LED_PREK=clear;
            ZUTA=clear;
            ZELENA=clear;
        }
            break;
    }
}
void vreme(byte x)
{
    byte k=((~x)&0xc0)>>6;
    switch(k)
    {
        case 0:
            delay_ms(500);
            break;
        case 1:
            delay_ms(1000);
            break;
        case 2:
            delay_ms(2000);
            break;
        case 3:
            delay_ms(4000);
            break;
    }

}
void main()
{
    RCAP2H = (-(F_CLK / (12 * F_INT))) >> 8;
    RCAP2L = (-(F_CLK / (12 * F_INT))) & 0xff;

    T2CON = 0x00;   //tajmer 2 -> 16-bitni auto-reload
    ET2 = 1;        //dozvola prekida tajmera 2
    TR2 = 1;
    EA=1;
    prek=(~LED_PREK);

    while(1)
    {

    while(i!=7)
        {
            prek=(~LED_PREK);
            LEDS=(LEDS<<1);
            boja(prek,(~LEDS));
            vreme(prek);
            i++;
        }
        i=0;
        while(j!=7)
        {
            prek=(~LED_PREK);
            LEDS=(LEDS>>1);
            boja(prek,(~LEDS));
            vreme(prek);
            j++;
        }
        j=0;
    }

}