#include "msp.h"

int main(void) {
    void delayMs(int n);
    P4->SEL1 &= ~0x0F;      /* configure P4.3-P4.0 as simple I/O output */
    P4->SEL0 &= ~0x0F;
    P4->DIR |= 0x0F;
    P6->SEL1 &= ~0x02;      /* configure P6.1 as simple I/O input */
    P6->SEL0 &= ~0x02;
    P6->DIR &= ~0x02;
    P6->REN |= 0x02;        /* P6.1 pull-up resistor enabled */
    P6->OUT |= 0x02;

    while (1) {
        if((P6->IN & 0x02) == 0) {  /* P6.1 == 0 */
            P4->OUT &= ~0x0F;       /* open all switches */
            delayMs(100);           /* wait 0.1 second */
            P4->OUT |= 0x09;        /* close SW1 & SW4 */
            while((P6->IN & 0x02) == 0);    /* wait till switch change */
        } else {                    /* P6.1 == 1 */
            P4->OUT &= ~0x0F;       /* open all switches */
            delayMs(100);           /* wait 0.1 second */
            P4->OUT |= 0x06;        /* close SW2 & SW3 */
            while((P6->IN & 0x02) != 0);    /* wait till switch change */
        }
    }
}

/* delay milliseconds when system clock is at 3 MHz */
void delayMs(int n) {
    int i, j;
    
    for (j = 0; j < n; j++)
        for (i = 750; i > 0; i--);      /* delay 1 ms */
}