/*
 * Digital I/O (dual 7-segment LED) lab program.
 *
 * This program demonstrates the use of buttons as input to control the count direction
 * (and contents of) the two-digit display.
 *
 * Initially it displays just a different number based on the state of the switches
 * (SW0 and SW1 on the STK500).  However, you wneed to modify it to count up/down in
 * the range 00..99, as well as handling rollover up through 99 and down through 0.
 * It's up to you to choose between rolling over between 00 and 99, or stopping at the
 * two extremes.
 *
 * All eight bits of PORTB are fed into 7447 decoder chips.  The high nibble (bits 4-7)
 * are for the left (upper) digit, and the low nibble (bits 0-3) for the right (low) digit
 * on the display.
 *
 * Last Modified 2010/09/29 17:20 (ebw)
 */

#include <avr/io.h>       // for PORTx, DDRx, AD*, etc.
#include <util/delay.h>   // for _delay_ms()

// _BV(n) values for switches
#define PORTA_SW_DOWN 0   // SW0 is on PA0, and used for downcounting
#define PORTA_SW_UP   1   // SW1 is on PA1, and used for upcounting


void init(void)
{
    DDRA = 0x00;             // our two switches are inputs
    DDRB = 0xFF;             // all eight bits of PORTB are outputs

    PORTA = _BV(PORTA_SW_DOWN) | _BV(PORTA_SW_UP);  // turn on pullup resistors for our switches
}


int main(void)
{
    uint8_t counter=0;       // for keeping track of the current count value

    init();                 // set up PORTS

    while (1)
    {
        uint8_t switches;

        switches = ~PINA;    // Q: why is it useful to do this instead of just using PINA...?

        switch (switches)
        {
            case 0b00000001:    // SW0 pressed, count down
                PORTB = 0x11;   // display 11, just for testing

                // FIXME: After the initial test deal with counting down, rolling over and
                //        perhaps displaying the digits here.  Decide what you will do when you get
                //        to 00 -- do you stop at 00 or do you rollover to 99 ?
					
                break;

            case 0b00000010:    // SW1 pressed, count up
                PORTB = 0x22;   // display 22, just for testing

                // FIXME: Same issues as above, but for counting up vs. down

                break;

            default:		// when switches are not in any of the specified states listed above
                PORTB = 0x00; 	// display 00, again, just for testing

                // FIXME: how do we even get to this case, and what should we do ?

                break;
        }
    }

    return 0;        // never executed...
}