Not getting input on STK600 with ATmega8515
Your code expects three possible states for PORTA inputs, PINA == 0b11111100 or PINA == 0b11111110 or PINA == 0b11111101.  

You want to check only PINA.0 and PINA.1 but instead you also check the rest of the bits in the port (b7:b2).  This would only work if you have enabled all the internal pull-ups of the port (unless you have connected eight external pull-ups which I doubt)

PORTA = 0xff;   // enables internal pull-ups for all bits


A better solution, just check the state of the two pins which are actually connected to the buttons, discarding the result for the rest of the port bits.

DDRA = 0x00;    //set to input
PORTA = 0x03;   // enable internal pull-ups for PORTA.0 and PORTA.1

if((PINA &amp; 0b00000011) == 0b00000000)   // check if both button are pressed
{
}

else
    if((PINA &amp; 0b00000011) == 0b00000010) // check if button in PORTA.0 is pressed
    {
    }

    else
        if((PINA &amp; 0b00000011) == 0b00000001) // check if  button in PORTA.1 is pressed
        {
        }