Keypress Debounce MSP430

 Normally keypresses are not direct change from one state to other , instead its a change with bit noise in between where the state seems undefined. To avoid the situation the common method is to recheck after certain delay 

if(PINState==Pressed)

{
delay(few_microsec);
if(PINState==Pressed)
    {
    ActionKeyPress();
    }
}

But if we are dealing with interrupt

PIN_ISR()
{
setkeypressflag();
}

main()
{
if (keypressflagset)
    if(PINState==Pressed)
    {
    DoKeyPressAction();
    }
}

Now the most advanced one with timer or WatchdogTimer

#pragma vector=PORT1_VECTOR
__interrupt void P1_Function()
{
    count=0; //Reset count
    TACTL|=TASSEL_2+MC_1+TAIE; //Start Timer0 with SMCLK clock source, UP mode and enable overflow interrupt
    state=(P1IN&BIT3)>>3; //Save the state of the switch
    P1IE&=~BIT3; //Disable interrupt on P1.3, now the Timer will take care of Debouncing
    P1IFG&=~BIT3; // Reset Port1 interrupt flag
}

#pragma vector=TIMER0_A1_VECTOR
__interrupt void TMR0()
{
    if(TAIV==TA0IV_TAIFG)   //Check if Timer overflow caused the interrupt
                            //This would be required in projects where multiple interrupts have
                            //the same interrupt vector. Here it is only optional.
        {
            if(state==((P1IN&BIT3)>>3)) //If the state of the LED is the same
                count++; //Increment the counter variable
            else
            {
                count=0; //If not same, reset the counter variable
                state=((P1IN&BIT3)>>3); //And save the present state of the switch
            }
        if(count==10) //If the state has been consistently the same
            {
            if(state==0) //If the switch was pressed
                P1OUT^=BIT0; //Toggle the LED
            P1IE|=BIT3; //We have handled the debouncing, now we again enable interrupt on P1.3, for it to again detect switch bounce
            TACTL=0; //Stop the Timer
            TACTL|=TACLR; //Clear the Timer counter
            }

            TACTL&=~(TAIFG); //Reset the interrupt flag
        }
}