MSP430G2553 WDT Interrupt Blinky

// Demo: Green LED blink from main code, red LED blink from WDT interrupt
// Target: MSP430G2 Launchpad, with MSP430G2553 IC

#include <stdint.h>
#include <msp430.h>

int main(void) {

    volatile uint16_t x;

    WDTCTL = WDTPW | WDTHOLD;   // stop watchdog timer

    P1DIR = 0b01000001; // Pin P1.6 (green LED) and P1.0 (red LED) are Outputs

    BCSCTL3 |= 32; // ACLK from internal VLOCLK

    // Resume WDT in Timer Mode, from ACLK, /8192, Reset count.
    WDTCTL = WDTPW | WDTTMSEL | WDTSSEL | WDTIS0 | WDTCNTCL;

    IE1 |= WDTIE; // Enable WDT interrupt
    __enable_interrupt();

    // Regular code to blink the green LED
    for ( ; ; ) {

        for (x = 25000; x; --x) {} // Poor man's delay
        P1OUT ^= 0b01000000; // Toggle green LED

    }

    return 0;
}


#pragma vector=WDT_VECTOR
__interrupt void WDT_ISR(void) {

    P1OUT ^= 0b00000001; // Toggle red LED

}