/* Copyright 2010 Ethan Blanton */

/*
 * Configure TimerA to run off VLOCLK/LFXT1, then toggle an LED (about)
 * once per second off the slow timer, with the processor sleeping (DCO
 * off) in between.
 * */

#include <io.h>
#include <signal.h>

/* Define USEXTAL if you have a 32kHz watch crystal installed and want
 * to use it as your time base -- giving you much more accurate
 * timings. */
#ifdef USEXTAL
#define TRIGGER 32767
#else
#define TRIGGER 12000
#endif

#define LED 0x01

int main()
{
    WDTCTL = WDTPW | WDTHOLD;

    /* Set the entire port P1 to output to reduce power consumption. */
    P1DIR = 0xff;
    P1OUT = LED;

#ifndef USEXTAL
    /* Set the LF clock to the internal VLO.  When using an external
     * crystal, it will be sourced for the LF clock by default. */
    BCSCTL3 |= LFXT1S_2;
#endif

    /* Configure the Timer A count limit */
    TACCR0 = TRIGGER;
    /* Enable the timer interrupt */
    TACCTL0 |= CCIE;
    /* Configure Timer A for ACLK, start the timer. */
    TACTL = TASSEL_1 | MC_1;

    /* Enable interrupts */
    eint();

    LPM3;    /* Sleep! */

    /* Unreached.  If this code were reached, the LED would stay
     * continuously lit. */
    while (1)
        P1OUT = LED;
}

/* On TimerA interrupt, toggle the LED status and then go back to
 * sleep. */
interrupt (TIMERA0_VECTOR) ta_handler()
{
    P1OUT ^= LED;
}