//******************************************************************************
//  MSP430F54x Demo - XT1 sources ACLK. Toggles P1.0
//
//  Description: This program demonstrates using XT1 to source ACLK
//  ACLK = LFXT1 = 32,768Hz   
//  //* An external watch crystal between XIN & XOUT is required for ACLK *// 
//
//               MSP430F5438
//             -----------------
//        /|\ |              XIN|-
//         |  |                 | 32kHz
//         ---|RST          XOUT|-
//            |                 |
//            |            P11.0|--> ACLK = ~32kHz
//            |                 |
//            |             P1.0|-->LED
//
//   W. Goh
//   Texas Instruments Inc.
//   February 2009
//   Built with CCE Version: 3.2.2 and IAR Embedded Workbench Version: 4.11B
//******************************************************************************

#include "msp430x54x.h"

void main(void)
{
  WDTCTL = WDT_ADLY_1000;                   // WDT 1000ms, ACLK, interval timer
  SFRIE1 |= WDTIE;                          // Enable WDT interrupt

  P1DIR |= BIT0;                            // P1.0 to output direction
  P11DIR |= BIT0;                           // P11.0 to output direction
  P11SEL |= BIT0;                           // P11.0 to output ACLK

  P7SEL |= 0x03;                            // Select XT1
  UCSCTL6 &= ~(XT1OFF);                     // XT1 On
  UCSCTL6 |= XCAP_3;                        // Internal load cap

  // Loop until XT1,XT2 & DCO stabilizes
  do
  {
    UCSCTL7 &= ~(XT2OFFG + XT1LFOFFG + XT1HFOFFG + DCOFFG);
                                            // Clear XT2,XT1,DCO fault flags
    SFRIFG1 &= ~OFIFG;                      // Clear fault flags
  }while (SFRIFG1&OFIFG);                   // Test oscillator fault flag

  UCSCTL6 &= ~(XT1DRIVE_3);                 // Xtal is now stable, reduce drive
                                            // strength

  __bis_SR_register(LPM3_bits + GIE);       // Enter LPM3 w/ interrupts
  __no_operation();                         // For debugger
}

// Watchdog Timer interrupt service routine
#pragma vector = WDT_VECTOR
__interrupt void watchdog_timer(void)
{
  P1OUT ^= 0x01;                            // Toggle P1.0 using exclusive-OR
}