msp430x21x1_lf_ofifg_extclk.c

C280x C/C++ Header Files and Peripheral Examples The DSP28xx C/C++ peripheral header files and exam

//******************************************************************************
//  MSP430x21x1 Demo - OFIFG ISR for LF Failsafe Operation on Ext Clk
//
//  Description: Toggle P1.0 using software timed by the WDT ISR. Toggle rate
//  is approximately 250ms based on 32768Hz ACLK when present. When the LFXT1
//  input signal faults during operation, the NMI ISR is entered and the fault
//  is serviced. During this time the LED will flash at a faster rate indicating
//  an ACLK fault. During this time the CPU is held in the NMI ISR.
//  Buffer ACLK on P2.0 and default SMCLK(DCO) on P1.4.
//  To measure SMCLK on P1.4 with the FET, use "Release JTAG on Go"
//  in the debugger to have access to the port. Then run the code.
//
//  ACLK = Ext Clk, MCLK = SMCLK = ~1.16 MHz
//
//               MSP430F21x1
//             -----------------
//         /|\|              XIN|<--LF Ext ACLK (10-50 kHz)
//          | |                 |
//          --|RST          XOUT|-
//            |                 |
//            |       P1.4/SMCLK|-->SMCLK = ~1.16MHz
//            |        P2.0/ACLK|-->ACLK = LF Ext ACLK
//            |             P1.0|-->LED
//
//  H. Grewal / A. Dannenberg
//  Texas Instruments, Inc
//  June 2005
//  Built with Code Composer Essentials Version: 1.0
//******************************************************************************
#include  <msp430x21x1.h>

void main(void)
{
  BCSCTL3 |= LFXT1S_3;                      // Ext Digital Clk
  WDTCTL = WDT_ADLY_250;                    // Set WDT interval to ~250ms from ACLK

  P1OUT = 0x00;
  P1DIR |= 0x11;                            // P1.0,1.4 outputs
  P1SEL |= 0x10;                            // P1.4 SMCLK output
  P2DIR |= 0x01;                            // P2.0 output
  P2SEL |= 0x01;                            // P2.0 ACLK output
  IE1 |= OFIE;                              // Enable osc fault int (NMI)
  IE1 |= WDTIE;                             // Enable WDT interrupt

  while(1)
  {
    _BIS_SR(LPM0_bits+GIE);                 // Enter LPM0 with ints
  }
}

// NMI interrupt service routine
__interrupt void osc_fault(void);
NMI_ISR(osc_fault)
__interrupt void osc_fault(void)
{
	volatile unsigned int i;

  do                                        // Loop until flag is clear
  {
    IFG1 &= ~OFIFG;                         // Clear fault flag
    for (i = 0xFFF; i; i--);                // Delay for crystal to start
    P1OUT ^= 0x01;                          // Toggle LED: rate is faster
  }
  while (IFG1 & OFIFG);                     // Test LF oscillator fault flag
  IE1 |= OFIE;                              // Re-enable osc fault int
}

// Basic Timer interrupt service routine
__interrupt void watchdog_timer(void);
WDT_ISR(watchdog_timer)
__interrupt void watchdog_timer(void)
{
  P1OUT ^= 0x01;                            // Toggle LED
}