//******************************************************************************
//  MSP430x11x1 Demo - Basic Clock, Implement Cont. SW FLL with Auto RSEL
//
//  Description; Set DCO clock to (Delta)*(4096) using software FLL. DCO clock
//  is output on P5.5 as SMCLK. DCO clock, which is the selected SMCLK source
//  for Timer_A is integrated over ACLK/8 (4096) continuously. CCR2 captures
//  ACLK/8. To use this SW FLL, Timer_A must be operating in continuous mode
//  with a watch crystal used for ACLK. Delta must be kept in a range that
//  allows possible DCO speeds. Minimum Delta must ensure the AdjDCO ISR can
//  complete. Maximum delta can be calculated by f(DCOx7) / 4096.
//  "f(DCOx7)" found in device specific datasheet.
//  ACLK = LFXT1/8 = 32768/8, MCLK = SMCLK = DCO = 4096xDelta
//  [] To measure SMCLK on P1.4 with the FET, use "Release JTAG on Run"
//  in the debugger to have access to the port. Then run the code.
//  //* An external watch crystal on XIN XOUT is required for ACLK *//	
//
//           MSP430F1121
//         ---------------
//     /|\|            XIN|-
//      | |               | 32kHz
//      --|RST        XOUT|-
//        |               |
//        |     P1.4/SMCLK|--> SMLCK = target DCO
//
//
//  M. Buccini / Z. Albus
//  Texas Instruments Inc.
//  May 2005
//  Built with Code Composer Essentials Version: 1.0
//*****************************************************************************

#include <msp430x11x1.h>

//#define DELTA 977                       // target DCO= DELTA*(4096) = 4Mhz
//#define DELTA 900                       // target DCO= DELTA*(4096) = 3686400
//#define DELTA 256                       // target DCO= DELTA*(4096) = 1048576
#define DELTA 70                            // target DCO= DELTA*(4096) = 286720

unsigned int Compare, Oldcapture;

void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT
  BCSCTL1 |= DIVA_3;                        // ACLK= LFXT1CLK/8
  CCTL2 = CM_1 + CCIS_1 + CAP + CCIE;       // CAP, ACLK, interrupt
  TACTL = TASSEL_2 + MC_2 + TACLR;          // SMCLK, cont-mode, clear
  P1DIR |= 0x10;                            // P1.4 output
  P1SEL |= 0x10;                            // P1.4 SMCLK output

  _BIS_SR(LPM0_bits + GIE);                 // Enter LPM0 w/ interrupt
}

// Timer_A3 Interrupt Vector (TAIV) handler
__interrupt void Timer_A(void);
TIMERA1_ISR(Timer_A)
__interrupt void Timer_A(void)
{
  switch( TAIV )
  {
    case  2: break;                         // CCR1 not used
    case  4:
    {
    Compare = CCR2;                         // Get current captured SMCLK
    Compare = Compare - Oldcapture;         // SMCLK difference
    Oldcapture = CCR2;                      // Save current captured SMCLK
    if (DELTA == Compare) break;            // If equal, leave "While(1)"
    if (DELTA < Compare)
      {
        DCOCTL--;
        if (DCOCTL == 0xFF)                 // DCO is too fast, slow it down
        {
          if (!(BCSCTL1 == (XT2OFF + DIVA_3)))
          BCSCTL1--;                        // DCO roll under?, Sel lower RSEL
        }
      }
    else
      {
        DCOCTL++;                           // DCO is too slow, speed it down
        if (DCOCTL == 0x00)
        {
          if (!(BCSCTL1 == (XT2OFF + DIVA_3 + 0x07)))
          BCSCTL1++;                        // DCO roll over? Sel higher RSEL
        }
      }
    }
  case 10: break;                           // not used
  }
}