MSP430FR2422: FLL unlock history

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//******************************************************************************
//  MSP430FR2422 Demo - Configure MCLK for 8MHz sourced from DCO.
//
//  Description: Default DCODIV is MCLK and SMCLK source.
//  By default, FR243x select XT1 as FLL reference.
//  If XT1 is present, the XIN and XOUT pin needs to configure.
//  If XT1 is absent, switch to select REFO as FLL reference automatically.
//  XT1 is considered to be absent in this example.
//  f(DCOCLK) = 2^FLLD * (FLLN+1) * (fFLLREFCLK / n).
//  FLLD = 0, FLLN =243, n=1, DIVM =1, f(DCOCLK) = 2^0 * (243+1)*32768Hz = 8MHz,
//  f(DCODIV) = (243+1)*32768Hz = 8MHz,
//  ACLK = default REFO ~32768Hz, SMCLK = MCLK = f(DCODIV) = 8MHz.
//  Toggle LED to indicate that the program is running.
//
//           MSP430FR2422
//         ---------------
//     /|\|               |
//      | |               |
//      --|RST            |
//        |          P1.0 |---> LED
//        |          P1.3 |---> MCLK  = 8MHz
//        |          P1.2 |---> SMCLK = 8MHz
//        |          P1.1 |---> ACLK  = 32768Hz
//
//
//   Ling Zhu
//   Texas Instruments Inc.
//   May 2017
//   Built with IAR Embedded Workbench v6.50 & Code Composer Studio v7.0.0
//******************************************************************************
#include <msp430.h>

void Software_Trim();                       // Software Trim to get the best DCOFTRIM value
#define MCLK_FREQ_MHZ 8                     // MCLK = 8MHz

int main(void)
{
    WDTCTL = WDTPW | WDTHOLD;               // Stop watchdog timer

    __bis_SR_register(SCG0);                // disable FLL
    CSCTL3 |= SELREF__REFOCLK;              // Set REFO as FLL reference source
    CSCTL1 = DCOFTRIMEN_1 | DCOFTRIM0 | DCOFTRIM1 | DCORSEL_3;// DCOFTRIM=3, DCO Range = 8MHz
    CSCTL2 = FLLD_0 + 243;                  // DCODIV = 8MHz
    __delay_cycles(3);
    __bic_SR_register(SCG0);                // enable FLL
    Software_Trim();                        // Software Trim to get the best DCOFTRIM value

    CSCTL4 = SELMS__DCOCLKDIV | SELA__REFOCLK; // set default REFO(~32768Hz) as ACLK source, ACLK = 32768Hz
                                            // default DCODIV as MCLK and SMCLK source

    P1DIR |= BIT0 | BIT1 | BIT2 | BIT3;     // set ACLK MCLK SMCLK and LED pin as output
    P1SEL1 |= BIT1 | BIT2 | BIT3;           // set ACLK MCLK and SMCLK pin as second function

    PM5CTL0 &= ~LOCKLPM5;                   // Disable the GPIO power-on default high-impedance mode
                                            // to activate previously configured port settings

    while(1)
    {
        P1OUT ^= BIT0;                      // Toggle P1.0 using exclusive-OR
        __delay_cycles(10000000);           // Delay for 10000000*(1/MCLK)=1.25s
    }
}

void Software_Trim()
{
    unsigned int oldDcoTap = 0xffff;
    unsigned int newDcoTap = 0xffff;
    unsigned int newDcoDelta = 0xffff;
    unsigned int bestDcoDelta = 0xffff;
    unsigned int csCtl0Copy = 0;
    unsigned int csCtl1Copy = 0;
    unsigned int csCtl0Read = 0;
    unsigned int csCtl1Read = 0;
    unsigned int dcoFreqTrim = 3;
    unsigned char endLoop = 0;

    do
    {
        CSCTL0 = 0x100;                         // DCO Tap = 256
        do
        {
            CSCTL7 &= ~DCOFFG;                  // Clear DCO fault flag
        }while (CSCTL7 & DCOFFG);               // Test DCO fault flag

        __delay_cycles((unsigned int)3000 * MCLK_FREQ_MHZ);// Wait FLL lock status (FLLUNLOCK) to be stable
                                                           // Suggest to wait 24 cycles of divided FLL reference clock
        while((CSCTL7 & (FLLUNLOCK0 | FLLUNLOCK1)) && ((CSCTL7 & DCOFFG) == 0));

        csCtl0Read = CSCTL0;                   // Read CSCTL0
        csCtl1Read = CSCTL1;                   // Read CSCTL1

        oldDcoTap = newDcoTap;                 // Record DCOTAP value of last time
        newDcoTap = csCtl0Read & 0x01ff;       // Get DCOTAP value of this time
        dcoFreqTrim = (csCtl1Read & 0x0070)>>4;// Get DCOFTRIM value

        if(newDcoTap < 256)                    // DCOTAP < 256
        {
            newDcoDelta = 256 - newDcoTap;     // Delta value between DCPTAP and 256
            if((oldDcoTap != 0xffff) && (oldDcoTap >= 256)) // DCOTAP cross 256
                endLoop = 1;                   // Stop while loop
            else
            {
                dcoFreqTrim--;
                CSCTL1 = (csCtl1Read & (~DCOFTRIM)) | (dcoFreqTrim<<4);
            }
        }
        else                                   // DCOTAP >= 256
        {
            newDcoDelta = newDcoTap - 256;     // Delta value between DCPTAP and 256
            if(oldDcoTap < 256)                // DCOTAP cross 256
                endLoop = 1;                   // Stop while loop
            else
            {
                dcoFreqTrim++;
                CSCTL1 = (csCtl1Read & (~DCOFTRIM)) | (dcoFreqTrim<<4);
            }
        }

        if(newDcoDelta < bestDcoDelta)         // Record DCOTAP closest to 256
        {
            csCtl0Copy = csCtl0Read;
            csCtl1Copy = csCtl1Read;
            bestDcoDelta = newDcoDelta;
        }

    }while(endLoop == 0);                      // Poll until endLoop == 1

    CSCTL0 = csCtl0Copy;                       // Reload locked DCOTAP
    CSCTL1 = csCtl1Copy;                       // Reload locked DCOFTRIM
    while(CSCTL7 & (FLLUNLOCK0 | FLLUNLOCK1)); // Poll until FLL is locked
}