TMS320F28388D: Modify the clock setting after the DCC triggered but the PLL could not lock

Part Number: TMS320F28388D

Tool/software:

Hi,

My system originally uses a 25 MHz external clock, and the PLL is configured to generate a 200 MHz PLLSYSCLK.

Now, when I cutoff the external clock, the DCC detects a clock failure, and then the system will switch the clock source to INTOSC1 and reconfigures the PLL so that PLLSYSCLK remains at 200 MHz.

However, when I call SysCtl_setClock() to update the clock settings, the function returns false. After checking the SysCtl_setClock(), I found that it times out while waiting for the PLL to lock, and the failure occurs during the SysCtl_isPLLValid() check.

The procedure for updating the clock settings after a clock failure is detected is as follows:

1. Configure oscillator source to INTOSC1
2. Delay of at least 60 OSCCLK cycles
3. Turn off PLL
4. Delay of at least 66 OSCCLK cycles required post powerdown of PLL
5. reset MCD
6. call the SysCtl_setClock(DEVICE_SETCLOCK_INTOSC)

define of the DEVICE_SETCLOCK_INTOSC:

#define DEVICE_SETCLOCK_INTOSC (SYSCTL_OSCSRC_OSC1 | SYSCTL_IMULT(80) | \
SYSCTL_REFDIV(2) | SYSCTL_ODIV(2) | \
SYSCTL_SYSDIV(1) | SYSCTL_PLL_ENABLE | SYSCTL_DCC_BASE_1 )

Is there any missing procedure that would lead the PLL lock timeout and the PLL valid failed?

Here is the code after the clock failure detected:

//
    // Wait till the ISR is hit on clock failure
    //
    while(isr_enter != 0x1U);

    //
    // Configure oscillator source to INTOSC1
    //
    SysCtl_selectOscSource(SYSCTL_OSCSRC_OSC1);

    //
    // Delay of at least 60 OSCCLK cycles
    //
    SysCtl_delay(11U);

    //
    // Turn off PLL
    //

    EALLOW;
    HWREGH(CLKCFG_BASE + SYSCTL_O_SYSPLLCTL1) &=
        ~SYSCTL_SYSPLLCTL1_PLLEN;
    EDIS;

    //
    // Delay of at least 66 OSCCLK cycles required post
    // powerdown of PLL
    //
    SysCtl_delay(12U);

    //
    // Set up PLL control and clock dividers
    //
    SysCtl_resetMCD();

    SysCtl_setClockTest(DEVICE_SETCLOCK_INTOSC);