Problem with defining external 32K oscillator as FLL source

[MichaelDavid]

I have a problem with configuring 32K as clock soure.. Attached is the configuration code.

    MCG_C2 = 0;        //new        MCG_C2 = MCG_C2_HGO_MASK | MCG_C2_EREFS_MASK;        //new    MCG_C1 = 0;        //new    /* Wait for crystal to initialize */    while (!(MCG_S & MCG_S_OSCINIT_MASK)) {};        /* Wait for Reference Clock Status bit to clear */    while (MCG_S & MCG_S_IREFST_MASK) {};        /* Wait for clock status bits to show clock source      * is external reference clock */    //while (((MCG_S & MCG_S_CLKST_MASK) >> MCG_S_CLKST_SHIFT) != 0x2) {};    //new    while (((MCG_S & MCG_S_CLKST_MASK) >> MCG_S_CLKST_SHIFT) != 0x0) {};        //new FEE    MCG_C4 |= MCG_C4_DMX32_MASK | MCG_C4_DRST_DRS(3);    /* Now in FBE     * Configure PLL Reference Divider, PLLCLKEN = 0, PLLSTEN = 0, PRDIV = 0x18     * The crystal frequency is used to select the PRDIV value.      * Only even frequency crystals are supported     * that will produce a 2MHz reference clock to the PLL.     */    //MCG_C5 = MCG_C5_PRDIV(BSP_REF_CLOCK_DIV - 1);    /* Ensure MCG_C6 is at the reset default of 0. LOLIE disabled,      * PLL disabled, clock monitor disabled, PLL VCO divider is clear     */    MCG_C6 = 0;        /* Calculate mask for System Clock Divider Register 1 SIM_CLKDIV1 */    SIM_CLKDIV1_COPY =  SIM_CLKDIV1_OUTDIV1(BSP_CORE_DIV    - 1) |                        SIM_CLKDIV1_OUTDIV2(BSP_BUS_DIV     - 1) |                        SIM_CLKDIV1_OUTDIV3(BSP_FLEXBUS_DIV - 1) |                        SIM_CLKDIV1_OUTDIV4(BSP_FLASH_DIV   - 1);       

[tr9]

1. Is your external 32 K oscillator connected to EXTAL  or  EXTAL32 / XTAL32 (the RTC oscillator) ?

[MichaelDavid]

That was the fault. can I configure the RTC clock as the system clock?

[tr9 · Accepted solution]

In the SIM module there is a register; SIM_SOPT2 that contains the field; MCGCLKSEL that allows you to map the RTS oscillator (EXTAL32 and XTAL32 inputs) to the FLL. You set this field = 1.

From there you can use FEE mode to generate higher clock rates out of the FLL.