RTOS/AM5728: Changing cores speed

Part Number:AM5728

Tool/software: TI-RTOS

Hi everybody , 

I am trying to change speed in my code   but   have some issue -->  A15 hangs 

So I did the following ( as per post suggestion ) :

    boardCfg = BOARD_INIT_PINMUX_CONFIG |

        BOARD_INIT_MODULE_CLOCK |

        BOARD_INIT_UART_STDIO | BOARD_INIT_ICSS_PINMUX | BOARD_INIT_PLL_OPP_HIGH;

    Board_init(boardCfg);

But it results in core stuck in some undefined state, like some unhandled exception occurred even before the application started.

If I do step by step debug over JTAG inside the Board_init function, the core runs just fine.  

what is wrong ?

should I also check  operating voltages point ?       where in the code to do it properly ?

thank you very  much 

regards

Carlo