RTOS/MSP430F5529: TI-RTOS : UART Baud set 115200 can’t work when my smclk is 24Mhz

Part Number:MSP430F5529

Tool/software:TI-RTOS

hi everyone,

ccsv7 for msp430;

TI-RTOS for msp43X  2.20.0.06

I run an example of TI-RTOS UART in the MSP-EXP5529LP development board, and I configure the SMCLK and MCLK clocks to 24MHZ in the Board_initGeneral() function (4M XT2 doubling via DCO)

#include <ti/drivers/UART.h>
#include <ti/drivers/uart/UARTUSCIA.h>

UARTUSCIA_Object uartUSCIAObjects[MSP_EXP430F5529LP_UARTCOUNT];

const UARTUSCIA_BaudrateConfig uartUSCIABaudrates[] = {
    /* {baudrate, input clock, prescalar, UCBRFx, UCBRSx, oversampling} */
    {   //my add
        .outputBaudrate = 115200,
        .inputClockFreq = 24000000,
        .prescalar = 13,
        .hwRegUCBRFx = 0,
        .hwRegUCBRSx = 0,
        .oversampling = 1
    },
    {
        .outputBaudrate = 115200,
        .inputClockFreq = 8192000,
        .prescalar = 4,
        .hwRegUCBRFx = 7,
        .hwRegUCBRSx = 0,
        .oversampling = 1
    },
    {9600,    32768,            3,         0,      3,      0},
};


const UARTUSCIA_HWAttrs uartUSCIAHWAttrs[MSP_EXP430F5529LP_UARTCOUNT] = {
    {
        .baseAddr       = USCI_A1_BASE,
        .clockSource    = USCI_A_UART_CLOCKSOURCE_MCLK, //#####MCLK = 24000000#####

        .bitOrder       = USCI_A_UART_LSB_FIRST,
        .numBaudrateEntries = sizeof(uartUSCIABaudrates)/sizeof(UARTUSCIA_BaudrateConfig),
        .baudrateLUT    = uartUSCIABaudrates
    },
};

const UART_Config UART_config[] = {
    {
        .fxnTablePtr    = &UARTUSCIA_fxnTable,
        .object         = &uartUSCIAObjects[0],
        .hwAttrs        = &uartUSCIAHWAttrs[0]
    },
    {NULL, NULL, NULL}
};

void uartFxn(UArg arg0, UArg arg1)
{
    UART_Handle uart;
    UART_Params uartParams;
    const char echoPrompt[] = "\fEchoing characters:\r\n";
    // Create a UART with data processing off.
    UART_Params_init(&uartParams);
    uartParams.writeDataMode    = UART_DATA_BINARY;
    uartParams.readDataMode     = UART_DATA_BINARY;
    uartParams.readReturnMode   = UART_RETURN_FULL;
    uartParams.readEcho         = UART_ECHO_OFF;
    uartParams.baudRate         = 115200;
    uart = UART_open(Board_UART0, &uartParams);
    if (uart == NULL) {
        System_abort("Error opening the UART");
    }

    UART_write(uart, echoPrompt, sizeof(echoPrompt));

    /* Loop forever echoing */
    while (1) {
        UART_write(uart, echoPrompt, sizeof(echoPrompt));
        Task_sleep((unsigned int)arg0);
    }

}

int main(void)
{
    /* Call board init functions */
    Board_initGeneral();
    Board_initGPIO();
    Board_initUART();
	
    Task_Params taskParams;
    Task_Params_init(&taskParams);
    taskParams.arg0         = 1000;
    taskParams.stackSize    = TASKSTACKSIZE;
    taskParams.stack        = &task0Stack;
    Task_construct(&task0Struct, (Task_FuncPtr)uartFxn, &taskParams, NULL);
	
    /* Start BIOS */
    BIOS_start();

    return (0);	
}

when I remove the const UARTUSCIA_BaudrateConfig uartUSCIABaudrates []

    {
        .outputBaudrate = 115200,
        .inputClockFreq = 8192000,
        .prescalar = 4,
        .hwRegUCBRFx = 7,
        .hwRegUCBRSx = 0,
        .oversampling = 1
    },

and I find UART_OPEN()  return ERR.  I don't know why?   

 Similarly, when I configure MCLK to 24MHZ, I must configure my cpufrq to be a multiple of 32768 in the .CFG file to work at the UART 9600 baud rate.  Someone explains why?

/* ================ Kernel (SYS/BIOS) configuration ================ */
var BIOS = xdc.useModule('ti.sysbios.BIOS');

BIOS.assertsEnabled = false;

BIOS.heapSize = 512;

BIOS.includeXdcRuntime = false;

BIOS.libType = BIOS.LibType_Custom;

BIOS.runtimeCreatesEnabled = true;

BIOS.logsEnabled = false;

BIOS.cpuFreq.hi = 0;
BIOS.cpuFreq.lo = 23986176;//32768*732

thank you!