RTOS/SECDEVTOOL-OMAPL138C6748: Task is not switching with using sprintf()

Part Number:SECDEVTOOL-OMAPL138C6748

Tool/software: TI-RTOS

My dev board is OMAP-L138/C6748 LC Dev Kit.

Tried to run Example 3-1 Time-Slice Scheduling in the document SPRUEX3Q—June 2016. 

In the hiPriTask while loop, I added the code as following:

if(TRUE == Semaphore_pend(sem, BIOS_WAIT_FOREVER))
{

       for(i=0;i<100;i++)
       {
              sprintf(tempStr, "%.6f,", fArray[i]);

       }

       System_printf("TestFloatArray() is done!\n");
}

hiPriTask is ran once and never switch back again. If I remove sprintf(), the task switching is running normally.

Please advise. Thanks.