RC16M

Hi,dialog.
I am learning "DSPS"code .In my board ,XTAL 16M is supplied by another MCU ,i want to use RC16M as the sysclk.But it does not work.it stopped at rwip_init(error).

here is my code about it:

SetBits16(CLK_16M_REG, RC16M_ENABLE, 1); // enable RC 16MHz
for (volatile int i = 0; i < 20; i++);

SetBits16(CLK_CTRL_REG, SYS_CLK_SEL, 1); // switch to RC16
while( (GetWord16(CLK_CTRL_REG) & RUNNING_AT_RC16M) == 0 ); // wait for actual switch

SetBits16(CLK_CTRL_REG, XTAL16M_DISABLE, 1); // disable XTAL16

Where I went wrong ?
Thanks