Doesn't show external crystal clock's status in RCU_CTL register.

Hi team,
I a'm very excited regarding the risc v architecture and would like to work with this future technology. Before a week, i started learning risc v architecture with help of a low cost development board. I have given by some basic details here to get you an idea about my working environment.
Gd32 dev board with lcd (seed studio)
Rv debugger(sipeed )
Platform io

The example led code is working fine. I would like to turn on external clock. That's why i read gd32 's reference manual and got regarding the RCU_CTL register. Then i have written a demo code.

Code

#include "gd32vf103.h"

Int main()
{
RCU_CTL|=(1<<16);// external Crystal turn on
While(RCU_CTL & (1<<17) != 0x00020000);// checking the external crystal turn on successful.

RCU_CTL|=(1<<16);// external Crystal turn off
While(RCU_CTL & (1<<17) == 0x00020000);// checking the external crystal turn off successful

return 0;
}

Here turn on working fine. But when code enter turn off checki it's not exit. So the status of external clock is enable.

Such as when i was searching this one i saw "system init" function definition inside of one of the gd32 firmware library file. It's enable internal oscillator like
RCU_CTL|=0x1;
Then it's not checking the status of oscillator with bit number 2.

So the RCU_CTL register showing bit number 2 for internal oscillator status and bit number 17 for external oscillator status.

All of you if you hqve any idea about this region pls help me. I'm still stucking?
.
If you have the gd32 related board could you pls check it for me?