Problem in setting timeout from user space for MPC 83x watchdog timer

I am using MPC 8323E processor and linux-2.6.24 kernel.
I tried to set watchdog timer from user space using ioctl with the case
WDIOC_SETTIMEOUT.
I am getting timeout value as seconds and calculating corresponding modulus
for the WDT.
After that I am setting SWTC of SWCRR and writing service sequence to SWSRR.

But SWCNR is setting back to 0xffff after service sequence written into
SWSRR, means it is not setting with configured SWTC.

Can anyone tell what is the problem?
Please suggest solution..

Regards,
Aswathi