[U-Boot] Watchdog and u-boot command prompt

[Sachin Rane]

Hi,
 
I have enabled 'watchdog' in u-boot using flag 'CONFIG_WATCHDOG'.
I wonder how the 'watchdog' gets reset when the cursor is waiting for
user input.
 
As per my understanding the 'WATCHDOG_RESET()' gets called in
'readline()' prior calling 'getc()'.
In our case, the 'getc()' has been mapped to 'serial_getc_dev()'  of
'cpu/ppc4xx/serial.c'.
The code of 'serial_getc_dev()'  executes in continous loop till user
presses a key.
The good thing is that the boad doesn't get reboot even if user doesn't
enter any key.
In 'serial_getc_dev()', I don't see any call to reset the watchdog  .
 
Can you help me to find out the how Watchdog is taken care (gets reset)
whicle executing a infinite loop (if user doesn't press any key) ? 
( Note: I am not using 'CONFIG_HW_WATCHDOG' flag)
 
Regards,
Sachin Rane