To set the system clock use the date command.
from "http://developer.axis.com/wiki/doku.php?id=faq" article,
date MMDDHHMMYYYY
Where MM=Month, DD=Day, HH=Hour, MM=Minute, and YY=Year
To permanently store the system clock in the RTC chip just type the following command
hwclock -w
This works with busybox.
