N2100 Debian FAQ

Why doesn't my Real Time Clock work?

According to Martin Michlmayr's installation instructions, you need to "make sure that there's a symlink from /dev/rtc to /dev/rtc0". However, if you create the symlink manually it will not survive beyond a reboot, and you get:
# hwclock --show
Cannot access the Hardware Clock via any known method.
Use the --debug option to see the details of our search for an access method.

The solution is to create a udev rule. I shamelesly stole this from the Debian nslu2-utils package.
Create /etc/udev/n2100-rtc.rules, containing this:
# The rtc-dev module registers a rtcN device; link the first to /dev/rtc.
KERNEL=="rtc0", SYMLINK+="rtc" GROUP="audio"

Then cd /etc/udev/rules.d and create a symlink:
ln -s ../n2100-rtc.rules z60_n2100-rtc.rules

Then if you run the udevtrigger command (or whenever you boot) the symlink is created.