RTC driver for the Atmel AT91SAM9x and AT91CAP9 internal RTT
(Real Time Timer). These timers are powered by the backup power
supply (such as a small coin cell battery), but do not need to
be used as RTCs.

(On AT91SAM9rl and AT91SAM9G45 chips you probably want to use the
dedicated RTC module and leave the RTT available for other uses.)