Atmel AT32UC3A3128, Manual

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32072H–AVR32–10/2012
AT32UC3A3
The RTC count value can be read from or written to the Value register (VAL). Due to synchroni-
zation, continuous reading of the VAL register with the lowest prescaler setting will skip every
other value.
8.5.1.3 RTC interrupt
The RTC interrupt is enabled by writing a one to the Top Interrupt bit in the Interrupt Enable Reg-
ister (IER.TOPI), and is disabled by writing a one to the Top Interrupt bit in the Interrupt Disable
Register (IDR.TOPI). The Interrupt Mask Register (IMR) can be read to see whether or not the
interrupt is enabled. If enabled, an interrupt will be generated if the TOPI bit in the Interrupt Sta-
tus Register (ISR) is set. The TOPI bit in ISR can be cleared by writing a one to the TOPI bit in
the Interrupt Clear Register (ICR.TOPI).
The RTC interrupt can wake the CPU from all sleep modes except DeepStop and Static modes.
8.5.1.4 RTC wakeup
The RTC can also wake up the CPU directly without triggering an interrupt when the ISR.TOPI
bit is set. In this case, the CPU will continue executing from the instruction following the sleep
instruction.
This direct RTC wake-up is enabled by writing a one to the Wake Enable bit in the CTRL register
(CTRL.WAKEN). When the CPU wakes from sleep, the CTRL.WAKEN bit must be written to
zero to clear the internal wake signal to the sleep controller, otherwise a new sleep instruction
will have no effect.
The RTC wakeup is available in all sleep modes except Static mode. The RTC wakeup can be
configured independently of the RTC interrupt.
8.5.1.5 Busy bit
Due to the crossing of clock domains, the RTC uses a few clock cycles to propagate the values
stored in CTRL, TOP, and VAL to the RTC. The RTC Busy bit in CTRL (CTRL.BUSY) indicates
that a register write is still going on and all writes to TOP, CTRL, and VAL will be discarded until
the CTRL.BUSY bit goes low again.