Datasheet

SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
530
Moreover, like the PCK, a status bit in PMC_SR indicates that the Programmable Clock is actually what has been
programmed in the Programmable Clock registers.
As the Programmable Clock Controller does not manage with glitch prevention when switching clocks, it is strongly
recommended to disable the Programmable Clock before any configuration change and to re-enable it after the
change is actually performed.
28.10 Fast Startup
The device allows the processor to restart in less than 10 microseconds while the device is in Wait mode. The
system enters Wait mode by executing the WaitForEvent (WFE) instruction of the processor while the LPM bit is
at 1 in the PMC Fast Startup Mode Register (PMC_FSMR).
Important: Prior to asserting any WFE instruction to the processor, the internal sources of wakeup provided by
RTT, RTC and USB must be cleared and verified too, that none of the enabled external wakeup inputs (WKUP)
hold an active polarity.
A Fast Startup is enabled upon the detection of a programmed level on one of the 16 wake-up inputs (WKUP) or
upon an active alarm from the RTC, RTT and USB Controller. The polarity of the 16 wake-up inputs is
programmable by writing the PMC Fast Startup Polarity Register (PMC_FSPR).
The Fast Restart circuitry, as shown in Figure 28-4, is fully asynchronous and provides a fast startup signal to the
Power Management Controller. As soon as the fast startup signal is asserted, the embedded 4/8/12 MHz Fast RC
oscillator restarts automatically.
Figure 28-4. Fast Startup Circuitry
Each wake-up input pin and alarm can be enabled to generate a Fast Startup event by writing 1 to the
corresponding bit in the Fast Startup Mode Register PMC_FSMR.
fast_restart
WKUP15
FSTT15
FSTP15
WKUP1
FSTT1
FSTP1
WKUP0
FSTT0
FSTP0
RTTAL
RTCAL
USBAL
RTT Alarm
RTC Alarm
USB Alarm