AT91SAM Datasheet, PDF (25/67 Pages) ATMEL Corporation – ARM-based Flash MCU

SAM4S Series [Preliminary]
5.7 Fast Startup
The SAM4S allows the processor to restart in a few microseconds while the processor is in wait
mode or in sleep mode. A fast start up can occur upon detection of a low level on one of the 19
wake-up inputs (WKUP0 to 15 + SM + RTC + RTT).
The fast restart circuitry, as shown in Figure 5-5, is fully asynchronous and provides a fast start-
up signal to the Power Management Controller. As soon as the fast start-up signal is asserted,
the PMC automatically restarts the embedded 4/8/12 MHz Fast RC oscillator, switches the mas-
ter clock on this 4 MHz clock and reenables the processor clock.
Figure 5-5. Fast Start-Up Sources
FSTT0
WKUP0
WKUP1
WKUP15
FSTP0
FSTT1
FSTP1
FSTT15
FSTP15 RTTAL
fast_restart
RTT Alarm
RTCAL
RTC Alarm
USBAL
USB Alarm
25
11100BS–ATARM–31-Jul-12