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SAM G51 [DATASHEET]
11209C–ATARM–20-Dec-13
Figure 23-3.
Fast Startup Circuitry
Each wake-up input pin and alarm can be enabled to generate a fast startup event by setting the corresponding bit in
PMC_FSMR.
The user interface does not provide any status for fast startup, but the user can easily recover this information by reading
the PIO Controller and the status registers of the RTC and RTT.
23.11 Startup from Embedded Flash
The inherent start-up time of the embedded Flash cannot provide a fast startup of the system.
If system fast start-up time is not required, the first instruction after a wait mode exit can be located in the embedded
Flash. Under these conditions, prior to entering wait mode, the Flash controller must be programmed to perform access
in 0 wait-state (see Flash controller section).
If the fast RC oscillator is configured to generate 16 MHz or 24 MHz (MOSCRCF=1 or 2 in CKGR_MOR), the first
instruction after an exit must not be located in the embedded Flash and the fast startup procedure must be used (see
the instructions managing start-up time can be located in any on-chip memory.
The procedure and conditions to enter wait mode and the circuitry to exit wait mode are strictly the same as fast startup
23.12 Main Clock Failure Detector
The clock failure detector monitors the main crystal oscillator or ceramic resonator-based oscillator to identify an eventual
failure of this oscillator.
The clock failure detector can be enabled or disabled by bit CFDEN in CKGR_MOR. After a VDDCORE reset, the
detector is disabled. However, if the oscillator is disabled (MOSCXTEN = 0), the detector is disabled too.
A failure is detected by means of a counter incrementing on the main oscillator clock edge and timing logic clocked on
the slow RC oscillator controlling the counter. Thus, the slow RC oscillator must be enabled.
fast_restart
WKUP15
FSTT15
FSTP15
WKUP1
FSTT1
FSTP1
WKUP0
FSTT0
FSTP0
RTTAL
RTCAL
RTT Alarm
RTC Alarm