
EM358x
Rev. 0.4
47
5.5.2
Basic Sleep Modes
The power management state diagram in Figure 5-3 shows the basic operation of the power management
controller.
DEEP SLEEP
EMULATED
DEEP SLEEP
PRE-DEEP
SLEEP
RUNNING
IDLE SLEEP
CDBGPWRUPREQ set
CDBGPWRUPREQ cleared
Deep sleep requested
(WFI instruction with SLEEP_DEEP=1)
CSY
SPW
RUP
REQ
& IN
HIBIT
Wake
up e
vent
(rese
ts the
proc
essor
)
Figure 5-3. Power Management State Diagram
In normal operation an application may request one of two low power modes through program execution:
Idle Sleep is achieved by executing a WFI instruction while the SLEEPDEEP bit in the Cortex System Control
register (SCS_SCR) is clear. This puts the CPU into an idle state where execution is suspended until an
interrupt occurs. This is indicated by the state at the bottom of the diagram. Power is maintained to the core
logic of the EM358x during the Idle Sleeping state.
Deep sleep is achieved by executing a WFI instruction with the SLEEPDEEP bit in SCS_SCR set. This
triggers the state transitions around the main loop of the diagram, resulting in powering down the EM358x’s
core logic, and leaving only the always-on domain powered. Wake up is triggered when one of the pre-
determined events occurs.
If a deep sleep is requested the EM358x first enters a pre-deep sleep state. This state prevents any section of the
chip from being powered off or reset until the SWJ goes idle (by clearing CSYSPWRUPREQ). This pre-deep
sleep state ensures debug operations are not interrupted.
In the deep sleep state the EM358x waits for a wake up event which will return it to the running state. In powering
up the core logic the ARM
®
Cortex
TM
-M3 is put through a reset cycle and Ember software restores the stack and
application state to the point where deep sleep was invoked.
5.5.3
Further options for deep sleep
By default the low-frequency internal RC oscillator (OSCRC) is running during deep sleep (known as deep
sleep 1).
Summary of Contents for EMBER EM358 series
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