10.3.1.5 EM4 Hibernate
The majority of peripherals are shutoff to reduce leakage power. A few selected peripherals are available. System memory and regis-
ters do not retain values. GPIO PAD state and RTCC RAM are retained. Wake-up from EM4 Hibernate requires a reset to the system,
returning it back to EM0 Active
• Cortex-M4 is off
• RFSENSE available. Radio is off.
• High frequency clock tree is off
• Some low frequency clock trees may be active
• The following oscillators are available
• LFRCO, LFXO, ULFRCO
• The following low frequency peripherals are available
• RTCC, CRYOTIMER
• Wake-up to EM0 Active through
• VMON, EMU Temperature Sensor, RTCC, RFSENSE, CRYOTIMER, reset pin, power on reset, asynchronous pin interrupt (on
GPIO_EM4WUx pins only)
• GPIO pin state may be retained (depending on EMU->EM4CTRL.EM4IORETMODE configuration)
• RTCC memory is retained
• The DC-DC converter can be configured to remain on in Low Power mode.
10.3.1.6 EM4 Shutoff
EM4 Shutoff is the lowest energy mode of the part. There is no retention except for GPIO PAD state. Wake-up from EM4 Shutoff re-
quires a reset to the system, returning it back to EM0 Active
• Cortex-M4 is off
• RFSENSE available. Radio is off.
• High frequency clock tree is off
• Low frequency clock tree may be active
• The following oscillators are available
• LFRCO, LFXO, ULFRCO
• The following low frequency peripherals are available
• CRYOTIMER
• Wake-up to EM0 Active through
• RFSENSE, CRYOTIMER, reset pin, power on reset, asynchronous pin interrupt (on GPIO_EM4WUx pins only)
• GPIO pin state may be retained (depending on EMU->EM4CTRL.EM4IORETMODE configuration)
• The DC-DC converter configuration is reset to its default Unconfigured configuration (DC-DC converter disabled and bypass switch
is off)
10.3.2 Entering Low Energy Modes
The following sections describe the requirements for entering the various energy modes.
Note:
If Voltage scaling is being used to save system energy, it is important to ensure the proper conditions for entry and exit of EM2
Deep Sleep, EM3 Stop or EM4 Hibernate be met. See
10.3.9.2.1 EM23 Voltage Scaling Guidelines
and
10.3.2.1 Entry Into EM1 Sleep
Energy mode EM1 Sleep is entered when the Cortex-M4 executes the Wait For Interrupt (WFI) or Wait For Event (WFE) instruction
while the SLEEPDEEP bit the Cortex-M4 System Control Register is cleared. The MCU can re-enter sleep automatically out of an Inter-
rupt Service Routine (ISR) if the SLEEPONEXIT bit in the Cortex-M4 System Control Register is set. Refer to ARM documentation on
entering Sleep modes.
Alternately, EM1 Sleep can be entered from either EM2 Deep Sleep or EM3 Stop from a Peripheral Wake-up Request allowing trans-
fers between the Peripheral and System RAM or Flash. On EFR32, ADC, IDAC, LESENSE, and LEUART peripherals can request this
wake-up event. Refer to their respective register specification to enable this option. The system will return back to EM2 DeepSleep or
EM3 Stop once the ADC, IDAC, LESENSE, or LEUART have completed its transfers and processing.
During Peripheral Wake-Up Request, additional system resources such as FLASH and other Peripherals can be enabled for access.
Reference Manual
EMU - Energy Management Unit
silabs.com
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