EM1P#

Beyond the energy modes available on prior devices, EFR32xG22 introduces EM1P, a new method to reduce energy consumption while using the radio. In this (intermediate) mode, the HF crystal oscillator (HFXO) is kept running (and the radio remains active) if the following conditions are met:

  • The radio state is anything other than idle (for example RX or TX), and

  • Power Manager or the application software requests to enter EM2.

This sequence puts the Cortex-M33 into sleep mode, and clocks to the core, and all high-speed peripherals are disabled (peripherals and oscillators capable of EM2, EM3, or EM4 operation remain available).

On earlier EFR32 devices, entering EM2 mode would unconditionally shut down the radio, regardless of the operation in progress. Doing so during certain radio activities would potentially incur undesirable side effects (for example, FIFO corruption).

Comparison of EM1P and Other Energy Modes#

EM1P is not technically a standalone energy mode (like EM1, EM2, and so on). Rather, it is an operating condition where most of the EFR32 enters EM2 Deep Sleep, but the radio (and its requisite HFXO clock source) are retained. As such, EM1P can be (perhaps confusingly) viewed as "EM2 with Radio".

This combination results in lower current consumption than EM1 mode, and higher consumption than full EM2. The following table depicts some observations of these influences on energy usage taken on a single device. Current consumption was measured initially at EM0, when the radio was idle and in RX. After transitioning into EM1/EM2, current was again measured. The cell in the bottom-right corner represents the EM1P measurement result (radio was in RX, device then transitioned to EM2).

Radio State

Initial (EM0) Current

Final Energy Mode

Resulting Current

Idle

2.36 mA

EM1

1.60 mA

"

"

EM2

1.56 μA

RX

5.92 mA

EM1

5.15 mA

"

"

EM2

4.85 mA

Note: The values above are not guaranteed, and will vary across devices and scenarios due to numerous factors. They are presented here as a single illustrative example of the general performance trends among these different modes of operation. Consult your device datasheet for all definitive guidance regarding specifications and performance.

Scheduled Radio Operations#

EM1P mode does not impact scheduled RX and scheduled TX operations, as in those cases the radio is in the idle state when the firmware enters EM2.