Cmu - Clock Management Unit; Introduction; Features - Silicon Laboratories EFR32xG14 Wireless Gecko Reference Manual

11. CMU - Clock Management Unit

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Oscillators CMU

11.1 Introduction

The Clock Management Unit (CMU) is responsible for controlling the oscillators and clocks in the EFR32. The CMU provides the capa-
bility to turn on and off the clock on an individual basis to all peripheral modules in addition to enable/disable and configure the available
oscillators. The high degree of flexibility enables software to minimize energy consumption in any specific application by not wasting
power on peripherals and oscillators that do not need to be active.

11.2 Features

• Multiple clock sources available:
• 38 MHz - 40 MHz High Frequency Crystal Oscillator (HFXO)
• 1 MHz - 38 MHz High Frequency RC Oscillator (HFRCO)
• 1 MHz - 38 MHz Auxiliary High Frequency RC Oscillator (AUXHFRCO)
• 32768 Hz Low Frequency Crystal Oscillator (LFXO)
• 32768 Hz Low Frequency RC Oscillator (LFRCO)
• 1000 Hz Ultra Low Frequency RC Oscillator (ULFRCO)
• All oscillator sources are low power.
• Fast start-up times.
• Separate prescalers for High Frequency Core Clocks (HFCORECLK), Radio Clocks (HFRADIOCLK), and Peripheral Clocks
(HFPERCLK).
• Individual clock prescaler selection for each Low Energy Peripheral.
• Clock gating on an individual basis to core modules and all peripherals.
• Selectable clock output to external pins and/or PRS.
• Wakeup interrupt for LFRCO or LFXO ready allows entry into EM2 Deep Sleep while waiting for low-frequency oscillator startup.
This avoids the need for software polling and saves power during oscillator startup.
• Auxiliary 1 MHz - 38 MHz RC oscillator (AUXHFRCO), which is asynchronous to the HFSRCCLK system clock, can be selected for
ADC operation, LESENSE timing and debug trace.
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WDOG clock
LETIMER clock
LEUART clock
Peripheral A clock
Peripheral B clock
Peripheral C clock
Peripheral D clock
CPU clock
CMU - Clock Management Unit
Quick Facts
What?
The CMU controls oscillators and clocks. EFR32
supports 6 different oscillators with minimized power
consumption and short start-up time. The CMU has
HW support for calibration of RC oscillators.
Why?
Oscillators and clocks contribute significantly to the
power consumption of an MCU. Low power oscilla-
tors combined with a flexible clock control scheme
make it possible to minimize the energy consump-
tion in any given application.
How?
The CMU can configure different clock sources, ena-
ble/disable clocks to peripherals on an individual ba-
sis and set the prescaler for the different clocks. The
short oscillator start-up times makes duty-cycling be-
tween active mode and the different low energy
modes (EM2 Deep Sleep, EM3 Stop, and EM4 Hi-
bernate/Shutoff) very efficient. The calibration fea-
ture ensures high accuracy RC oscillators. Several
interrupts are available to avoid CPU polling of flags.
Reference Manual
Rev. 1.1 | 279