10. CMU - Clock Management Unit
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Oscillators
CMU
WDOG clock
LETIMER clock
LEUART clock
Peripheral A clock
Peripheral B clock
Peripheral C clock
Peripheral D clock
CPU clock
Quick Facts
What?
The CMU controls oscillators and clocks. EFM32
Jade Gecko 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 the MCU. With the low power
oscillators combined with the flexible clock control
scheme, it is possible to minimize the energy con-
sumption 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 DeepSleep, 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.
10.1 Introduction
The Clock Management Unit (CMU) is responsible for controlling the oscillators and clocks in the EFM32 Jade Gecko. The CMU pro-
vides the capability to turn on and off the clock on an individual basis to all peripheral modules in addition to enable/disable and config-
ure 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.
10.2 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)
• Low power oscillators.
• Low start-up times.
• Separate prescalers for High Frequency Core Clocks (HFCORECLK), 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 clocks can be output to external pins and/or PRS.
• Wakeup interrupt based on LFRCO or LFXO ready, allowing to wait for low frequency oscillator startup while being in EM2 Deep-
Sleep avoiding the need for polling.
• Auxiliary 1 MHz - 38 MHz RC oscillator (AUXHFRCO), which is asynchronous to the HFSRCCLK system clock, can be selected for
ADC operation and debug trace.
EFM32JG1 Reference Manual
CMU - Clock Management Unit
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