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2014-07-02 - Gecko Family - d0001_Rev1.30
100
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During the start-up period HFCLK will stop since the oscillator driving it is not ready. This effectively
stalls the Core Modules and the High-Frequency Peripherals. It is possible to avoid this by first enabling
the HFXO and then wait for the oscillator to become ready before switching the clock source. This way,
the system continues to run on the HFRCO until the HFXO has timed out and provides a reliable clock.
This sequence of events is shown in Figure 11.3 (p. 100) .
A separate flag is set when the oscillator is ready. This flag can also be configured to generate an
interrupt.
Figure 11.2. CMU Switching from HFRCO to HFXO before HFXO is ready
HFXO
CMU_STATUS..HFXORDY
CMU_STATUS.HFXOENS
CMU_STATUS.HFXOSEL
HFRCO
HFCLK
HFXO t im e- out period
CMU_STATUS.HFRCORDY
CMU_STATUS.HFRCOENS
CMU_STATUS.HFRCOSEL
CMU_OSCENCMD.HFXOEN
CMU_OSCENCMD.HFXODIS
c
lo
c
k
s
CMU_CMD.HFCLKSEL
CMU_OSCENCMD.HFRCOEN
CMU_OSCENCMD.HFRCODIS
c
o
m
m
a
n
d
s
ta
tu
s
00
02
00
Figure 11.3. CMU Switching from HFRCO to HFXO after HFXO is ready
00
02
00
HFXO
CMU_STATUS.HFXORDY
CMU_STATUS.HFXOENS
CMU_STATUS.HFXOSEL
HFRCO
HFCLK
HFXO t im e- out period
CMU_STATUS.HFRCORDY
CMU_STATUS.HFRCOENS
CMU_STATUS.HFRCOSEL
CMU_OSCENCMD.HFXOEN
CMU_OSCENCMD.HFXODIS
c
lo
c
k
s
CMU_CMD.HFCLKSEL
CMU_OSCENCMD.HFRCOEN
CMU_OSCENCMD.HFRCODIS
c
o
m
m
a
n
d
s
ta
tu
s
Summary of Contents for EFM32G
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