There is one exception concerning the Generator 0. As it is used as GCLK_MAIN, it cannot be locked. It
is reset by any Reset and will start up in a known configuration. The software reset (CTRLA.SWRST) can
not unlock the registers.
In case of an external Reset, the Generator source will be disabled. Even if the WRTLOCK bit is written to
'1' the peripheral channels are disabled (PCHCTRLm.CHEN set to '0') until the Generator source is
enabled again. Then, the PCHCTRLm.CHEN are set to '1' again.
Related Links
on page 133
on page 138
16.6.4. Additional Features
16.6.4.1. Peripheral Clock Enable after Reset
The Generic Clock Controller must be able to provide a generic clock to some specific peripherals after a
Reset. That means that the configuration of the Generators and Peripheral Channels after Reset is
device-dependent.
Refer to GENCTRLn.SRC for details on GENCTRLn reset.
Refer to PCHCTRLm.SRC for details on PCHCTRLm reset.
16.6.5. Sleep Mode Operation
16.6.5.1. SleepWalking
The GCLK module supports the SleepWalking feature.
If the system is in a sleep mode where the Generic Clocks are stopped, a peripheral that needs its clock
in order to execute a process must request it from the Generic Clock Controller.
The Generic Clock Controller receives this request, determines which Generic Clock Generator is
involved and which clock source needs to be awakened. It then wakes up the respective clock source,
enables the Generator and Peripheral Channel stages successively, and delivers the clock to the
peripheral.
The RUNSTDBY bit in the Generator Control register controls clock output to pin during standby sleep
mode. If the bit is cleared, the Generator output is not available on pin. When set, the GCLK can
continuously output the generator output to GCLK_IO. Refer to
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16.6.5.2. Minimize Power Consumption in Standby
The following table identifies when a Clock Generator is off in Standby Mode, minimizing the power
consumption:
Table 16-2. Clock Generator n Activity in Standby Mode
Request for Clock n
present
GENCTRLn.RUNSTDB
Y
GENCTRLn.OE
Clock Generator n
yes
-
-
active
no
1
1
active
no
1
0
OFF
Atmel SAM L22G / L22J / L22N [DATASHEET]
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