24.6.6. Sleep Mode Operation
The WDT will continue to operate in any sleep mode where the source clock is active except backup
mode. The WDT interrupts can be used to wake up the device from a sleep mode. An interrupt request
will be generated after the wake-up if the Interrupt Controller is configured accordingly. Otherwise the
CPU will wake up directly, without triggering an interrupt. In this case, the CPU will continue executing
from the instruction following the entry into sleep.
24.6.7. Synchronization
Due to asynchronicity between the main clock domain and the peripheral clock domains, some registers
need to be synchronized when written or read.
The following registers are synchronized when written:
•
Enable bit in Control A register (CTRLA.ENABLE)
•
Window Enable bit in Control A register (CTRLA.WEN)
•
Always-On bit in control Control A (CTRLA.ALWAYSON)
The following registers are synchronized when read:
•
Watchdog Clear register (CLEAR)
Required write-synchronization is denoted by the "Write-Synchronized" property in the register
description.
Required read-synchronization is denoted by the "Read-Synchronized" property in the register
description.
24.6.8. Additional Features
24.6.8.1. Always-On Mode
The Always-On mode is enabled by setting the Always-On bit in the Control A register
(CTRLA.ALWAYSON=1). When the Always-On mode is enabled, the WDT runs continuously, regardless
of the state of CTRLA.ENABLE. Once written, the Always-On bit can only be cleared by a power-on reset.
The Configuration (CONFIG) and Early Warning Control (EWCTRL) registers are read-only registers
while the CTRLA.ALWAYSON bit is set. Thus, the time period configuration bits (CONFIG.PER,
CONFIG.WINDOW, EWCTRL.EWOFFSET) of the WDT cannot be changed.
Enabling or disabling Window mode operation by writing the Window Enable bit (CTRLA.WEN) is allowed
while in Always-On mode, but note that CONFIG.PER cannot be changed.
The Interrupt Clear and Interrupt Set registers are accessible in the Always-On mode. The Early Warning
interrupt can still be enabled or disabled while in the Always-On mode, but note that
EWCTRL.EWOFFSET cannot be changed.
Table WDT Operating Modes With Always-On shows the operation of the WDT for
CTRLA.ALWAYSON=1.
Table 24-2. WDT Operating Modes With Always-On
WEN
Interrupt Enable
Mode
0
0
Always-on and normal mode
0
1
Always-on and normal mode with Early Warning interrupt
1
0
Always-on and window mode
1
1
Always-on and window mode with Early Warning interrupt
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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