configured to select one of these channels, as shown in
. The channel is selected with the
Channel bit group in the User register (USERm.CHANNEL).
The user multiplexer must always be configured before the channel. A list of all user multiplexers is found
in the User (USERm) register description.
Related Links
on page 588
30.6.2.4. Event System Channel
An event channel can select one event from a list of event generators. Depending on configuration, the
selected event could be synchronized, resynchronized or asynchronously sent to the users. When
synchronization or resynchronization is required, the channel includes an internal edge detector, allowing
the Event System to generate internal events when rising, falling or both edges are detected on the
selected event generator.
An event channel is able to generate internal events for the specific software commands. A channel block
diagram is shown in
30.6.2.5. Event Generators
Each event channel can receive the events form all event generators. All event generators are listed in
the Event Generator bit field in the Channel n register (CHANNELn.EVGEN). For details on event
generation, refer to the corresponding module chapter. The channel event generator is selected by the
Event Generator bit group in the Channel register (CHANNELn.EVGEN). By default, the channels are not
connected to any event generators (ie, CHANNELn.EVGEN = 0)
30.6.2.6. Channel Path
There are three different ways to propagate the event from an event generator:
•
Asynchronous path
•
Synchronous path
•
Resynchronized path
The path is decided by writing to the Path Selection bit group of the Channel register (CHANNELn.PATH).
Asynchronous Path
When using the asynchronous path, the events are propagated from the event generator to the event
user without intervention from the Event System. The GCLK for this channel
(GCLK_EVSYS_CHANNEL_n) is not mandatory, meaning that an event will be propagated to the user
without any clock latency.
When the asynchronous path is selected, the channel cannot generate any interrupts, and the Channel
Status register (CHSTATUS) is always zero. The edge detection is not required and must be disabled by
software. Each peripheral event user has to select which event edge must trigger internal actions. For
further details, refer to each peripheral chapter description.
Synchronous Path
The synchronous path should be used when the event generator and the event channel share the same
generator for the generic clock. If they do not share the same clock, a logic change from the event
generator to the event channel might not be detected in the channel, which means that the event will not
be propagated to the event user. For details on generic clock generators, refer to
GCLK - Generic Clock
Controller
.
When using the synchronous path, the channel is able to generate interrupts. The channel busy n bit in
the Channel Status register (CHSTATUS.CHBUSYn) are also updated and available for use.
Atmel SAM L22G / L22J / L22N [DATASHEET]
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