Datasheet

311
Atmel | SMART SAM D20 [DATASHEET]
Atmel-42129K–SAM-D20_datasheet–06/2014
Synchronous Path
The synchronous path should be used when the event generator and the event channel share the same 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.
When using the synchronous path, the channel is capable of generating interrupts. The channel status bits in the
Channel Status register (CHSTATUS) are also updated and available for use.
If the Generic Clocks Request bit in the Control register (CTRL.GCLKREQ) is zero, the channel operates in
SleepWalking mode and request the configured generic clock only when an event is to be propagated through the
channel. If CTRL.GCLKREQ is one, the generic clock will always be on for the configured channel.
Resynchronized Path
The resynchronized path should be used when the event generator and the event channel do not share the same clock.
When the resynchronized path is used, resynchronization of the event from the event generator is done in the channel.
When the resynchronized path is used, the channel is capable of generating interrupts. The channel status bits in the
Channel Status register (CHSTATUS) are also updated and available for use.
If the Generic Clocks Request bit in the Control register (CTRL.GCLKREQ) is zero, the channel operates in
SleepWalking mode and request the configured generic clock only when an event is to be propagated through the
channel. If CTRL.GCLKREQ is one, the generic clock will always be on for the configured channel.
22.6.2.6 Edge Detection
When synchronous or resynchronized paths are used, edge detection must be used. The event system can perform
edge detection in three different ways:
z Generate an event only on the rising edge
z Generate an event only on the falling edge
z Generate an event on rising and falling edges.
Edge detection is selected by writing to the Edge Selection bit group in the Channel register (CHANNEL.EDGSEL).
If the generator event is a pulse, the Both Edges method must not be selected. Use the Rising Edge or Falling Edge
detection method, depending on the generator event default level.
22.6.2.7 Channel Status
The Channel Status register (CHSTATUS) updates the status of the channels when a synchronous or resynchronized
path is in use. There are two different status bits in CHSTATUS for each of the available channels: The
CHSTATUS.CHBUSYx bit is set to one if an event on the corresponding channel x has not been handled by all event
users connected to that channel.
The CHSTATUS.USRRDYx bit is set to one if all event users connected to the corresponding channel x are ready to
handle incoming events on that channel.
22.6.2.8 Software Event
A software event can be initiated on a channel by writing a one to the Software Event bit in the Channel register
(CHANNEL.SWEVT) together with the Channel bits (CHANNEL.CHANNEL). This will generate a software event on the
selected channel.
The software event can be used for application debugging, and functions like any event generator. To use the software
event, the event path must be configured to either a synchronous path or resynchronized path (CHANNEL.PATH = 0x0
or 0x1), edge detection must be configured to rising-edge detection (CHANNEL.EDGSEL= 0x1) and the Generic Clock
Request bit must be set to one (CTRL.GCLKREQ=0x1).
22.6.3 Interrupts
The EVSYS has the following interrupt sources:
z Overrun Channel x interrupt (INTFLAG)