25.5.3.5 Event Input Actions
The event input actions are available only on the least significant DMA channels. For details on channels with event input support, refer to the Event System documentation.
Before using event input actions, the event controller must be configured first according to the following table, and the Channel Event Input Enable bit in the Channel Event Control register (CHEVCTRL.EVIE) must be written to '1'. Refer also to 25.5.5 Events.
| Action | CHEVCTRL.EVACT | CHCTRLA.TRIGSRC |
|---|---|---|
| None | NOACT | - |
| Normal Transfer | TRIG | DISABLE |
| Conditional Transfer on Strobe | TRIG | Any peripheral |
| Conditional Transfer | CTRIG | |
| Conditional Block Transfer | CBLOCK | |
| Channel Suspend | SUSPEND | |
| Channel Resume | RESUME | |
| Skip Next Block Suspend | SSKIP | |
| Increase priority | INCPRI |
Normal Transfer
The event input is used to trigger a beat or burst transfer on peripherals.
The event is acknowledged as soon as the event is received. When received, both the Channel Pending status bit in the Channel Status register (CHSTATUS.PEND) and the corresponding Channel n bit in the Pending Channels register (PENDCH.PENDCHn) are set. If the event is received while the channel is pending, the event trigger is lost.
The figure below shows an example where beat transfers are enabled by internal events.
Conditional Transfer on Strobe
The event input is used to trigger a transfer on peripherals with pending transfer requests. This event action is intended to be used with peripheral triggers, e.g., for timed communication protocols or periodic transfers between peripherals: only when the peripheral trigger coincides with the occurrence of a (possibly cyclic) event the transfer is issued.
The event is acknowledged as soon as the event is received. The peripheral trigger request is stored internally when the previous trigger action is completed (i.e., the channel is not pending) and when an active event is received. If the peripheral trigger is active, the DMA will wait for an event before the peripheral trigger is internally registered. When both event and peripheral transfer trigger are active, both CHSTATUS.PEND and PENDCH.PENDCHn are set. A software trigger will now trigger a transfer.
The figure below shows an example where the peripheral beat transfer is started by a conditional strobe event action.
Conditional Transfer
The event input is used to trigger a conditional transfer on peripherals with pending transfer requests. As example, this type of event can be used for peripheral-to-peripheral transfers, where one peripheral is the source of event and the second peripheral is the source of the trigger.
Each peripheral trigger is stored internally when the event is received. When the peripheral trigger is stored internally, the Channel Pending status bit is set (CHSTATUS.PEND), the respective Pending Channel n Bit in the Pending Channels register is set (PENDCH.PENDCHn), and the event is acknowledged. A software trigger will now trigger a transfer.
The figure below shows an example where conditional event is enabled with peripheral beat trigger requests.
Conditional Block Transfer
The event input is used to trigger a conditional block transfer on peripherals.
Before starting transfers within a block, an event must be received. When received, the event is acknowledged when the block transfer is completed. A software trigger will trigger a transfer.
The figure below shows an example where conditional event block transfer is started with peripheral beat trigger requests.
