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Architecture
613
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Enhanced Direct Memory Access (EDMA3) Controller
17.2.10 Event Queue(s)
Event queues are a part of the EDMA3 channel controller. Event queues form the interface between the
event detection logic in the EDMA3CC and the transfer request (TR) submission logic of the EDMA3CC.
Each queue is 16 entries deep, that is, a maximum of 16 queued events per event queue. If there are
more than 16 events, then the events that cannot find a place in the event queue remain set in the
associated event register.
The number of event queues in the EDMA3CC determines the number of transfer controllers connected to
the EDMA3CC. By default, there is a one-to-one mapping between the queues and transfer controllers.
Therefore, the transfer requests (TRs) associated with events in Q0 get submitted to TC0. Similarly,
transfer requests associated with events in Q1 get submitted to TC1, and so on.
An event that wins prioritization against other DMA and/or QDMA pending events is placed at the end of
the appropriate event queue. Each event queue is serviced in a FIFO (first in–first out) order. Once the
event reaches the head of its queue and the corresponding transfer controller is ready to receive another
TR, the event is dequeued and the PaRAM set corresponding to the dequeued event is processed and
submitted as a transfer request packet (TRP) to the associated EDMA3 transfer controller.
A lower numbered queue has a higher dequeuing priority then a higher numbered queue. For example,
Q0 has higher priority than Q1, if Q0 and Q1 both have at least one event entry and if both TC0 and TC1
can accept transfer requests, then the event in Q0 is dequeued first and its associated PaRAM set is
processed and submitted as a transfer request (TR) to TC0.
All the event entries in all the event queues are software readable (not writeable) by accessing the event
queue entry registers (Q
x
E
y
). Each event entry register characterizes the queued event in terms of the
type of event (manual, event, chained or autotriggered) and the event number. See
for
a description of the bit fields in the queue event entry registers.
17.2.10.1 DMA/QDMA Channel to Event Queue Mapping
Each DMA channel and QDMA channel is independently programmed to map to a specific queue using
the DMA queue number register
n
(DMAQNUM
n
) and the QDMA channel queue number register
(QDMANUM). The mapping of DMA/QDMA channels is critical to achieving the desired performance level
for the EDMA and most importantly in meeting real-time deadlines.
NOTE:
If an event is ready to be queued and both the event queue and the EDMA3 transfer
controller associated to the event queue are empty, then the event bypasses the event
queue, and goes to the PaRAM processing logic and eventually to the transfer request
submission logic for submission to the EDMA3TC. In this case, the event is not logged in the
event queue status registers.