Synchronizing Channel Activity - Texas Instruments OMAP5910 Reference Manual

DSP DMA
7.2.12

Synchronizing Channel Activity

7.2.12.1 DMA Channel Read Synchronization vs. Write Synchronization
142 DSP Subsystem
Activity in a channel can be synchronized to a request from a DSP public
peripheral or MPU/DSP shared peripheral. Each peripheral request is tied to
a DMA synchronization event. You can use a DMA synchronization event to
trigger channel activity using the SYNC bits of DMACCR.
Each channel has an FS bit in DMACCR that allows you to choose between
two synchronization modes:
Element synchronization mode (FS = 0) requires one event per element
-
transfer. When the selected synchronization event occurs, a read access
request is sent to the source port and then a write access request is sent
to the destination port. When all the bytes of the current element are
transferred, the channel makes no more requests until the next
synchronization event occurrence.
Frame synchronization mode (FS = 1) requires one event to trigger an
-
entire frame of elements. When the event occurs, the channel sends a
read access request and a write access request for each element in the
frame. When all the elements are transferred, the channel makes no more
requests until the next occurrence of the event.
If you specify a synchronization event, the DMA access to the source and
destination are handled as described in section 7.2.12.1. Once the request is
received, it is handled according to the predefined position and the
programmed priority of the channel in the DMA service chain (section 7.2.6).
If you choose not to synchronize the channel (SYNC = 00000b), the channel
sends an access request to the source port as soon as the channel is enabled
(EN = 1 in DMACCR). Setting EN = 1 initiates the transfer of the entire block
defined for the channel.
If the DMA controller is configured to recognize a synchronization event
(SYNC is something other than 00000b) and the synchronization event occurs
before the channel is enabled, the synchronization event will be latched and
serviced as soon as the channel is enabled. Set the SYNC field to 00000b
while the channel is disabled to ignore the synchronization events that occur
before the channel is enabled.
When a DMA channel is configured for synchronization, the synchronization
event is tied to the element read operation or the element write operation
depending on the source and destination ports.
SPRU890A