2.4
Initiating a DMA Transfer
2.4.1 DMA Channel
2.4.1.1
Event-Triggered Transfer Request
Initiating a DMA Transfer
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There are multiple ways to initiate a programmed data transfer using the EDMA3 channel controller.
Transfers on DMA channels are initiated by three sources:
•
Event-triggered transfer request
(this is the more typical usage of EDMA3): Allows for a peripheral,
system, or externally-generated event to trigger a transfer request.
•
Manually-triggered transfer request:
The CPU manually triggers a transfer by writing a 1 to the
corresponding bit in the event set register (ESR/ESRH).
•
Chain-triggered transfer request:
A transfer is triggered on the completion of another transfer or
subtransfer.
Transfers on QDMA channels are initiated by two sources:
•
Autotriggered transfer request:
A transfer is triggered when the programmed trigger word is written
to.
•
Link-triggered transfer requests:
When linking occurs, the transfer is triggered when the trigger word
is written to.
When an event is asserted from a peripheral or device pins, it gets latched in the corresponding bit of the
event register (ER.E
n
= 1). See
for peripheral event to DMA event mapping. If the
corresponding event in the event enable register (EER) is enabled (EER.E
n
= 1), then the EDMA3CC
prioritizes and queues the event in the appropriate event queue. When the event reaches the head of the
queue, it is evaluated for submission as a transfer request to the transfer controller.
If the PaRAM set is valid (not a NULL set), then a transfer request packet (TRP) is submitted to the
EDMA3TC and the E
n
bit in ER is cleared. At this point, a new event can be safely received by the
EDMA3CC.
If the PaRAM set associated with the channel is a NULL set (see
), then no transfer request
(TR) is submitted and the corresponding E
n
bit in ER is cleared and simultaneously the corresponding
channel bit is set in the event miss register (EMR.E
n
= 1) to indicate that the event was discarded due to
a null TR being serviced. Good programming practices should include cleaning the event missed error
before retriggering the DMA channel.
When an event is received, the corresponding event bit in the event register is set (ER.E
n
= 1), regardless
of the state of EER.E
n
. If the event is disabled when an external event is received (ER.E
n
= 1 and
EER.E
n
= 0), the ER.E
n
bit remains set. If the event is subsequently enabled (EER.E
n
= 1), then the
pending event is processed by the EDMA3CC and the TR is processed/submitted, after which the ER.E
n
bit is cleared.
If an event is being processed (prioritized or is in the event queue) and another sync event is received for
the same channel prior to the original being cleared (ER.E
n
!= 0), then the second event is registered as a
missed event in the corresponding bit of the event missed register (EMR.E
n
= 1).
gives an example of the synchronization events associated with each of the programmable
DMA channels in the TMS320DM357 device. See the device-specific data manual to determine the event
to channel mapping.
Table 2-5. EDMA3 Channel Synchronization Events
EDMA3 Channel
Event Name
Event Description
0-1
-
Unused
2
XEVT
Audio Serial Port (ASP) Transmit Event
3
REVT
Audio Serial Port (ASP) Receive Event
4
HISTEVT
VPSS Histogram Event
5
H3AEVT
VPSS H3A Event
38
EDMA3 Architecture
SPRUG34 – November 2008
Содержание TMS320DM357
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