Architecture
591
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Enhanced Direct Memory Access (EDMA3) Controller
A LINK value of FFFFh is referred to as a NULL link that should cause the EDMA3CC to perform an
internal write of 0 to all entries of the current PaRAM set, except for the LINK field that is set to FFFFh.
Also, see
for details on terminating a transfer.
17.2.3.3 Null PaRAM Set
A null PaRAM set is defined as a PaRAM set where all count fields (ACNT, BCNT, and CCNT) are
cleared to 0. If a PaRAM set associated with a channel is a NULL set, then when serviced by the
EDMA3CC, the bit corresponding to the channel is set in the associated event missed register (EMR or
QEMR). This bit remains set in the associated secondary event register (SER or QSER).
This implies that
any future events on the same channel are ignored by the EDMA3CC and you are required to clear the bit
in SER or QSER for the channel.
This is considered an error condition, since events are not expected on
a channel that is configured as a null transfer. See
and
for more
information on the SER and EMR registers, respectively.
17.2.3.4 Dummy PaRAM Set
A dummy PaRAM set is defined as a PaRAM set where at least one of the count fields (ACNT, BCNT, or
CCNT) is cleared to 0 and at least one of the count fields is nonzero.
If a PaRAM set associated with a channel is a dummy set, then when serviced by the EDMA3CC, it will
not set the bit corresponding to the channel (DMA/QDMA) in the event missed register (EMR or QEMR)
and the secondary event register (SER or QSER) bit gets cleared similar to a normal transfer. Future
events on that channel are serviced. A dummy transfer is a legal transfer of 0 bytes. See
and
for more information on the SER and EMR registers,
respectively.
17.2.3.5 Dummy Versus Null Transfer Comparison
There are some differences in the way the EDMA3CC logic treats a dummy versus a null transfer request.
A null transfer request is an error condition, but a dummy transfer is a legal transfer of 0 bytes. A null
transfer causes an error bit (E
n
) in EMR to get set and the E
n
bit in SER remains set, essentially
preventing any further transfers on that channel without clearing the associated error registers.
summarizes the conditions and effects of null and dummy transfer requests.
Table 17-2. Dummy and Null Transfer Request
Feature
Null TR
Dummy TR
EMR/QEMR is set
Yes
No
SER/QSER remains set
Yes
No
Link update (STATIC = 0 in OPT)
Yes
Yes
QER is set
Yes
Yes
IPR and CER is set using early completion
Yes
Yes
17.2.3.6 Parameter Set Updates
When a TR is submitted for a given DMA/QDMA channel and its corresponding PaRAM set, the
EDMA3CC is responsible for updating the PaRAM set in anticipation of the next trigger event. For nonfinal
events, this includes address and count updates; for final events, this includes the link update.
The specific PaRAM set entries that are updated depend on the channel’s synchronization type (A-
synchronized or B-synchronized) and the current state of the PaRAM set. A B-update refers to the
decrementing of BCNT in the case of A-synchronized transfers after the submission of successive TRs. A
C-update refers to the decrementing of CCNT in the case of A-synchronized transfers after BCNT TRs for
ACNT byte transfers have submitted. For AB-synchronized transfers, a C-update refers to the
decrementing of CCNT after submission of every transfer request.
See
for details and conditions on the parameter updates. A link update occurs when the
PaRAM set is exhausted, as described in