2.3.3 Null PaRAM Set
2.3.4 Dummy PaRAM Set
2.3.5 Dummy Versus Null Transfer Comparison
2.3.6 Parameter Set Updates
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Parameter RAM (PaRAM)
You should make sure to program the LINK field correctly, so that link update is requested from a PaRAM
address that falls in the range of the available PaRAM addresses on the device.
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.
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,
EMRH, or QEMR). This bit remains set in the associated secondary event register (SER, SERH, 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, SERH, 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.
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, EMRH, or
QEMR) and the secondary event register (SER, SERH, 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.
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 2-3. Dummy and Null Transfer Request
Feature
Null TR
Dummy TR
EMR/EMRH/QEMR is set
Yes
No
SER/SERH/QSER remains set
Yes
No
Link update (STATIC = 0 in OPT)
Yes
Yes
QER is set
Yes
Yes
IPR/IPRH CER/CERH is set using early completion
Yes
Yes
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.
SPRUG34 – November 2008
EDMA3 Architecture
33
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