
IDT DMA Controller
PES32NT24xG2 User Manual
15 - 13
January 30, 2013
Notes
pletions to memory write requests on the fly. As a result, the memory writes issued by the
DMA may not arrive at the destination location in the order in which the read requests
were issued. A user that wishes to keep a strict order between the order in which the
bytes are read and written, may do so by programming the descriptor such that the
address/length combination does not cross 4KB boundaries, and ensuring that the Byte
Count (BCOUNT) field is less than or equal to the Maximum Read Request Size (MRRS)
field. Alternatively, the DMA channel may configured for one outstanding request, as
described in section DMA Outstanding Requests on page 15-21.
Immediate Data Transfer Descriptor
An immediate data transfer descriptor is used to instruct the DMA channel to transfer data that is
embedded in the descriptor to a destination device (i.e., there is no source device associated with the DMA
transfer).
The format of an immediate data transfer descriptor is shown in Figure 15.10 and the fields are
described in Table 15.6. Following the PCI convention, the format is shown in little-endian.
Figure 15.10 Immediate Data Transfer DMA Descriptor Format
Field
DWord
Bit
Position
Description
LST
0
4
Last. When this bit is set, it indicates that this descriptor is the
last descriptor in the list. Setting this bit is equivalent to setting
the next descriptor address fields (NEXTL and NEXTU) to zero.
Refer to section DMA Descriptor Processing on page 15-15 for
details.
DTC
0
10:8
Destination Traffic Class. This field specifies the traffic class
used by destination TLPs.
DRO
0
11
Destination Relaxed Ordering. This field specifies the state of
the relaxed ordering attribute in destination TLPs.
DNS
0
12
Destination No Snoop. This field specifies the state of the no
snoop attribute in destination TLPs.
Table 15.6 Immediate Data Transfer DMA Descriptor Fields (Part 1 of 2)
DATAL
DATAU
DADDRL
DADDRU
NEXTL
NEXTU
Reserved
31
DSTS
I
O
F
D
N
S
D
R
O
DTC
24 23
16 15
8
7
0
DTYPE
0
1
2
3
4
5
6
7
0
L
S
T
BCOUNT
0
0
Содержание PCI Express 89HPES32NT24xG2
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