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Figure 28: Composition of the AXI4-Stream Packet for UR and CA Completions
7
0
1
2
3
4
5
6
7
+4
0
1
2
3
4
5
6
7
+5
0
1
2
3
4
5
6
7
+6
0
1
2
3
4
5
6
7
+7
DW 3
32
first_be
63
R
DW 0
DW 1
Completion Descriptor DW 1
Completion Descriptor DW 0
DW 2
Completion Descriptor DW 2
DW 4
DW 5
DW
DW 7
last_ be
R
Request Descriptor, DW 3
Request Descriptor, DW 2
Request Descriptor, DW 1
Request Descriptor, DW 0
X24889-120620
Straddle Option on CC Interface
The core has the capability to start the transfer of a new Completion packet on the completer
completion interface in the same beat when the previous request has ended on or before Dword
position 7 on the data bus. This straddle option is enabled during core customization in the
Vivado
®
IDE. The straddle option can be used only with the Dword-aligned mode.
When the straddle option is enabled, Completion TLPs are transferred on the AXI4-Stream
interface as a continuous stream, with no packet boundaries. Thus, the signals
m_axis_cc_tkeep
and
m_axis_cc_tlast
are not useful in determining the boundaries of
TLPs delivered on the interface. Instead, delineation of TLPs is performed using the following
signals provided within the
m_axis_cc_tuser
bus.
•
is_sop[0]
: This input must be set High in a beat when there is at least one Completion TLP
starting in the beat. The position of the first byte of the descriptor of this TLP is determined as
follows:
○
If the previous TLP ended before this beat, the first byte of the descriptor is in byte lane 0.
○
If a previous TLP is continuing in this beat, the first byte of this descriptor is in byte lane
32. This is possible only when the previous TLP ends in the current beat, that is when
is_eop[0]
is also set.
•
is_sop0_ptr[:0]
: When
is_sop[0]
is set, this field must indicate the offset of the first
Completion TLP starting in the current beat. Valid settings are
2'b00
(TLP starting at Dword
0) and
2'b10
(TLP starting at Dword 8).
Chapter 4: Designing with the Core
PG346 (v3.3) November 16, 2022
CPM Mode for PCI Express
151