Common Packet Header Fields

All Transaction Layer Packet (TLP) prefixes and headers contain the following fields (see
Figure 2-4):
􀂉 Fmt[2:0] – Format of TLP (see Table 2-2) – bits 7:5 of byte 0
􀂉 Type[4:0] – Type of TLP – bits 4:0 of byte 0
A-0784
Byte 0 > Fmt Type {Fields in bytes 1 through 3 depend on Fmt and Type Fields
+0 +1 +2 +3
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
Figure 2-4: Fields Present in All TLPs
The Fmt field(s) indicate the presence of one or more TLP Prefixes and the Type field(s) indicates
the associated TLP Prefix type(s).
The Fmt and Type fields of the TLP Header provide the information required to determine the size
of the remaining part of the TLP Header, and if the packet contains a data payload following the
header.
The Fmt, Type, TD, and Length fields of the TLP Header contain all information necessary to
determine the overall size of the non-prefix portion of the TLP. The Type field, in addition to
defining the type of the TLP also determines how the TLP is routed by a Switch. Different types of
TLPs are discussed in more detail in the following sections.
􀂉 Permitted Fmt[2:0] and Type[4:0] field values are shown in Table 2-3.
• All other encodings are reserved (see Section 2.3).
􀂉 TC[2:0] – Traffic Class (see Section 2.4.2) – bits [6:4] of byte 1
􀂉 TH – 1b indicates the presence of TLP Processing Hints (TPH) in the TLP header and optional
TPH TLP Prefix (if present) – bit 0 of byte 1 (see Section 2.2.7.1)
􀂉 Attr[1:0] – Attributes (see Section 2.2.6.3) – bits [5:4] of byte 2
􀂉 Attr[2] – Attribute (see Section 2.2.6.3) – bit 2 of byte 1
􀂉 TD – 1b indicates presence of TLP digest in the form of a single DW at the end of the TLP (see Section 2.2.3) – bit 7 of byte 2
􀂉 EP – indicates the TLP is poisoned (see Section 2.7) – bit 6 of byte 2
􀂉 Length[9:0] – Length of data payload in DW (see Table 2-4) – bits 1:0 of byte 2 concatenated
with bits 7:0 of byte 3
• TLP data must be 4-byte naturally aligned and in increments of 4-byte Double Words (DW).
• Reserved for TLPs that do not contain or refer to data payloads, including Cpl, CplLk, and
Messages (except as specified)
OM14540B
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
Attr TD
EP
Type R TC AT Length
+0 +1 +2 +3
Byte 0 > TH
Fmt R R
Figure 2-5: Fields Present in All TLP Headers
Table 2-2: Fmt[1:0] Field Values
Fmt[1:0] Corresponding TLP Format
000b 3 DW header, no data
001b 4 DW header, no data
010b 3 DW header, with data
011b 4 DW header, with data
100b TLP Prefix
All encodings not shown above are
reserved (see Section 2.3).
Table 2-3: Fmt[1:0] and Type[4:0] Field Encodings
TLP Type Fmt
[2:0]2
(b)
Type
[4:0]
(b)
Description
MRd 000
001
0 0000 Memory Read Request
MRdLk 000
001
0 0001 Memory Read Request-Locked
MWr 010
011
0 0000 Memory Write Request
IORd 000 0 0010 I/O Read Request
IOWr 010 0 0010 I/O Write Request
CfgRd0 000 0 0100 Configuration Read Type 0
CfgWr0 010 0 0100 Configuration Write Type 0
CfgRd1 000 0 0101 Configuration Read Type 1
CfgWr1 010 0 0101 Configuration Write Type 1
TCfgRd 000 1 1011 Deprecated TLP Type3
TCfgWr 010 1 1011 Deprecated TLP Type3
Msg 001
1 0r2r1r0 Message Request – The sub-field r[2:0]
specifies the Message routing mechanism
(see Table 2-18).
MsgD 011
1 0r2r1r0 Message Request with data payload – The
sub-field r[2:0] specifies the Message
routing mechanism (see Table 2-18).
Cpl 000 0 1010 Completion without Data – Used for I/O and
Configuration Write Completions with any
Completion Status. Also used for AtomicOp
Completions and Read Completions (I/O,
Configuration, or Memory) with Completion
Status other than Successful Completion.
CplD 010 0 1010 Completion with Data – Used for Memory,
I/O, and Configuration Read Completions.
Also used for AtomicOp Completions.
CplLk 000 0 1011 Completion for Locked Memory Read
without Data – Used only in error case.
CplDLk 010 0 1011 Completion for Locked Memory Read –
otherwise like CplD.
2 Requests with two Fmt[2:0] values shown can use either 32 bits (the first value) or 64 bits (the second value)
Addressing Packet formats.
3 Deprecated TLP Types: previously used for TCS, which is no longer supported by this specification. If a Receiver
does not implement TCS, the Receiver must treat such Requests as Malformed Packets.
TLP Type Fmt
[2:0]2
(b)
Type
[4:0]
(b)
Description
FetchAdd 010
011
0 1100 Fetch and Add AtomicOp Request
Swap 010
011
0 1101 Unconditional Swap AtomicOp Request
CAS 010
011
0 1110 Compare and Swap AtomicOp Request
LPrfx 100 0L3L2L1L0 Local TLP Prefix – The sub-field L[3:0]
specifies the Local TLP Prefix type (see
Table 2-29).
EPrfx 100 1E3E2E1E0 End-End TLP Prefix – The sub-field E[3:0]
specifies the End-End TLP Prefix type (see
Table 2-30).
All encodings not shown above are
reserved (see Section 2.3).
Table 2-4: Length[9:0] Field Encoding
Length[9:0] Corresponding TLP Data Payload Size
00 0000 0001b 1 DW
00 0000 0010b 2 DW
... ...
11 1111 1111b 1023 DW
00 0000 0000b 1024 DW