6–20
Chapter 6: IP Core Interfaces
Avalon-ST TX Interface
Arria V GZ Hard IP for PCI Express
November 2012
Altera Corporation
Avalon-ST Packets to PCI Express TLPs
The following figures illustrate the mappings between Avalon-ST packets and PCI
Express TLPs. These mappings apply to all types of TLPs, including posted,
non-posted, and completion TLPs. Message TLPs use the mappings shown for four
dword headers. TLP data is always address-aligned on the Avalon-ST interface
whether or not the lower dwords of the header contains a valid address, as may be the
case with TLP type (message request with data payload).
f
For additional information about TLP packet headers, refer to
Transaction Layer Packet (TLP) Header Formats
and
Section 2.2.1 Common Packet
Header Fields
PCI Express Base Specification 2.1
tx_cred_fc_infinite
6
O
component
specific
When asserted, indicates that the corresponding credit type has
infinite credits available and does not need to calculate credit
limits. The 6 bits of this vector correspond to the following 6
types of credit types:
■
[5]: posted headers
■
[4]: posted data
■
[3]: non-posted header
■
[2]: non-posted data
■
[1]: completion header
■
[0]: completion data
tx_cred_hdrfccp
8
O
component
specific
Header credit limit for the FC completions. Each credit is 20
bytes.
tx_cred_hdrfcnp
8
O
component
specific
Header limit for the non-posted requests. Each credit is 20 bytes.
tx_cred_hdrfcp
8
O
component
specific
Header credit limit for the FC posted writes. Each credit is 20
bytes.
ko_cpl_spc_header
8
O
component
specific
The Application Layer can use this signal to build circuitry to
prevent RX buffer overflow for completion headers. Endpoints
must advertise infinite space for completion headers; however,
RX buffer space is finite.
ko_cpl_spc_header
is a static signal
that indicates the total number of completion headers that can be
stored in the RX buffer.
ko_cpl_spc_data
12
O
component
specific
The Application Layer can use this signal to build circuitry to
prevent RX buffer overflow for completion data. Endpoints must
advertise infinite space for completion data; however, RX buffer
space is finite.
ko_cpl_spc_data
is a static signal that reflects
the total number of 16 byte completion data units that can be
stored in the completion RX buffer.
Note to
(1) To be Avalon-ST compliant, your Application Layer must have a
readyLatency
of 1 or 2 cycles.
Table 6–5. 64-, 128-, or 256-Bit Avalon-ST TX Datapath (Part 4 of 4)
Signal
Width
Dir
Avalon-ST
Type
Description