Altera IP Compiler for PCI Express - Manual (Page 103)

Chapter 5: IP Core Interfaces 5–17
Avalon-ST Interface
August 2014 Altera Corporation IP Compiler for PCI Express User Guide
tx_cred<n> (3) (4) (5) (6) 36 O
component
specific
This vector contains the available header and data credits
for each type of TLP (completion, non-posted, and
posted). Each data credit is 4 dwords or 16 bytes as per
the PCI Express Base Specification. Use of the signal is
optional.
If more TX credits are available than the tx_cred bus can
display, tx_cred shows the maximum number given the
number of bits available for that particular TLP type.
tx_cred
is a saturating bus and for a given TLP type, it
does not change until enough credits have been
consumed to fall within the range tx_cred can display.
Refer to Figure 5–16 for the layout of fields in this signal.
For information about how to use the tx_cred signal to
optimize flow control, refer to
“TX Datapath” on
page 4–6 .
Component Specific Signals for Arria II GX, Arria II GZ, and Stratix IV Devices
nph_alloc_1cred_vc0 (5) (6) 1 O
component
specific
Used in conjunction with the optional tx_cred<n>
signal. When 1, indicates that the non-posted header
credit limit was initialized to only 1 credit. This signal is
asserted after FC Initialization and remains asserted until
the link is reinitialized.
npd_alloc_1cred_vc0 (5) (6) 1 O
component
specific
Used in conjunction with the optional tx_cred<n>
signal. When 1, indicates that the non-posted data credit
limit was initialized to only 1 credit. This signal is
asserted after FC Initialization and remains asserted until
the link is reinitialized.
npd_cred_vio_vc0 (5) (6) 1 O
component
specific
Used in conjunction with the optional tx_cred<n>
signal. When 1, means that the non-posted data credit
field is no longer valid so that more credits were
consumed than the tx_cred signal advertised. Once a
violation is detected, this signal remains high until the IP
core is reset.
nph_cred_vio_vc0 (5) (6) 1 O
component
specific
Used in conjunction with the optional tx_cred<n>
signal. When 1, means that the non-posted header credit
field is no longer valid. This indicates that more credits
were consumed than the tx_cred signal advertised.
Once a violation is detected, this signal remains high until
the IP core is reset.
Notes to Table 5–4 :
(1) For all signals, <n> is the virtual channel number, which can be 0 or 1.
(2) To be Avalon-ST compliant, you must use a readyLatency of 1 or 2 for hard IP implementation, and a readyLatency of 1 or 2 or 3 for the
soft IP implementation. To facilitate timing closure, Altera recommends that you register both the tx_st_ready and tx_st_valid signals. If
no other delays are added to the ready-valid latency, this corresponds to a readyLatency of 2.
(3) For the completion header, posted header, non-posted header, and non-posted data fields, a value of 7 indicates 7 or more available
credits.
(4) These signals only apply to hard IP implementations in Arria II GX and Stratix IV GX devices.
(5) In Stratix IV and Arria II GX hard IP implementations, the non-posted TLP credit field is valid for systems that support more than 1 NP credit.
In systems that allocate only 1 NP credit, the receipt of completions should be used to detect the credit release.
(6) These signals apply only to hard IP implementations in Arria II GX and Stratix IV devices.
Table 5–4. 64- or 128-Bit Avalon-ST TX Datapath (Part 3 of 3)
Signal Width Dir
Avalon-ST
Type
Description