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6–26
Chapter 6: IP Core Interfaces
Avalon-ST TX Interface
Stratix V Hard IP for PCI Express
June 2012
Altera Corporation
Single Packet Per Cycle
In single packer per cycle mode, all received TLPs start at the lower 128-bit boundary
on a 256-bit Avalon-ST interface. Turn on
Enable Multiple Packets per Cycle
on the
System Settings tab of the parameter editor to change multiple packets per cycle.
Single packet per cycle mode requires simpler Application Layer packet decode logic
on the TX and RX paths because packets always start in the lower 128-bits of the
Avalon-ST interface. Although this mode simplifies the Application Layer logic,
failure to use the full 256-bit Avalon-ST may slightly reduce the throughput of a
design.
illustrates the layout of header and data for a three dword header on a
256-bit bus with aligned and unaligned data.
Figure 6–30. 256-Bit Avalon-ST tx_st_data Cycle Definition for 3-Dword Header TLP with Qword Addresses
01
10
clk
tx_st_data[63:0]
Aligned Data
Unaligned Data
tx_st_data[127:64]
tx_st_data[191:128]
tx_st_data[255:192]
tx_st_sop
tx_st_eop
tx_st_empty[1:0]
Header 1 Header 0
XXXXXXXX Header 2
XXXXXXXX Data 0
XXXXXXXXX XXXXXXXX
Header 1 Header 0
Data 0 Header 2
XXXXXXXXX XXXXXXXX
XXXXXXXXX XXXXXXXX