Altera Arria V Avalon-ST - Manual (Page 142)

• ACK/NAK Packets—The ACK/NAK block handles ACK/NAK DLLPs and generates the sequence
number of transmitted packets.
• Transaction Layer Packet Checker—This block checks the integrity of the received TLP and generates
a request for transmission of an ACK/NAK DLLP.
• TX Arbitration—This block arbitrates transactions, prioritizing in the following order:
• Initialize FC Data Link Layer packet
• ACK/NAK DLLP (high priority)
• Update FC DLLP (high priority)
• PM DLLP
• Retry buffer TLP
• TLP
• Update FC DLLP (low priority)
• ACK/NAK FC DLLP (low priority)
Physical Layer
The Physical Layer is the lowest level of the PCI Express protocol stack. It is the layer closest to the serial
link. It encodes and transmits packets across a link and accepts and decodes received packets. The
Physical Layer connects to the link through a high-speed SERDES interface running at 2.5 Gbps for Gen1
implementations and a5 2.5 or 5.0 Gbps for Gen2 implementations.
The Physical Layer is responsible for the following actions:
• Initializing the link
• Scrambling/descrambling and 8B/10B encoding/decoding for 2.5 Gbps (Gen1) and 5.0 Gbps (Gen2)
per lane
• Serializing and deserializing data
• Operating the PIPE 3.0 Interface
• Implementing auto speed negotiation (Gen2 and Gen3)
• Transmitting and decoding the training sequence
• Providing hardware autonomous speed control
• Implementing auto lane reversal
2014.12.15
Physical Layer 9-9
IP Core Architecture Altera Corporation
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