PCI Express System Architecture

Transaction Layer Packets

In PCI Express terminology, high-level transactions originate at the device core of the transmitting device and terminate at the core of the receiving device. The Transaction Layer is the starting point in the assembly of outbound Transaction Layer Packets (TLPs), and the end point for disassembly of inbound TLPs at the receiver. Along the way, the Data Link Layer and Physical Layer of each device contribute to the packet assembly and disassembly as described below.

TLPs Are Assembled And Disassembled

Figure 4-2 on page 158 depicts the general flow of TLP assembly at the transmit side of a link and disassembly at the receiver. The key stages in Transaction Layer Packet protocol are listed below. The numbers correspond ...