PCI Express System Architecture

Introduction to PCI Express Transactions

PCI Express employs packets to accomplish data transfers between devices. A root complex can communicate with an endpoint. An endpoint can communicate with a root complex. An endpoint can communicate with another endpoint. Communication involves the transmission and reception of packets called Transaction Layer packets (TLPs).

PCI Express transactions can be grouped into four categories:

1) memory, 2) IO, 3) configuration, and 4) message transactions. Memory, IO and configuration transactions are supported in PCI and PCI-X architectures, but the message transaction is new to PCI Express. Transactions are defined as a series of one or more packet transmissions required to complete an information transfer ...