PCI Express System Architecture

Flow Control Initialization

Prior to sending any transactions, flow control initialization must be performed. Initialization occurs for each link in the system and involves a handshake between the devices attached to the same link. TLPs associated with the virtual channel being initialized cannot be forwarded across the link until Flow Control Initialization is performed successfully.

Once initiated, the flow control initialization procedure is fundamentally the same for all Virtual Channels. The small differences that exist are discussed later. Initialization of VC0 (default VC) must be done in hardware so that configuration transactions can traverse the PCI Express fabric. Other VCs initialize once configuration software has set up and enabled ...