PCI Express System Architecture

Operation of the Flow Control Model - An Example

The purpose of this example is to explain the operation of the Flow Control mechanism based on the conceptual model presented by the specification. The example uses the non-posted header Flow Control buffer type, and spans four stages to capture the nuances of the flow control implementation:

Stage One — Immediately following initialization, the several transactions are tracked to explain the basic operation of the counters and registers as they track transactions as they are sent across the link. In this stage, data is accumulating within the Flow Control buffer, but no transactions are being removed.

Stage Two — If the transmitter sends non-posted transactions at a rate such that the Flow Control ...