5–6
Chapter 5: IP Core Architecture
Transaction Layer
Arria V GZ Hard IP for PCI Express
November 2012
Altera Corporation
Tracing a transaction through the TX datapath involves the following steps:
1. The Transaction Layer informs the Application Layer that sufficient flow control
credits exist for a particular type of transaction using the TX credit signals. The
Application Layer may choose to ignore this information.
2. The Application Layer requests permission to transmit a TLP. The Application
Layer must provide the transaction and must be prepared to provide the entire
data payload in consecutive cycles.
3. The Transaction Layer verifies that sufficient flow control credits exist and
acknowledges or postpones the request.
4. The Transaction Layer forwards the TLP to the Data Link Layer.
Figure 5–3. Architecture of the Transaction Layer: Dedicated Receive Buffer
Transaction Layer TX Datapath
Transaction Layer RX Datapath
Avalon-ST
RX Control
Configuration Space
TLPs to
Data Link Layer
RX Transaction
Layer Packet
Avalon-ST RX Data
Avalon-ST
TX Data
to Application Layer
ConfigurationRequests
Reordering
RX Buffer
Posted & Completion
Non-Posted
Flow Control Update
Transaction Layer
Packet FIFO
Width
Adapter
( <256
bits)
Packet
Alignment
TX
Control
RX
Control
TX Flow
Control