Altera Arria V Avalon-ST - Manual (Page 138)

Transaction Layer
The Transaction Layer is located between the Application Layer and the Data Link Layer. It generates and
receives Transaction Layer Packets. The following illustrates the Transaction Layer. The Transaction
Layer includes three sub-blocks: the TX datapath, Configuration Space, and RX datapath.
Tracing a transaction through the RX datapath includes the following steps:
1. The Transaction Layer receives a TLP from the Data Link Layer.
2. The Configuration Space determines whether the TLP is well formed and directs the packet based on
traffic class (TC).
3. TLPs are stored in a specific part of the RX buffer depending on the type of transaction (posted, non-
posted, and completion).
4. The TLP FIFO block stores the address of the buffered TLP.
5. The receive reordering block reorders the queue of TLPs as needed, fetches the address of the highest
priority TLP from the TLP FIFO block, and initiates the transfer of the TLP to the Application Layer.
6. When ECRC generation and forwarding are enabled, the Transaction Layer forwards the ECRC dword
to the Application Layer.
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.
2014.12.15
Transaction Layer 9-5
IP Core Architecture Altera Corporation
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