Introduction to Network-on-Chip Design - Microarchitecture of Network-on-Chip Routers - page 6

Write Data

flow control

Write Adr/Cmd

flow control

Write Response
flow control

Read Data
flow control

Read Adr/Cmd
flow control

Fig. 1.4 An example of master and slave interfaces as needed by the AXI transaction protocol

1.4 Transactions on the Network: The Transport Layer

Directly supporting all the interfaces of the transaction layer in all links of the
system is an overkill that requires an enormous number of wiring resources.
Following the encapsulation principle followed by any network, the required
interfaces can be substituted by transport layer interfaces that exchange packets
of information that include in their headers the information delivered by each
encapsulated interface (Mathewson 2010 ). Each packet can be either a read or
a write packet consisting of a header word and some payload words.The packet
header encodes the read/write address of the transaction and all other transaction
parameters and control signals included in the original transaction-layer interface.
Also, the header signal should include the necessary identification information that
would guide the packet to its appropriate destination.

1.4.1 Network Interfaces

Interfacing between the transport and the transaction layer of communication is
done at the network interfaces (NIs), located at the NoC periphery. The NI is respon-
sible for both sending packets to the network as well as receiving packets from the
network and after the appropriate manipulation to present it to the connected IP core
according to the semantics of the transaction-layer interface (Saponara et al. 2014 ).