Ethernet Variable Exchange

Ethernet Variable Exchange (ETH VE) is a simple protocol based on TCP/UDP for exchanging data over the Ethernet.

The TCP/UDP utilizes Lightweight IP (lwIP) library provided by Xilinx.

The protocol runs as a bare-metal application and deterministic execution rate is guaranteed.

ETH VE Setup

ETH VE Setup component and dialog window are shown in the table below.

Table 1. ETH VE Setup

Component	Component dialog	Component properties
ETH VE Setup		Override HIL device ID IP Address #N Subnet mask

Component properties are described in the table below.

If Ethernet Variable Exchange protocol is used, exactly one ETH VE Setup comonent must exist in the model. Through this component, configuration for all HIL devices are specified. If multiple HIL devices are specified in the model by using Device/Signal markers, IP address # property will be created automaticaly for each HIL.

ETH VE Send

ETH VE Send component is presented in the table below. This block lets you alter basic settings for the send socket. In this case, the HIL device will be the client in a client-server application.

ETH VE Send represents a client. The client tries to connect to the remote server specified with Destination IP address and Destination Port after simulation starts. If the server is accessible, an active connection is open, system variables are packed, and transferred over Ethernet. In a case of remote server failure, the client will continue trying to reconnect.

Table 3. ETH VE Send

Component	Component dialog	Component propert
ETH VE Send		General Sample time Execution rate Network Protocol Specify local send port Local send port Destination IP address Destination port Data Configuration

Component properties are listed in the table below.

Configuration parameters

To change the Configuration property, use Generate configuration button in the Data tab.

In the configuration menu, one can define custom payload of the data sent over Ethernet.

In the table below there is an overview of the Configuration menu.

ETH VE Receive

ETH VE Receive component is presented in the table below. This component enables you to perform basic settings for the receive socket. For ETH VE Receive, the HIL device will represent a server in a client-server application. In the schematic model can be more then one ETH VE Receive component, with at least different receive port.

ETH VE Receive represents server with a passive opened connection. It waits for any client to try to connect. Server can be configured to accept an incoming connection from any client IP and port (deactivated Specify source port and Specify source IP address respectively), or to accept only from specified IP and specified Port. After the connection has been accepted, the server starts receiving packets, parses them, and dispatches data to the target component.

Table 6. ETH VE Receive

Component	Component dialog	Component properties
ETH VE Receive		General Execution rate Network Protocol Local receive port Specify source port Source port Specify source IP address Source IP address Data Configuration

Component properties are listed in the table below.

Configuration parameters

To change the Configuration property, use Generate configuration button in the Data sub menu.

In the configuration menu, one can define custom payload of the data received over the Ethernet.

In the table below there is an overview of the Configuration menu.

Connection Establishment

To establish a connection, TCP uses a three-way handshake. Before a client attempts to connect with a server, the server must first bind to a port and listen for incoming connections - this is called a passive open. Once the passive open is established, a client may initiate an active open. To establish a connection, this three-way (or 3-step) handshake occurs in the following order:

1. SYN: The active open is performed by the client sending a SYN to the server. The client sets the segment's sequence number to a random value A.
2. SYN-ACK: In response, the server replies with a SYN-ACK. The acknowledgment number is set to one more than the received sequence number i.e. A+1. The sequence number that the server chooses for the packet is another random number, B.
3. ACK: Finally, the client sends an ACK back to the server. The sequence number is set to the received acknowledgement value i.e. A+1, and the acknowledgement number is set to one more than the received sequence number i.e. B+1.

At this point, both the client and server have received an acknowledgment of the connection. The steps 1, 2 establish the connection parameter (sequence number) for one direction and it is acknowledged. The steps 2, 3 establish the connection parameter (sequence number) for the other direction and it is acknowledged. This way, a full-duplex communication is established (Transmission Control Protocol).

Ethernet packet

Size of payload data depends on the size of the input signal of ETH VE Send component. The structure of the ETH VE payload data is shown on the figure below.

Network setup

To establish the communication between HIL device and a PC the following must be satisfied:

Virtual HIL support

Virtual HIL currently does not support this protocol. When using a Virtual HIL environment (e.g. when running the model on a local computer), inputs to this component will be discarded and outputs from this component will be zeroed.