Each line of an EDG specification describes the format or type of the data, and also the mechanism used to relay that data to or from a host system attached to the system under test. EDG generates source code to produce and consume test signals in real-time. MetaH specifications that compose these source modules into real-time processes are also generated, where these processes have input or output ports that receive or send the test signals. Each process also has an output event that is raised when the end of the test signal is reached. The following diagrams show the MetaH interfaces for the processes used to generate the input signal (on the left) and collect the output signal (on the right) for the missile example.
In this example, the input data is included as part of the device_25MS source code and is down-loaded with the image. Output data is collected in a shared data area. This shared data area appears in the interface for the device_2S process above, and the device_2S process stores the test samples into this data area as they are received. A third process is used to upload the collected data at the conclusion of the run. This third process, called acmd_guide in this example, encapsulates the hardware-dependent I/O code.
This configuration does not allow input signals to be passed from the host to the target in real-time during the test, and does not make output signals available until the conclusion of the test. Alternative configurations can also be used that feed input and output data to and from the system under test in real-time.
The overall MetaH application specification shows how these pieces are combined with all the others to form a complete executable system.