EuroSim Hardware Interfaces During Simulation

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EuroSim Hardware Interfaces During Simulation
For projects which are in later phases of development, there is often a need to combine pure simulation with real equipment or breadboards. This could be necessary for testing onboard software running on a separate platform; or maybe experimenting with an engineering model.

Alternatively, it may be desirable to interface to another simulation facility which offers dedicated support in a specialised area.

EuroSim offers all of the above possibilities, by providing a set of standardised interfaces so that communication is possible with other equipment or simulators at runtime. The various possibilities are described below.

Interfacing External Devices to EuroSim
Support for the following interfaces/protocols is available: serial, VME, TCP/IP, MIL1553B and GPIB. All of these allow equipments to be included as input and/or outputs within the simulation processes: so-called hardware-in-the-loop simulations.

To maintain the real-time performance of the simulator, any calls to these interfaces from EuroSim models need to use the provided library calls which are based on standard Unix communication calls.

Synchronising Another Simulator with EuroSim
By default, EuroSim uses the SGI internal clock (itimer) to synchronise the scheduling. However, if an interface to another simulator is required, the synchronisation of the two sets of simulation activities is an important factor.

Various options are available through the use of the external interrupt device driver (available on SGI Challenge/Onyx platforms):

EuroSim tasks can generate output interrupts to one of the external interrupt drivers (which can be used to generate pulses to synch the other simulator)
EuroSim tasks can be triggered on receipt of an incoming interrupt
a user defined handler can be installed for incoming interrupts
input interrupts can be used as the (external) realtime clock of the EuroSim scheduler, instead of the default itimer mechanism

Exchanging Data/Events Asynchronously With Another Simulator
A library is also provided to allow another simulator (acting as an external client) to connect to a Eurosim simulator across a TCP/IP interface and to establish a loose (asynchronous) coupling between the two simulations. From the moment that the two simulations are coupled, the client will receive the state changes of the EuroSim simulator, and has read/write access to (a subset of) the EuroSim data dictionary.

The data access is implemented through creating a 'view' of the data dictionary, which can be the complete set of model data items, or a subset chosen according to the local simulation needs. A 'view' is a local copy of the required data variables, which is then updated at regular intervals across the network. The client can specify the update frequency and if the data is to be compressed (sending updated values).