Rest-bus Simulation is a technique that can be employed when testing devices on communication networks where the ‘rest of the bus’ is simulated in order to facilitate testing the controller in question.
Rest-bus simulation usually entails simulating more than one ECU (electronic control unit) bus connection or node. Sometimes an entire network’s ECUs need to be simulated to represent the communications bus load and provide the appropriate signals to test the ECUs’ functionality.
Model-based design advantages
Using model-based design in your overall design offers many advantages when using rest-bus simulation. The model of each ECU’s functionality can be taken and reused to perform those functions, then deployed on a hardware-in-the-loop test system to create closely representative bus traffic without the need for actual ECUs.
Rest-bus simulation can save considerable amounts of program time by enabling testing of one or more components earlier than would be possible using final system test. Finding functional issues early within a system design allows for software and even hardware re-iterations, without impacting on overall program times.
Advantages of simplification
It is not always necessary to simulate the communications bus precisely to still offer significant advantages as a test methodology. Some ECUs or bus nodes will not contribute directly to the functional behaviour of the ECU being tested. To test this ECU therefore, assumptions may be made about other nodes less relevant to the functionality being tested; for example by broadcasting invariant or approximated data without simulating a sub-system that is not relevant to the functions being tested.
Simulating the bus traffic is still worthwhile however, as it tests for incorrectly programmed message filtering and more realistic bus-loading.
Another use for rest-bus simulation is to support essential services normally required for even the most basic testing operation, such as security services configuration and heartbeat messages, without the need for those controllers being present within the test system.
A tool for suppliers
Even if you are not an OEM, the benefit of these improved testing methods, simplified testing and easily supported essential services make rest-bus simulation a powerful tool to the ECU designer and manufacturer.
Depending on the level of precision required for the system and bus simulation, a wide range of test hardware can support rest-bus simulation; from enhanced gateway controllers through to powerful hardware-in-the-loop target hardware. An example of hardware that can assist is MICROGen.
Enhanced communications gateways
Communications gateways are related to rest-bus simulators in many ways, as they provide all the communications data required by a particular ECU by passing the system bus through to the ECU being tested, modifying or simulating functionality which may be missing from the main bus where required.
A logical step on from this is to simulate the incoming bus further or to provide an entire rest-bus simulation set-up.