2004-01-1240 An Overview of Hardware-In-the-Loop ... - dSPACE

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object-oriented language with programming syntax andusage very similar to Basic. It has been said that pythoncan speed up development by a factor of 10 over otherprogramming languages, such as C [4]. Pythonprovides all of the control constructs and modularprogramming functionality needed for the developmentand maintenance of complex test sequences. TheControlDesk software has an integrated pythoninterpreter and a function selector tool, to make pythondevelopment as easy as possible for the user. Testscripts can be run directly, or they can also beconnected to events, including GUI events such asCommand buttons. Visteon has been able to programvery complex test sequences and make them functionalin very short periods of time.Test stimulus generationControlDesk also provides mechanisms to assist in thegeneration of test stimuli (data streams) for specific testruns. The test stimulus is generated through python,using a library designed to generate the stimuli. In orderto generate this data in real-time, software and hardwaremechanisms have been built into ControlDesk and thedSPACE hardware, which allows for full fidelity ofstimulus generation, with time based events guaranteedto occur during testing. A sequence generator tool isincluded with ControlDesk, which allows for interactivegraphical user design of test stimuli. The sequencegenerator is based on time tags and specific functiontypes, which can be combined in different manners.There are also control constructs, which allow for easylooping and conditional execution of the data streams.The tool also assists the user by providing a pregenerationof the data, for verification prior to the test,and then it provides the functions to allow the user tomap the data to model variables and execute thestimulus both interactively and within test sequences.Another feature of the Sequence generator is thecapability to playback recorded data streams, capturedduring either simulations or actual test runs. Thiscapability has been used very effectively by Visteon tosimulate drive cycles and control specific testsequences. Any data waveform stored in a predesignedMAT file format can be used for this purpose.The dSPACE hardware and software systems providethe automatic buffering and interpolation processes thatallow for real-time data playback during simulation runs.Using test stimulus to control test execution is anexample of a data-driven system. This has manyadvantages over a model driven system, in that changesin the data streams do not require model changes andprovide greater flexibility in the modeling process. Themodels are simpler to design with less real-timeoverhead, and this also allows for using the samemodels for both offline simulation and real-time testing.Advanced test scripting capabilitiesControlDesk Test Automation provides libraries offunctions for controlling the user interface andControlDesk environment. It also has a MacroRecorder, which gives the user an easy method forcapturing testing sequences performed through the GUI.The Macro Recorder saves these captured sequencesas python scripts, which can then be easily replayed andalso modified to extend and augment their functionality.There are interface libraries for communicationprotocols, such as RS-232 and GPIB, which allow forinterfacing to external devices and systems. Librariesare also provided to allow for report generation and datacapture into several windows COM OLE programs, suchas Word and Excel. Finally, sets of functions areincluded which allow the user to access and controldiagnostic devices and calibration tools, using eitherstandard protocols or the ASAP/MCD standards [3].Future pathPython is an extremely powerful tool and can be used todo every one of the tasks required for test automation.Visteon has had a successful experience with the use oftest automation because of this. The next step in thefuture involves using a new 4GL testing system fromdSPACE, called AutomationDesk, which is based ongraphically designing test sequences. The system is stillbased on python, but it eases the development andmaintenance process by providing a more intuitivegraphical design environment, as opposed to writingcode scripts. It is not a code generator, but insteadgenerates testing process objects from clearly definedtest system classes. AutomationDesk also provides avery powerful test management functionality, whichallows for more robust management of all of the facetsof a test. These include the scripts, models, test data,test results, stimulus and parameter data, etc. [5].FAILURE INSERTION AND CLOSING THE LOOPGeneral overviewIn order to fully test a PCM, the PCM must be connectedto hardware interfaces that simulate the real plantenvironment as closely as possible. The PCM isgenerally designed to test these interfaces for anyfailures, such as short circuits, missing sensors, etc, atwhich time the PCM will store a diagnostic code in itsmemory. A large percentage of the actual code in aproduction PCM is for diagnostics. If one of thesefailures occurs, the PCM software is designed to recoverfrom this failure and ensure the safety of the passengersand the environment. The dSPACE HIL systemprovides a configurable set of relays in a FailureInsertion Unit (FIU), which can be commanded tosimulate these failures. A failure for a PCM input cangenerally be simulated in software and standardhardware. By sending a 0, 5 or vehicle battery voltage
input from simulated sensor different types of sensorfailure can be simulated. To simulate failures for PCMoutputs, however, this involves using electronic relays toprovide open circuits, short circuits to battery voltage orground, or even pin-to-pin short circuits. In addition,PCM outputs generally expect to have a specific loadattached, and failures are triggered if this is not the case.process [6]. This allows for the following standard testsequence:1. Place PCM in desired performance state2. Inject a failure3. Evaluate the PCM performance during the faultcondition4. Debrief the diagnostics tool to determine if the faultwas properly detected5. Reset the fault codes to allow for further testingThe above test sequence is fully repeatable and byusing it, full lights-out testing sequences are possible.All of the diagnostic codes for a PCM may be evaluatedin a single test run (with a combination of sequences)and a complete test report will be automaticallygenerated to record the results. Once this process isimplemented, the daunting task of test regression foriterative software releases is easily contained.BENEFITS – HIL IN EVERY DEVELOPMENTALPHASEFigure 4 Failure Insertion Unit Block DiagramTest scripting interfaceThe control of the FIU system is done using a pythonlibrary in the test automation environment. A PCMoutput channel is wired to a HIL load interface, but first itis routed through a FIU channel (See Figure 4). Thisallows for exposing the channel to the failures neededfor testing. The dSPACE FIU interface is based on aserial communications protocol, which can becommanded directly from the Host PC. Simple functioncalls are used in order to control a particular FIUchannel, which eliminates the need for the user to learnthe details of the FIU serial communication protocol.With our experience during the developmental andimplementation stages of the HIL systems we foundseveral advantages of using HIL systems in testing andvalidating our software product. Although, the initialscope for using the HIL system was limited, we now usethe system in every phase of the PCM softwaredevelopment process. Figure 5 illustrates the SystemEngineering V with the phases of software developmentand highlights how HIL is being used in every stage ofthe software development.Integration of diagnostic tools for closed loop testingIt is sometimes enough to simulate failures duringtesting only for the analysis of the effects on systemperformance. However, in order to fully read systemdiagnostics and also reset the error conditions, it isnecessary to connect a diagnostic tester/device. Thisdevice is used to debrief the error codes registered inthe PCM following any diagnostic error and report thesecodes back to the tester. The python test automationlibraries also include functions to interface to and controlthese diagnostic devices. These testers generally use astandard serial or CAN-based protocol for interfacing tothe PCM. Others utilize the ASAM/MCD standard forexternal operation of the device. By providing thecapabilities for controlling these diagnostic tools,ControlDesk can fully close the loop on the testingFigure 5 HIL used in every step of developmentcycle.Broadly, the HIL applications for PCM testing in thedesign phase can be classified as Open Loop Testing(OLT) and Closed-Loop Testing (CLT). In the OLT a
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