WEMUCS - Techniques and tools for iterative development and optimization of software for embedded multicore systems

Director:Philippsen, M.
Period:October 15, 2012 - November 30, 2014
Coworker:Kellermann, D.; Oster, N.; Veldema, R.

Multicore processors are of rising importance in embedded systems as these processors offer high performance while maintaining low power consumption. Developing parallel software for these platforms poses new challenges for many industrial sectors because established tools and software libraries are not multicore enabled. The efficient development, optimization and testing of multicore-software is still open research, especially for reliable real-time embedded systems.
In the multi-partner project WEMUCS new methods and tools for efficient iterative development, optimization, and testing of multicore software have been created over the past two years. Innovative tools and technologies for modeling, simulation, visualization, tracing, and testing have been developed and integrated into a single tool chain. Using case studies from different industries (automotive, telecommunications, industry automation) these tools were evaluated and improved.
Although several well-known methods for test case generation and best practice coverage measures for classical single-core applications exist, no such methods for multi-core software have established themselves yet. Unfortunately, it is the interaction of concurrent threads that can cause faults that cannot be discovered by testing the individual threads in isolation. As part of the WEMUCS project (more precisely: work package AP3 ) and based on an industrial size case study, we developed a generic technique (called a "testing pipeline" below) that systematically creates test cases to find and analyze the impact of concurrent side effects.
To evaluate the new testing pipeline (including the automated parallelization of sequential code) on real world examples, our project partner Siemens created a complete model of a large luggage conveyor belt, including the code to control the belt. Such a luggage conveyor can be found at every airport. The case study's model is used to automatically derive luggage conveyor belt systems of different sizes, i.e., built from an arbitrary number of feeder or outlet belts. The hardware of the conveyor belt is emulated on the SIMIT simulation tool from Siemens and the control software (written in the programming language AWL) runs on a software-based PLC.
The first step of the testing pipeline converts the AWL code into a more comprehensible and human-readable programming language called HLL. We have completed this converter during this reporting period. In step two, our tool then transforms previously sequential parts of the AWL code into HLL units that are executed in parallel. When applied to a luggage conveyor belt system built from eight feeders, eight outlets and an inteconnecting circular belt of straight and curved segments, our tool automatically transcoded 11.704 lines of sequential AWL code into 34 KB of parallel HLL code.
In step three another tool developed by the chair then analyzes the HLL code and automatically generates a testing model. This model represents the interprocedural control flow of the concurrent subroutines and also holds all the thread switches that might be relevant for testing. The testing model consists of a set of hierarchically organized UML activities (currently encoded as an XMI document that can be imported into Enterprise Architect by Sparx Systems). When applied to the case study outlined above, our tool automatically generates 103 UML activity diagrams (with 1,302 nodes and 2,581 edges).
Step four is optional. The tester can manually adapt the testing model as needed (e.g. by changing priorities or inserting additional verification points). Then the completed model can be loaded into the MBTsuite tool, a model-based testing tool developed by our project partner sepp.med GmbH. This tool is highly configurable to generate test cases that cover as many parts of the testing model as possible. We ran MBTsuite on a standard PC and applied it to the testing model of our case study; within six minutes MBTSuite generated a highly optimized test set consisting of only 10 test cases that nevertheless cover 99% of the nodes and 78% of the edges.
In cooperation with our project partner sepp.med GmbH we built two export modules for the above-mentioned MBTsuite. One module outputs the generated test cases as a human-readable spreadsheet, the other module outputs an executable test set in the Java language. The exported spreadsheet contains one individual sheet per test case, with one column per thread. The rows visualize the thread interleaving that gets tested. The Java file holds a Java class with a test method per test case. Every method holds a sequence of test steps that discretely control thread interleavings. This way, each test case execution leads to a unique and reproducible execution of the parallel System Under Test (SUT) written in HLL. Each run of a test instructs our HLL emulator to load and initialize the SUT and each subsequent test step instructs the HLL emulator to execute a certain set of instructions from a certain thread. During this fully controlled execution, each test case emits a detailed protocol of its execution for the final visualization step.
A plug-in from sepp.med that creates a visualization layer in Enterprise Architect's UML editor visualizes the resulting log file. Colored nodes and edges tell the user which control flow paths a test has covered. If a test case "fails" (if a race condition or a logic error is found in the tested program), its graphical trace ends at the failing statement. The tester can then follow the control flow back in time in order to understand the underlying reason for the failure.
We have implemented a prototype of the full testing pipeline and demonstrated its applicability to an industrial size case study. This tool is a major contribution to testing concurrent code for embedded systems. It is a contribution of the Programming Systems Group to the ESI initiative .

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