Dennis Brylow

Static checking of interrupt-driven software

Resource-constrained devices are becoming ubiquitous. Examples include cell phones, Palm Pilots and digital thermostats. It can be difficult to fit the required functionality into such a device without sacrificing the simplicity and clarity of the software. Increasingly complex embedded systems require extensive brute-force testing, making development and maintenance costly. This is particularly true for system components that are written in assembly language. Static checking has the potential of alleviating these problems, but until now there has been little tool support for programming at the assembly level. In this paper, we present the design and implementation of a static checker for interrupt-driven Z86-based software with hard real-time requirements. For six commercial microcontrollers, our checker has produced upper bounds on interrupt latencies and stack sizes, as well as verified fundamental safety and liveness properties. Our approach is based on a known algorithm for the model checking of pushdown systems and produces a control-flow graph annotated with information about time, space, safety and liveness. Each benchmark is approximately 1000 lines of code, and the checking is done in a few seconds on a standard PC. Our tool is one of the first to give an efficient and useful static analysis of assembly code. It enables increased confidence in code correctness, significantly reduced testing requirements and support for maintenance throughout the system life-cycle.

An experimental laboratory environment for teaching embedded operating systems

This paper describes Marquette Universitys efforts to build an experimental embedded systems laboratory for hands-on projects in an operating systems course. Our prototype laboratory is now serving as the basis for a coherent sequence of class projects threaded throughout courses in hardware systems, operating systems, networking, and embedded systems. We describe the major components of our Embedded XINU laboratory environment, the operating systems course, and related improvements in other core courses of our curriculum.

Nexos: a next generation embedded systems laboratory

The Nexos Project is a joint effort at Marquette University (MU) and University of Buffalo (UB) to build curriculum materials and a supporting experimental laboratory for hands-on projects in embedded systems courses. Our approach focuses on inexpensive, flexible, commodity embedded hardware, (the Linksys WRT54GL wireless router,) freely available development and debugging tools, and a fresh implementation of a classic operating system that is now ideal for embedded system exploration. The prototype laboratory environment is being used in multiple courses at our respective Universities, with excellent results. We report on the infrastructure we have developed, the goals and content of our initial course offerings at both schools, and an evaluation of our success thus far.

Computational thinking in high school courses

The number of undergraduates entering computer science has declined in recent years. This is paralleled by a drop in the number of high school students taking the CS AP exam and the number of high schools offering computer science courses. The declines come at a time when career opportunities in CS continue to grow and computer science graduates are seen as crucial in building a globally competitive workforce for the 21st century. Efforts aimed at reversing the declining interest in computer science include curriculum revisions at the undergraduate level at many institutions, a re-design of computer science AP courses [1], and the inclusion of computational thinking into disciplines outside computer science [3]. This panel discusses four projects of computer science researchers collaborating with high school teachers on integrating computing and computational thinking into their courses. The majority of the high school teachers involved is teaching science and math courses. They are teaching a diverse group of talented and college-bound students. The goal of all projects is to integrate computing into disciplines represented in the high school curriculum and to raise the awareness of computer science as an exciting and intellectually rewarding field. This panel will outline recent and on-going activities and interaction with high school teachers. Each panelist will describe how he/she got involved and the nature of the interaction. The panelists will talk about their individual projects, outline their visions for future interactions, and how their effort can be replicated by others. The session will briefly describe NSFs RET program which provided teacher support for three of the four projects. The session will then be opened for discussion; the audience will be encouraged to ask questions and contribute additional ideas for the inclusion of computational thinking in high school courses.

An experimental laboratory environment for teaching embedded hardware systems

This paper describes Marquette Universitys efforts to build an experimental embedded systems laboratory for hands-on projects in an introductory hardware systems course. Our prototype laboratory is now serving as the basis for a coherent sequence of class projects threaded throughout subsequent courses in operating systems, networking, and embedded systems, among others. We describe the major components of our laboratory environment, how it is used in our hardware systems course, and how this has contributed to significant improvements in other core courses in our curriculum.

Xest: an automated framework for regression testing of embedded software

As embedded systems permeate an ever-widening circle of safety- and mission-critical applications, robust testing of embedded software remains of paramount importance. Yet narrow I/O channels, scarce memory and processor resources, real-time and interrupt-driven behavior, and low-level source languages make state-of-the-art validation techniques much more difficult in an embedded context. For students, for whom testing is often already a secondary concern, the challenges in methodical testing of embedded systems can appear insurmountable. We present the Xinu External Suite Tester (XEST) framework, a tool for automated, parallelized regression testing of embedded software kernels running directly on real embedded hardware. We discuss the requirements for such a system, and evaluate its power as both a quality control mechanism in an actively developing system and as an assessment tool for students in conjunction with the Embedded Xinu experimental laboratory.

Deadline analysis of interrupt-driven software

Real-time, reactive, and embedded systems are increasingly used throughout society (e.g., flight control, railway signaling, vehicle management, medical devices, and many others). For real-time, interrupt-driven software, timely interrupt handling is part of correctness. It is vital for software verification in such systems to check that all specified deadlines for interrupt handling are met. Such verification is a daunting task because of the large number of different possible interrupt arrival scenarios. For example, for a Z86-based microcontroller, there can be up to six interrupt sources and each interrupt can arrive during any clock cycle. Verification of such systems has traditionally relied upon lengthy and tedious testing; even under the best of circumstances, testing is likely to cover only a fraction of the state space in interrupt-driven systems. This paper presents the Zilog architecture resource bounding infrastructure (ZARBI), a tool for deadline analysis of interrupt-driven Z86-based software. The main idea is to use static analysis to significantly decrease the required testing effort by automatically identifying and isolating the segments of code that need the most testing. Our tool combines multiresolution static analysis and testing oracles in such a way that only the oracles need to be verified by testing. Each oracle specifies the worst-case execution time from one program point to another, which is then used by the static analysis to improve precision. For six commercial microcontroller systems, our experiments show that a moderate number of testing oracles are sufficient to do precise deadline analysis.

Compiler construction with a dash of concurrency and an embedded twist

We describe the renovation of our compilers curriculum to meld together an established object-oriented textbook compiler with an inexpensive embedded target platform. The result is a modern compiler implementation course with aspects of concurrency and embedded systems, and a palpable increase in student enthusiasm. We discuss the trade-offs in retargeting our compiler, gauge the difficulty of supporting thread-level concurrency in our target language, and outline the resulting structure of the course and integration with the rest of our computer science curriculum.

Hands-on networking labs with embedded routers

We present extensions to the Embedded Xinu educational operating system that, when coupled with a target device like the Cisco-Linksys WRT54GL, provide for an extremely attractive hands-on laboratory platform in network courses. We present classroom and research lab evidence for the usefulness of this platform as a network education tool, and discuss its significance in the context of a wide spectrum of competitor systems. This project is part of a larger effort to bring cost-effective, hands-on embedded system laboratory experiences into systems courses throughout the undergraduate computer science core.

Interactive Real-Time Embedded Systems Education Infused with Applied Internet Telephony

The transition from traditional circuit-switched phone systems to modern packet-based Internet telephony networks demands tools to support Voice over Internet Protocol (VoIP) development. In this paper, we introduce the XinuPhone, an integrated hardware/software approach for educating users about VoIP technology on a real-time embedded platform. We propose modular course topics for design-oriented, hands-on laboratory exercises: filter design, timing, serial communications, interrupts and resource budgeting, network transmission, and system benchmarking. Our open-source software platform encourages development and testing of new CODECs alongside existing standards, unlike similar commercial solutions. Furthermore, the supporting hardware features inexpensive, readily available components designed specifically for educational and research users on a limited budget. The XinuPhone is especially good for experimenting with design trade-offs as well as interactions between real-time software and hardware components.