Adjunct Facluty, Dept. of Electrical and Computer Engineering
Real-Time Embedded Systems Research Page
IEEE RTSS 2000 WIP Paper - Multi-Epoch Scheduling (PDF)
IEEE RTAS 1997 WIP Paper - RT EPA Mixed Hard/Soft Admission, Control, and Monitoring (PDF)
Committee:
Gary Nutt, Chair (CS) Ken Anderson (CS) Elizabeth Bradley (EE/CS) Elaine Hansen (Space Grant College) Ren Su (EE)
Exam: July 3rd, 9:00 AM, Room 831, Eng. Center
Demo Sessions: Available Upon Request in CU Simlab (ECME 269)
Original Proposal Accepted by Committee
The use of microprocessors and software to build real-time applications is expanding from traditional domains such as digital control, data acquisition, robotics, and digital switching, to include emerging domains like multimedia, virtual reality, optical navigation, and audio processing. These emerging real-time application domains require much more bandwidth and processing capability than the traditional real-time systems applications. Furthermore, at the same time, the potential performance and complexity of microprocessor and I/O architectures is also rapidly evolving to meet these new application demands (e.g. a super-scalar, pipelined architecture with multilevel cache with burst transmission I/O bus). Finally, the complexity of typical real-time system algorithms is increasing given functions such as image processing, rule-based fault protection, and intelligent sensor processing. The foundation of real-time systems theory is the recognition that bandwidth and processing resources will always be constrained (a more demanding application always exists that can make use of increased resources as they become available). Given this reality, the question is how does an engineer formally ensure, given resource constraints, that the system will not only function correctly, but function correctly and meet timing deadlines. Since the introduction of Liu and Layland's rate-monotonic analysis and the development of the formal theory of hard real-time systems, significant progress has been made on extending this theory and developing an engineering process for it. The problem is that the current hard real-time theory and process assumes full reliability and overly constrains systems by requiring either deterministic use of resources or worst-case models of such usage. Real-time systems engineering requires translation of requirements into a system meeting cost, performance, and reliability objectives. If deadline performance was the only consideration in the engineering process, and there were no cost or reliability requirements, then current hard real-time theory is mostly sufficient. In reality though, it is clear that cost and reliability must be considered, especially since emerging application domains may be more cost and reliability sensitive than traditional hard real-time domains. Typically a direct trade can be made between cost and reliability for a given performance level.
There are three main problems that exist with application of current hard real-time theory to systems requiring a balance of cost, reliability and peformance. First, there is no formal approach for the design of systems for less than full reliability. Second, the assumptions and constraints of applying hard real-time theory severely limit performance. Finally, safe mixing of hard and soft real-time execution is not supported. Without a better framework for mixed hard and soft real-time requirements implementation, the engineer must either adapt hard real-time theory on a case by case basis, or risk implementing a best effort system which provides no formal assurance of performance. Soft real-time quality-of-service frameworks are also an option. However, not only are these approaches not fully mature, more fundamentally, they do not address the concept of mixed hard and soft real-time processing, nor is it clear that any of these approaches provide concretely measurable reliability. In this thesis we present an alternative framework for the implementation of real-time systems which accommodates mixed hard and soft real-time processing with measurable reliability by providing a confidence-based scheduling and execution fault handling framework. This framework, called the RT EPA (real-time execution performance agent), provides a more natural and less constraining approach to translating both timing and functional requirements into a working system. The RT EPA framework is based on an extension to deadline monotonic theory. The RT EPA has been evaluated with simulated loading, an optical navigation test-bed, and the RT EPA monitoring module will be flown on an upcoming NASA space telescope in late 2001. The significance of this work is that it directly addresses the shortcomings in the current process for handling reliability and provides measurable reliability and performance feedback during the implementation, systems integration, and maintenance phases of the process.
Ph.D. Research Overview -- Related Papers
Figure 1: 5 DOF Position Feedback Robot Testbed
Figure 2: RACE (Rail-guided, Air-powered Controls Experiment) Optical Navigation Testbed
Figure 3: RACE NTSC-PCI Bus Camera System
Figure 4: RACE Rail-guided Ramp
The RACE testbed and the 5 DOF Position Feedback Robot will be demonstrated at the Dissertation review along with performance results included in the thesis. The RACE demonstration includes optical ranging and position hold along with a video compression pipeline so the RACE view can be displayed in real-time. The 5 DOF Position Feeback Robot will perform a simple target pick-and-place sequence.
Figure 5: RACE View of Optical Navigation Target
Briand, Loïc and Roy, Daniel, Meeting Deadlines in Hard Real-Time Systems - The Rate Monotonic Approach, IEEE Computer Society Press, 1999.
Liu, C., and Layland, J., "Scheduling Algorithms for Multiprogramming in a Hard-Real-Time Environment", Journal of the Association for Computing Machinery, pp. 46-61, Vol. 20, No. 1, January 1973.
Tom Shanley and Don Anderson, "PCI System Architecture", 4th Edition, 1999, (ISBN 0-201-30974-2) MindShare, Inc. publisher link.
In the past I worked on a lighter-than-air vehicle called FLOATERS which ultimately became the RACE experiment (Ph.D. research above).
FLOATERS Command Set and Sensors - Control is comprised of three levels of commands including: level-0 "joysticking", level-1 "digital control", and level-2 "agent control". A free flying version of the vehicle is being used in a VR shared-control experiment wi th a user interface to heading and range navigation sensors, propulsion control, and continuous video downlink.