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Real-Time Computing Systems and Applications, 2000. Proceedings. Seventh International Conference on

Date 12-14 Dec. 2000

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  • Proceedings Seventh International Conference on Real-Time Computing Systems and Applications

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  • Author index

    Page(s): 527 - 528
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    Freely Available from IEEE
  • DC2 scheduling for aperiodic tasks in strongly partitioned real-time systems

    Page(s): 368 - 375
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    The strongly partitioned real time system (SP-RTS) provides temporal and spatial partitioning for its integrated real time applications. The SP-RTS architecture adopts a two-level hierarchical scheduling mechanism. In the lower level, multiple partitions (applications) are dispatched under a cyclic scheduling, whereas, in the higher level, multiple periodic tasks of each partition are scheduled according to a fixed priority algorithm. The authors focus on designing algorithms for online scheduling of aperiodic tasks in the SP-RTS environment. The Distance Constraint guaranteed Dynamic Cyclic (DC2 ) scheduler that is proposed uses these basic operations: Left Sliding (LS), Right Putting (RP), and Compacting. These operations dynamically schedule aperiodic tasks within a distance-constrained cyclic schedule. We show that the dynamic applications of these operations do not violate the distance constraint characteristics of a partition cyclic schedule. In addition, the slack time calculation of these dynamic operations can be applied for scheduling hard aperiodic tasks. With the simulation studies, we observed that the DC2 can result in a significant performance enhancement in terms of the average response time of soft aperiodic tasks and the acceptance rate for hard aperiodic tasks View full abstract»

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  • Testing embedded real-time systems

    Page(s): 417 - 424
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    An embedded real-time system consists of a number of components (processes) that run concurrently and communicate with each other under predefined timing constraints. The correctness of such systems is important, since they are used in an increasingly number of safety-critical systems. To improve the quality of these systems, two techniques can be used, namely verification of the specification and testing of the implementation. In this paper, we consider the testing of embedded real-time components. In our model, the system is modeled as a set of communicating timed input-output automata (CTIOA). One CTIOA specifies the component to be tested and the remaining CTIOAs represent the context. The relationship between the component to be tested and the other ones should be taken into account for test case generation. We discuss how testing in context differs from testing in isolation. We review the fault model in the context of CTIOA and we propose an approach for test case generation from an embedded CTIOA. This approach consists of three steps. First, we avoid the composition of all machines by selecting, based on a specific criterion, only some parts of the CTIOA's context that affect (or are affected by) the specification. Then we determine the partial product of the specification and the selected parts of the context. Finally, we apply the timed Wp-method (A. En-Nouaary et al., 1998) to the resulting timed input-output automata. The quality of the resulting partial product is strongly dependent on the criterion used to select the parts of the context to consider in test case generation View full abstract»

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  • Two-step backup mechanism for real-time main memory database recovery

    Page(s): 453 - 457
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    Proposes a recovery mechanism for real-time main-memory database systems (RT-MMDBSs) which aims at reducing the system recovery time, as well as ensuring a fast response time and predictability. Conventional main-memory database (MMDB) recovery schemes usually use logging with checkpointing, which involves many disk I/Os during transaction processing. Consequently, it not only ensures the predictability of the response time, but also fast recovery, because undo/redo logs should be analyzed and applied after failure. Our recovery mechanism replaces logging and checkpointing activities with a single backup activity, which results in eliminating the need for log writing. Furthermore, it performs transaction processing and backup processing in separate areas, as a result minimizing their interference with each other. We use part of the main memory as a shadow memory area and the stable memory as a backup buffer. In our scheme, a two-step page-based backup is made: the first backup step is done from the shadow memory to the backup buffer, and the second step is performed from the backup buffer to a backup disk. We briefly show the worst-case performance analysis of our mechanism View full abstract»

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  • An improved feasible shortest path real-time fault-tolerant scheduling algorithm

    Page(s): 363 - 367
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    Fault tolerance is an important aspect of real time computer systems, since timing constraints must not be violated. For a real time single processor environment, S. Ghosh et al. (1995) proposed two queue based scheduling techniques: an FSP (feasible shortest path) algorithm and LTH (linear time heuristics). Even though the FSP algorithm can produce optimal fault tolerant schedules, it is not practical due to its time complexity. The LTH algorithm is a greedy heuristics that closely approximates the optimal. However, since Ghosh's algorithm assumes that there is at most one fault within time interval Δf and does not consider inter-fault time, it can deteriorate real time scheduling performance due to unnecessary backup scheduling. The authors propose an improved FSP algorithm based on the more realistic assumption that there is no additional fault during minimum inter-fault time ΔF after one fault occurs. The proposed algorithm can improve system performance by including more primary tasks in a fault tolerant schedule and can also reduce time complexity in generating backup schedules View full abstract»

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  • Using importance of transactions and optimistic concurrency control in firm real-time databases

    Page(s): 463 - 467
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    In a real-time database system, it is difficult to meet all of the timing constraints due to the consistency requirements of the underlying database. However, when the transactions in the system are heterogeneous, they are not all of the same importance-some are of greater importance than others. In this paper, we propose a new protocol called OCC-PDATI (Optimistic Concurrency Control Protocol using Dynamic Adjustment of serialization order and Transaction Importance), which uses information about the importance of the transactions in the conflict resolution. Performance studies of our protocol have been carried out in a prototype real-time database system. The results clearly indicate that OCC-PDATI meets the goal of favoring transactions of high importance View full abstract»

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  • Control tasks delay reduction under static and dynamic scheduling policies

    Page(s): 522 - 526
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    Industrial application of digital control requires the synergy between well designed control algorithms and carefully implemented control systems. The control performances can be strongly influenced depending on the data acquisition and control action delays. The paper shows how to evaluate these delays (jitter) under static or dynamic scheduling policies. An evaluation of several sets of tasks executed under both scheduling policies is analysed and compared. The results allow us to determine the goodness of both algorithms with respect to the delays due to scheduling. While worst case response time in static scheduling can be easily determined, under EDF scheduling the result is not trivial. A method to determine the worst case response time under EDF scheduling is proposed. The measurement of these delays can be drastically reduced with a task decomposition. This decomposition is studied and evaluated from the delays point of view. The reduction of the data acquisition interval (DAI) and control action interval (CAI) under both scheduling policies can be considered in the control design phase in order to properly adjust the control algorithm View full abstract»

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  • Debugging protocol for remote cross development environment

    Page(s): 394 - 398
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    To develop the applications for Internet appliances, embedded software development tools need various host tools such as cross compilers and binary utilities as well as a remote debugger, an interactive shell, and real time resource monitors. The heavy host-target communication overhead and inconsistency caused by various host tools make target monitor programs more complex. The authors propose a debugging protocol for these tools that supports several host-resident tools under the existence of RTOS. To abstract the details of the target systems, we have developed a target agent running as a task on the RTOS. The target agent is the counterpart of the host agent that supports host tools through communication over UDP/IP. The proposed architecture is implemented and tested on Esto (Embedded Systems Toolset), a development tool for Internet based embedded applications View full abstract»

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  • Parametric verification of the IEEE 1394a Root Contention protocol using LPMC

    Page(s): 207 - 214
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    This paper presents an application of mechanical verification using LPMC, a new version of the PMC model checker tool. The focus is on the modeling and the automatic verification of a protocol contained in the IEEE 1394a standard, the Root Contention protocol. The Root Contention protocol involves both real-time and randomization. As is shown, the study demonstrates the power of the new LPMC capability of handling linear constraints in order to exploit parametric real-time model checking. LPMC generates parameter relations and parameter timing intervals associated with fair TCTL properties View full abstract»

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  • Real-time scheduling on multithreaded processors

    Page(s): 155 - 159
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    This paper investigates real-time scheduling algorithms on upcoming multithreaded processors. As evaluation testbed we introduce a multithreaded processor kernel which is specifically designed as core processor of a micro-controller or system-on-a-chip. Handling of external real-time events is performed through multithreading. Real-time threads are used as interrupt service threads (ISTs) instead of interrupt service routines (ISRs). Our proposed micro-controller supports multiple ISTs with zero-cycle context switching overhead. We investigate the behavior of fixed priority preemptive, earliest deadline first, least laxity first and guaranteed percentage scheduling with respect to multithreaded processors. Our finding is that the strategies GP and LLF result in a good blending of instructions of different threads thus enabling a multithreaded processor to utilize latencies best. Assuming a zero-cycle context switch LLF performs best, however implementation cost context, are prohibitive View full abstract»

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  • Effect of scheduling jitter on end-to-end delay in TDMA protocols

    Page(s): 223 - 230
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    We address the problem of guaranteeing end-to-end (ETE) delay of packets in a distributed system where the technique of time division multiple access (TDMA) is adopted, and the application at the destination node requires to process the packets at a regular rate. We present a time slot allocation algorithm to satisfy the transmission rate requirement, and to minimize the scheduling jitter. Each packet of a stream is delivered in an allocated time slot according to one of the two delivery protocols proposed. A worst case ETE delay bound is derived for each protocol. The performance of applying our scheduling algorithm to different delivery protocols is compared and evaluated via simulations View full abstract»

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  • Chopping and versioning real-time transactions to avoid remote blocking

    Page(s): 93 - 101
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    Locking protocols for hard real time systems have not generalized well from uniprocessors to multiprocessors. Bounding and reducing so-called “remote blocking” is widely recognized as an important problem for hard real time computing. We describe a combination of locking and versioning protocols adapted from database concurrency control, together with a “chopping” analysis to shorten critical sections. Selective application of chopping and versioning reduces remote blocking and relates constraints imposed by pure locking protocols for multiprocessors. The protocol ensures 1-version serializability. Using the same design time information required for schedulability analysis in pure locking protocols, the mixed locking and versioning protocol can be implemented using only simple data structures with small bounded overheads and worst case access times. We illustrate the protocol with examples adapted from the literature View full abstract»

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  • Testing timed systems with timed purposes

    Page(s): 166 - 171
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    Although untimed system testing has already been far studied, its timed counterpart is still a rather new field and few methodologies have been proposed so far. This paper develops a method for testing timed systems through the generation of test purposes from the specification, modeled as a timed input/output automaton (TIOA), i.e. an automaton where each transition is labeled with time constraints in addition to the usual input or output symbol. This automaton is first translated into a semantically equivalent LTS (Labeled Transition System) from which we derive both the timed test purposes and their canonical tester. The test sequences are then executed on the implementation through a dedicated test architecture. This execution allows both to discriminate between the different cases (input, output or waiting) and to test a representative part of the infinite set of clock values View full abstract»

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  • Dragon: soft real-time event delivering architecture for networked sensors and appliances

    Page(s): 425 - 432
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    Presents a new framework for constructing flexible event-driven systems for distributed networked devices and appliances, referred to as Dragon. Dragon enables constructing and modifying an event-driven system easily by visualizing distributed services which are handled in an integrated manner. The updating of the system is conducted immediately following a modification by Dragon. Dragon is built on to of Jini/Java and can be executed on any Jini/Java-compliant machines. In addition, Dragon incorporates soft real-time event delivery to enhance the predictability of behavior of the constructed system. In this paper, we describe in detail the design and implementation of Dragon View full abstract»

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  • Extracting safe and precise control flow from binaries

    Page(s): 23 - 30
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    As a starting point for static program analysis, a control flow graph (CFG) is needed. If only the binary executable is available, this CFG has to be reconstructed from sequences of instructions. The usual way to do this is a top-down approach: the executable's information about routines is used to split the sequence into routines, and then each instruction is analysed for branch targets in order to compute basic block boundaries. When analysing safety-critical real-time systems, safe and precise results are needed. The CFG that the analyses traverse has to satisfy the same safety and precision requirements, because the analyses inherit all deficiencies. In this paper, a bottom-up approach for CFG approximation is presented. It starts at a set of entry points and clusters the sequence of instructions into larger units like blocks and routines. In this way, the algorithm is able to account for uncertainties early enough to generate a safe CFG View full abstract»

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  • Low-level analysis of a portable Java byte code WCET analysis framework

    Page(s): 39 - 46
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    To support portability, worst-case execution time (WCET) analysis of Java byte code is performed at two levels - machine-independent program flow analysis at a higher level and machine-dependent timing analysis of individual program constructs at a lower level. This paper contributes a WCET analysis that computes worst-case execution frequencies of Java byte codes within the software being analysed and accounts for platform-dependent information, i.e. the processor's pipeline. The main part of the approach is platform-independent; only a limited analysis is needed on a per-platform basis View full abstract»

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  • Real-time task scheduling algorithms for maximum utilization of secondary batteries in portable devices

    Page(s): 347 - 354
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    The spread of portable devices emphasizes the importance of low power energy techniques. The authors present dynamic real time scheduling algorithms which maximize utilized time of the secondary battery while preserving a deadline of real time tasks with frequency control. Firstly, we show that the decrease in secondary battery consumption is minimum when executing a program with as low a CPU frequency as possible. Secondly, we present a real time scheduling algorithm with arbitrary frequency control, and its correctness and computational complexity. For each task, the computational complexity of the algorithm is O(n) in general, where n is the number of tasks waiting execution; and that is O(1) in the amortized analysis when each task arrives in the order of its deadline. Thirdly, we address a scheduling problem with discrete frequency control. A decision problem corresponding to the scheduling problem is shown to be NP-complete when a frequency can be changed only at a task switching. Then, when the frequency can be changed at an arbitrary time, we describe an optimal scheduling algorithm which maximizes the utilized time of the secondary battery. The computational complexity of the algorithm has the same order as an algorithm in the case of arbitrary frequency View full abstract»

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  • Support for dynamic QoS in the HARTIK kernel

    Page(s): 65 - 72
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    HARTIK (HArd Real-TIme Kernel) is a real-time kernel that was originally developed for supporting complex robot applications and hard real-time control applications in general. However, in the last few years, the kernel has been modified to introduce support for soft real-time and multimedia applications. Major changes include the development of a new service mechanism, which provides the abstraction of temporal protection, and the implementation of a QoS manager that is capable of adapting the reserved resources to the actual tasks' requirements. In this paper, we report our experience with the new support for dynamic QoS applications, showing how our theoretical solutions have been applied on a real, stable and freely available kernel View full abstract»

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  • PRED-DF - a data flow based semantic concurrency control protocol for real-time main-memory database systems

    Page(s): 468 - 472
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    In real-time systems, the use of databases is increasing. If the application is safety-critical, one must guarantee in advance, by suitable verification methods, that all deadlines hold in all possible cases of use. Predictability of the database's concurrency control protocol is one of the most important prerequisites for this. However, most real-time concurrency control protocols are influenced by traditional database requirements. For hard real-time systems, they are usually unsuitable, because they are not predictable and they noticeably interfere with task scheduling. We present a new semantic concurrency control protocol called PRED-DF (PREDeclaration and Data Flow analysis) for main-memory real-time database systems. PRED-DF uses pre-declaration, is locking-based and generates serializable schedules. It uses additional knowledge gained from advance analysis of the application's data flow to minimize blocking times. PRED-DF's behavior is predictable and so the verification of real-time requirements is possible View full abstract»

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  • Frame packing in real-time communication

    Page(s): 399 - 403
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    A common computational model in distributed embedded systems is that the nodes exchange signals via a network. Most often, a signal represents the state of some physical device and has a signal size ranging from a single bit up to a few bytes. Furthermore, each signal typically has a deadline requirement. The communication networks used are often based on a broadcast bus where fixed or variable sized frames are transmitted. The amount of data that can be transmitted in each frame is almost always bigger than the size of a signal. Thus, from a resource perspective it would be desirable if each frame could transport several signals. The authors investigate how to assign signals to periodic frames with the objective function to minimise the network bandwidth requirement while not violating specified deadlines. This problem is NP-hard, but can for most typical applications be solved efficiently by using simple heuristics. The effectiveness of our algorithm is demonstrated by applying it to signal sets derived from automotive applications for a CAN based system and for the newly developed, low cost and low speed, Local Interconnect Network (LIN). The results can be of great use in cost sensitive embedded systems such as car control systems, where the used hardware, communication networks and nodes (typically microcontrollers), have to be highly utilised to keep the production cost at a minimum level View full abstract»

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  • Checkpointing strategy for multiple real-time tasks

    Page(s): 517 - 521
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    We analyze a checkpointing strategy for multiple real time tasks with deadlines. Real time tasks usually have deadlines associated with them. For multiple real time tasks, a checkpointing strategy considering deadlines of all tasks is very difficult to derive. We analyze the problem of checkpoint placement for such multiple tasks. In our strategy, the interval between checkpoints are determined for each task. An approximated failure probability over a specified interval is derived. Then the number of checkpoints for each task is selected to minimize the approximated failure probability. To show the usefulness of our strategy, the error bound between the exact and the approximated failure probability is estimated, which is revealed to be quite small View full abstract»

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  • Explicit binding interface for supporting native ATM networks in a CORBA system

    Page(s): 199 - 206
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    This paper describes a native ATM support for CORBA. The system provides three advanced features. The first feature is to extend the CORBA interface to explicitly support network bandwidth reservation provided by ATM. The second feature is to support the negotiation between a client and a server to reserve network bandwidth. The last feature is to support multiple transport protocols simultaneously. The system allows a programmer to select either IIOP to invoke methods in a best effort way or GIOP over ATM for timing critical invocations View full abstract»

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  • Including user-defined timing exception support in FRTL

    Page(s): 255 - 262
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    In previous papers, we have presented both a new framework for building flexible hard real-time systems (FRTS) and a corresponding run-time support system, called Flexible Real-Time Linux (FRTL). This paper presents how timing exception support can be integrated in both the framework and the run-time system. In particular, the paper proposes detecting and handling two types of timing exceptions: tasks overrunning their worst-case execution times (wcets) and tasks missing their deadlines. This paper shows that the support for these two types of exceptions is required in order to deal with excessive CPU consumption of the application tasks and the kernel itself, respectively. The handling mechanism for wcet exceptions incorporates the possibility of attaching a user-defined handler to each application task. Handlers are defined to be scheduled as either mandatory or optional components at any priority. The specific overhead related to all these mechanisms has been incorporated into the system's complete feasibility test, which is also presented View full abstract»

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  • Real-time transaction processing with partial validation at mobile clients

    Page(s): 473 - 477
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    Conventional concurrency control protocols are inapplicable in mobile computing environments due to a number of constraints of wireless communication. In this paper, we design a protocol for processing mobile transactions. The protocol can detect data conflicts between transactions by a two-stage validation mechanism that is shared by the server and the mobile clients. In addition to relieving the server from excessive validation workload, conflicting mobile transactions can be identified at the mobile clients without sending to the server for validation. Such an early data conflict detection feature can save processing and communication resources. Moreover, the protocol allows more transaction execution schedules, such that unnecessary transaction aborts can be avoided. These desirable features help mobile transactions to meet their deadlines by removing any avoidable delays attributed to the asymmetric property of wireless communication View full abstract»

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