Optimizing Performance of Continuous-Time Stochastic Systems using Timeout Synthesis

We consider parametric version of fixed-delay continuous-time Markov chains (or equivalently deterministic and stochastic Petri nets, DSPN) where fixed-delay transitions are specified by parameters, rather than concrete values. Our goal is to synthesize values of these parameters that, for a given cost function, minimise expected total cost incurred before reaching a given set of target states. We show that under mild assumptions, optimal values of parameters can be effectively approximated using translation to a Markov decision process (MDP) whose actions correspond to discretized values of these parameters

Exact Speedup Factors and Sub-Optimality for Non-Preemptive Scheduling

Fixed priority scheduling is used in many real-time systems; however, both preemptive and non-preemptive variants (FP-P and FP-NP) are known to be sub-optimal when compared to an optimal uniprocessor scheduling algorithm such as preemptive earliest deadline first (EDF-P). In this paper, we investigate the sub-optimality of fixed priority non-preemptive scheduling. Specifically, we derive the exact processor speed-up factor required to guarantee the feasibility under FP-NP (i.e. schedulability assuming an optimal priority assignment) of any task set that is feasible under EDF-P. As a consequence of this work, we also derive a lower bound on the sub-optimality of non-preemptive EDF (EDF-NP). As this lower bound matches a recently published upper bound for the same quantity, it closes the exact sub-optimality for EDF-NP. It is known that neither preemptive, nor non-preemptive fixed priority scheduling dominates the other, in other words, there are task sets that are feasible on a processor of unit speed under FP-P that are not feasible under FP-NP and vice-versa. Hence comparing these two algorithms, there are non-trivial speedup factors in both directions. We derive the exact speed-up factor required to guarantee the FP-NP feasibility of any FP-P feasible task set. Further, we derive the exact speed-up factor required to guarantee FP-P feasibility of any constrained-deadline FP-NP feasible task set

Towards a file system interface for mobile resources in networked embedded systems

Networks for real-time embedded systems are a key emerging technology for current and future systems. Such networks need to enable reliable communication without requiring significant resources, and provide an easy programming interface. This paper considers a file-system interface across all resources in a networked embedded system, ie. an application can access local, remote and mobile resources using a file interface. The approach is based on Styx [1,2], part of the network protocol of the Inferno/Plan 9 OS [1]. The Styx protocol provides file system level abstractions for ease of developing and management at an application layer. To this, we have added limited fault-tolerance and potential mobility for resources. To ensure applicability in a low-resource context, we have defined and implemented a (hardware) Styx IP-core Module 1, removing the need for a CPU and software overhead. © 2006 IEEE

The Styx IP-core for ubiquitous network device interoperability

Application level interoperability between ubiquitous networked communication devices (e.g. Mobile phones, PDA, CCD camera, etc.) poses many problems. In this paper we consider the issue of efficient application level access to resources on remote devices whilst achieving both network and distribution transparency. Provision of such transparency is difficult as low-resource devices are usually limited to one or two standard communication mediums (e.g. WiFi, Bluetooth, ZigBee). Thus, it is unlikely that an application node can communicate directly with all other nodes, with the requirement for some to act as intermediaries. Also, direct control of remote devices (potentially via some intermediary) in the same manner as local devices is not usually provided by conventional OSs. In this paper we consider the Styx protocol (from the Inferno OS) as a solution to these problems. Styx is defined to provide a file based interface to devices, within a namespace that provides distribution transparency (coping with intermediary devices). However, Styx currently is only available as software, requiring a OS (and CPU). We define and implement a (hardware) Styx IP-core Moduleι to provide both network and distribution transparency for applications that control physically remote devices. For lowresource devices, such an approach removes the need for a CPU (to execute a software OS and Styx implementation). The implementation of the hardware Styx IP-core (and subsequent demonstration) presented within the paper show the efficacy of this hardware Styx approach