Input-dependency analysis for hard real-time software

The execution time of soft-ware for hard real-time systems must be predictable. Further safe and not overly pessimistic bounds for the worst-case execution time (WCET) must be computable. We conceived a programming strategy called WCET-oriented programming and a code transformation strategy, the single-path conversion, that aid programmers in producing code that meets these requirements. These strategies avoid respectively eliminate input-data dependencies in the code. The paper describes the formal analysis, based on abstract interpretation, that identifies input-data dependencies in the code and thus forms the basis for the strategies provided for hard real-time code development

Formal derivation of concurrent assignments from scheduled single assignments

Concurrent assignments are commonly used to describe synchronous parallel computations. We show how a sequence of concurrent assignments can be formally derived from the schedule of an acyclic single assignment task graph and a memory allocation. In order to do this we develop a formal model of memory allocation in synchronous systems. We use weakest precondition semantics to show that the sequence of concurrent assignments computes the same values as the scheduled single assignments. We give a lower bound on the memory requirements of memory allocations for a given schedule. This bound is tight: we define a class of memory allocations whose memory requirements always meets the bound. This class corresponds to conventional register allocation for DAGs and is suitable when memory access times are uniform. We furthermore define a class of simple ``shift register'' memory allocation. These allocations have the advantage of a minimum of explicit storage control and they yield local or nearest-neighbour accesses in distributed systems whenever the schedule allows this. Thus, this class of allocations is suitable when designing parallel special-purpose hardware, like systolic arrays

Computing transitive closure on systolic arrays of fixed size

Forming the transitive closure of a binary relation (or directed graph) is an important part of many algorithms. When the relation is represented by a bit matrix, the transitive closure can be efficiently computed in parallel in a systolic array. Various such arrays for computing the transitive closure have been proposed. They all have in common, though, that the size of the array must be proportional to the number of nodes. Here we propose two ways of computing the transitive closure of an arbitrarily big graph on a systolic array of fixed size. The first method is a simple partitioning of a well-known systolic algorithm for computing the transitive closure. The second is a block-structured algorithm for computing the transitive closure. This algorithm is suitable for execution on a systolic array, that can multiply fixed size bit matrices and compute transitive closure of graphs with a fixed number of nodes. The algorithm is, however, not limited to systolic array implementations; it works on any parallel architecture that can form the transitive closure and product of fixed-size bit matrices efficiently. The shortest path problem, for directed graphs with weighted edges, can also be solved for arbitrarily large graphs on a fixed-size systolic array in the same manner, devised above, as the transitive closure is computed

Data Cache Locking for Higher Program Predictability

ABSTRACT Caches have become increasingly important with the widening gap between main memory and processor speeds. However, they are a source of unpredictability due to their characteristics, resulting in programs behaving in a different way than expected. Cache locking mechanisms adapt caches to the needs of real-time systems. Locking the cache is a solution that trades performance for predictability: at a cost of generally lower performance, the time of accessing the memory becomes predictable. This paper combines compile-time cache analysis with data cache locking to estimate the worst-case memory performance (WCMP) in a safe, tight and fast way. In order to get predictable cache behavior, we first lock the cache for those parts of the code where the static analysis fails. To minimize the performance degradation, our method loads the cache, if necessary, with data likely to be accessed. Experimental results show that this scheme is fully predictable, without compromising the performance of the transformed program. When compared to an algorithm that assumes compulsory misses when the state of the cache is unknown, our approach eliminates all overestimation for the set of benchmarks, giving an exact WCMP of the transformed program without any significant decrease in performance

Timing Analysis of Parallel Software Using Abstract Execution

Abstract. A major trend in computer architecture is multi-core processors. To fully exploit this type of parallel processor chip, programs running on it will have to be parallel as well. This means that even hard real-time embedded systems will be parallel. Therefore, it is of utmost importance that methods to analyze the timing properties of parallel real-time systems are developed. This paper presents an algorithm that is founded on abstract interpretation and derives safe approximations of the execution times of parallel programs. The algorithm is formulated and proven correct for a simple parallel language with parallel threads, shared memory and synchronization via locks

Technical Report: Feedback-Based Generation of Hardware Characteristics

ABSTRACT In large complex server-like computer systems it is difficult to characterise hardware usage in early stages of system development. Many times the applications running on the platform are not ready at the time of platform deployment leading to postponed metrics measurement. In our study we seek answers to the questions: (1) Can we use a feedbackbased control system to create a characteristics model of a real production system? (2) Can such a model be sufficiently accurate to detect characteristics changes instead of executing the production application? The model we have created runs a signalling application, similar to the production application, together with a PIDregulator generating L1 and L2 cache misses to the same extent as the production system. Our measurements indicate that we have managed to mimic a similar environment regarding cache characteristics. Additionally we have applied the model on a software update for a production system and detected characteristics changes using the model. This has later been verified on the complete production system, which in this study is a large scale telecommunication system with a substantial market share

Australian community pharmacy services: a survey of what people with chronic conditions and their carers use versus what they consider important

Objective To explore the purpose/s for which people with chronic conditions and their carers use Australian community pharmacies, and compare this to what pharmacy services they consider important, from the perspectives of both consumers and pharmacists. Design An exploratory study involving a survey, which asked participants to indicate the pharmacy services they had ever used, and rate the importance of 22 pharmacy services to them, or the person they care for, or for their consumers if a pharmacist. Setting Four regions of Australia: Logan-Beaudesert and Mt Isa/North West region, Queensland, Northern Rivers, New South Wales, and the Greater Perth area, Western Australia. Participants Surveys were undertaken with 602 consumers and 91 community pharmacists. Results Community pharmacy is predominantly used to obtain advice about medication and whether a doctor's visit is necessary, as well as for monitoring and screening services. Pharmacy services that were patient centric were important, such as individualised medication advice and respectful care, as well as tools or procedures to facilitate streamlined medication access. Less important services included adult vaccinations and health and wellness programmes. Carers identified services that assisted them with their specific role/s to be important. Overall, community pharmacists had a good understanding of the services that were important to people with chronic conditions and their carers. Conclusions People with chronic conditions and their carers not only care about what services are delivered, but how they are delivered; they sought services that generally improved their access to medication and information, but in a way that was patient centred. Ultimately, pharmacists understood the importance of patient-centred care for people with chronic conditions and their carers, perhaps indicating a greater acceptance of integrating patient-centred care into their everyday practice