Browsing by Author "Audsley, Neil"
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- Errata for Three Papers (2004-05) on Fixed-Priority Scheduling with Self-SuspensionsPublication . Bletsas, Konstantinos; Audsley, Neil; Huang, Wen-Hung; Chen, Jian-Jia; Nelissen, GeoffreyThe purpose of this article is to (i) highlight the flaws in three previously published works [Audsley, 2004a; Audsley, 2004b; Bletsas, 2005] on the worst-case response time analysis for tasks with self-suspensions and (ii) provide straightforward fixes for those flaws, hence rendering the analysis safe.
- A Globally Arbitrated Memory Tree for Mixed-Time-Criticality SystemsPublication . Gomony, Manil Dev; Garside, Jamie; Åkesson, Benny; Audsley, Neil; Goossens, KeesEmbedded systems are increasingly based on multi-core platforms to accommodate a growing number of applications, some of which have real-time requirements. Resources, such as off-chip DRAM, are typically shared between the applications using memory interconnects with different arbitration polices to cater to diverse bandwidth and latency requirements. However, traditional centralized interconnects are not scalable as the number of clients increase. Similarly, current distributed interconnects either cannot satisfy the diverse requirements or have decoupled arbitration stages, resulting in larger area, power and worst-case latency. The four main contributions of this article are: 1) a Globally Arbitrated Memory Tree (GAMT) with a distributed architecture that scales well with the number of cores, 2) an RTL-level implementation that can be configured with five arbitration policies (three distinct and two as special cases), 3) the concept of mixed arbitration policies that allows the policy to be selected individually per core, and 4) a worst-case analysis for a mixed arbitration policy that combines TDM and FBSP arbitration. We compare the performance of GAMT with centralized implementations and show that it can run up to four times faster and have over 51% and 37% reduction in area and power consumption, respectively, for a given bandwidth.
- Many suspensions, many problems: a review of self-suspending tasks in real-time systemsPublication . Chen, Jian-Jia; Nelissen, Geoffrey; Huang, Wen-Hung; Yang, Li; Brandenburg, Björn B.; Bletsas, Konstantinos; Liu, Cong; Richard, Pascal; Ridouard, Frédéric; Audsley, Neil; Rajkumar, Raj; Niz, Dionísio de; von der Brüggen, GeorgIn general computing systems, a job (process/task) may suspend itself whilst it is waiting for some activity to complete, e.g., an accelerator to return data. In real-time systems, such self-suspension can cause substantial performance/schedulability degradation. This observation, first made in 1988, has led to the investigation of the impact of self-suspension on timing predictability, and many relevant results have been published since. Unfortunately, as it has recently come to light, a number of the existing results are flawed. To provide a correct platform on which future research can be built, this paper reviews the state of the art in the design and analysis of scheduling algorithms and schedulability tests for self-suspending tasks in real-time systems. We provide (1) a systematic description of how self-suspending tasks can be handled in both soft and hard real-time systems; (2) an explanation of the existing misconceptions and their potential remedies; (3) an assessment of the influence of such flawed analyses on partitioned multiprocessor fixed-priority scheduling when tasks synchronize access to shared resources; and (4) a discussion of the computational complexity of analyses for different self-suspension task models.