| 1. |
- Thompson, Paul M., et al.
(författare)
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The ENIGMA Consortium : large-scale collaborative analyses of neuroimaging and genetic data
- 2014
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Ingår i: BRAIN IMAGING BEHAV. - : Springer Science and Business Media LLC. - 1931-7557 .- 1931-7565. ; 8:2, s. 153-182
-
Tidskriftsartikel (refereegranskat)abstract
- The Enhancing NeuroImaging Genetics through Meta-Analysis (ENIGMA) Consortium is a collaborative network of researchers working together on a range of large-scale studies that integrate data from 70 institutions worldwide. Organized into Working Groups that tackle questions in neuroscience, genetics, and medicine, ENIGMA studies have analyzed neuroimaging data from over 12,826 subjects. In addition, data from 12,171 individuals were provided by the CHARGE consortium for replication of findings, in a total of 24,997 subjects. By meta-analyzing results from many sites, ENIGMA has detected factors that affect the brain that no individual site could detect on its own, and that require larger numbers of subjects than any individual neuroimaging study has currently collected. ENIGMA's first project was a genome-wide association study identifying common variants in the genome associated with hippocampal volume or intracranial volume. Continuing work is exploring genetic associations with subcortical volumes (ENIGMA2) and white matter microstructure (ENIGMA-DTI). Working groups also focus on understanding how schizophrenia, bipolar illness, major depression and attention deficit/hyperactivity disorder (ADHD) affect the brain. We review the current progress of the ENIGMA Consortium, along with challenges and unexpected discoveries made on the way.
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| 2. |
- Wanschers, Bas F. J., et al.
(författare)
-
A mutation in the human CBP4 ortholog UQCC3 impairs complex III assembly, activity and cytochrome b stability
- 2014
-
Ingår i: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 23:23, s. 6356-6365
-
Tidskriftsartikel (refereegranskat)abstract
- Complex III (cytochrome bc(1)) is a protein complex of the mitochondrial inner membrane that transfers electrons from ubiquinol to cytochrome c. Its assembly requires the coordinated expression of mitochondrial-encoded cytochrome b and nuclear-encoded subunits and assembly factors. Complex III deficiency is a severe multisystem disorder caused by mutations in subunit genes or assembly factors. Sequence-profile-based orthology predicts C11orf83, hereafter named UQCC3, to be the ortholog of the fungal complex III assembly factor CBP4. We describe a homozygous c.59T > A missense mutation in UQCC3 from a consanguineous patient diagnosed with isolated complex III deficiency, displaying lactic acidosis, hypoglycemia, hypotonia and delayed development without dysmorphic features. Patient fibroblasts have reduced complex III activity and lower levels of the holocomplex and its subunits than controls. They have no detectable UQCC3 protein and have lower levels of cytochrome b protein. Furthermore, in patient cells, cytochrome b is absent from a high-molecular-weight complex III. UQCC3 is reduced in cells depleted for the complex III assembly factors UQCC1 and UQCC2. Conversely, absence of UQCC3 in patient cells does not affect UQCC1 and UQCC2. This suggests that UQCC3 functions in the complex III assembly pathway downstream of UQCC1 and UQCC2 and is consistent with what is known about the function of Cbp4 and of the fungal orthologs of UQCC1 and UQCC2, Cbp3 and Cbp6. We conclude that UQCC3 functions in complex III assembly and that the c.59T > A mutation has a causal role in complex III deficiency.
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| 3. |
- van den Heuvel, Martijn, et al.
(författare)
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Towards Verification-based Development of In-Vehicle Safety Critical Software : A Case Study
- 2010
-
Ingår i: ACM International Conference Proceeding Series. - New York, New York, USA : ACM Press. - 9781605589152 ; , s. 35-38
-
Konferensbidrag (refereegranskat)abstract
- The ever increasing software complexity in the safety critical automotive domain induces new challenges in ensuring a fault-free system design. In this paper we propose a novel approach using Analytical Software Design (ASD). The ASD toolsuite provides means to develop software that is robust by construction. We show the integration of the ASD approach in the commonly used development workflow using Matlab/Simulink by means of a case study.
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| 4. |
- Bril, Reinder J., et al.
(författare)
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Generalized fixed-priority scheduling with limited preemptions
- 2012
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Ingår i: Proceedings - Euromicro Conference on Real-Time Systems, 2012. - 9780769547398 ; , s. 209-220
-
Konferensbidrag (refereegranskat)abstract
- Fixed-priority scheduling with deferred preemption(FPDS) and fixed-priority scheduling with preemption thresholds(FPTS) have been proposed in the literature as viable alternatives to fixed-priority preemptive scheduling (FPPS), that reduce memory requirements, reduce the cost of arbitrary preemptions, and may improve the feasibility of a task set even when preemption overheads are neglected. This paper aims at advancing the relative strength of limited preemptive schedulers by combining FPDS and FPTS. In particular, we present a refinement of FPDS with preemption thresholds for both jobs and sub-jobs, termed FPGS. We provide an exact schedulability analysis for FPGS, and show how to maximize the feasibility of a set of sporadic tasks under FPGS for given priorities, computation times, periods, and deadlines of tasks. We evaluate the effectiveness of FPGS by comparing the feasibility of task sets under FPGS with other fixed-priority scheduling algorithms by means of a simulation. Our experiments show that FPGS allows an increase of the number of task sets that are schedulable under fixed-priority scheduling.
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| 5. |
- Bril, Reinder J., et al.
(författare)
-
Improved feasibility of fixed-priority scheduling with deferred preemption using preemption thresholds for preemption points
- 2013
-
Ingår i: RTNS '13 Proceedings of the 21st International conference on Real-Time Networks and Systems. - New York, NY, USA : ACM. - 9781450320580 ; , s. 255-264
-
Konferensbidrag (refereegranskat)abstract
- This paper aims at advancing the relative strength of limited-preemptive schedulers by improving the feasibility of a task set and simultaneously limiting, or even precluding, arbitrary preemptions. In particular, we present a refinement of existing limited-preemptive fixed-priority scheduling (FPS) schemes with preemption thresholds for preemption points next to preemption thresholds for sub-jobs, termed fixed-priority scheduling with varying preemption thresholds (FPVS). We derive exact schedulability analysis for FPVS and we develop algorithms to maximize the schedulability of a set of sporadic tasks for given priorities. Since FPVS generalizes existing FPS schemes, we apply our algorithms to those schemes to compare the ratio of schedulable systems. Our experiments show that FPVS can achieve the same schedulability ratio with limited-preemptive sub-jobs as with entirely non-preemptive sub-jobs.
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| 6. |
- Bril, Reinder J., et al.
(författare)
-
Integrating Cache-Related Pre-emption Delays into Analysis of Fixed Priority Scheduling with Pre-emption Thresholds
- 2015
-
Ingår i: Proceedings - Real-Time Systems Symposium. - 9781479972890 ; , s. 161-172
-
Konferensbidrag (refereegranskat)abstract
- Cache-related pre-emption delays (CRPD) have been integrated into the schedulability analysis of sporadic tasks with constrained deadlines for fixed-priority pre-emptive scheduling (FPPS). This paper generalizes that work by integrating CRPD into the schedulability analysis of tasks with arbitrary deadlines for fixed-priority pre-emption threshold scheduling (FPTS). The analysis is complemented by an optimal threshold assignment algorithm that minimizes CRPD. The paper includes a comparative evaluation of the schedulability ratios of FPPS and FPTS, for constrained-deadline tasks, taking CRPD into account.
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| 7. |
- J. Bril, Reinder, et al.
(författare)
-
Fixed priority scheduling with pre-emption thresholds and cache-related pre-emption delays : integrated analysis and evaluation
- 2017
-
Ingår i: Real-time systems. - : Springer Science and Business Media LLC. - 0922-6443 .- 1573-1383. ; 53:4, s. 403-466
-
Tidskriftsartikel (refereegranskat)abstract
- Commercial off-the-shelf programmable platforms for real-time systems typically contain a cache to bridge the gap between the processor speed and main memory speed. Because cache-related pre-emption delays (CRPD) can have a significant influence on the computation times of tasks, CRPD have been integrated in the response time analysis for fixed-priority pre-emptive scheduling (FPPS). This paper presents CRPD aware response-time analysis of sporadic tasks with arbitrary deadlines for fixed-priority pre-emption threshold scheduling (FPTS), generalizing earlier work. The analysis is complemented by an optimal (pre-emption) threshold assignment algorithm, assuming the priorities of tasks are given. We further improve upon these results by presenting an algorithm that searches for a layout of tasks in memory that makes a task set schedulable. The paper includes an extensive comparative evaluation of the schedulability ratios of FPPS and FPTS, taking CRPD into account. The practical relevance of our work stems from FPTS support in AUTOSAR, a standardized development model for the automotive industry. [(This paper forms an extended version of Bril et al. (in Proceedings of 35th IEEE real-time systems symposium (RTSS), 2014). The main extensions are described in Sect. 1.2.].
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| 8. |
- Kaboodvand, Neda, et al.
(författare)
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Macroscopic resting state model predicts theta burst stimulation response : A randomized trial
- 2023
-
Ingår i: PloS Computational Biology. - : Public Library of Science (PLoS). - 1553-734X .- 1553-7358. ; 19:3
-
Tidskriftsartikel (refereegranskat)abstract
- Repetitive transcranial magnetic stimulation (rTMS) is a promising alternative therapy for treatment-resistant depression, although its limited remission rate indicates room for improvement. As depression is a phenomenological construction, the biological heterogeneity within this syndrome needs to be considered to improve the existing therapies. Whole-brain modeling provides an integrative multi-modal framework for capturing disease heterogeneity in a holistic manner.Computational modelling combined with a probabilistic nonparametric fitting was applied to the resting-state fMRI data from 42 patients (21 women), to parametrize baseline brain dynamics in depression. All patients were randomly assigned to two treatment groups, namely active (i.e., rTMS, n = 22) or sham (n = 20). The active treatment group received rTMS treatment with an accelerated intermittent theta burst protocol over the dorsomedial prefrontal cortex. The sham treatment group underwent the identical procedure but with the magnetically shielded side of the coil.We stratified the depression sample into distinct covert subtypes based on their baseline attractor dynamics captured by different model parameters. Notably, the two detected depression subtypes exhibited different phenotypic behaviors at baseline. Our stratification could predict the diverse response to the active treatment that could not be explained by the sham treatment. Critically, we further found that one group exhibited more distinct improvement in certain affective and negative symptoms. The subgroup of patients with higher responsiveness to treatment exhibited blunted frequency dynamics for intrinsic activity at baseline, as indexed by lower global metastability and synchrony.Our findings suggested that whole-brain modeling of intrinsic dynamics may constitute a determinant for stratifying patients into treatment groups and bringing us closer towards precision medicine.
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| 9. |
- Schophuizen, Carolien M. S., et al.
(författare)
-
Cationic uremic toxins affect human renal proximal tubule cell functioning through interaction with the organic cation transporter
- 2013
-
Ingår i: Pflügers Archiv. - : Springer Science and Business Media LLC. - 0031-6768. ; 465:12, s. 1701-1714
-
Tidskriftsartikel (refereegranskat)abstract
- Several organic cations, such as guanidino compounds and polyamines, have been found to accumulate in plasma of patients with kidney failure due to inadequate renal clearance. Here, we studied the interaction of cationic uremic toxins with renal organic cation transport in a conditionally immortalized human proximal tubule epithelial cell line (ciPTEC). Transporter activity was measured and validated in cell suspensions by studying uptake of the fluorescent substrate 4-(4-(dimethylamino)styryl)-N-methylpyridinium-iodide (ASP(+)). Subsequently, the inhibitory potencies of the cationic uremic toxins, cadaverine, putrescine, spermine and spermidine (polyamines), acrolein (polyamine breakdown product), guanidine, and methylguanidine (guanidino compounds) were determined. Concentration-dependent inhibition of ASP(+) uptake by TPA, cimetidine, quinidine, and metformin confirmed functional endogenous organic cation transporter 2 (OCT2) expression in ciPTEC. All uremic toxins tested inhibited ASP(+) uptake, of which acrolein required the lowest concentration to provoke a half-maximal inhibition (IC50 = 44 +/- 2 mu M). A Dixon plot was constructed for acrolein using three independent inhibition curves with 10, 20, or 30 mu M ASP(+), which demonstrated competitive or mixed type of interaction (K (i) = 93 +/- 16 mu M). Exposing the cells to a mixture of cationic uremic toxins resulted in a more potent and biphasic inhibitory response curve, indicating complex interactions between the toxins and ASP(+) uptake. In conclusion, ciPTEC proves a suitable model to study cationic xenobiotic interactions. Inhibition of cellular uptake transport was demonstrated for several uremic toxins, which might indicate a possible role in kidney disease progression during uremia.
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| 10. |
- Smits, Paulien, et al.
(författare)
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Reconstructing the evolution of the mitochondrial ribosomal proteome
- 2007
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Ingår i: Nucleic Acids Research. - : Oxford University Press (OUP). - 0305-1048 .- 1362-4962. ; 35:14, s. 4686-4703
-
Tidskriftsartikel (refereegranskat)abstract
- For production of proteins that are encoded by the mitochondrial genome, mitochondria rely on their own mitochondrial translation system, with the mitoribosome as its central component. Using extensive homology searches, we have reconstructed the evolutionary history of the mitoribosomal proteome that is encoded by a diverse subset of eukaryotic genomes, revealing an ancestral ribosome of alpha-proteobacterial descent that more than doubled its protein content in most eukaryotic lineages. We observe large variations in the protein content of mitoribosomes between different eukaryotes, with mammalian mitoribosomes sharing only 74 and 43% of its proteins with yeast and Leishmania mitoribosomes, respectively. We detected many previously unidentified mitochondrial ribosomal proteins (MRPs) and found that several have increased in size compared to their bacterial ancestral counterparts by addition of functional domains. Several new MRPs have originated via duplication of existing MRPs as well as by recruitment from outside of the mitoribosomal proteome. Using sensitive profile-profile homology searches, we found hitherto undetected homology between bacterial and eukaryotic ribosomal proteins, as well as between fungal and mammalian ribosomal proteins, detecting two novel human MRPs. These newly detected MRPs constitute, along with evolutionary conserved MRPs, excellent new screening targets for human patients with unresolved mitochondrial oxidative phosphorylation disorders.
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| 11. |
- Tempelaars, Coen, et al.
(författare)
-
Real-time priority processing on the Cell platform
- 2011
-
Ingår i: Digest of Technical Papers - IEEE International Conference on Consumer Electronics. - 9781424487127 ; , s. 157-158
-
Konferensbidrag (refereegranskat)abstract
- Flexible signal processing on programmable platforms are increasingly important for consumer electronic applications. Scalable video algorithms (SVAs) using the novel principle of priority processing guarantee real-time performance on programmable platforms, even with limited resources. Dynamic resource allocation is required to maximize the overall output quality of independent, competing priority processing algorithms that are executed on a shared platform. In this paper we describe the mapping of a priority processing application on the Cell/B.E. platform. We compare the performance of different implementations for dynamic-resource-allocation mechanisms, and show that priority processing achieves real-time performance.
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| 12. |
- van den Heuvel, Martijn, et al.
(författare)
-
Budget allocations for hierarchical fixed-priority scheduling of sporadic tasks with deferred preemptions upon EDP resources
- 2013
-
Ingår i: 6th International Workshop on Compositional Theory and Technology for Real-Time Embedded Systems CRTS'13.
-
Konferensbidrag (refereegranskat)abstract
- In this paper we revisit the admission of applicationsupon a processor share modeled by the explicit-deadlineperiodic (EDP) resource-supply model. In particular, we considerapplications that represent a fixed-priority sporadic task system.Existing works heavily build on the analysis of a hierarchy ofpreemptive task schedulers. We instead consider the feasibilityof such tasks and applications for a hierarchy of deferredpreemptiveschedulers, so that we can efficiently deal with thescenario where tasks and applications execute their work in nonpreemptivechunks. Our model therefore gives better control overpreemptions of tasks of different applications.We present exact analysis for deferred-preemptive schedulingof tasks on EDP resources. In addition, we propose algorithmsfor dimensioning an application’s budget tightly.
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| 13. |
- van den Heuvel, Martijn, et al.
(författare)
-
Constant-bandwidth supply for priority-processing
- 2011
-
Ingår i: Digest of Technical Papers - IEEE International Conference on Consumer Electronics. - Las Vegas, United States. - 9781424487127 ; , s. 857-858
-
Konferensbidrag (refereegranskat)abstract
- Today's consumer electronic devices feature multiple applications which have to share scarcely available resources. We consider a priority-processing- based video application, which comprises multiple scalable video algorithms (SVAs) that are executed on a shared, virtual platform. This application is given a guaranteed processor share by means of a constant-bandwidth server (CBS), which in addition efficiently reclaims all spare processor time. A decision scheduler distributes the assigned processor share among the SVAs, with the aim to maximize their overall output quality. To correctly distribute this processor share we introduce the concept of a virtual timer. This timer only advances when its associated virtual platform is executing.
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| 14. |
- van den Heuvel, Martijn, et al.
(författare)
-
Constant bandwidth supply for priority processing
- 2011
-
Ingår i: IEEE transactions on consumer electronics. - 0098-3063 .- 1558-4127. ; 57:2, s. 873-881
-
Tidskriftsartikel (refereegranskat)abstract
- Today's consumer electronic devices feature multiple applications which have to share scarcely available resources. We consider a priority-processing- based video application, which comprises multiple scalable video algorithms (SVAs) that are executed on a shared, virtual platform. This application is given a guaranteed processor share by means of a constant-bandwidth server (CBS). A decision scheduler distributes the assigned processor share among the SVAs on a time-slot basis, with the aim to maximize their overall output quality. To correctly distribute this processor share based on fixed-sized time slots, we introduce the concept of a virtual timer. This timer only advances when its associated virtual platform is executing. Because priority processing can guarantee real-time performance even under fluctuating load, we apply a resource reclaiming mechanism to our CBS which makes it possible to efficiently exploit spare processor time.
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| 15. |
- van den Heuvel, Martijn, et al.
(författare)
-
Dependable resource sharing for compositional real-time systems
- 2011
-
Ingår i: Proceedings - 17th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications, RTCSA 2011. - 9780769545028 ; , s. 153-163
-
Konferensbidrag (refereegranskat)abstract
- Hierarchical scheduling frameworks (HSFs) have been extensively investigated as a paradigm for facilitating temporal isolation between components that need to be integrated on a single shared processor. In the presence of shared resources, however, temporal isolation may break when one of the accessing components executes longer than specified during global resource access. The ability to confine such temporal faults makes the HSF more dependable. As a solution we propose a stack-resource-policy (SRP)-based synchronization protocol for HSFs, named Hierarchical Synchronization protocol with Temporal Protection (HSTP). When a component exceeds its specified critical-section length, HSTP enforces a component to self-donate its own budget to accelerate the resource release. In addition, a component that blocks on a locked resource may donate budget. The schedulability of those components that are independent of the locked resource is unaffected. HSTP efficiently limits the propagation of temporal faults to resource-sharing components by disabling local preemptions in a component during resource access. We finally show that HSTP is SRP-compliant and applies to existing synchronization protocols for HSFs.
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| 16. |
- van den Heuvel, Martijn, et al.
(författare)
-
Dynamic resource allocation for real-time priority processing applications
- 2010
-
Ingår i: IEEE transactions on consumer electronics. - 0098-3063 .- 1558-4127. ; 56:2, s. 879-887
-
Tidskriftsartikel (refereegranskat)abstract
- Flexible signal processing on programmable platforms are increasingly important for consumer electronic applications and others. Scalable video algorithms (SVAs) using novel priority processing can guarantee real-time performance on programmable platforms even with limited resources. Dynamic resource allocation is required to maximize the overall output quality of independent, competing priority processing algorithms that are executed on a shared platform. In this paper, we describe basic mechanisms for dynamic resource allocation and compare the performance of different implementations on a general purpose platform.
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| 17. |
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| 18. |
- van den Heuvel, Martijn, et al.
(författare)
-
Limited preemptive scheduling of mixed time-triggered and event-triggered tasks
- 2013
-
Konferensbidrag (refereegranskat)abstract
- Many embedded systems have complex timing constraints and, at the same time, have flexibility requirements which prohibit offline planning of the entire system. To support a mixture of time-triggered and event-triggered tasks, some industrial systems deploy a table-driven dispatcher for time-triggered tasks complemented with a preemptive scheduler to allocate the free time slots to event-driven tasks. Contrary to fully preemptive scheduling, limiting the preemptions of tasks to fixed preemptions points may reduce memory requirements and it alleviates the preemption costs in the system. We revisit slotshifting, which at run time mixes time-triggered and event-triggered tasks in a preemptive EDF schedule. In this paper, we extend slotshifting with limited-preemptive execution of event-triggered tasks. We present a synchronization protocol to arbitrate the executions of non-preemptive regions, so that time-triggered tasks keep meeting their timing constraints implicitly. Furthermore, we investigate how to disable preemptions of event-triggered tasks during the execution of the offline-scheduled time-triggered tasks, while keeping the feature of slotshifting to reallocate their slots of execution dynamically at run time.
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| 19. |
- van den Heuvel, Martijn, et al.
(författare)
-
Opaque Analysis for Resource Sharing in Compositional Real-Time Systems
- 2011
-
Ingår i: 4th Workshop on Compositional Theory and Technology for Real-Time Embedded Systems (CRTS'11).
-
Konferensbidrag (refereegranskat)abstract
- In this paper we propose opaque analysis methods to integrate dependent real-time components into hierarchical fixed-priority scheduled systems. To arbitrate mutually exclusive resource access between components, we consider two existing protocols: HSRP - comprising overrun with and without payback - and SIRAP. An opaque analysis allows to postpone the choice of a synchronization protocol until component integration time. First, we identify the sources of pessimism in the existing analysis techniques and we conclude that both protocols assume different models in their local analysis. In particular, the compo- sitional analysis for overrun with payback (OWP) is not opaque and is pessimistic. The latter makes OWP expensive compared to its counter part without a payback mechanism (ONP). This paper presents an opaque and less pessimistic OWP analysis. Secondly, SIRAP requires more timing information to perform a task-level schedulability analysis. In many practical situations, however, detailed timing characteristics of tasks are hard to obtain. We introduce an opaque analysis for SIRAP using the analysis of ONP to reduce the required timing information during the local analysis. We show that the analysis for ONP cannot deem systems schedulable which are infeasible with SIRAP. The SIRAP analysis may therefore reduce the required system resources of a component by sacrificing the choice for an arbitrary synchronization protocol at system integration time.
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| 20. |
- van den Heuvel, Martijn, et al.
(författare)
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Protocol Transparent Resource Sharing in Hierarchically Scheduled Real-Time Systems
- 2010
-
Ingår i: Proceedings of the 15th IEEE International Conference on Emerging Technologies and Factory Automation, ETFA 2010. - 9781424468508
-
Konferensbidrag (refereegranskat)abstract
- Hierarchical scheduling frameworks (HSFs) provide means for composing complex real-time systems from well-defined, independently analyzed subsystems. To support resource sharing within two-level HSFs, three synchronization protocols based on the stack resource policy (SRP) have recently been presented, i.e. HSRP [1], SIRAP [2] and BROE [3]. This paper describes the first implementation presenting these three SRP-based synchronization protocols side-by-side in a HSF-enabled real-time operating system. We base our implementations on the commercially available real-time operating system μC/OS-II, extended with proprietary support for periodic tasks, idling periodic servers and two-level preemptive scheduling. Moreover, we investigate the system overhead of the synchronization primitives of each protocol. Transparent interfaces allow a protocol to be selected during integration time based on its relative strengths.
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| 21. |
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| 22. |
- van den Heuvel, Martijn, et al.
(författare)
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RTOS support for mixed time-triggered and event-triggered task sets
- 2012
-
Ingår i: Proceedings - 15th IEEE International Conference on Computational Science and Engineering, CSE 2012 and 10th IEEE/IFIP International Conference on Embedded and Ubiquitous Computing, EUC 2012. - 9780769549149 ; , s. 578-585
-
Konferensbidrag (refereegranskat)abstract
- Many embedded systems have complex timing constraints and, at the same time, have flexibility requirements which prohibit offline planning of the entire system. To support a mixture of time-triggered and event-triggered tasks, some industrial systems deploy an RTOS with a table-driven dispatcher complemented with a preemptive scheduler to allocate the free time slots to event-driven tasks. Rather than allocating dedicated time-slots to time-triggered tasks, in this work we provide RTOS support to dynamically re-allocate time-slots of time triggered tasks within a pre-computed time range to maximize the available processing capacity for event-triggered tasks. Although the concept - called slotshifting - is not new, we are the first to extend a commercial RTOS with such support. In addition, we extend slot shifting with a run-time mechanism to reclaim resources of time-triggered tasks when their reserved capacities are unused. This mechanism eliminates over-provisioning of capacities to (event-triggered) tasks that have been converted to periodic tasks to resolve interdependencies during off-line synthesis, e.g. allowing for a resource-efficient implementation of a polling task. After implementing our unique RTOS extensions, we investigate the run-time overheads for the corresponding scheduling mechanisms. Measurements show that the increase in terms of absolute run-time overhead is minor compared to an off-the-shelf micro-kernel with a fixed-priority scheduler
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| 23. |
- van den Heuvel, Martijn, et al.
(författare)
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Temporal isolation in an HSF-enabled real-time kernel in the presence of shared resources
- 2011
-
Ingår i: <em>Proceedings of the 7th International Workshop on Operating Systems Platforms for Embedded Real-Time Applications</em>. ; , s. 41-50
-
Konferensbidrag (refereegranskat)abstract
- Hierarchical scheduling frameworks (HSFs) have been extensively investigated as a paradigm for facilitating temporal isolation between components that need to be integrated on a single shared processor. To support resource sharing within two-level, fixed priority scheduled HSFs, two synchronization protocols based on the stack resource policy (SRP) have recently been presented, i.e. HSRP [1] and SIRAP [2]. In the presence of shared resources, however, temporal isolation may break when one of the accessing components executes longer than specified during global resource access. As a solution we propose a SRP-based synchronization protocol for HSFs, named Basic Hierarchical Synchronization protocol with Temporal Protection (B-HSTP). The schedulability of those components that are independent of the unavailable resource is unaffected.This paper describes an implementation to provide HSFs, accompanied by SRP-based synchronization protocols, with means for temporal isolation. We base our implementations on the commercially available real-time operating system μC/OS-II, extended with proprietary support for two-level fixed priority preemptive scheduling. We specifically show the implementation of B-HSTP and we investigate the system overhead induced by its synchronization primitives in combination with HSRP and SIRAP. By supporting both protocols in our HSF, their primitives can be selected based on the protocol’s relative strengths.
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| 24. |
- van den Heuvel, Martijn, et al.
(författare)
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Towards RTOS support for mixed time-triggered and event-triggered task sets
- 2012
-
Ingår i: IEEE Symposium on Emerging Technologies and Factory Automation, ETFA, 2012. - 9781467347372 ; , s. 1-4
-
Konferensbidrag (refereegranskat)abstract
- Many embedded systems have complex timing constraints and, at the same time, have flexibility requirements which prohibit offline planning of the entire system. To support a mixture of time-triggered and event-triggered tasks, some industrial systems deploy a real-time operating system (RTOS) with a table-driven dispatcher complemented with a preemptive scheduler to allocate free time slots to event-driven tasks. Rather than allocating dedicated time-slots to time-triggered tasks, we propose to dynamically re-allocate time-slots of time-triggered tasks within a pre-computed time range to maximize the available processing capacity for event-triggered tasks. Although the concept - called slotshifting - is not new, we are unaware of a commercial RTOS with such support. After identifying the mechanisms for an RTOS implementation of slotshifting, we discuss the run-time overheads for admitting aperiodic requests into the system1.
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| 25. |
- van den Heuvel, Martijn, et al.
(författare)
-
Transparent synchronization protocols for compositional real-time systems
- 2012
-
Ingår i: IEEE Transactions on Industrial Informatics. - 1551-3203 .- 1941-0050. ; 8:2, s. 322-336
-
Tidskriftsartikel (refereegranskat)abstract
- Hierarchical scheduling frameworks (HSFs) provide means for composing complex real-time systems from well-defined, independently analyzed components. To support resource sharing in two-level HSFs, three synchronization protocols based on the stack resource policy (SRP) have recently been presented for single-processor execution platforms, i.e., HSRP, SIRAP, and BROE. This paper presents a transparent implementation of these three protocols side-by-side in an HSF-enabled real-time operating system. Transparent synchronization interfaces make it possible to select a protocol during integration time based on its relative strengths.A timing interface describes the required budget to execute a component on a shared platform and an accessor's maximum critical- section execution time to global shared resources. These resources are arbitrated based on the available budget of the accessing task.We enable this explicit synchronization of virtual time with global time by means of a novel virtual-timer mechanism. Moreover, we investigate system overheads caused by each synchronization protocol, so that these can be included in the system analysis. Based on the analytical and implementation overheads of each protocol, we present guidelines for the selection of a synchronization protocol during system integration. Finally, we show that unknown task-arrival times considerably complicate an efficient implementation of SIRAP's self-suspension mechanism. We briefly discuss the implementation complexity caused by these arrivals for bandwidth-preserving servers, e.g., deferrable servers and BROE.
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| 26. |
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| 27. |
- van den Heuvel, Martijn, et al.
(författare)
-
Virtual scheduling for compositional real-time guarantees
- 2013
-
Ingår i: Proceedings of the 8th IEEE International Symposium on Industrial Embedded Systems, SIES 2013. - 9781479906581 ; , s. 151-160
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Konferensbidrag (refereegranskat)abstract
- In this paper, we extend the compositional scheduling framework to enable the integration of an existing (legacy) application as a component on a faster processor which needs to be shared with other components. After admission of this application into the framework, the integrated component still has to satisfy its tasks' deadline constraints and it must execute jobs in the same order as it did previously on the dedicated processor, regardless of the actual supply of processor resources. We propose a method - called virtual scheduling - which establishes this by reconstructing an appropriate order of delivering events. Virtual scheduling is therefore independent of the component-level scheduling policy and it is transparent to a component, so that it is even applicable without making modifications to the code or specification of the application.
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