Validating a timing simulator for the NGMP multicore processor

Timing simulation is a key element in multicore systems design. It enables a fast and cost effective design space exploration, allowing to simulate new architectural improvements without requiring RTL abstraction levels. Timing simulation also allows software developers to perform early testing of the timing behavior of their software without the need of buying the actual physical board, which can be very expensive when the board uses non-COTS technology. In this paper we present the validation of a timing simulator for the NGMP multicore processor, which is a 4 core processor being developed to become the reference platform for future missions of the European Space Agency.The research leading to these results has received funding from the European Space Agency under contract NPI 4000102880 and the Ministry of Science and Technology of Spain under contract TIN-2015-65316-P. Jaume Abella has been partially supported by the Ministry of Economy and Competitiveness under Ramon y Cajal postdoctoral fellowship number RYC-2013-14717.Peer ReviewedPostprint (author's final draft

Contention-aware performance monitoring counter support for real-time MPSoCs

Tasks running in MPSoCs experience contention delays when accessing MPSoC’s shared resources, complicating task timing analysis and deriving execution time bounds. Understanding the Actual Contention Delay (ACD) each task suffers due to other corunning tasks, and the particular hardware shared resources in which contention occurs, is of prominent importance to increase confidence on derived execution time bounds of tasks. And, whenever those bounds are violated, ACD provides information on the reasons for overruns. Unfortunately, existing MPSoC designs considered in real-time domains offer limited hardware support to measure tasks’ ACD losing all these potential benefits. In this paper we propose the Contention Cycle Stack (CCS), a mechanism that extends performance monitoring counters to track specific events that allow estimating the ACD that each task suffers from every contending task on every hardware shared resource. We build the CCS using a set of specialized low-overhead Performance Monitoring Counters for the Cobham Gaisler GR740 (NGMP) MPSoC – used in the space domain – for which we show CCS’s benefits.The research leading to these results has received funding from the European Space Agency under contracts 4000109680, 4000110157 and NPI 4000102880, and the Ministry of Science and Technology of Spain under contract TIN-2015-65316-P. Jaume Abella has been partially supported by the Ministry of Economy and Competitiveness under Ramon y Cajal postdoctoral fellowship number RYC-2013-14717.Peer ReviewedPostprint (author's final draft

AHRB: A High-Performance Time-Composable AMBA AHB Bus

Abstract-Hard real-time systems are moving toward complex systems comprising chips with different IP components connected with standard buses. AMBA is one of the most used bus interfaces and has already been included in processors in the real-time domain. However, AMBA was not designed to provide time composable Worst Case Execution Time (WCET) estimates, which are desirable to reduce timing validation and verification costs. This paper analyzes and extends the AMBA Advanced Highperformance Bus (AHB) specification to enable time-composable WCET estimates by design. Concretely, (1) we analyze in detail the AMBA AHB in the context of hard real-time systems proving that it fails to provide time composability; (2) we define a restricted subset of AMBA AHB features, named restricted AHB (resAHB), that allows deriving time-composable, yet not tight, WCET estimates; and (3) we define an extension of resAHB, named Advanced High-performance Real-time Bus (AHRB), that includes the timing constraints in the specification. This allows deriving time-composable and tight WCET estimates. Our results show that AHRB can provide 3.5x tighter estimates than resAHB on average for EEMBC benchmarks

A dualcriticality memory controler (DCmc): Proposal and evaluation of a space case study

Abstract-Multicore Dual-Criticality systems comprise two types of applications, each with a different criticality level. In the space domain these types are referred as payload and control applications, which have high-performance and realtime requirements respectively. In order to control the interaction (contention) among payload and control applications in the access to the main memory, reaching the goals of highbandwidth for the former and guaranteed timing bounds for the latter, we propose a Dual-Criticality memory controller (DCmc). DCmc virtually divides memory banks into real-time and high-performance banks, deploying a different request scheduler policy to each bank type, which facilitates achieving both goals. Our evaluation with a multicore cycle-accurate simulator and a real space case study shows that DCmc enables deriving tight WCET estimates, regardless of the co-running payload applications, hence effectively isolating the effect of contention in the access to memory. DCmc also enables payload applications exploiting memory locality, which is needed for high performance

Real-Time Java in Space: Potential Benefits and Open Challenges

In this paper we analyze potential benefits of using the Java programming language in spacecraft on-board applications as well as problems with current Real-Time Java implementations that would have to be solved to make this possible. We base our experience on porting the Ovm Real-Time Java Virtual Machine to RTEMS/LEON2 and also our findings in the Real-Time Java Assessment Project funded by ESA

Scheduling success ratios and computational cost of the mechanism

2015 IEEE 18th International Symposium on Real-Time Distributed Computing (ISORC), Auckland, 13-17 April 2015The .xls spreadsheet contains scheduling success ratios and computational cost of the mechanism related to the publication "Seeking Time-Composable Partitions of Tasks for COTS Multicore Processors".European Commission: SAFURE - SAFety and secURity by design for interconnected mixed-critical cyber-physical systems (644080)Peer reviewe

Validating a timing simulator for the NGMP multicore processor

Timing simulation is a key element in multicore systems design. It enables a fast and cost effective design space exploration, allowing to simulate new architectural improvements without requiring RTL abstraction levels. Timing simulation also allows software developers to perform early testing of the timing behavior of their software without the need of buying the actual physical board, which can be very expensive when the board uses non-COTS technology. In this paper we present the validation of a timing simulator for the NGMP multicore processor, which is a 4 core processor being developed to become the reference platform for future missions of the European Space Agency.The research leading to these results has received funding from the European Space Agency under contract NPI 4000102880 and the Ministry of Science and Technology of Spain under contract TIN-2015-65316-P. Jaume Abella has been partially supported by the Ministry of Economy and Competitiveness under Ramon y Cajal postdoctoral fellowship number RYC-2013-14717.Peer Reviewe

Data Bus Slicing for Contention-Free Multicore Real-Time Memory Systems

Memory access contention is one of the main contributors to tasks' execution time variability in real-Time multicores. Existing techniques to control memory contention based on time-sharing memory access do not scale well with increasing complexity of multicores, leading to a rapid increase of WCET estimates. This is due to fact that requests from different tasks interleave in the access to memory, and for each of its requests a task has to make worstcase time allowances to account for the memory state left by the previous request, that may belong to a different task. In this paper, we propose a memory organization that controls contention by dividing the data bus into narrower independent data buses, thus removing conflicts among different tasks accessing memory. While narrower data buses require extra transfers, they allow exploiting memory locality, hence only slightly affecting average performance. Our evaluation on a solid space case-study shows that the proposed memory organization provides contention-free memory access facilitating timing analysis and tightening WCET estimates.The research leading to these results has received funding from the European Space Agency under contract NPI 4000102880 and the Ministry of Science and Technology of Spain under contract TIN-2015-65316-P. Jaume Abella has been partially supported by the Ministry of Economy and Competitiveness under Ramon y Cajal postdoctoral fellowship number RYC-2013-14717.Peer ReviewedPostprint (author's final draft

Deconstructing bus access control policies for real-time multicores

Multicores may satisfy the growing performance requirements of critical Real-Time systems which has made industry to consider them for future real-time systems. In a multicore, the bus contention-control policy plays a key role in system's performance and the tightness of the Worst-Case Execution Time (WCET) estimates. In this paper we develop analytical models of the contention that requests from different tasks running in different cores suffer for the two most-used contention control policies: Time-Division Multiple Access (TDMA) and Interference-Aware Bus Arbiter (IABA), which allows us to compare them. We further show the benefits of having such models for real-time system designers and chip providers. Our results show that WCET estimates obtained with TDMA are slightly (2%) tighter than those obtained with IABA, at the cost of knowing the exact cycle at which every access of every task accesses the bus. However, average performance is 10% worse with TDMA than with IABA. Overall, IABA is the most appealing contention-control policy since it allows achieving tight WCET estimates and high average performance with little burden for the user

Data bus slicing for contention-free multicore real-time memory systems

Memory access contention is one of the main contributors to tasks' execution time variability in real-Time multicores. Existing techniques to control memory contention based on time-sharing memory access do not scale well with increasing complexity of multicores, leading to a rapid increase of WCET estimates. This is due to fact that requests from different tasks interleave in the access to memory, and for each of its requests a task has to make worstcase time allowances to account for the memory state left by the previous request, that may belong to a different task. In this paper, we propose a memory organization that controls contention by dividing the data bus into narrower independent data buses, thus removing conflicts among different tasks accessing memory. While narrower data buses require extra transfers, they allow exploiting memory locality, hence only slightly affecting average performance. Our evaluation on a solid space case-study shows that the proposed memory organization provides contention-free memory access facilitating timing analysis and tightening WCET estimates.The research leading to these results has received funding from the European Space Agency under contract NPI 4000102880 and the Ministry of Science and Technology of Spain under contract TIN-2015-65316-P. Jaume Abella has been partially supported by the Ministry of Economy and Competitiveness under Ramon y Cajal postdoctoral fellowship number RYC-2013-14717.Peer Reviewe