Browsing by Author "Li, Yonghui"
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- Mode-Controlled Data-Flow Modeling of Real-Time Memory ControllersPublication . Li, Yonghui; Salunkhe, Hrishikesh; Bastos, João; Moreira, Orlando; Åkesson, Benny; Goossens, KeesSDRAM is a shared resource in modern multi-core platforms executing multiple real-time (RT) streaming applications. It is crucial to analyze the minimum guaranteed SDRAM bandwidth to ensure that the requirements of the RT streaming applications are always satisfied. However, deriving the worst-case bandwidth (WCBW) is challenging because of the diverse memory traffic with variable transaction sizes. In fact, existing RT memory controllers either do not efficiently support variable transaction sizes or do not provide an analysis to tightly bound WCBW in their presence. We propose a new mode-controlled data-flow (MCDF) model to capture the command scheduling dependencies of memory transactions with variable sizes. The WCBW can be obtained by employing an existing tool to automatically analyze our MCDF model rather than using existing static analysis techniques, which in contrast to our model are hard to extend to cover different RT memory controllers. Moreover, the MCDF analysis can exploit static information about known transaction sequences provided by the applications or by the memory arbiter. Experimental results show that 77% improvement of WCBW can be achieved compared to the case without known transaction sequences. In addition, the results demonstrate that the proposed MCDF model outperforms state-of-the-art analysis approaches and improves the WCBW by 22% without known transaction sequences.
- Modeling and Verification of Dynamic Command Scheduling for Real-Time Memory ControllersPublication . Li, Yonghui; Åkesson, Benny; Goossens, KeesIn modern multi-core systems with multiple real-time (RT) applications, memory traffic accessing the shared SDRAM is increasingly diverse, e.g., transactions have variable sizes. RT memory controllers with dynamic command scheduling can efficiently address the diversity by issuing appropriate commands subject to the SDRAM timing constraints. However, the scheduling dependencies between commands make it challenging to derive tight bounds for the worst-case response time (WCRT) and the worst-case bandwidth (WCBW) of a memory controller. Existing modeling and analysis techniques either do not provide tight WCRT and WCBW bounds for diverse memory traffic with variable transaction sizes or are difficult to adapt to different RT memory controllers. This paper models a memory controller using Timed Automata (TA), where model checking is applied for analysis. Our TA model is modular and accurately captures the behavior of a RT memory controller with dynamic command scheduling. We obtain WCRT and WCBW bounds, which are validated by simulating the worst-case transaction traces obtained by model checking with a cycle-accurate model of the memory controller. Our method outperforms three state-of-the-art analysis techniques. We reduce WCRT bound by up to 20%, while the average improvement is 7.7%, and increase the WCBW bound by up to 25% with an average improvement of 13.6%. In addition, our modeling is generic enough to extend to memory controllers with different mechanisms.
- Multi-agent Adaptive Architecture for Flexible Distributed Real-time SystemsPublication . Chniter, Hamza; Li, Yonghui; Khalgui, Mohamed; Koubaa, Anis; Li, Zhiwu; Jarray, FethiRecent critical embedded systems become more and more complex and usually react to their environment that requires to amend their behaviors by applying run-time reconfiguration scenarios. A system is defined in this paper as a set of networked devices, where each of which has its own operating system, a processor to execute related periodic software tasks, and a local battery. A reconfiguration is any operation allowing the addition-removal-update of tasks to adapt the device and the whole system to its environment. It may be a reaction to a fault or even optimization of the system functional behavior. Nevertheless, such scenario can cause the violation of real-time or energy constraints, which is considered as a critical run-time problem. We propose a multi-agent adaptive architecture to handle dynamic reconfigurations and ensure the correct execution of the concurrent real-time distributed tasks under energy constraints. The proposed architecture integrates a centralized scheduler agent (ScA) which is the common decision making element for the scheduling problem. It is able to carry out the required run-time solutions based on operation research techniques and mathematical tools for the system's feasibility. This architecture assigns also a reconfiguration agent (RA p ) to each device p to control and handle the local reconfiguration scenarios under the instructions of ScA. A token-based protocol is defined in this case for the coordination between the different distributed agents in order to guarantee the whole system's feasibility under energy constraints.