| 1. |
- Afanasov, Mikhail, et al.
(författare)
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Battery-less zero-maintenance embedded sensing at the mithræum of circus maximus
- 2020
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Ingår i: SenSys 2020 - Proceedings of the 2020 18th ACM Conference on Embedded Networked Sensor Systems. - New York, NY, USA : Association for Computing Machinery, Inc. - 9781450375900 ; , s. 368-381
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Konferensbidrag (refereegranskat)abstract
- We present the design and evaluation of a 3.5-year embedded sensing deployment at the Mithræum of Circus Maximus, a UNESCO-protected underground archaeological site in Rome (Italy). Unique to our work is the use of energy harvesting through thermal and kinetic energy sources. The extreme scarcity and erratic availability of energy, however, pose great challenges in system software, embedded hardware, and energy management. We tackle them by testing, for the first time in a multi-year deployment, existing solutions in intermittent computing, low-power hardware, and energy harvesting. Through three major design iterations, we find that these solutions operate as isolated silos and lack integration into a complete system, performing suboptimally. In contrast, we demonstrate the efficient performance of a hardware/software co-design featuring accurate energy management and capturing the coupling between energy sources and sensed quantities. Installing a battery-operated system alongside also allows us to perform a comparative study of energy harvesting in a demanding setting. Albeit the latter reduces energy availability and thus lowers the data yield to about 22% of that provided by batteries, our system provides a comparable level of insight into environmental conditions and structural health of the site. Further, unlike existing energy-harvesting deployments that are limited to a few months of operation in the best cases, our system runs with zero maintenance since almost 2 years, including 3 months of site inaccessibility due to a COVID19 lockdown
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| 2. |
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| 3. |
- Afanasov, Mikhail, et al.
(författare)
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The FlyZone Testbed Architecture for Aerial Drone Applications
- 2020
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Ingår i: GetMobile. - : Association for Computing Machinery (ACM). - 2375-0529 .- 2375-0537. ; 24:1
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Tidskriftsartikel (refereegranskat)abstract
- Aerial drones represent a new breed of mobile computing. Compared to mobile phones and connected cars that only opportunistically sense or communicate, aerial drones offer direct control over their movements. They can thus implement functionality that were previously beyond reach, such as collecting high-resolution imagery, exploring near-inaccessible areas, or inspecting remote areas to gather fine-grain environmental data.
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| 4. |
- Ahmed, Saad, et al.
(författare)
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Demystifying Energy Consumption Dynamics in Transiently Powered Computers
- 2020
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Ingår i: ACM Transactions on Embedded Computing Systems. - : Association for Computing Machinery. - 1539-9087 .- 1558-3465. ; 19:6
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Tidskriftsartikel (refereegranskat)abstract
- Transiently powered computers (TPCs) form the foundation of the battery-less Internet of Things, using energy harvesting and small capacitors to power their operation. This kind of power supply is characterized by extreme variations in supply voltage, as capacitors charge when harvesting energy and discharge when computing. We experimentally find that these variations cause marked fluctuations in clock speed and power consumption. Such a deceptively minor observation is overlooked in existing literature. Systems are thus designed and parameterized in overly conservative ways, missing on a number of optimizations.We rather demonstrate that it is possible to accurately model and concretely capitalize on these fluctuations. We derive an energy model as a function of supply voltage and prove its use in two settings. First, we develop EPIC, a compile-time energy analysis tool. We use it to substitute for the constant power assumption in existing analysis techniques, giving programmers accurate information on worst-case energy consumption of programs. When using EPIC with existing TPC system support, run-time energy efficiency drastically improves, eventually leading up to a 350% speedup in the time to complete a fixed workload. Further, when using EPIC with existing debugging tools, it avoids unnecessary program changes that hurt energy efficiency. Next, we extend the MSPsim emulator and explore its use in parameterizing a different TPC system support. The improvements in energy efficiency yield up to more than 1000% time speedup to complete a fixed workload.
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| 5. |
- Ahmed, Saad, et al.
(författare)
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Fast and Energy-Efficient State Checkpointing for Intermittent Computing
- 2020
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Ingår i: ACM Transactions on Embedded Computing Systems. - : Association for Computing Machinery. - 1539-9087 .- 1558-3465. ; 19:6
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Tidskriftsartikel (refereegranskat)abstract
- Intermittently powered embedded devices ensure forward progress of programs through state checkpointing in non-volatile memory. Checkpointing is, however, expensive in energy and adds to the execution times. To minimize this overhead, we present DICE, a system that renders differential checkpointing profitable on these devices. DICE is unique because it is a software-only technique and efficient because it only operates in volatile main memory to evaluate the differential. DICE may be integrated with reactive (Hibernus) or proactive (MementOS, HarvOS) checkpointing systems, and arbitrary code can be enabled with DICE using automatic code-instrumentation requiring no additional programmer effort. By reducing the cost of checkpoints, DICE cuts the peak energy demand of these devices, allowing operation with energy buffers that are one-eighth of the size originally required, thus leading to benefits such as smaller device footprints and faster recharging to operational voltage level. The impact on final performance is striking: with DICE, Hibernus requires one order of magnitude fewer checkpoints and one order of magnitude shorter time to complete a workload in real-world settings.
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| 6. |
- Ahmed, Saad, et al.
(författare)
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Intermittent Computing with Dynamic Voltage and Frequency Scaling
- 2020
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Ingår i: EWSN '20. ; , s. 97-107
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Konferensbidrag (refereegranskat)abstract
- We present D2VFS, a run-time technique to intelligently regulate supply voltage and accordingly reconfigure clock frequency of intermittently-computing devices. These devices rely on energy harvesting to power their operation and on small capacitors as energy buffer. Statically setting their clock frequency fails to achieve energy efficiency, as the setting remains oblivious of fluctuations in capacitor voltage and of their impact on a microcontroller operating range. In contrast, D2VFS captures these dynamics and places the microcontroller in the most efficient configuration by regulating the microcontroller supply voltage and changing its clock frequency. Our evaluation shows that D2VFS markedly increases energy efficiency; for example, ultimately enabling a 30-300% reduction of workload completion times.
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| 7. |
- Asad, H. A., et al.
(författare)
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On Securing Persistent State in Intermittent Computing
- 2020
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Ingår i: ENSsys 2020 - Proceedings of the 8th International Workshop on Energy Harvesting and Energy-Neutral Sensing Systems. - New York, NY, USA : Association for Computing Machinery, Inc. ; , s. 8-14, s. 8-14, s. 8-14
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Konferensbidrag (refereegranskat)abstract
- We present the experimental evaluation of different security mechanisms applied to persistent state in intermittent computing. Whenever executions become intermittent because of energy scarcity, systems employ persistent state on non-volatile memories (NVMs) to ensure forward progress of applications. Persistent state spans operating system and network stack, as well as applications. While a device is off recharging energy buffers, persistent state on NVMs may be subject to security threats such as stealing sensitive information or tampering with configuration data, which may ultimately corrupt the device state and render the system unusable. Based on modern platforms of the Cortex M*series, we experimentally investigate the impact on typical intermittent computing workloads of different means to protect persistent state, including software and hardware implementations of staple encryption algorithms and the use of ARM TrustZone protection mechanisms. Our results indicate that i) software implementations bear a significant overhead in energy and time, sometimes harming forward progress, but also retaining the advantage of modularity and easier updates; ii) hardware implementations offer much lower overhead compared to their software counterparts, but require a deeper understanding of their internals to gauge their applicability in given application scenarios; and iii) TrustZone shows almost negligible overhead, yet it requires a different memory management and is only effective as long as attackers cannot directly access the NVMs.
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| 8. |
- Bambusi, Fulvio, et al.
(författare)
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The Case for Approximate Intermittent Computing
- 2022
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Ingår i: 2022 21st ACM/IEEE International Conference on Information Processing in Sensor Networks (ISPN 2022). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665496247 - 9781665496254 ; , s. 463-476
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Konferensbidrag (refereegranskat)abstract
- We present the concept of approximate intermittent computing and concretely demonstrate its application. Intermittent computations stem from the erratic energy patterns caused by energy harvesting: computations unpredictably terminate whenever energy is insufficient and the application state is lost. Existing solutions maintain equivalence to continuous executions by creating persistent state on non-volatile memory, enabling stateful computations to cross power failures. The performance penalty is massive: system throughput reduces while energy consumption increases. In contrast, approximate intermittent computations trade the accuracy of the results for sparing the entire overhead to maintain equivalence to a continuous execution. This is possible as we use approximation to limit the extent of stateful computations to the single power cycle, enabling the system to completely shift the energy budget for managing persistent state to useful computations towards an immediate approximate result. To this end, we effectively reverse the regular formulation of approximate computing problems. First, we apply approximate intermittent computing to human activity recognition. We design an anytime variation of support vector machines able to improve the accuracy of the classification as energy is available. We build a hw/sw prototype using kinetic energy and show a 7x improvement in system throughput compared to state-of-the-art system support for intermittent computing, while retaining 83% accuracy in a setting where the best attainable accuracy is 88%. Next, we apply approximate intermittent computing in a sharply different scenario, that is, embedded image processing, using loop perforation. Using a different hw/sw prototype we build and diverse energy traces, we show a 5x improvement in system throughput compared to state-of-the-art system support for intermittent computing, while providing an equivalent output in 84% of the cases.
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| 9. |
- El Yaacoub, Ahmed, 1996-, et al.
(författare)
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NeRTA : Enabling Dynamic Software Updates in Mobile Robotics
- 2022
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Konferensbidrag (refereegranskat)abstract
- We present NeRTA (Next Release Time Analysis), a technique to schedule dynamic software updates of the low-level control loops of mobile robots. Dynamic software updates enable software correction and evolution during system operation. In mobile robotics, they are crucial to resolve software defects without interrupting system operation or to enable on-the-fly extensions. Low-level control loops of mobile robots, however, are time sensitive and run on resource-constrained hardware with no operating system support. To minimize the impact of the update process, NeRTA safely schedules updates during times when the computing unit would otherwise be idle. It does so by utilizing information from the existing scheduling algorithm without impacting its operation. As such, NeRTA works orthogonal to the existing scheduler, retaining the existing platform-specific optimizations and fine-tuning, and may simply operate as a plug-in component. Our experimental evaluation shows that NeRTA estimates are within 15% of the actual idle times in more than three-quarters of the cases. We also show that the processing overhead of NeRTA is essentially negligible.
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| 10. |
- El Yaacoub, Ahmed, et al.
(författare)
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Poster Abstract: Scheduling Dynamic Software Updates in Safety-critical Embedded Systems : the Case of Aerial Drones
- 2022
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Ingår i: 2022 ACM/IEEE 13th International Conference on Cyber-Physical Systems (ICCPS). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665409674 - 9781665409681 ; , s. 284-285
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Konferensbidrag (refereegranskat)abstract
- Dynamic software updates enable software evolution and bug fixes to embedded systems without disrupting their run-time operation. Scheduling dynamic updates for safety-critical embedded systems, such as aerial drones, must be done with great care. Otherwise, the system's control loop will be delayed leading to a partial or even complete loss of control, ultimately impacting the dependable operation. We propose an update scheduling algorithm called NeRTA, which schedules updates during the short times when the processor would have been idle. NeRTA consequently avoids the loss of control that would occur if an update delayed the execution of the control loop. The algorithm computes conservative estimations of idle times to determine if an update is possible, but is also sufficiently accurate that the estimated idle time is typically within 15% of the actual idle time.
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