127,274 research outputs found
Combining Time-Triggered Plans with Priority Scheduled Task Sets
The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-39083-3_13Time-triggered and concurrent priority-based scheduling are
the two major approaches in use for real-time and embedded systems.
Both approaches have their own advantages and drawbacks. On the one
hand, priority-based systems facilitate separation of concerns between
functional and timing requirements by relying on an underlying real-
time operating system that takes all scheduling decisions at run time.
But this is at the cost of indeterminism in the exact timing pattern of
execution of activities, namely variable release jitter. On the other hand,
time-triggered schedules are more intricate to design since all schedul-
ing decisions must be taken beforehand in the design phase, but their
advantage is determinism and more chances for minimisation of release
jitter. In this paper we propose a software architecture that enables the
combined and controlled execution of time-triggered plans and priority-
scheduled tasks. We also describe the implementation of an Ada library
supporting it. Our aim is to take advantage of the best of both ap-
proaches by providing jitter-controlled execution of time-triggered tasks
(e.g., control tasks), coexisting with a set of priority-scheduled tasks,
with less demanding jitter requirements.This work has been partly supported by the Spanish Government’s project M2C2 (TIN2014-56158-C4-1-P-AR) and the European Commission’s project EMC2 (ARTEMIS-JU Call 2013 AIPP-5, Contract 621429).Real Sáez, JV.; Sáez Barona, S.; Crespo, A. (2016). Combining Time-Triggered Plans with Priority Scheduled Task Sets. En Reliable Software Technologies – Ada-Europe 2016. Springer. 195-212. https://doi.org/10.1007/978-3-319-39083-3_13S195212Liu, C., Layland, J.: Scheduling algorithms for multiprogramming in a hard real-time environment. J. ACM 20(1), 46–61 (1973)MartĂ, P., Fuertes, J., Fohler, G.: Jitter compensation for real-time control systems. In: Real-Time Systems Symposium (2001)Dobrin, R.: Combining off-line schedule construction and fixed priority scheduling in real-time computer systems. Ph.D. thesis. Mälardalen University (2005)Cervin, A.: Integrated control and real-time scheduling. Ph.D. thesis. Lund Institute of Technology, April 2003Balbastre, P., Ripoll, I., Vidal, J., Crespo, A.: A task model to reduce control delays. Real-Time Syst. 27(3), 215–236 (2004)Hong, S., Hu, X., Lemmon, M.: Reducing delay jitter of real-time control tasks through adaptive deadline adjustments. In: 22nd Euromicro Conference on Real-Time Systems - ECRTS, pp. 229–238. IEEE Computer Society (2010)ISO/IEC-JTC1-SC22-WG9: Ada Reference Manual ISO/IEC 8652:2012(E) (2012). http://www.ada-europe.org/manuals/LRM-2012.pdfBaker, T.P., Shaw, A.: The cyclic executive model and Ada. In: Proceedings IEEE Real Time Systems Symposium 1988, Huntsville, Alabama, pp. 120–129 (1988)Liu, J.W.S.: Real-Time Systems. Prentice-Hall Inc., Upper Saddle River (2000)Pont, M.J.: The Engineering of Reliable Embedded Systems: LPC1769. SafeTTy Systems Limited, Skelmersdale (2014). ISBN: 978-0-9930355-0-0Aldea Rivas, M., González Harbour, M.: MaRTE OS: an Ada kernel for real-time embedded applications. In: Strohmeier, A., Craeynest, D. (eds.) Ada-Europe 2001. LNCS, vol. 2043, pp. 305–316. Springer, Heidelberg (2001)Palencia, J., González-Harbour, M.: Schedulability analysis for tasks with static and dynamic offsets. In: 9th IEEE Real-Time Systems Symposium (1998)Wellings, A.J., Burns, A.: A framework for real-time utilities for Ada 2005. Ada Lett. XXVI XXVII(2), 41–47 (2007)Real, J., Crespo, A.: Incorporating operating modes to an Ada real-time framework. Ada Lett. 30(1), 73–85 (2010)Sáez, S., Terrasa, S., Crespo, A.: A real-time framework for multiprocessor platforms using Ada 2012. In: Romanovsky, A., Vardanega, T. (eds.) Ada-Europe 2011. LNCS, vol. 6652, pp. 46–60. Springer, Heidelberg (2011
Software dependability modeling using an industry-standard architecture description language
Performing dependability evaluation along with other analyses at
architectural level allows both making architectural tradeoffs and predicting
the effects of architectural decisions on the dependability of an application.
This paper gives guidelines for building architectural dependability models for
software systems using the AADL (Architecture Analysis and Design Language). It
presents reusable modeling patterns for fault-tolerant applications and shows
how the presented patterns can be used in the context of a subsystem of a
real-life application
Real-time on-board obstacle avoidance for UAVs based on embedded stereo vision
In order to improve usability and safety, modern unmanned aerial vehicles
(UAVs) are equipped with sensors to monitor the environment, such as
laser-scanners and cameras. One important aspect in this monitoring process is
to detect obstacles in the flight path in order to avoid collisions. Since a
large number of consumer UAVs suffer from tight weight and power constraints,
our work focuses on obstacle avoidance based on a lightweight stereo camera
setup. We use disparity maps, which are computed from the camera images, to
locate obstacles and to automatically steer the UAV around them. For disparity
map computation we optimize the well-known semi-global matching (SGM) approach
for the deployment on an embedded FPGA. The disparity maps are then converted
into simpler representations, the so called U-/V-Maps, which are used for
obstacle detection. Obstacle avoidance is based on a reactive approach which
finds the shortest path around the obstacles as soon as they have a critical
distance to the UAV. One of the fundamental goals of our work was the reduction
of development costs by closing the gap between application development and
hardware optimization. Hence, we aimed at using high-level synthesis (HLS) for
porting our algorithms, which are written in C/C++, to the embedded FPGA. We
evaluated our implementation of the disparity estimation on the KITTI Stereo
2015 benchmark. The integrity of the overall realtime reactive obstacle
avoidance algorithm has been evaluated by using Hardware-in-the-Loop testing in
conjunction with two flight simulators.Comment: Accepted in the International Archives of the Photogrammetry, Remote
Sensing and Spatial Information Scienc
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