Authors:
Karl-Erik Arzen,
Anton Cervin,
Johan Eker,
Lui Sha,
Volume: 1, Page 4865 Paper number 4301
Abstract:
The paper presents the emerging field of integrated control and CPU-time
scheduling, where more general scheduling models and methods that better
suit the needs of control systems are developed. This creates possibilities
for dynamic and flexible integrated control and scheduling frameworks,
where the control design methodology takes the availability of computing
resources into account during design and allows on-line trade-offs
between control performance and computing resource utilization.
Authors:
Anton Cervin,
Johan Eker,
Volume: 1, Page 4871 Paper number 4302
Abstract:
The paper presents a feedback scheduling mechanism in the context of
co-design of the scheduler and the control tasks. We are particularly
interested in controllers where the execution time may change abruptly
between different modes, such as in hybrid controllers. The proposed
solution attempts to keep the CPU utilization at a high level, avoid
overload, and distribute the computing resources evenly among the tasks.
The feedback scheduler is implemented as a periodic or sporadic task
that assigns sampling periods to the controllers based on execution-time
measurements. The controllers may also communicate feedforward mode-change
information to the scheduler. As an example, we consider hybrid control
of a set of double-tank processes. The system is evaluated, from both
scheduling and control performance perspectives, by co-simulation of
controllers, scheduler, and tanks.
Authors:
Lui Sha,
Xue Liu,
Marco Caccamo,
Giorgio Buttazzo,
Volume: 1, Page 4877 Paper number 4303
Abstract:
In many real-time control applications, the task periods are typically
fixed and worst-case execution times are used in schedulability analysis.
With the advancement of robotics, flexible visual sensing using cameras
becomes a popular alternative to the use of embedded sensors. Unfortunately,
the execution time of visual tracking varies greatly. In this paper,
we integrate load driven online scheduling with direct digital designs
to optimize control performance as a function of varying workload.
Authors:
Giorgio Buttazzo,
Luca Abeni,
Volume: 1, Page 4883 Paper number 4304
Abstract:
In real-time computing systems, timing constraints imposed on application
tasks are typically guaranteed off line using schedulability tests
based on fixed parameters and worst-case execution times. However,
a precise estimation of tasks' computation times is very hard to achieve,
due to the non deterministic behavior of several low-level processor
mechanisms, such as caching, prefetching, and DMA data transfer. The
disadvantage of relying the guarantee test on a priori estimates is
that an underestimation of computation times may jeopardize the correct
behavior of the system, whereas an overestimation will certainly waste
system resources and causes a performance degradation. In this paper,
we propose a new methodology for automatically adapting the rates of
a periodic task set without forcing the programmer to provide a priori
estimates of tasks' computation times. Actual executions are monitored
by a runtime mechanism and used as feedback signals for predicting
the actual load and achieving rate adaptation. Load balancing is performed
using an elastic task model, according to which tasks utilizations
are treated as springs with given elastic coefficients.
Authors:
Pedro Albertos,
Alfons Crespo,
Ismael Ripoll,
Marina Vallés,
Patricia Balbastre,
Volume: 1, Page 4889 Paper number 4305
Abstract:
In the framework of RT digital control, two fundamental parameters
are defined, the control effort and the control action interval. The
first one is related to the strength of the control that, due to the
intersampling open-loop control, determines the degrading of performances
under unexpected delays. The second one refers to the unavoidable delays
in the multitasking environment due to interactions among the tasks.
As a consequence, the scheduling policy should consider not only the
tasks delays but also their influence in the control loop behavior,
being calculated to minimize the overall degrading of performances.
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