Upload
bruce-morgan
View
231
Download
1
Tags:
Embed Size (px)
Citation preview
2004-11-23 @ SaabTech Jönköping
FLEXCON = Real-Time & Control
Real-TimeComputing
ControlEngineeringFLEXCON
Control in Real-Time Computing
Real-Time Techniques in Control System Implementation
2004-11-23 @ SaabTech Jönköping
Temporal Non-Determinism• Decreases:
– improvements in worst-case analysis methods
– tool development
– development of more deterministic implementation techniques
• Increases:– developments in general purpose computer systems
– new types of applications, e.g., Internet-based, operating in open and unpredictable environments
– next generation micro-chips• stochastics will play a larger role
• sacrifice temporal determinism to maintain functional determinism
Increasing, at least for non-critical systems.....
2004-11-23 @ SaabTech Jönköping
Flexibilitet• F m.a.p osäkerhet om resursutnyttjande
• F m.a.p osäkerhet om egenskaper hos implementationsplattform
• F m.a.p. osäkerhet om extern omgivning
• F m.a.p. osäkerhet om # tasks (last)
• F m.a.p. specifikationer (interval/max/min vs fixa värden)
• F m.a.p. dynamisk systemuppdatering (plug’n play) (komponenter, applikationer, systemprogramvara)
• F. i bemärkelsen event-triggered vs time-triggered (dynamic vs static)
• F. i utvecklingsprocessen (vid design-time), använda komponenter etc, konfigurering,
• F. m.a.p. virtuell resp fysisk miljö
2004-11-23 @ SaabTech Jönköping
WP1: Flexibility in real-time embedded control system design using COTS platforms, languages and
components
• Component Technology (Ivica Crnkovic)– embedded control systems
– real-time issues
– flexibility
– PhD student Johan Fredriksson (2003) (SAVE)
• Language Technology – Java (Klas Nilsson)– dynamic aspects
– flexibility
– PhD student Sven Gestegård Robertz • Cont. of ARTES project
• Feedback scheduling in dynamic memory allocation (RT-Java)
2004-11-23 @ SaabTech Jönköping
WP23
• WP2: Control-Based Approaches in Embedded Systems
• WP3: Quality-of-Service and Resource Negotiation in Embedded Control
• Combined into a single WP with focus on control systems
2004-11-23 @ SaabTech Jönköping
Temporal Determinism• Computer-based control theory is based on
– equidistant sampling– negligible input-output latencies that can be ignored or constant
latencies that easily can be compensated for
• Reality:– Varying execution times due to preemption, blocking, data-
dependencies, caches, pipelines, network communication, …
• Result:– Sampling interval jitter– Non-negligible and varying latencies
2004-11-23 @ SaabTech Jönköping
Control Community
A new implementation and resource-aware control paradigm is needed!
Resource-Constrained Control
2004-11-23 @ SaabTech Jönköping
Hard Control Implementation Approach
• Strive to maximize the temporal determinism• E.g. using time-triggered and synchronous programming
models• Pros:
– Simplifies attempts at formal verification for, e.g. safety-critical applications
– However, a large amount of ”hard” real-time control applications are not safety-critical
• Cons:– Often requires special purpose solutions, i.e., less efficient and more
expensive– Requires complete knowledge about resource utilization, load, ..– May result in under-utilized systems with possibly poor control
performance
2004-11-23 @ SaabTech Jönköping
Hard R-T Task Model
• Periodic/sporadic tasks with constant period, hard deadline, and known WCET
• Just a model:– Does not fit all control problems
• E.g. hybrid controllers, event-based controllers
– Overly restrictive for most control problems• a missed deadline no catastrophy
• a late control signal is better than no signal at all
2004-11-23 @ SaabTech Jönköping
Soft Control Implementation Approach
• View the temporal nondeterminism caused by the implementation platform as an uncertainty or disturbance acting on the control loop
• Use control-based approach– Inherent robustness of feedback
– Design for robustness against implementation uncertainties
– Active compensation, cp feedforward from measurable disturbances and adaptive control
2004-11-23 @ SaabTech Jönköping
Implementation-Robust Control
A tremendous amount of theory for plant uncertainties
?
Very little theory for implementation platform uncertainties
?
2004-11-23 @ SaabTech Jönköping
Implementation-Robust Control1. Temporal robustness
• timing variations• Theory that allows us to decide which level of temporal determinims
that a given control loop really requires in order to meet given objectives on stability and performance
• Is it necessary to use a time-triggered approach or will an event-triggered approach do?
• How large jitter in sampling interval and i-o latency can be tolerated?• Is it Ok to now and then skip a sample?• …..
2. Functional robustness• Fault-tolerance towards computer-level faults leading to data errors• An increasing problem in future deep sub-micron technology
hardware
2004-11-23 @ SaabTech Jönköping
Resource Allocation as a Control Problem
• In an applications with multiple (control) tasks the dynamic allocation of resources to the tasks can be viewed as a control problem in itself!
• The control performance can be viewed as a quality-of-service attribute (Quality-of-Control)
2004-11-23 @ SaabTech Jönköping
Control in Real-Time Computing• Use of control-based approaches for
uncertainty management in large real-time computer and communication systems is receiving increased attention
• The worst-case approach no longer feasible• Feedback, feedforward, ...• Control-oriented models capturing dynamics
2004-11-23 @ SaabTech Jönköping
Feedback Scheduling
• Dynamic on-line allocation of computing resources
• Feedback from actual resource utilization
• In principle, any computing resource
2004-11-23 @ SaabTech Jönköping
Feedback Scheduling Structures
• Feedback– Reactive
• Feedforward– Proactive
– Mode changes and admission control
2004-11-23 @ SaabTech Jönköping
Requirements on Scheduling Theory
• Relax the standard hard-real time assumptions
• Theory that better matches the needs of control systems
2004-11-23 @ SaabTech Jönköping
Requirements on Control Theory
• Co-design methods– control design methods that take resoure
constraints into account
• Improved understanding of how temporal non-determinism effect control performance– analysis methods– Tools
• Theory for aperiodic systems
2004-11-23 @ SaabTech Jönköping
Examples of recent developments• Jitterbug (Cervin, Lincoln):
– Matlab toolbox
– analysis of how sampling period and i/o delay distributions effect control performance
• TrueTime (Cervin, Henriksson):– Simulink toolbox
– co-simulation of temporal effects of real-time kernels and communication networks, and control performance
• New simple stability results (Lincoln):
– control loops with variations in delay
– networked control loops
2004-11-23 @ SaabTech Jönköping
Tool Usage
SchedulingParameters
(T,D,Prio, …)
Task TimingParameters
(latencies, jitter, …)
ControlPerformance
(variance, rise time, overshoot, ….)
Complex, ”nonlinear”relationship
Non-trivialrelationship
Simulation withTrueTime
Analysis withJitterbug
2004-11-23 @ SaabTech Jönköping
WP4: Testing-Based Verification and Monitoring of Embedded Control Systems
• Högskolan i Skövde (Sten Andler)
• Focus on event-driven control systems
• Run-time properties for testability
• Test case selection and generation.
• Connection to MdH (Thane)
2004-11-23 @ SaabTech Jönköping
WP5: Robotics and Automation Demonstrator
• Common platform for demonstrating project results
• Maintain the project focused• Not a “moon-lander” demonstrator• Based on Robotics Laboratory in Lund
(Klas Nilsson)• EU project HRTC, incl. TTP• EU project AUTOFETT with ABB, …• Strong links to ABB• EU project SMErobot starting...
2004-11-23 @ SaabTech Jönköping
Thing in common with Saab• Separation of concerns, modularity• Multi-CPU VME+PCI/PMC systems• Dependable communication/control• COTS hardware• Long-lasting platforms• Safe execution• Testing and monitoring• Combination with formal methods desired• Engineering efficiency/practices....
2004-11-23 @ SaabTech Jönköping
Possible SaabTech Issues
• Flexibility techniques for improved robustness• Combining – for mission-critical systems:
– Safe languages (Well-defined execution)– Certified run-time techniques (VM+HW)– Safe partitioning with shared resources.– Formal verification (FLEXCON+SAVE)– Improved testing techniques (pre-runtime)– Embedded on-line monitoring (run-time)
• Questions?