Time is not necessarily what a clock reports. There is an uncertainty in time which is often not reported. Quantifying this timing uncertainty with clock parameters such as accuracy, precision, jitter or wander, is what introduces quality in time. Modern operating systems such as Linux lacks this perception of Quality of Time (QoT). It exposes some default clocks which are time synchronized / syntonized on best-effort basis through NTP or PTP, irrespective of the applications demand and the resources at hand.
General purpose operating systems (OS) are concurrent and multithread, and the primary goal of thread scheduler is to enforce fairness among all threads. This design is unsuitable for Real-Time (RT) systems, because tasks have soft or hard deadline of finishing time. Concurrency breaks timing of RT applications because users never know when their program is actually running. Explicitly allocation of processor resource to programs (threads) is thus necessary for timing-aware applications.
It's common in controller design to assume that the controller reads the sensors and writes to the actuators at the same time instant. This assumption is often violated in practice because the controller executes its code sequentially on a microprocessor. If the microprocessor is "fast enough," often the controller will still work.
Submitted by Anonymous on Thu, 10/08/2015 - 12:03pm
30th IEEE International Parallel & Distributed Processing Symposium
PDPS is an international forum for engineers and scientists from around the world to present their latest research findings in all aspects of parallel computation. In addition to technical sessions of submitted paper presentations, the meeting offers workshops, tutorials, and commercial presentations & exhibits.
