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Questions tagged [real-time]

35 questions
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3 answers

What guarantees do "soft" real-time operating systems actually provide

I think I know what a "hard" real-time operating system is. It is an operating system with a scheduler that provides a contract with the application programmer. An application provides a deadline with each resource allocation request. If the…
Wandering Logic
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Realtime hardware/software versus PC software/hardware, how are these distinct and alike?

This question stems from a few answers and comments on a question I posted in signal processing found here. I guess I am a little confused. Are there any concrete differences between realtime software/hardware and just a regular PC? I would try to…
KDecker
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Priority inversion in Hoare and Mesa monitors

I understand the difference between Hoare and Mesa monitors. However I don't understand why priority inversion (when a lower priority process gets done before a higher priority process) is possible in the Hoare type but not possible in the Mesa…
user39930
5
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1 answer

Can multiple tasks in an RTOS share one stack to save memory?

Many small embedded systems have a limited amount of RAM, 10k or less. I know you can run an RTOS on such systems, however, a realistic number of tasks in such a system is very low, mainly because every task needs its own stack area. Is it possible…
Johan Bezem
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4
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3 answers

What does it mean that HDLs "explicitly include the notion of time"?

I got onto the topic of HDLs (Hardware Description Languages) from a comment elsewhere on this site. The Wikipedia article states, rather tantalizingly: One important difference between most programming languages and HDLs is that HDLs explicitly…
Wildcard
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timed automata - advance only in certain states

I am currently looking into timed automata for a project. I am thinking about a timed automaton where a clock only advances when the automaton is in a certain state. However, my little knowledge in the domain makes me wonder whether somebody already…
stklik
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If current time in milliseconds is considered good enough random seed for a pseudorandom number generator, why not just use that time directly?

I was reading about pseudorandom number generators and how they need a seed and how that seed is usually current system time in milliseconds. One of the most common algorithms is the linear congruential generator, which is an algorithm that based on…
stackzebra
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Agreeing on a Time in a Trustless Network

Imagine a chord-like network $N$. each machine $m \in N$ is directly connected to $N_m \subset N$. Without relying on official timeservers, I want all machines to synchronize to some time with millisecond precision. my algorithm is executed some…
option 12
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Avoiding collisions in space and time

Say I have an image, represented as a 2D array of pixel values. Also, say I have a set of points on that image where each has a current (x, y) position and a Destination (x, y) associated with it. I want to find a path for each point to its…
Michael O'Brien
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Optimality of EDF

For Earliest Deadline First, I have read that if utilization is less or equal to 1, the task set is schedulable under EDF. But does this criteria expresses the optimality for EDF? If not, how can we express optimality of EDF? So if I get asked is…
Dumbo
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A real-world example for a kind of real-time applications

I submitted a paper regarding hard real-time systems to an engineering journal. But the referees generally agreed my task model is too limited. My task model is a frame-based real-time application where all the tasks in the application have a common…
Code
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How to simulate a Discrete Event Simulation model with a real-time server?

My Problem is having to work with real-time server in a DES model. I have the following situation: I want to build a discrete event simulation model (Using event scheduling world view). However, this model needs to be connected to another real-time…
M. Pour
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What algorithm to use for substractive machining RT simulation?

For a CAM (Computer Aided Manufacturing) software, and more specifically, for the simulation of the subtractive manufacturing, I would like to understand how to design the representation. In subtractive manufacturing (e.g. a Mill), a piece of raw…
Adrian Maire
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Early Deadline First (EDF) scheduling in real-time systems feasibility test proof

I am trying to prove Theorem 6.2 on page 127 of the book Real-Time Systems by Jane W. S. Liu: http://www.cse.hcmut.edu.vn/~thai/books/2000%20_%20Liu-%20Real%20Time%20Systems.pdf It is based on Early Deadline First(EDF) scheduling. It says the proof…
Matt
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Why can't OS's keep audio and video recording in sync?

It seems every program that purports to record webcams fails to keep audio and video in sync. Moreover, there are probably man millenia being spent by people trying to correct for this during editing. While it is understandable that OS's may have…
James Bowery
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