The Concepts of Real-Time Systems

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En provenance du cours de EIT Digital

Development of Real-Time Systems

295 notes

EIT Digital

Development of Real-Time Systems

295 notes

Cours 3 sur 4 dans Specialization Development of Secure Embedded Systems

This course is intended for the Master's student and computer engineer who likes practical programming and problem solving! After completing this course, you will have the knowledge to plan and set-up a real-time system both on paper and in practice. The course centers around the problem of achieving timing correctness in embedded systems, which means to guarantee that the system reacts within the real-time requirements. Examples of such systems include airbags, emergency breaks, avionics, and also multi-media systems like video playback and QoS in web servers. The course teaches how to plan real-time systems in theory using established mathematical proofs and how to implement them in practice by using the most common scheduling methods. We also learn and how to program the system in the C language using the FreeRTOS real-time kernel. Finally we have a look at the future of real-time systems namely multi-core real-time systems! This course focus on the learn-by-doing approach with many examples and real-world programming assignments. We have 5 modules, each with a gentle graded quiz in the end and one peer reviewed programming assignment. In case you have no experience with C programming, please check you a practical course like: https://www.coursera.org/learn/arduino-platform The course is actually quite fun! -Simon Holmbacka / Åbo Akademi University Check out our whole curriculum: https://research.it.abo.fi/

À partir de la leçon

Introduction to Real-Time Systems

Here is where it all starts! We will make a brave attempt to start your future career in real-time systems! This week starts by learning the basic building stones in real-time systems and the system parameters required to successfully construct a real-time system. We introduce you to the corner stone of real-time systems, namely the scheduler – and its task in real-time schedules. You learn also what kind of real-time guarantees are needed in which systems. Concretely, you will learn (1) What is needed to create a real-time system (2) Where real-time requirements are needed. (3) The task and job structure and the parameters needed to schedule a task. (4) Difference between pre-emptive and non-pre-emptive tasks. This course is also part of a Blended Master Programme in Embedded Systems.

The Concepts of Real-Time Systems6:10

The Concept of Real-TimeTasks10:03

Rencontrer les enseignants

Simon Holmbacka
Dr
Åbo Akademi University, Faculty of Science and Engineering

[MUSIC]

In one sentence, a real-time system is one in which the correctness of

the system depends not only on the logical results of computation, but

also on the time at which the results are generated.

This means that they both have to look at the output of the system and

at the time at which the output was generated

to determine whether an execution is successful.

In fact, almost all types of automated systems we use in daily life is some

kind of real-time system.

The most common one you might think of are digital control systems for cars and

airplanes, and machinery.

And here we have a lot of critical functionality, which makes sure that

the systems can be safely operated without putting the user into danger.

There are also embedded real-time systems in the medical field.

And one important example here is of pacemaker,

which helps the heart maintain a steady pace.

Things usually hidden from the everyday user are the telecommunication systems for

Internet and mobile phones.

Such systems must deliver data packages at a certain rate to be useful, and

are therefore also real-time systems.

We have also the entertainment and

multimedia systems, which today are real-time systems

mostly because of streaming capabilities from DVB broadcast or the Internet.

A typical property of embedded systems is that they are hidden from the user.

You mostly notice embedded systems when they are not working and

this can sometimes even pose a danger to the user.

Of all computer systems in the world, about 98% of them are embedded systems and

many of them are real-time systems.

So, this is certainly an area worth exploring.

For example, the electronic control units or

ECUs in luxury class cars were only two in the mid-80s cars.

Then in the 90s, cars started to use more electronic control systems and

ECUs grew to about 7 and then rapidly to 30 in the early 2000s.

Car manufacturers have since then started to reduce the rapid growth of ECUs because

of cost, but the number of ECUs is still growing and the number soon reaches 100.

An Airbus A380 has 10,000 sensors in each wing.

And a computer system in such an airliner generates 2.5 terabytes of data each day.

2014 was the first year with more than 100,000 flights every day and

this number is still growing up.

So even with these numbers, airliners not often crash due to the very sophisticated

real-time systems controlling elevators and rudders for pitch and yaw.

The ailerons for roll and flaps, and slats, and spoilers for

aerodynamics, and all this thing is done via fly by wire.

So this means that the computer is ultimately in charge of the airliner.

A simple control system for actuation is the PID controller.

It works so that we have a plant, which is the actual system to control.

We have a sensor, measuring the results from the plant, and this is then

compared to the set point telling us what the result was supposed to be.

We can then calculate the difference between the set point and

the actual value, and use control-law for the PID controller to adjust the system

in order to have a result closer to the set point at the next measurement.

An actuator steers, then, the plant in the direction told by the PID controller.

For example, the ailerons on an airliner are continuously adjusting the roll of

the aircraft.

So, it's stable and it's not tipping over.

The PID controller adjusts the actuators by first reading the sensors monitoring

the plant.

It has a memory,

which stores the information about parameters from all iterations.

And dynamic parameters,

which tells how much to adjust the actuator compared to the input.

The PID controller calculates the deviation e(t) as a difference

between the reference, r(t) and the measured value, y(t).

This is then stored as the error value.

A PID controller can be implemented in C with only a few lines of C code.

The C function takes the error as an argument called In.

And In is then multiplied with P, I and D_gain parameters.

And some of those is then calculated.

Then the state variables are updated for next iteration and

the sum variable Out is returned.

In its simplest form,

the PID controller can be implemented with only 10 to 20 machine instructions.

And yet, provide a very powerful and stable control system.

In this course, we're going to learn how to build these things.

You will learn how to design a real-time system.

You will learn how to implement a real-time system in practice, and

you will learn how to verify a real-time system.

For this, it is recommended that you have some basic knowledge about

operating systems in general.

Also, a bit of C and Python is good to have here.

We will often refer to computer architecture,

so it is recommended that you have such a course in your backpack.

And we will use the book of Liu as our reference and

a free RTOS kernel as our implementation environment.

Some assignments will require some simulations, so

please have a look at the SimSo simulator for this.

So, now we are ready to actually begin the course.

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