18 Questions
A real-time system is a system that operates 'fast' in terms of processing speed.
False
A real-time system must react after a set deadline, otherwise, it is considered a failure.
False
The execution time of an activity in a real-time system is always constant.
False
Real-time systems are usually embedded in specialized equipment to control the equipment and its environment.
True
A real-time operating system guarantees 100% reliability without the need for any hardware duplication or formal verifications.
False
An embedded system consists only of software without any hardware components.
False
In a cooperative multitasking system, tasks are assigned processor time based on their priority levels.
False
If a task gets blocked in a cooperative multitasking system, it does not affect the execution of other tasks.
False
Multitasking preemptive systems use a scheduler to assign processor time to tasks based on their priorities.
True
Real-Time Operating Systems (RTOS) extension approach involves enhancing general-purpose OS with real-time features such as tailored schedulers and timers.
True
RTOS specialized kernels are known for their compatibility with existing systems and known environments.
False
Real-Time Operating Systems (RTOS) can be categorized into two main approaches: extensions of general-purpose OS and standalone specialized OS kernels.
True
In a soft real-time system, the system's response after deadlines are gradually reduced is not of interest.
False
In a firm real-time system, the response of the system within deadlines is crucial.
True
Real-time critical systems in avionics utilize both hardware and software redundancy.
True
An Airbus A340 has 3 calculators dedicated to implementing piloting laws.
False
Real-time operating systems typically consist of a control system and an operational system.
False
In a real-time system, missing deadlines may not have catastrophic consequences.
False
Study Notes
Real-Time Systems
- A real-time system is not just a fast system, but one that satisfies time constraints, which depend on the application and environment.
- Key characteristics of real-time systems:
- Receive and send signals to and from the process being controlled
- Signals can be periodic or non-periodic
- Must react before a specified deadline or date
- No event should be missed
- Failure to respond on time is considered a failure
Temporal Characteristics of Real-Time Systems
- Execution time of an activity is not constant (due to branching, iteration, synchronization)
- Periodicity of an activity: cadence of repetition
- Wake-up date: does not necessarily imply execution (due to processor unavailability)
- Deadline: must be respected imperatively in applications with strict time constraints
- Response time: difference between wake-up date and activity completion date
Examples of Real-Time Systems
- Often embedded in specialized equipment to control the equipment and/or its environment
- Examples: avionics, industrial control systems, medical devices
Definition of Embedded Systems
- A combination of software and hardware, specifically designed for a particular application
- Examples: control systems, consumer appliances, automotive systems
- Two possible implementations: cooperative or preemptive
- Multitasking operating systems: cooperative (used until Windows 3.1 and MacOS 9) and preemptive (time sharing between tasks and users)
Real-Time Operating Systems (RTOS)
- Two approaches:
- Extending general-purpose OS with real-time features (e.g., Linux-rt, RTX Real-Time Extension for Windows)
- Specialized OS (e.g., QNX, VxWORKS)
- Advantages of both approaches: compatibility with existing systems, performance, and adaptation to needs
Functioning of Real-Time Systems
- Simplified model:
- Infinite loop with:
- Reading input data
- Calculating orders to send to the process
- Emitting orders
- Infinite loop with:
- Modes of operation:
- Cyclic or cadenced: iteration at fixed intervals
- Event-driven: activation of the system at each event (interrupt concept)
- Mixed: cyclic with event-driven perturbations
Necessary Characteristics of Real-Time Systems
- Reliability: fault-tolerant, predictable behavior, and determinism
- Embedded systems: no human intervention possible
- Dedicated systems: designed from a material and software perspective for a specific application to eliminate uncertainty and risk of fatal errors
Real-Time Categories
- Soft real-time: response time is not catastrophic, but progressive degradation of service quality
- Hard real-time: response time is essential, and late response is useless
- Examples: video projection (soft real-time), video projection (hard real-time), financial transactions (hard real-time)
Examples of Real-Time Systems
- Avionics: critical real-time system with time constraints, redundancy, and validation
- Airbus A340 example: 115 equipment sets, 200,000 data exchanges, multiple calculators for inertial parameters, guidance laws, and pilotage laws
Learn about different types of real-time systems such as soft real-time and firm real-time, and understand the importance of meeting deadlines in these systems. Explore examples like video projections and stock market transactions.
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