12 Questions
What is the primary reason why latency is considered a critical real-time property?
To minimize the time difference between an event and the reaction to it
What is the main difference between a firm deadline and a hard deadline?
The consequences of missing the deadline
In a real-time system, what is the purpose of continuously updating the internal image of the system state?
To maintain an accurate representation of the system state
What is the key difference between an event-triggered system and a time-triggered system?
The method of updating the internal image of the system state
What is the primary concern when considering the WCET of a program?
The maximum possible execution time of the program
What is the main characteristic of a real-time system?
It maintains an internal image of the system state
The time difference from event to ______ is known as latency.
reaction
[Blank] is the difference of max and min latency.
Jitter
In real-time systems, ______ is crucial for guaranteeing determinism.
WCET
A ______ deadline is one where delivering result after the deadline is useless (no benefit).
Firm
In a time-triggered system, the image update occurs in fixed ______.
intervals
Real-time architecture can be classified into event-triggered and ______ triggered systems.
time
Study Notes
Real Time Properties
- Latency refers to the time difference between an event and the reaction to it.
- Jitter is the difference between the maximum and minimum latency.
- High importance of latency in feedback control systems.
- Execution time is the time difference between the start and end of a task.
- Worst Case Execution Time (WCET) is the maximum possible execution time, considering all possible causes of delay, such as interrupts and caching, and is dependent on the platform.
Soft, Firm, and Hard Deadlines
- Soft deadline: delivering a result after the deadline reduces the benefit, but does not make it useless.
- Example: a car's radio volume increasing as the car speeds up.
- Firm deadline: delivering a result after the deadline makes it useless, with no benefit.
- Example: a SatNav system powering up after receiving an incoming traffic bulletin.
- Hard deadline: delivering a result after the deadline causes damage or harm, with a negative benefit.
- Example: a car's brake pedal being pushed, and the car decelerating.
Real Time Systems
- Real time systems maintain an internal image of the system state in memory.
- The system state is described by a set of variables.
- The internal image needs continuous updates to reflect the current system state.
Real Time Architecture
- Event-triggered system: the internal image is updated with every change of state.
- Time-triggered system: the internal image is updated in fixed intervals.
- Time-triggered systems use an internal or global clock, which requires synchronization.
Real Time Properties
- Latency refers to the time difference between an event and the reaction to it.
- Jitter is the difference between the maximum and minimum latency.
- High importance of latency in feedback control systems.
- Execution time is the time difference between the start and end of a task.
- Worst Case Execution Time (WCET) is the maximum possible execution time, considering all possible causes of delay, such as interrupts and caching, and is dependent on the platform.
Soft, Firm, and Hard Deadlines
- Soft deadline: delivering a result after the deadline reduces the benefit, but does not make it useless.
- Example: a car's radio volume increasing as the car speeds up.
- Firm deadline: delivering a result after the deadline makes it useless, with no benefit.
- Example: a SatNav system powering up after receiving an incoming traffic bulletin.
- Hard deadline: delivering a result after the deadline causes damage or harm, with a negative benefit.
- Example: a car's brake pedal being pushed, and the car decelerating.
Real Time Systems
- Real time systems maintain an internal image of the system state in memory.
- The system state is described by a set of variables.
- The internal image needs continuous updates to reflect the current system state.
Real Time Architecture
- Event-triggered system: the internal image is updated with every change of state.
- Time-triggered system: the internal image is updated in fixed intervals.
- Time-triggered systems use an internal or global clock, which requires synchronization.
Understand key concepts in real-time systems, including latency, jitter, and execution time. Learn about the importance of latency in feedback control systems and the concept of Worst Case Execution Time (WCET).
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