Intro

Question 1

What is Real-time computing

Answer 1

Has guaranteed or predictable response time

Worst-case execution time is most interesting

Optimized for predictability while general purpose is optimized for speed and throughput

Not really possible to do with general-purpose operating systems

Not a fancy way of saying fast computing

Not irrelevant even if hardware is fast enough

Question 2

Types of constraints and what does a missed deadline lead to?

Answer 2

Hard real-time - total system failure

Firm real-time - results have no value

Soft real-time - results have less value

Question 3

What are the different types of task triggers?

Answer 3

Periodic - at a regular time interval

Sporadic - when event occurs, limits on how often the event can occur

Aperiodic - when event occurs, no limitations on when it can occur

Question 4

How do we separate general purpose vs. real-time computers?

Answer 4

• General purpose
• Optimized for speed and througput
• Usually comes with a wide range of applications, tools, etc.
• Mouse, keyboard and screen
• Real-time
• Optimized for predictability
• Usually a minimized system without anything that is not necessary
• Serial interface or SSH (Specialized I/O)

Question 5

Characteristics of FreeRTOS

Answer 5

• Minimalistic operating system for microcontrollers that often do not use operating systems
• Run on many platforms

Question 6

Characteristics of VxWorks and QNX

Answer 6

• Proprietary operating systems for embedded and real-time systems
• Stable and proven platforms
• Expensive licenses

Question 7

Characteristics of Real-time variants of Linux

Answer 7

• Various methods for improving the real-time capabilities of Linux
• RT-Linux, RTAI, Xenomai, preempt-RT

Question 8

Real time system definition

Answer 8

Any system in which the time at which output is produced is significant. This is usually because the input corresponds to some movement in the physical world, and the output has to relate to that same movement. The lag from input time to output time must be sufficiently small for acceptable timeliness.

Question 9

Cohesion

Answer 9

Cohesion is concerned with how well a module holds together – its internal strength.

Question 10

Coupling

Answer 10

Coupling, by comparison is a measure of the interdependence of program modules. If two modules pass control information between them, they are said to possess high (or tight) coupling.

Question 11

Types of real-time systems:

Answer 11

reactive systems, time-aware systems, time-triggered and event-triggered systems

Question 12

Characteristics of a general real-time or embedded computer system

Answer 12

Real-time control, concurrent control of separate system components, low-level programming, support for numerical computation, largeness and complexity, extreme reliability and safety

Question 13

Stages of design

Answer 13

1. Requirements specification 2. system design,
2. detailed design,
3. coding
4. testing