Download Embedded And Real

Chapter 1
Embedded And Real-Time System
Department of Computer Science
Hsu Hao Chen
Professor
Hsung-Pin Chang
Outline
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What is an embedded system？
Characteristics of embedded systems
Real-time systems concept
Real-time operating systems and realtime kernels
Processes, tasks, and threads
Architecture of real-time systems
What is an embedded system？
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For practical purposes
Embedded system consisting of a
compact, fast, and extremely reliable
operating system
Microprocessor located inside a device
Embedded system is a collection of
programs that run under operating
system
Characteristics of embedded systems(1/2)
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Virtually all kinds of computing systems
Temporal determinism
Time required to process any task is
finite and predictable
Less concerned with average response
time than worst-case response time
Must have a guarantee on the upper
time limit
Characteristics of embedded systems(2/2)
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It is typically encapsulated by the
hardware it controls, so end-users are
unaware of its presence
It is actually a computer system that
does not have the outward appearances
of a computer system.
Real-time systems concept
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Operate within specified time constraints
System must respond to inputs or events
within prescribed time limits
Real-time constraints:
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Hard Real-Time
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Example: air traffic control system.
Soft Real-Time
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Example: PS2
Real-time operating systems and
real-time kernels
RTOS kernel
Other RTOS services
Kernel
Processes, tasks, and threads
Program
Program
Process
Thread 1
Thread 2
Figure 1.2 Comparison of processes and threads
…
Thread n
Architecture of real-time systems(1/2)
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Threads are process two common
architecture
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Control loop with polling
Polling of the kernel executes an infinited loop
Advantage:
easy to implement
Disadvantage:
difficult to give threads with critical fast access
to the processor
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Architecture of real-time systems(2/2)
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Preemptive scheduling method
ThreadX use is preemptive scheduling method
Advantage:
priority solved critical fast access to the
processor
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