22-01-2013, 09:47 AM
Real Time Embedded System
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• Definition: An Embedded system is a computer system designed to perform
one or a few dedicated functions. It is embedded as part of a complete device
often including hardware and mechanical parts .
For example, your IPOD is an embedded system.
• Definition : A Real Time Application is an application which has time
constrains. This is a pre-defined operational deadlines from event to system
response, the time must be met even if the system runs at full load (worse case
scenario).
For example, a car engine control system is a real-time system because a delayed signal may cause
engine failure or damage.
Real Time System
• System is described as being deterministic if its response time is
Predictable
• Lag time between the occurrence of an event and response to that
event is called latency
• Deterministic response is key to real-time performance
Hard vs. Soft Real Time
• Hard Real Time is necessary for critical missions such as heart
Pacemaker and industrial process controllers, where failure to meet
a guaranteed response time could lead to catastrophic results
• In Soft Real Time users are happier when the system responds
Optimally, but which is not considered to have "failed" when the system doesn't meet each and every desired response time.
On average, a soft real-time system meets a particular response time goal.
Embedded System Design introduction
Performance
– The system performance is a key issue and must be kept in all
circumstance
– Performance is a major factor in choosing the processor, the clock
frequency , ram size , code size etc..
Re-use
– In many projects the system relies on already developed components,
which the designer must reuse. These components already have
embedded constrains in addition to the new system constraints.
Recovering from Failures
– Working in a distributed environment – connection failure…
C++ language
– C++ language is NOT processor dependent
– Reuse to other processor is extremely common
– Known to a very large number of programmers
– Medium effort require for testing and debug
– NOT efficient in terms of execution time and code size