Embedded Systems
What is Embedded System? What are the main features?
General Definition
Embedded Systems:
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coputer is part of enclosing system
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computer is not recognizable as such
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computer is used to control physical systems
โ cyber-physical systems
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computer is communicating with the environment via sensors and actuators
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computer is communicating with users via dedicated HMIs (switches, buttons, LEDs, (touch-)displays)
Specialized Definition
Embedde systems in cars:
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every systems which is based on an microcontroller (ECU: embedded control unit)
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domains with different requirements with respect to the application area
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ECUs are coupled by a set of different networks/field busses
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sw&hw = 40% of the production cost of a car
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Requirements
(1)
Functional - Requirements
What happens if you push button x?
Functional Requirements define actino-reaction pairs what the system should do
โ Definition of all โwhat if โฆ then โฆโ actions
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If button A is pressed the system is toggled(on/off)
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If button B is pressed the system produces a pot of coffee
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โฆ
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If water is low then LED 1 is switched on
Can we buid a system if we have all functional requirements?
(2)
Functional - Requirements - Non Functional
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The production of a pot of coffee has to be completed in less than 40s
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The power consumption of the system in standby mode has to be less than 1W
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โฆ
Real-time Systems
Definitions
Categories
Categorization based on the neccessary QoS
Hard Real-Time Constraints
Missing the time constraints can lead to damage and/or danger to the system and/or users.
(ex: automatic driving, heart pacemaker)
Real-Time
constraints
Fixed Real-Time
Constraints
Missing the time constraints
โ System reactions is of no use
โ No damage or danger
(ex. GPS-position of a vehicle)
Soft Real-Time
Constraints
Timing constraints or โonlyโ guidelines. missing them only leads to less QoS
(ex. digital video/audio transmission)
Operating Systems
Usage of an OS depends on the application and the uC.
Application
Simple
8/16 Bit uC
no OS (bare metal)
Complex
16/32 Bit uC
(hard) Real-Time constraints
real time OS (RTOS)
โ FreeRTOS, mbed, AUTOSAR-OS, QNX, โฆ
(no/soft) Real-Time constraints
General purpose OS (Linux, Windows, โฆ)
Efficient programming of embedded applications
(Deep) understanding of uC & RTOS are helpful/mandatory
Microcontrollers (uC) and ECUs
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