Embedded Systems Software Development

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Embedded Systems Software Development

• Robert Oshana
• National Technological University

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Lecture 1

• Introduction to Embedded Systems

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Agenda

• What is an Embedded System?
• Characteristics of embedded systems
• Requirements for embedded systems

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What is an embedded system?

• Specialized computer system
• Part of a larger system or machine
• Information processing subsystems integrated in a
  larger system
• As part of a larger system it largely determines
  its functionality
• An embedded system usually contains an embedded
  processor
• Some embedded systems include an operating system

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What is an embedded system?

• Some embedded systems are very specialized
  resulting in the entire logic being implemented
  as a single program
• These systems are embedded into some device for
  some specific purpose other than to provide
  general purpose computing

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Embedded system dominate
Close to 4 billion embedded processors sold each
year
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Embedded system components
(Koopman)
Software
Memory
FPGA/ ASIC
CPU
D/A conversion
Actuators
A/D conversion
Sensors
Aux system (power cooling, etc
User interface
Diagnostic port
Electromechanical Backup and safety
External environment
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Major functions

• Monitor the environment embedded systems read
  data from input sensors
• This data is then processed and the results
  displayed in some format to a user or users
• Control the environment embedded systems
  generate and transmit commands for actuators
• Transform the information embedded systems
  transform the data collected in some meaningful
  way, such as data compression/decompression

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Sensors and actuators

• A sensor is a device that responds to a physical
  stimulus (as heat, light, sound, pressure,
  magnetism, or a particular motion) and transmits
  a resulting impulse (as for measurement or
  operating a control).
• An actuator is a mechanical device for moving or
  controlling something

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Sensors and Actuators
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Perform meaningful operations

• Embedded systems typically execute applications
  such as control laws, finite state machines, and
  signal processing algorithms
• These systems must also detect and react to
  faults in both the internal computing environment
  as well as the surrounding electromechanical
  systems

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Characteristics of embedded systems

• Application Specific Systems
• Embedded systems are not general-purpose
  computers
• Optimized for a specific application
• Many of the job characteristics are known before
  the hardware is designed
• allows the designer to focus on the specific
  design constraints of a well defined application

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Characteristics of embedded systems

• Application Specific Systems
• Embedded S/W usually cannot run on other embedded
  systems without modification
• Hardware tailored to application
• Unnecessary circuitry eliminated
• Resources shared if possible

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Characteristics of embedded systems

• Reactive Systems
• typical embedded systems model responds to the
  environment via sensors and control the
  environment using actuators
• requires embedded systems to run at the speed of
  the environment
• this characteristic is called reactive.
• Reactive computation means that the system
  (primarily the software component) executes in
  response to external events
• External events can be either periodic or
  aperiodic

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Characteristics of embedded systems

• One of the biggest challenges for embedded system
  designers is performing an accurate worst case
  design analysis on systems with statistical
  performance characteristics (e.g., cache memory
  on a DSP or other embedded processor)
• Accurately predicting the worst case may be
  difficult on complicated architectures
• Often leads to overly pessimistic estimates
  erring on the side of caution

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Characteristics of embedded systems

• Distributed Systems
• communicating processes executing on several CPUs
  or ASICs
• connected by communication links
• economical 4 8-bit microcontrollers may be
  cheaper than a 32-bit processors (even with comm
  links)

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Characteristics of embedded systems

• Heterogeneous Architectures
• different processors in the same system solution
• may also be mixed signal systems
• combination of I/O interfaces, local and remote
  memories, and sensors and actuators makes
  embedded system design unique
• heterogeneity provides better design flexibility
  in tight design constraints

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Heterogeneous systems
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Characteristics of embedded systems

• Harsh environment
• Many embedded systems do not operate in a
  controlled environment
• Excessive heat is often a problem, especially in
  applications involving combustion (e.g., many
  transportation applications)
• protection from vibration, shock, lightning,
  power supply fluctuations, water, corrosion,
  fire, and general physical abuse
• challenges to the embedded system designer,
  including accurately modeling the thermal
  conditions of these systems

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Characteristics of embedded systems

• System safety and reliability
• embedded systems control more and more of the
  safety aspects of the overall system
• these safety measures may be in the form of
  software as well as hardware control
• challenges to embedded designers include
  designing reliable software and building cheap,
  available systems using unreliable components

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Characteristics of embedded systems

• Control of physical systems
• when controlling physical equipment, large
  current loads may need to be switched in order to
  operate motors and other actuators
• embedded systems may need large computer circuit
  boards with many non-digital components
• must carefully balance system tradeoffs among
  analog components, power, mechanical, network,
  and digital hardware with corresponding software

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Characteristics of embedded systems

• Small and low weight
• many embedded computers are physically located
  within some larger system
• form factor for the embedded system may be
  dictated by aesthetics
• challenge is to develop non-rectangular
  geometries for certain solutions
• weight can also be a critical constraint

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Other differences from desktop

• Human interface varies
• Flashing light
• Real-time robotic system
• Diagnostic port used for diagnosing the
  controlled system not the computer
• FPGA and ASIC and non-digital H/W used to
  increase performance or safety

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A generic embedded system
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Generic embedded system

• Processor
• Just enough to get the job done
• Register width is important
• General purpose 32- bit and 64- bit
• Embedded processors 8- and 16-bit
• Memory
• ROM (executable program)
• RAM (data to manipulate)
• Register width drives amount of memory

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Generic embedded system

• Development cost
• Dependent of product
• High volume products can stand for a higher
  development cost
• Smaller volume is more sensitive to development
  cost
• Number of units
• Expected lifetime
• Drives design decisions

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Generic embedded system

• Reliability
• Children's toys do not always have to work right
• Space shuttle is a different story

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Common design requirements
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Attributes of some embedded systems
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Requirements for embedded systems
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Functional requirements

• Functional requirements describe the type of
  processing the system will perform 
• Data Collection requirements
• Sensoring requirements
• Signal conditioning requirements
• Alarm monitoring requirements
• Direct Digital Control requirements
• Actuator control requirements
• Man-Machine Interaction requirements (Informing
  the operator of the current state of a controlled
  object for example

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Temporal requirements

• Embedded systems have many tasks to perform, each
  having its own deadline
• Temporal requirements define the stringency in
  which these time-based tasks must complete
• Minimal latency jitter
• Minimal Error-detection latency
• Temporal requirements can be very tight (for
  example control-loops ) or less stringent (for
  example response time in a user interface)

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Dependability requirements

• Reliability
• considered at the system rather than the
  individual component level (emergent)
• three dimensions to consider
• Hardware reliability probability of a hardware
  component failing
• Software reliability probability that a software
  component will produce an incorrect result
• Operator reliability how likely that the
  operator of a system will make an error

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Dependability requirements

• Metrics used to determine system reliability
• Probability of failure on demand likelihood that
  the system will fail when a service request is
  made
• Rate of failure occurrence frequency of
  occurrence with which unexpected behavior is
  likely to occur
• Mean Time to Failure the average time between
  observed system failures.

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Dependability requirements

• Safety critical failure modes and what types of
  certification are required for the system
• Maintainability constraints on the system such
  as type of Mean Time to Repair (MTTR)
• Availability the probability that the system is
  available for use at a given time. Availability
  is measured as
• Availability MTTF / (MTTFMTTR)
• Security unacceptable system behavior

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Embedded processor alternatives
Low cost
Higher
Off the shelf general
Flexibility
Purpose processor
Off the shelf DSP, MCU
Low power
Embedded Core Processors
DSP, MCU
Higher speed
Faster
Time to
market
Hardwired Integrated
Circuit (ASIC)
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Embedded programming languages

• C has become the language of embedded programmers
• Advantages of C
• Small
• Easy to learn
• Wide compiler support
• Large body of experience
• Processor independent
• Low level programming language

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Embedded programming languages

• C gives embedded programmers large degree of
  direct hardware control without sacrificing the
  benefits of a HLL
• Produces relatively compact efficient code for a
  wide variety of processors
• C and Ada are also good
• No more assembly required (mostly)

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Trends in embedded systems

• Increasing code size
• average code size for embedded systems has been
  increasing dramatically
• 1992 avg code size - range of 16-64K bytes
• 1996 the average size had grown to 64K-512K
• This trend is continuing
• Migration to higher level language from sssembly
• As applications become more and more complex,
  programmers are transitioning to higher level
  languages for productivity reasons

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Trends in embedded systems

• Increasing reuse of pre-designed components
• these include DSP chips as well as other
  microprocessors and microcontrollers
• Migration to a core-based design
• Systems becoming more complex and heterogeneous
• There are more ASIC-based designs with high speed
  as well as high integration
• Larger microprocessors are used with 32-bit
  processors becoming the norm