CS 546: Intelligent Embedded Systems

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CS 546 Intelligent Embedded Systems

• Gaurav S. Sukhatme
• Robotic Embedded Systems Lab
• Center for Robotics and Embedded Systems
• Computer Science Department
• University of Southern California
• gaurav_at_usc.edu
• http//robotics.usc.edu/gaurav/CS546

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Today we will..

• Assign homework 1
• Karthik will give a brief explanation
• Homework is online on the class website
• Form teams for homeworks
• only for homeworks (not project)
• 2 students in each team
• your homework team is fixed for all four
  homeworks
• Sort out further registration woes
• Cover a quick history of embedded systems
• Give a broad overview of embedded systems

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Homework 1

• Karthik just gave you details
• Due a week from today no extensions
• Teams of two for each homework same team
  members for each homework
• Lab keys are available with Julieta in SAL 302
  starting Thursday morning at 10 am (dont ask
  before that she is short of keys right now)

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Of Registration and Rooms..

• The CS dept is working on a bigger room for the
  class
• The class is currently officially capped to 40 so
  the University does not allow more people to sign
  up
• Cant increase the cap until a bigger room is
  found
• I am assured that a new room will be found soon
  and all those who I have cleared to register will
  be allowed to register (how many ?)

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Is there anyone here

• who has not yet filled the questionnaire ?
• who has filled the questionnaire and not got a
  response from me ?
• who wants to be in the class, and is not on the
  class mailing list ?

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So what is this class about ?

• How to design scalable, distributed,
  application-level software for embedded systems
  which have constraints on processing, power,
  communication
• In particular our interest is in systems that
  interact with the physical world through sensors
  and (to a lesser extent) actuators
• Combine a set of readings about state of the art
  research with learning by doing

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Course Outline

• Introduction
• Background and building blocks
• Principles of sensing and actuation
• Networking overview
• Time synchronization
• Localization
• Energy management
• Adaptive sampling and data management
• Project presentations
• Spring break
• Environmental monitoring
• NAMOS
• Project presentations
• NIMS
• Guest lecture Cyclops
• Final project presentations

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What is an Embedded System ?

• A special-purpose computer system completely
  enclosed or encapsulated within a physical device
  
• Usually the embedded system controls the
  physical device
• Embedded systems provide a function(s) that is
  not itself a computer

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Examples are everywhere

• Consumer electronics
• Toys
• Home appliances
• Factory automation
• Space and warfare
• Transportation
• Construction
• Medicine
• Communication
• Entertainment
• Sports

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Historical Notes

• First modern embedded system Apollo Guidance
  Computer
• inertial guidance system for the moon missions
• used ICs novel and risky at the time
• Early missiles had mass produced embedded systems
  reprogrammable logic hard disk

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Embedded System Characteristics

• Generally designed to perform specific functions
  at low cost
• Often have a real-time constraint (more on this
  in the next slide)

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Real Time Constraints

• Real time does not imply fast
• Real time can affect the system architecture
  e.g. caching is usually a no-no in a strict real
  time system
• Generally meet the real time constraint with
  custom hw and some high performance sw, e.g.
  digital satellite TV box
• Processes 10s MB continuous data per second
• Custom hw takes care of parsing and decoding the
  multi-channel digital stream into a single video
  output
• Embedded CPU handles interrupts at frame
  boundaries, generates and displays graphics etc.

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Cost and Design

• Often separate out the low performance part of
  the overall functionality and simplify this piece
  i.e. a CPU thats good enough
• Lower cost compared to a general-purpose system
  accomplishing the same task
• High volume embedded systems need major cost
  reductions
• Few chips, highly integrated CPU, single memory
  chip
• Custom chip to control other functions
• What about embedded systems that are not high
  volume ? Convert a PC class machine into an
  embedded system
• Limit sw options/install a RTOS
• Replace special purpose hw with high performance
  CPU

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Common Hardware Limitations

• No disk drive
• No OS
• No file system
• May have one but it sits on a flash drive
  (essentially EEPROM)
• No peripherals (keyboard/screen)
• May have a touchpad or a small LCD
• Some hw limitations are from reliability
  considerations (e.g. avoiding moving parts like
  disk drives)

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Software for Embedded Systems

• Often exists as firmware software embedded in a
  hardware device usually sits in a ROM or an
  EPROM chip (typical example is the x86 BIOS)
• Hardware and access limitations means the sw has
  to be very reliable

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Reliability

• Key ability is to function uninterrupted over
  long periods of time
• Automatic restart even if a catastrophic data
  corruption occurs
• Watchdog timer hw reset unless the onboard sw
  resets the timer
• Built-in Self-test
• CPU, Memory (usually at power on)
• Power levels, communications tests, operations,
  safety etc.

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Building Blocks

• Platform
• OS and SW architecture
• Tools
• User interface
• Application

Figure adapted from Pottie and Kaiser 2005
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Building Blocks

• Platform
• OS and SW architecture
• Tools
• User interface
• Application

Figure adapted from Pottie and Kaiser 2005
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Constituents

• Platform
• OS and SW architecture
• Tools
• User interface
• Application (often folded into SW arch)

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Platform

• CPU architectures ARM, MIPS, X86, Atmel AVR,
  PIC, etc.
• there are many more than general purpose machines
• almost all are RISC
• emphasis is on minimizing interrupt latency
  rather instruction throughput
• The PC/104 is a popular standard (processor and
  bus) runs DOS, Linux, QNX etc.
• System on a chip Application specific IC (ASIC)
  or a Field-programmable gate array (FPGA)

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OS

• Often none
• When it exists designed to be compact and
  efficient, often real time
• Examples eCos, NetBSD, QNX, VxWorks, etc.

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Software Architecture

• Control loop
• Non-preemptive multitasking
• Preemptive timers
• Preemptive tasks

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Control Loop

• Basic loop which calls subroutines
• Interrupts set flags (or counter values) which
  are read globally
• A subroutine manages a list of sw timers using a
  periodic real time interrupt when timer expires
  the associated subroutine is run

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Control Loop

• Complex calculations are replaced by table lookup
• Difficult to modify
• There is (generally) no OS in this paradigm
  understanding the system is easy

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Nonpreemptive Multitasking

• Similar to control loop except loop is hidden in
  an API
• Define a series of tasks, each with its own
  subroutine stack
• When task is idle it calls the idle routine
  (pause or wait)
• Can also do this using an event queue
• Pretty much like the control loop but easy to add
  new sw write a new task

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Preemptive Timers

• Like before but add a timer that runs subroutines
  from a timer interrupt
• Timer routines can occur at guaranteed times
• Code can step on own data structures

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Preemptive Tasks

• Take the nonpreemptive task system and run it
  from a preemptive timer (or interrupts)
• Now need some serious data synchronization (e.g.
  semaphores)

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Tools

• Compilers
• Specialized compliers
• Cross-compilers (often from GNU)
• Utilities to add a checksum to a program check
  program data before execution
• Synchronous programming languages (e.g.
  Aeverest) tooks to specify and implement reactive
  programs (special compiler, model checker, hw/sw
  synthesis tools)
• Assemblers and Debuggers

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Debuggers and Debugging

• In-circuit emulator
• CPU-based debugger
• High-level debugger (break points, single
  stepping)
• Often code is developed and debugged on a general
  purpose machine, then ported to an embedded
  system

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Start-up and Troubleshooting

• Start-up code disables interrupts, sets up
  electronics, runs the built-in self-tests, starts
  the application
• LEDs are useful troubleshooting aids on extreme
  embedded systems they may also be the only
  debugging aid

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Our Emphasis

• Assignments focused on three platforms
• Mote (small processor, exotic OS)
• iPaq (reasonable processor, desktop OS)
• ENS box (dual processor, dual network, energy
  management, desktop OS)
• Projects focused on ENS box for the most part
• Papers and assigned reading on the bigger end,
  but some papers for smaller devices

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Next time

• ENSbox HW architecture (guest lecture by Jeff
  Tseng)
• Principles of sensing and actuation