Research Overview

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Research Overview

• John Regehr
• Fall 2008

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Part 1 Embedded Systems
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Embedded Systems

• Account for gt99 of new microprocessors
• Consumer electronics
• Vehicle control systems
• Medical equipment
• Etc.

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Definitions of Embedded System

• A special-purpose computer that interacts with
  the real world through sensing and/or actuation
• A computer that you dont think of as a computer
• Almost any computer that isnt a PC

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What Do Embedded Systems Do?

• Five main categories
• Digital signal processing
• Control open loop or closed loop
• Networking wired or wireless
• User interfacing speech, text, graphics,
• Data storage
• Most embedded systems do 1-4 of these
• Which apply to
• Cell phone?
• LinkSys home router?
• Cruise control?
• iPod?

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Fun Microcontroller Example ChipCon 2430

• 8051 processor
• Old-style 8-bit, originated at Intel
• 32 MHz, 8 KB RAM, 128 KB Flash
• 802.15.4 radio on-chip
• Short-range, low-power wireless
• Zigbee is based on this
• Low power 25 mA for CPU Zigbee receive
• Low cost lt4 in large quantities
• This has potential to be big
• Cheaply add wireless connectivity to any device
• Examples?

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Why Are Microcontrollers Cool?

• Because they add computation to almost any device
• Computation is amazingly useful
• Theyre cheap
• MCU contains almost everything you need
• Development tools are free in many cases
• The hardware is really good
• Often, hardest part of embedded system design is
  creating good software
• This is a serious problem

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Problem

• Significant number of projects fail due to
  problems creating good embedded software
• Fail means
• Project unacceptably delayed
• Software has unacceptably low quality
• Worst cases
• Patients killed
• Nuclear plant owned
• Spacecraft lost

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Solutions

• Industry needs developers who can
• Understand systems from multiple points of view
• Debug rapidly
• Test aggressively
• Think critically
• Learn rapidly
• Creating really solid software is 5-10 times
  harder than creating working software

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Future of Embedded Systems

• Future is bright
• 1.6 B ARM processors sold in 2005
• Trends for new systems
• Software intensive
• Networked
• Many new designs will use 32-bit chips
• Many new designs will be heterogeneous
  multiprocessors / networks on chip
• CE is a great major
• People skilled in software control, signals,
  circuits, analog are extremely valuable
• CS and EE curricula both miss the boat on this
• Lots of jobs for people like you

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Part 2 Research Overview
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My Research

• Find a problem that embedded system programmers
  have
• Another embarrassment of riches
• Create a software tool that solves the problem
• Solution should involve ideas from compilers and
  operating systems

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Example Tool Saving RAM

• Observation 1 RAM is often the most limited
  resource on a microcontroller
• lt 1 KB is common on inexpensive chips
• Running out of RAM hosed
• Observation 2 Many programs use RAM very poorly
• We ran an experiment showing that many programs
  use only 1 bit out of every allocated byte, on
  average
• Example
• int x where x is a true or false flag

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How to Save RAM?

• Identify variables that use RAM poorly, e.g.
• Boolean A uses 1 bit
• Enumerated type B with 6 variants uses 3 bits
• Pointer C that references a buffer of 16 elements
  uses 4 bits
• Integer D with range -10 to 20 uses 5 bits
• Perform bit-level packing
• struct
• A_compressed 1
• B_compressed 3
• C_compressed 4
• D_compressed 5
• compressed_variables
• Challenge Do this all automatically!

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How to Save RAM Contd

• How do we automatically find limited-bitwidth
  variables?
• look at the types WRONG
• E.g. bools, enums, etc.
• These can lie! if they do, compressing will
  break the system
• use dataflow analysis RIGHT
• Analysis is conservative if it says a variable
  has limited bit-width, it does

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Dataflow Analysis
x 0,? y 7,11 w 0, ?
x y-7
x 0,4 y,w remains the same
test x
Z-flag ? If z1 then x0,0 If z0 then x1,4
z-flag set?
NO
YES
w 10
w 2x
x 1,4 w 2,8
w 10,10 x 0,0
x 0,4 w 2,10
memw 7
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RAM Compression

• Difficulties
• Dataflow analysis is difficult when there are
  interrupts, threads, pointers, etc.
• This transformation will slow down execution
• This transformation will bloat code size
• Results
• Reduce RAM usage by 22 for a collection of
  embedded programs

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We also created tools to

• Avoid the need to declare variables as volatile
• Detect potential for stack overflow errrors
• Predict worst-case execution time
• Prevent ALL pointer and array errors in C code
• Do automatic stress testing
• Optimize much better than GCC
• Compile towards application-specific goals

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Summary

• Embedded systems are fun
• Courses to keep in mind
• Myers Embedded Systems
• Regehr Advanced Embedded Systems
• Probably should be called Advanced Embedded
  Software
• Provancher (ME) Advanced Mechatronics
• Research is fun
• Im always looking for smart people to work in my
  group
• But generally people who have taken my advanced
  embedded systems course