Research Overview John Regehr Sept 06

Part 1 – Embedded Systems

Embedded Systems  Account for >99% of new microprocessors  Consumer electronics  Vehicle control systems  Medical equipment  Etc.

Definitions of “Embedded System” 1. A special-purpose computer that interacts with the real world through sensing and/or actuation 2. A computer that you don’t think of as a computer 3. Almost any computer that isn’t a PC 4. …

More definitions  Microprocessor: A regular CPU  Microcontroller: A system on chip that contains extra support for dealing with the real world  Analog to digital and digital to analog converters  Pulse width modulation  Networks: serial, I2C, CAN, USB, , etc…  General-purpose I/O pins  Lots of interrupts  Low-power sleep modes  Voltage / frequency scaling  Temperature / vibration resistance  Incremental cost of an extra feature is near zero

Why Are Microcontrollers Cool?  Because you can easily make almost anything smart  Microcontroller: Under $1  Contains almost everything you need  Board space + support logic: Cheap  GNU compilers: Free  Hardest part: Writing the software  Embarrassment of riches…  But, this is a serious problem

Fun Microcontroller Example: ChipCon 2430  8051 processor  Old-style 8-bit, originated at Intel  32 MHz, 8 KB RAM, 128 KB Flash  radio on-chip  Short-range, low-power wireless  Zigbee is based on this  Low power: 25 mA for CPU + Zigbee receive  Low cost: <$4 in large quantities  This has potential to be big  Cheaply add wireless connectivity to any device  Examples?

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?

Issues Cutting Across System Designs  These are external system requirements not directly tied to what a system does  Safety critical  Real-time  Upgradeable  Energy-efficient  Cost sensitive  Highly available or fault-tolerant  Secure  Distributed  Dealing with these is very hard

Problems Creating Software  Significant number of projects fail due to problems creating good software  Fail means…  Project unacceptably delayed  Software has unacceptably low quality  Extreme cases: Spacecraft lost or people killed  Important skills for you to have:  System-level understanding  Debugging  Testing  Critical thinking  Selective paranoia  Don’t underestimate the difficulty of creating good software

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 / NoC  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

Part 2 – Research Overview

A Day in the Life…  Teaching – 20%  Research  Advising students – 15%  Writing papers – 15%  Writing grants – 10%  Travel – 10%  My own research – 10%  Service  Department service – 10%  External service – 10%

My Research Algorithm 1. Find a problem that embedded system programmers have  Another embarrassment of riches 2. Create a software tool that solves the problem  Solution should involve ideas from compilers and operating systems 3. Publish paper describing the solution  As a professor, must do this 4. Sometimes: Release tool as open source  Doing this well is a lot of work  It’s (sometimes) easy and (usually) fun!

Example Tool: Saving RAM  Observation 1: RAM is often the most limited resource on a microcontroller  < 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

How to Save RAM? 1. 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 2. Perform bit-level packing struct { A_compressed : 1; B_compressed : 3: C_compressed : 4; D_compressed : 5; } compressed_variables;  Challenge: Do this all automatically!

How to Save RAM Cont’d  Machine-generated compression and decompression functions are needed void * decompress_ptr (int compressed) { switch (compressed) { case 0: return (void *)0xabcd; case 1: return (void *)0x1214; case 2: return (void *)0xaa55; … }

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

Dataflow Analysis x = y-7 test x z-flag set? w = 10w = 2*x mem[w] = 7 YES NO Z-flag =  If z=1 then x=[0,0] If z=0 then x=[1,4] x = [0,  ] y = [7,11] w = [0,  ] x = [0,4] y,w remains the same w = [10,10] x = [0,0] x = [1,4] w = [2,8] x = [0,4] w = [2,10]

RAM Compression  Difficulties:  Dataflow analysis is difficult when there are interrupts, threads, pointers, etc.  We solved these problems  This transformation will slow down execution  How to deal with this?  This transformation will bloat code size  How to deal with this?  Work is ongoing – no real results yet  Being done by Nathan Cooprider, a PhD student

We also created tools to:  Avoid the need to declare variables as volatile  Detect potential for stack overflow  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

Summary  Embedded systems are fun  Courses to keep in mind  Myers: Embedded Systems  Regehr: Advanced Embedded Systems  Provancher (ME): Advanced Mechatronics  Research is fun  I’m always looking for smart people to work in my group  But generally people who have taken my advanced embedded systems course