cyberphysical systems & embedded processors een 417 fall 2013 8/27/13, dr. eric rozier, v1.0,...

CYBERPHYSICAL SYSTEMS&EMBEDDED PROCESSORS

EEN 417Fall 2013

8/27/13, Dr. Eric Rozier, V1.0, ECE

CYBERPHYSICAL SYSTEMS

Model-Based Design

Cyber Physical Systems:Computational +

Physical

CPS is Multidisciplinary

Computer Science:

Carefully abstracts the physical world

System Theory:

Deals directly with physical quantities

Challenge

What this course is about

• A principled and scientific approach to engineering embedded systems– Modeling, Design, Implementation, Testing,

Analysis– Not just hacking!

Traditionally, embedded systems has been an industrial (not academic) problem, about resource limitations.

small memory small data word sizes relatively slow clocks

•When these are the key problems, emphasize efficiency: write software at a low level (in assembly code or C) avoid operating systems with a rich suite of services develop specialized computer architectures:

– programmable DSPs– network processors

develop specialized networks– Can, FlexRay, TTP/C, MOST, etc.

•This is how embedded SW has been designed for 30 years

But embedded systems do have more fundamental differences from general-purpose computation:

•time matters– “as fast as possible” is not good enough

•concurrency is intrinsic– it’s not an illusion (as in time sharing), and– it’s not (necessarily) about exploiting parallelism

•processor requirements can be specialized– predictable, repeatable timing– support for common operations (e.g. FIR filters)– need for specialized data types (fixed point, bit vectors)

•programs need to run (essentially) forever– memory usage has to be bounded (no leaks!!)– rebooting is not acceptable

What about “real time”?

Make it faster!What if you need “absolutely positively on time”?

Today, most embedded software engineers write code, build your system, and test for timing. Model-based design seeks to specify dynamic behavior (including timing) and “compile” implementations that meet the behavior.

Prioritize and Pray!

Real-Time Multitasking?

All too often, real-time operating systems (RTOSs) are used in a rather ad hoc way. Without any particular principles, engineers tweak priorities until the prototype works under test.

The resulting system is brittle, meaning the small changes in the operating conditions (or in the design of the system) can cause big changes in behavior. For example, replacing the processor with a faster one can cause real-time failures.

An engineer’s responsibility

Korean Air 747 in Guam, 200 deaths (1997) 30,000 deaths and 600,000 injuries from medical devices (1985-2005)

– perhaps 8% due to software?

•source: D. Jackson, M. Thomas, L. I. Millett, and the Committee on Certifiably Dependable Software Systems, "Software for Dependable Systems: Sufficient Evidence?," National Academies Press, May 9 2007.

A Story

•A “fly by wire” aircraft, expected to be made for 50 years, requires a 50-year stockpile of the hardware components that execute the software.

•All must be made from the same mask set on the same production line. Even a slight change or “improvement” might affect timing and require the software to be re-certified.

Abstraction Layers•The purpose for an abstraction is to hide details of the implementation below and provide a platform for design from above.

Abstraction Layers•Every abstraction layer has failed for time-sensitive applications.

Is the problem intrinsic in the technology?

•Electronics technology delivers highly repeatable and precise timing…•… and the overlaying software abstractions discard it.

20.000 MHz (± 100 ppm)

EMBEDDED PROCESSORS

Typical PC Architecture• Single processor

• (plus GPU)• Not a lot of concurrency

• Market is dominated by a single architecture and instruction set

• x86

Image courtesy of Wikimedia Commons GPL

Example Embedded System: Apple iPhone• A5 Processor• Qualcomm DSP

Images courtesy of iFixit © 2012, CC-BY-NC-SA


…

• Texas Instruments touchscreen microcontroller

• Cirrus Logic DSP

Images courtesy of iFixit © 2012, CC-BY-NC-SA


…



Barely begun to examine this system!


…




Four different embedded processors!


…





Four different manufacturers!


…





Four different manufacturers!

Four different architectures!


…



Lots of concurrency!


…



Lots of concurrency!

Different instruction sets!


…



Highly Specialized!

What advantages might there be to specialization?

What advantages might there be to specialization?

Energy consumption, specialized hardware, efficiency, etc

ATMEGA328,

AVR PROCESSORS,

& ARDUINO

Dueling Architectures

Advantages/Disadvantagesto each?

Complexity, dedicated buses

Von Neumann bottleneck

Advantages/Disadvantagesto each?

ATmega328

ATmega328• CPU

• (Details later)

ATmega328• Flash – program

memory• 32K

• SRAM – data memory• 2K

• EEPROM• 1K• Nonvolatile memory

What kind of architecture?

AVR CPU

AVR CPU

Instruction fetch and decode

AVR CPU

ALU instructions

AVR CPU

I/O and special functions

AVR CPU32 8-bit general purpose registersPart of SRAM memory space

AVR CPUX, Y, and Z registers16-bit registers made using registers 26-31Support indirect addressing

AVR Memory

FLASH

BOOT SECTION

32 registers

64 I/O registers

160 Ext I/O Registers

Internal SRAM

EEPROM

AVR Architecture• Three timers• Flexible

• Choose clock rate• Choose “roll-over”• Generate interrupts• Generate PWM

signals

AVR Architecture• Interface to pins• Each pin directly

programmable• Program direction (I/O)• Program value• Program pull-ups

• Some special pins• Analog/Digital• Clocks• Reset

AVR Architecture• 3 8-bit ports (B, C, D)• Each port controlled by

3 8-bit registers• Each bit controls one I/O pin• DDRx – direction register

• Defines Input(0) or Output(1)

• PINx – Pin input value• Reading this “register” returns

value of the pin

• PORTx – Pin output value• Writing to this register sets

value of pin

Pin Circuitry

Pin Input

PINx

DDRx=0

PORTx

Synchronization and Timing

Takes a clock cycle for data output to be reflected on the input

Why is this necessary?

Why is this necessary?What if the pin changes value near the falling edge of a clock cycle?

Why is this necessary?What if the pin changes value near the falling edge of a clock cycle?

Metastability

Pin Output

PINx

DDRx=1

PORTx

Pin Input – PORT controls pullup

PINx

DDRx=0

PORTx

Pullups

• Pullups– If a pin is an input (DDRxi = 0)

• PORTxi = 0 – Pin is floating• PORTxi = 1 – connects pullup to the pin

– Keeps pin from floating if noone is driving– Llows wired-OR bus

– Individual bits can be set cleared using bit-ops– A bit can be toggled by writing I to PINxi

Arduino Uno

ATmega328

Arduino Uno

ATmega328ATmega16U2

Arduino Digital and Analog I/O Pins

• Digital pins– Pins 0-7: PORT D– Pins 8-13: PORT B– Pins 14-19: PORT C

• Named A0 – A5• Arduino analog

– Pins 0 and 1 are RX and TX for serial comms

– Pin 13 connected to base board LED

More Info

• Too much to cover!

• See data sheets for Arduino and ATmega328– http

://www.atmel.com/Images/8271s.pdf

– http://www.atmel.com/images/doc0856.pdf

– http://arduino.cc/en/Main/ArduinoBoardUno

http://www.atmel.com/Images/8271s.pdf



http://www.atmel.com/images/doc0856.pdf



http://arduino.cc/en/Main/ArduinoBoardUno

http://arduino.cc/en/Main/ArduinoBoardUno

PARALLELISM

Parallelism vs. Concurrency

• What’s the difference?

Parallelism vs. Concurrency

• Concurrency is central to embedded systems!

– Concurrency – different parts of the program conceptually execute simultaneously

– Parallel – different parts physically execute simultaneously

Pipelining

Sample five stage pipeline

What’s going on here?

Reservation Table

Pipeline hazards represented by dashed lines

Pipeline Hazards!

Pipeline Interlock to prevent hazard

Other types of parallelism

• CISC vs. RISC• Superscalar processors• Hyperthreading• Multicore

WRAP UP

Industrial Connection

• Mr. Tony Kaap– Motion Picture Industry: Motion Capture

• Mr. Robert Zeh– Financial Industry: Real-time systems

• Stanford University– Tagging of Pelagic Predators

• MBARI– Deep sea embedded systems

and data collection• Dr. Kristin Rozier

– NASA: Safety Critical Systems

For next time

• Read Chapter 2 (Continuous Dynamics)

• Assignment 1: Problems 1, 2, and 3 of Chapter 7.

cyberphysical systems & embedded processors een 417 fall 2013 8/27/13, dr. eric rozier, v1.0,...

Documents

ece slide

acceptable slide

challenge slide

dependable software

dependable systems

embedded software engineers

modelbased design slide

cyber physical systems