01 Big Picture

Embedded Systems

Sandip KunduSandip Kundu

1ECE 354 © Moritz 2011, some slides modified from Moritz/Koren/Burleson/Kundu, UMass ; Wolf, Computers as Components, Morgan Kaufman, 2005

ECE 354 Lecture 1 The Big PictureECE 354 Lecture 1 The Big Picture

What are embedded systems? Challenges in embedded

computing system design. Design methodologies Design methodologies.

Sophisticated functionality. Real-time operation Real-time operation. Low manufacturing cost. Low power. Designed to tight deadlines by Designed to tight deadlines by

small teams.


DefinitionDefinition

Embedded system: any device that includes a programmable y y p gcomputer but is not itself a general‐purpose computer.

Take advantage of application characteristics to optimize the design:• don’t need all the general‐purpose bells and whistles.


Embedding a computer: a very simplified viewEmbedding a computer: a very simplified view…

output analog

inp t analogCPU input analog

memembeddedembeddedcomputer


ExamplesExamples

Personal digital assistant (PDA).g ( ) Printer. Cell phone.Cell phone. Automobile: engine, brakes, dash, etc. Television.Television. Household appliances.


More examplesMore examples

Cell phones, Ipod and MP 3 players, Webcams, Navigation p , p p y , , gSystems

Routers, Blade servers, Wireless PC cards Automobiles, Car Alarms, Keyless Entry Systems Building Security, card swiping systemsg y p g y Embedded Medical Devices ‐ Pacemakers


Characteristics of embedded systemsCharacteristics of embedded systems

Sophisticated functionality.p y Real‐time operation. Low manufacturing cost.Low manufacturing cost. Low power. Reliable and secureReliable and secure Designed to tight deadlines by small teams.


Functional complexityFunctional complexity

Often have to run sophisticated algorithms or multiple p g palgorithms.• Cell phone, laser printer.

Often provide sophisticated user interfaces.


Real time operationReal-time operation

Must finish operations by deadlines.p y• Hard real time: missing deadline causes failure.• Soft real time: missing deadline results in degraded performance.

Many systems are multi‐rate: must handle operations at widely varying rates.


Non functional requirementsNon-functional requirements

Many embedded systems are mass‐market items that must y yhave low manufacturing costs.• Limited memory, microprocessor power, etc.

Power consumption is critical in battery‐powered devices.• Excessive power consumption increases system cost even in wall‐

d d ipowered devices.


Design teamsDesign teams

Often designed by a small team of designers.g y g Often must meet tight deadlines.

• 6 month market window is common.• E.g., can’t miss back‐to‐school window for calculator.


Microprocessors in Embedded Systems


Microprocessor alternatives for embedded systemsMicroprocessor alternatives for embedded systems

Ordinary microprocessor: CPU plus on‐chip cache units.y p p p Microcontroller: includes I/O devices, on‐board memory. Digital signal processor (DSP): microprocessor optimized forDigital signal processor (DSP): microprocessor optimized for

digital signal processing. Hard core vs. soft core. Typical embedded word sizes: 8‐bit, 16‐bit, 32‐bit.


Embedded microprocessorsEmbedded microprocessors

ARM, MIPS, Power PC, Freescale, 8051, X86, , , , , Various purposes

• Networks – MIPS• Mobile phone – ARM dominated• Industrial – Freescale Coldfire• Security – 8051 based, Infineon• High performance – X86, Intel Epic, other VLIW and superscalars


Von Neumann CPU ArchitectureVon Neumann CPU Architecture

Memory holds data and instructions.y Central processing unit (CPU) fetches instructions from

memory.• Separation between CPU and memory distinguishes programmable

computer.

CPU i CPU registers: • program counter (PC)• general purpose registers• general‐purpose registers


CPU + memoryCPU + memory

address

200memory

CPU

PCdata 200

IRADD r5,r1,r3200 ADD r5,r1,r3


Harvard architectureHarvard architecture

address

data memory data

CPUPC

addressPC

program memory instructions IR


RISC vs CISCRISC vs. CISC Complex instruction set computer (CISC):

• many addressing modes• most operations can access memory• variable length instructionsvariable length instructions

Reduced instruction set computer (RISC):• only load/store can access memory• fixed‐length instructions

Instruction set architectures – characteristics:Fi d i bl l th• Fixed vs. variable length.

• Addressing modes.• Number of operands.• Types of operands.


Multiple implementations of an ISAMultiple implementations of an ISA

Instruction set architectures may have several yimplementations:• varying clock speeds;• different bus widths;• different cache sizes;• etc• etc.


PipeliningPipelining

Execute several instructions simultaneously but at different ystages.

Pipeline hazards Simple three‐stage pipe:

y

fetc

h

deco

de

exec

ute

mem

ory

d em


Soft Core ProcessorsSoft Core Processors

Are soft, i.e. specified through field programming just like p g p g g jprogrammable logic • Shipped as hardware description files, which can be mapped onto

FPGA e g: Nios 2FPGA. e.g: Nios 2.• Are bundled with software development tools (compiler, simulator,

etc.)Off fl ibili i b d Offer flexibility as microprocessor parameters can be tuned to the application with tight on‐chip interconnection with additional circuitry.y

Designs can be marketed quickly. You can test and validate many designs quickly without making any specific board; no ld i d i i !soldering and no wiring!


What is Nios 2?What is Nios 2?

A 32‐bit soft core processor from Alterap Comes in three flavors: Fast, Standard, Light The three cores trade FPGA area and power consumption forThe three cores trade FPGA area and power consumption for

speed of execution. Is a RISC, Harvard Architecture: Simple instructions, separate p p

data and instruction memories. Has 32 levels of interrupts. Uses the Avalon Bus interface Programs compiled using GNU C/C++ toolchain.


Nios 2 Architecture:Nios 2 Architecture:


Three forms of Nios 2:Three forms of Nios 2:

Nios II/f—The Nios II/f “fast” core is designed for fast performance. As a result, this core presents the most configuration options allowing you to fine‐tune the processor for performance.

Nios II/s—The Nios II/s “standard” core is designed for small size while Nios II/s The Nios II/s standard core is designed for small size while maintaining performance.

Nios II/e—The Nios II/e “economy” core is designed to achieve the smallest possible core size. As a result, this core has a limited feature set, and many settings are not available when the Nios II/e core is selected.

All three are available to you !y


Selection in SOPC (System On a Programmable Chip):Selection in SOPC (System On a Programmable Chip):


Why use microprocessors?Why use microprocessors?

Alternatives: random logic on a field‐programmable gate g p g garrays (FPGAs), custom logic, etc.

Microprocessors are often very efficient: can use same logic to perform many different functions.

Microprocessors simplify the design of families of products.


The performance paradoxThe performance paradox

Microprocessors use much more logic to implement a p g pfunction than does custom logic.

But microprocessors are often at least as fast:• heavily pipelined;• sophisticated design ‐ large design teams;• aggressive VLSI technology.


PowerPower

Custom logic is a clear winner for low power devices.g p Modern microprocessors offer features to help control

power consumption. Software design techniques can help reduce power

consumption.


Design Aspects In Embedded Systems


Challenges in embedded system designChallenges in embedded system design

How much hardware do we need?• How big is the CPU? Memory?

How do we meet our deadlines?• Faster hardware or cleverer software?

How do we minimize power?• Turn off unnecessary logic? Reduce memory accesses?


Design methodologiesDesign methodologies

A procedure for designing a system.p g g y Understanding your methodology helps you ensure you

didn’t skip anything. Compilers, software engineering tools, computer‐aided

design (CAD) tools, etc., can be used to:• help automate methodology steps;• keep track of the methodology itself.

l l i ( d Altera CAD tools: Quartus 2 , SOPC, Nios 2 IDE (Integrated Development Environment).


Design goalsDesign goals

Performance.• Overall speed, deadlines.

Functionality and user interface. Manufacturing cost. Power consumption.p Other requirements (physical size, etc.)


Levels of abstractionLevels of abstraction

irequirements

specification

architecture

tcomponentdesign

systemintegration


Top down vs bottom upTop-down vs. bottom-up

Top‐down design:p g• start from most abstract description;• work to most detailed.

Bottom‐up design:• work from small components to big system.

Real design uses both techniques.


Typical CAD design flow:Typical CAD design flow:


Designing hardware and software componentsDesigning hardware and software components

Must spend time architecting the system before you start p g y ycoding.

Some components are ready‐made, some can be modified from existing designs, others must be designed from scratch.

Example: SOPC for Hardware design and Nios 2 IDE for Software Design.


JTAG TESTINGJTAG - TESTING

JTAG ‐ Joint Test Action Group: IEEE 1149.1 standard pentitled: Standard Test Access Port and Boundary‐Scan Architecture for test access ports used for testing printed circuit boards (and chips) using boundary scan.

Currently used also for programming embedded devices.• Most FPGAs and PLDs are programmed via a JTAG port.

JTAG ports commonly available in ICsB d h i bi t l i bi t t d• Boundary scan, scan chains, mbist, logic bist connected

• Chips chained together with Jtag signals and connected to main JTAG interface on PCB


SOPCSOPC

System On a Programmable Chip – a hardware development tool. Used for integrating various hardware components together like:

• Microprocessors, such as the Nios II processor• Timers• Serial communication interfaces: UART, SPI• General purpose I/O• Digital signal processing (DSP) functions

C i i i h l• Communications peripherals• Interfaces to off‐chip devices

• Memory controllers• Buses and bridges• Buses and bridges• Application‐specific standard products (ASSP)• Application‐specific integrated circuits (ASIC)• ProcessorsProcessors

Generates files in Verilog or VHDL which can be added to the Quartus 2 project.


Example SOPC system:Example SOPC system:


SOPC system having NIOS:SOPC system having NIOS:



SummarySummary

Embedded computers are all around us.p• Many systems have complex embedded hardware and software.

Embedded systems pose many design challenges: design time, deadlines, power, etc.

Design methodologies help us manage the design process. CAD tools like SOPC can reduce design time.


What’s Next in Lecture 2?What s Next in Lecture 2?

We will peek inside CPU, addressing, assembly languages etc.p , g, y g g You will learn about I/Os and Caches. You will learn about some cool features of SOPC and Nios 2You will learn about some cool features of SOPC and Nios 2

IDE !


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