Choosing a Micro for an Embedded System

Application

Dr. Manuel JiménezDSP Slides: Luis Francisco

UPRM - Spring 2010

Outline

MCU Vs. CPU Vs. DSPSelection FactorsEmbedded PeripheralsSample ArchitecturesSelection GuidesDevelopment Tools

HardwareSoftware

Introduction

Choosing the right MCU: A Difficult TaskWide Selection of VendorsLarge Number of Alternatives

CPU Architecture/ProgrammingEmbedded peripheralsCostPowerPackages

Try a Search in the DigiKey on-line CatalogMore than 16,000 entries for “Microcontroller”

MCU, MPU, or DSP?

Let your application dictate the needs & requirements for the system CPU

MicroprocessorSelectionProcess

MicroprocessorSelectionProcess

RequirementsEmbedded Systems

Application

Embedded Systems

Application

Application Processor

Application Processor

MPUMPUDSPDSPMCUMCU

Classic Microprocessor-based Systems (MPU)

MPU

Control Bus

Program

Memory

DataMemory

I/O

Glue

Logic

Data Bus

Address Bus

Chip/Board

Chip/Board Chip/Board Chip/Board

Chip/Board

Inter‐chip level

MPU

Microcontroller-based Systems (MCU)

MPU

Control Bus

Program

Memory

DataMemory

I/O

Glue

Logic

Data Bus

Address Bus

External

I/O Lines

Single Chip 

Device

Intra‐chip level

Embedded Microprocessors Systems

MPU

Control Bus

Program

Memory

DataMemory

I/O

ExternalBus

Peripherals&

Memory

Data Bus

Address Bus

Chip/BoardChip/Board

Intra‐chip levelInter‐chip level

I/O

Lines

I/OPeripherals

Single Chip 

Device

Embedded DSP / DSC Systems

Control Bus

DataMemory

DSP 

Operation

s moduleAnalog

I/O

ExternalBus

Peripherals&

Memory

Data Bus

Chip/Board

Chip/Board

Intra‐chip levelInter‐chip level

I/O

LinesI/O

Peripherals

Single Chip DeviceRAM/

High‐speed 

peripherals 

controllers

Program

Memory

MPU

I/O 

Line

s

Address Bus

Critical IndicatorsSystemSpecs

Memory

ProcessingSpeed

PeripheralRequired

Large

Fast

Bus Type MPUDomain

MCUDomain

I/O Type

Small

“Slow”

DSP Math

DSPDomain

Yes

NoDSP Math

DSCDomain

Typical MCU Structure

Core CPU Architecture

Word WidthData resolutionComputing power

Register StructureHow many?Register types

Accumulator-based Vs. Register File Vs. Load/StoreStack type and depth

Assembly Language StructureCISC Vs. RISC

Bus ArchitectureHarvard Vs. Stanford (Von Neuman)Internal Vs. External

Digital Signal Processor Architecture Characteristics

MPU designed to perform Digital Signal Processing math operations

Multiply and accumulate (MAC) Digital Filters: IIR & IIF FFT

MAC instructions in a single cycleMultiple access to memory in a single instruction cycleMAC operations with fixed-point or floating-point

Embedded DSP vs. DSCDSP

High speed processingHigh speed external peripheralsLots of external memoryImage & Video processing, powerful DSP algorithms

DSCLow speed processingI/O type peripheralsApplications: Consumer electronics applications, motors controls, power electronics controllers, etc.

Architectural Considerations for Embedded DSP / DSC (1/2)

SpeedMAC operationsBuses Sampling

Internal Modules for DSP Math operationsFFTFilters

Arithmetical Format and lengthFixed-pointFloating-point

Architectural Considerations for Embedded DSP / DSC (2/2)

On-Chip MemoryCodeInternal RAMSampling

Controllers external RAMOn-Chip PeripheralsBuses

Programmability

ProgrammabilityPrefer FLASH devices

Many erase/reprogram cyclesOn-board reprogrammable

Other types:EEPROMEPROMOTPExternal Memory

FLASH/EEPROMRAMEPROM

On-chip MCU Peripherals (1/2)

I/O portsNumber of I/OsIndividually or byte programmableDriving capability

TimersNumber of TimersCounting bitsPrescaler(s)Operating modes:

Event/timerWatchdog

On-chip MCU Peripherals (2/2)

UARTs/USARTsClocking sourcesBaud rate generation

Data ConvertersResolution (No. of bits)Analog ChannelsConversion MethodSpeedReferencing

Other PWMComparatorsI2C, CAN, USB, etc.JTAG, BlueTooth, 802.11

Other Considerations

Physical PackagingImportant for prototypingPLCC, QFP, BGA, DIP

Supply voltageCompatibility with add-on components

MemoryProgram memoryData memory

Application requirementsWord width

Power Down ModesPower ConsumptionSleep/wake-up time

Embedded MPU Examples

Embedded DSP Example

Product Selection GuidesAllow choosing specific members within a family

Product Selection Guides

Hardware Development Tools

Availability of Development KitsMost Kits sold for $50 or lessAsk for samples or student discount

Minimum HW ContentsDevelopment BoardJTAG debugger or EmulatorPower supplySpare chipsCables

Software Development ToolsAllow for Software Development

ProgrammingDebuggingDownloadingTesting

Minimum SupportIntegrated Development Environment (IDE)EmulatorAssemblerC-Compiler (Demo)

Resources

http://www.instructables.comhttp://www.freescale.com/files/microcontrollers/doc/app_note/AN1057.pdfhttp://www.microchip.com/stellenthttp://archive.chipcenter.com/circuitcellar/march01/c0301cg1.htm