AVR Fundamentals

AVR

Modified Harvard architecture 8-bit RISC single chip microcontrollerComplete System-on-a-chip

On Board Memory (FLASH, SRAM & EEPROM)On Board Peripherals

Advanced (for 8 bit processors) technologyDeveloped by Atmel in 1996First In-house CPU design by Atmel

8 Bit tinyAVRSmall package – as small as 6 pins

8 Bit megaAVRWide variety of configurations and packages

8 / 16 Bit AVR XMEGASecond Generation Technology

32 Bit AVR UC3Higher computational throughput

Processor corePeripheralsHardware Example – Polulu 3pi robotDevelopment EnvironmentsSoftware Example - PID algorithm walkthrough

What is Harvard Architecture?Before we can answer that…

Separate instruction and data pathsSimultaneous accesses to instructions & dataHardware can be optimized for access type and bus width.

Special instructions can access data from program space.Data memory is more expensive than program memoryDon’t waste data memory for non-volatile data

Reduced Instruction Set ComputerAs compared to Complex Instruction Set Computers, i.e. x86Assumption: Simpler instructions execute fasterOptimized most used instructionsOther RISC machines: ARM, PowerPC, SPARCBecame popular in mid 1990s

Faster clock ratesSingle cycle instructions (20 MIPS @ 20 MHz)Better compiler optimizationTypically no divide instruction in core

32 8 Bit registersMapped to address 0-31 in data spaceMost instructions can access any register and complete in one cycleLast 3 register pairs can be used as 3 16 bit index registers32 bit stack pointer

R0R1R3R4R5R6

R26R27R28R29R30R31

•••

7 00x00

0x01

0x02

0x03

0x04

0x05

0x1A

0x1B

0x1C

0x1D

0x1E

0x1F

addr

x register low byte

x register high byte

z register low byte

z register high byte

y register low byte

y register high byte

Non-volatile program space storage16 Bit widthSome devices have separate lockable boot sectionAt least 10,000 write/erase cycles

0x7FF

Application Flash0x000

ATmega 48

Application Flash

Boot Flash

0x000

ATmega 88/168/328

0x1FFF0x3FFF0x7FFF

Data space storage8 Bit width

32 Registers

64 I/O Registers160 External I/O

RegInternal SRAM

(512/1024/2048x8)

0x0000 – 0x001F

0x0020 – 0x005F

0x00060– 0x00FF

0x0100

0x04FF/0x6FF/0x8FF

External SRAM

Electrically Erasable Programmable Read Only Memory8 bit widthRequires special write sequenceNon-volatile storage for program specific data, constants, etc.At least 100,000 write/erase cycles

DEVICE FLASH EEPROM SRAMATmega48A 4K Bytes 256 Bytes 512 Bytes

ATmega48PA 4K Bytes 256 Bytes 512 Bytes

ATmega88A 8K Bytes 512 Bytes 1K Bytes

ATmega88PA 8K Bytes 512 Bytes 1K Bytes

ATmega168A 16K Bytes 512 Bytes 1K Bytes

ATmega168PA 16K Bytes 512 Bytes 1K Bytes

ATmega328 32K Bytes 1K Bytes 2K Bytes

ATmega328P 32K Bytes 1K Bytes 2K Bytes

I/O registers visible in data spaceI/O can be accessed using same instructions as dataCompilers can treat I/O space as data access

Bit manipulation instructionsSet/Clear single I/O bitsOnly work on lower memory addresses

Directly connected to all 32 general purpose registersOperations between registers executed within a single clock cycleSupports arithmetic, logic and bit functionsOn-chip 2-cycle Multiplier

131 instructions Arithmetic & LogicBranchBit set/clear/testData transferMCU control

Register ↔ register in 1 cycleRegister ↔ memory in 2 cyclesBranch instruction 1-2 cyclesSubroutine call & return 3-5 cyclesSome operations may take longer for external memory

Clock control module generates clocks for memory and IO devicesMultiple internal clock sourcesProvisions for external crystal clock source (max 20 MHz)Default is internal RC 8 MHz oscillator with ÷ 8 prescale yielding 1 MHz CPU clockDefault is only 5-10% accurate

System Clock

Prescaler

Timer/CounterOscillator

Crystal Oscillator

External Clock

Low Freq Crystal

Oscillator

Calibrated RC Oscillator

ClockMux

AVRClock

Control

FLASH & EEPROM

RAM

CPU Core

ADC

IO Modules

Timer/Counters

÷ 8

Multiple power down modesPower down mode

Wake on external reset or watchdog resetPower save mode

Wake on timer eventsSeveral standby modes

Unused modules can be shut down

Power on resetExternal resetWatchdog system resetBrown out detect (BOD) reset

ATmega328 has 26 reset/interrupt sources1 Reset source2 External interrupt sourcesI/O Pin state change on all 24 GPIO pinsPeripheral device events

Each vector is a 2 word jump instructionVectors start at program memory address 0Reset vector is at address 0Sample vector table:Address Labels Code Comments0x0000 jmp RESET ; Reset Handler0x0002 jmp EXT_INT0 ; IRQ0 Handler0x0004 jmp EXT_INT1 ; IRQ1 Handler0x0006 jmp PCINT0 ; PCINT0 Handler0x0008 jmp PCINT1 ; PCINT1 Handler ...

Fuses configure system parametersClock selection and optionsBoot optionsSome IO pin configurationsReset options

Three 8 bit fuse registersUse caution! Some configurations can put the device in an unusable state!

23 General Purpose IO BitsTwo 8 bit & one 16 bit timer/countersReal time counter with separate oscillator6 PWM Channels6 or 8 ADC channels (depends on package)Serial USARTSPI & I2C Serial InterfacesAnalog comparatorProgrammable watchdog timer

Three 8 Bit IO PortsPort B, Port C & Port DPins identified as PBx, PCx or PDx (x=0..7)

Each pin can be configured as:Input with internal pull-upInput with no pull-upOutput lowOutput high

Most port pins have alternate functionsInternal peripherals use the alternate functionsEach port pin can be assigned only one function at a time

8/16 Bit registerIncrements or decrements on every clock cycleCan be read on data busOutput feeds waveform generator

Clock SourcesInternal from clock prescalerExternal Tn Pin (Uses 1 port pin)

Multiple Operating modesSimple timer / counterOutput Compare Function

Waveform generatorClear/set/toggle on match

Frequency controlPulse Width Modulation (PWM)

TCNTnClockSelect

OCRnA

OCRnB

Waveform

Generator

=

Waveform

Generator

=

TCCRnA

TCCRnB

Tn

OCnA

OCnB

IRQ

IRQ

DATA BUS

DATA BUS

Use Clear Timer on Compare Match (CTC) ModeOCnx Toggles on Compare Match

0

TOP = OCRnx

OCnx(toggle)

Dynamically change duty cycle of a waveformUsed to control motor speed

Fast PWM ModeCounter counts from BOTTOM (0) to MAXCounter reset to 0 at MAXOCnx cleared at TOPOCnx set at BOTTOM

MAX

BOTTOM

TOP

OCnx

Clear on TOP

Set on BOTTOM

Timer 1 has capture modeCapture can be triggered by ICP1 pin or ACO from analog comparatorCapture event copies timer into input capture register ICR1Can be used to time external events or measure pulse widthsRange finders generate pulse width proportional to distance

10 Bit Successive Approximation ADC8 Channel multiplexer using port pins ADC0-7Max conversion time 260 μsec.

Compares voltage between pins AIN0 and AIN1Asserts AC0 when AIN0 > AIN1AC0 can trigger timer capture function

Range finders indicate distance with pulse withTimer capture mode can compute pulse width

Industry standard serial protocol for communication between local devicesMaster/Slave protocol3 Wire interfaceSlaves addressed via Slave Select (SS) inputs

SCLK Serial Clock

MOSI Master Out Slave In

MISO Master In Slave Out

SS Slave Select

Industry standard serial protocol for communication between local devicesMaster/Slave protocol2 Wire interfaceByte oriented messagesSlave address embedded in command

SDA Serial Data

SCL Serial Clock

EEPROMIO ExpandersReal Time ClocksADC & DACTemperature sensorsUltrasonic range findersCompassServo / Motor ControllerLED Display

Universal Synchronous and Asynchronous serial Receiver and TransmitterFull Duplex OperationHigh Resolution Baud Rate GeneratorCan provide serial terminal interface

Some chips have JTAG interfaceIndustry standard for debugging chips in circuitConnect to special JTAG signalsCan program

FLASHEEPROMAll fusesLock bits

ISP (In-System Programmer)Connect to 6 or 10 pin connectorSPI interfaceSpecial cable required

Can program FLASHEEPROMSome fusesLock bits

CW: PD5 & PD6 PWM mode (OC0B, OC0A)CCW: PD3 & PB3 PWM mode (OC2B, OC2A)Motor interface uses H-Bridge controllerSpeed and direction controlled by port bitsController standby controlled by PC6

M

V+

V-

1

3

2

4

M

V+

V-

1

3

2

4

PD5=1

PD6 (OC0A) PMW

M

V+

V-

1

3

2

4PD3=1

PB3 (OC2A) PMW

PC5 enables the IR emittersOne port pin for each of 5 sensors, PC0-4Port pin used as input and output

Set pin as output high for 10 μsec to charge RC circuitSet pin as inputMeasure time for voltage to drop (using TCNT2)Time indicates level of light

1. Output: 10 μsec pulse on PC0

2. Input: measure decay

t indicates amountof reflected light

ADC6: battery voltage monitorADC7: reads trimmer pot voltage

Buzzer: Timer1 PB2 (OC1B)User defined (can be USART) : PD0, PD1Device (ISP) Programming: PB3, PB4, PB520 MHz crystal: PB6, PB7

Choose a languageBASCOM C/C++Assembler (machine language)

Choose a platformLinuxWindows

Text Editor / IDETool Chain

CompilerLibraries

Programmer (cable & software)

Windows based BASIC compiler for AVR FamilyComplete IDEIncludes simulatorExtensive library for AVR peripheral controlIncludes ISP programmerDemo versions available – limited code space

LinuxAVR-GCC

Based on GNU toolsetOpen Source AVR-LIBC libraries

WindowsWIN-AVR

Port of AVR-GCC to Windows

LinuxEditors & command line toolsEclipse IDE

WindowsAtmel AVR Studio

Includes ISP programming supportEclipse IDE

STK 200/300/400/500Atmel AVR starter kit and development systemInterfaces to AVR Studio

avrdudeProgramming support for all memories

Win-AVRAVR-StudioProprietary libraries

PID AlgorithmPID Code Walkthrough

Simple Line FollowerThree sensors can provide position information

left of centeron centerright of sensors

React to current position only

Three choices:

Guaranteed to zig-zag back and fort h

Anticipates where we want to goContinuously adjusts direction to get thereAdjustable constants control behavior

P

I

D

ΣΣ ProcessSet point(center line)

Error Output+

–

(P) ProportionalWhere we are relative to where we want to be.

(I) IntegralSum of previous errors. History of where we were.

(D) DerivativeRate of change. Affects how fast we react to changes.

Useful functionsread_line

Returns a value between 0 – 40000 – 1000: robot is far right of line1000 – 3000: robot is approximately centered3000 – 4000: robot is far left of line

set_motorsSet speed and direction of both motors

-255 – 0 : reverse direction0 – 255: forward direction

// Introductory messages. The "PROGMEM" identifier causes the data to// go into program space.const char welcome_line1[] PROGMEM = " Pololu";const char welcome_line2[] PROGMEM = "3\xf7 Robot";const char demo_name_line1[] PROGMEM = "PID Line";const char demo_name_line2[] PROGMEM = "Follower";

// A couple of simple tunes, stored in program space.const char welcome[] PROGMEM = ">g32>>c32";const char go[] PROGMEM = "L16 cdegreg4";A

// Auto-calibration: turn right and left while calibrating the// sensors.for(counter=0;counter<80;counter++){

if(counter < 20 || counter >= 60)set_motors(40,-40);

elseset_motors(-40,40);

// This function records a set of sensor readings and keeps// track of the minimum and maximum values encountered. The// IR_EMITTERS_ON argument means that the IR LEDs will be// turned on during the reading, which is usually what you// want.calibrate_line_sensors(IR_EMITTERS_ON);

// Since our counter runs to 80, the total delay will be// 80*20 = 1600 ms.delay_ms(20);

}set_motors(0,0);

// Get the position of the line. Note that we *must* provide// the "sensors" argument to read_line() here, even though we// are not interested in the individual sensor readings.unsigned int position = read_line(sensors,IR_EMITTERS_ON);// The "proportional" term should be 0 when we are on the line.int proportional = ((int)position) - 2000;

// Compute the derivative (change) and integral (sum) of the position.int derivative = proportional - last_proportional;integral += proportional;

// Remember the last position.last_proportional = proportional;

// Compute the difference between the two motor power settings,// m1 - m2. If this is a positive number the robot will turn// to the right. If it is a negative number, the robot will// turn to the left, and the magnitude of the number determines// the sharpness of the turn.int power_difference = proportional/20 + integral/12000 + derivative*7/4;

// Compute the actual motor settings. We never set either motor// to a negative value.const int max = 250;if(power_difference > max)

power_difference = max;if(power_difference < -max)

power_difference = -max;

// One Motor will always be full speed

if(power_difference < 0)set_motors(max+power_difference, max);

elseset_motors(max, max-power_difference);

Open source elections prototyping platformHardware

Based on Atmega (328 & others)Software

Wiring language, based on c++Boot loaderArduino IDE

ATmega 48/88/168/328What we have been talking about

ATmega 164/324/644/1284JTAG interfaceAll 4 IO Ports A,B,C & DMore memory

PDIP – Plastic Dual In-line PackageGood for hobbyists

TQFP – Thin Quad Flat PackSurface mount

MLF – MicroLeadFrame28 & 32 pinSurface mount / higher temperature

www.atmel.comwww.polulu.comhttp://winavr.sourceforge.netwww.avrfreaks.netwww.wrighthobbies.netwww.eclipse.orgJust Google AVR