AVR Microcontrollers

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AVR Microcontrollers

• What is a microcontroller?
• microprocessor
• Read-write memory
• Flash memory
• EEPROM
• Input/Output Control
• Peripheral Devices (AD/DA)?
• Billions sold per year, most processors
• Emphasis is on cost. (pennies)?
• Alternative/paired to ASIC/DSP
• Emphasis on power consumption

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Uses

• Consumer electronics
• Appliances
• Automotive
• Electrical/Heating
• Computers / Hard Drives
• Hobbyist projects!
• Installation art
• Musical instruments
• Home automation
• Audio Distribution
• Web Server!!
• MANY MORE!!

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Other Examples
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Other Examples
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Manufacturers

• Intel, Freescale, Microchip (PIC), TI, Zilog
• Atmel AVR
• Many Types, tinyAT, megaAT, automotive
• Lighting, LCD
• Share unified platform
• Different s of I/O control
• Built-in Pull-up resistors
• Ethernet, Serial Data, Auxiliary Power, USB
• Analog I/O, Packaging, Interrupts, Math, JTAG
• Get the right amount of memory for the job

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Development Platforms

• Everything Needed, All-In-One
• Arduino / Diecimila
• ATMega8 / ATMega168 based
• Open source, multiplatform IDE
• Cheap (33 assembled!)?
• Great Online Community
• USB, power, protoshield available, breadboard,
  LEDs
• Parallax (PIC)?
• PICAXE (PIC)?
• ArmExpress
• Many Others

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Cheaper

• A Transistor Saved is a Transistor Earned
• No Lack Floating Point
• Non-Pipeline
• No cache
• Limited Math / Branching
• Very Slow (1 to 32MHz)?
• Very Little Memory (64bytes to 256KB)?
• From under a dollar to 20 for advanced
• Cheaper in volume
• Important for large product runs

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Atmel / AVR History

• Conceived by two students at Norwegian Institute
  of Technology (NTH)?
• Alf-Egil Bogen and Vegard Wollan
• Originally Known as µRISC (Micro RISC)?
• Sold to Atmel, continued working under Atmel
  Norway subsidiary
• AVR supposedly not acronym
• May mean Advanced Virtual RISC
• Beauty in simplicity
• Can wrap mind around entire CPU

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ATMega168 Specifications

• Low-Power 8-bit AVR Microcontroller
• Modified Harvard Architecture
• Around 4 individual, 2.50 in Volume
• 32 8-bit general-purpose registers
• 131 Instructions, Multi-cycle Implementation
• Most are single-cycle
• 2-cycle multiply, 2-cycle memory access
• Thus up to 1MIPS/MHz
• 20MHz, up to 20MIPS
• 16KB self-programmable Flash
• 512 Bytes EEPROM
• 1KB SRAM

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ATMega168 IO

• 6 PWM Shared Input/Outputs (Analog)?
• 8 digital input/outputs
• SPI-serial, 2-wire serial, ISP, others
• Monitoring, debugging, programming, power
• USART serial interface
• (interfaces with USB on Arduino)?

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Instruction Set

• Mostly unified across all AVR
• With exceptions for feature differences
• 32 or 16 bit instructions
• 8-bit fields, vary depending on instructions
• I/O manipulation treated in similar fashion to
  registers
• Allows for clean and simple usage
• Parallel Instruction Fetch
• Uses Skip instead of Branches
• Use software libraries for more complex
  functionality (divide)?

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Example Code

• Assembly Code Example(1)?
• ...
• Define pull-ups and set outputs high
• Define directions for port pins
• ldi r16,(1ltltPB7)(1ltltPB6)(1ltltPB1)(1ltltPB0)?
  
• ldi r17,(1ltltDDB3)(1ltltDDB2)(1ltltDDB1)(1ltltDD
  B0)?
• out PORTB,r16
• out DDRB,r17
• Insert nop for synchronization
• nop
• Read port pins
• in r16,PINB
• ...

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Registers

• 32 general purpose registers
• Addressable as first 32 memory addresses
• 4 Different Simultaneous Access Schemes
• X, Y, Z registers for indirect memory
• Dual-purpose, 16 bit
• 26/27, 28/29, 30/31
• 200 I/O, settings, timers, interrupts registers
• Overflow at 256 / 65K!

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Registers
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Memories

• 3 different memories
• SRAM
• Flash
• EEPROM
• Direct/Indirect Addressing (5 modes total)?
• Flash is divided into two 8KB sections
• Independently addressable
• Flash has reserved Bootloader section for
  software security

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Additional Functionality

• Registers for serial access
• Interrupts
• External Interrupts
• Power Management
• Timers
• Analog Comparators
• Other Goodies
• All handled via special registers
• Some settings via bit-flags

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Compilers

• Meant for Assembly Programming
• Many environments available
• BASIC and FORTRAN compilers available
• Open Source Tools and Compilers
• avr-GCC for C/C support
• AVR Studio Assembler / Simulator
• Supported, official, Windows-only IDE

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Operating System?

• No common operating systems available
• None would work!
• EEPROM Bootloader / Initializer
• Real-Time Operating Systems
• Commercial Systems
• Salvo
• AVRX
• NutOS
• Proc

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FreeRTOS

• Free and Open Source Operating System
• Portable across many platforms
• Royalty Free
• 1-2KB storage
• 50-100Bytes Memory
• Can spawn off tasks
• Guaranteed timings, simple
• Coroutines
• Less memory, more complex, coexist, portable
• Commercial Sister Projects

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Loading

• EEPROM burner / custom Programmer
• ISP-interface
• Serial / Parallel Programming (AVRdude)?
• USB tty support
• Most IDE's available will make this job easy

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Future

• Smaller, Better, Faster, Cheaper
• Many new products become possible
• Children's toys
• Ubiquitous Computing
• Physical Computing
• Becoming very popular among Hobbyists
• Great introduction for CS people into EE-land

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Websites / References

• ATMEL
• www.atmel.com
• Arduino
• www.arduino.cc
• Adafruit Industries
• www.adafruit.com
• FreeRTOS
• www.freertos.org
• AVR Freaks
• www.avrfreaks.net