How to Install an ATtiny Bootloader With Virtual USB

Contributors: Shawn Hymel

Create an Arduino Board Definition

To be able to program the ATtiny84 from Arduino, we need to make a custom board definition. There are three main parts for a board definition, and we'll create each one:

• boards.txt -- Information about the microcontroller (clock speed, program space, etc.)
• platform.txt -- Extra information the compiler might need and which loader tool to use (e.g., AVRDUDE)
• pins_ardiuno.h -- Tells the compiler which pins in code map to which pins on the microcontroller

Additionally, we'll need to copy over the micronucleus loader tool from the micronucleus project directory to the Arduino directory. The loader tool will be used to send compiled firmware to the ATtiny84 (much as AVRDUDE does).

boards.txt

Navigate to \/hardware and create a directory that corresponds to the class of platforms or company name that our ATtiny84 will belong to. I'll call mine mytiny.

In that directory, create another directory that corresponds to the target microcontroller family, "avr" in this case.

In the avr directory, create a file named boards.txt and copy in the following text:

menu.cpu=Processor

################################################################################

MyTiny.name=MyTiny (ATtiny84, 3.3V, 8Mhz)

MyTiny.upload.using=micronucleusprog
MyTiny.upload.protocol=usb
MyTiny.upload.tool=micronucleus
MyTiny.upload.maximum_size=6012

MyTiny.build.mcu=attiny84
MyTiny.build.f_cpu=8000000L
MyTiny.build.board=MYTINY
MyTiny.build.core=arduino:arduino
MyTiny.build.variant=tiny14

platform.txt

In the avr directory, create a file named platform.txt and copy in the following:

name=MyTiny Boards
version=0.0.1

# Default "compiler.path" is correct, change only if you want to overidde the initial value
compiler.path={runtime.tools.avr-gcc.path}/bin/
compiler.c.cmd=avr-gcc
compiler.c.flags=-c -g -Os -w -ffunction-sections -fdata-sections -MMD
compiler.c.elf.flags=-Os -Wl,--gc-sections
compiler.c.elf.cmd=avr-gcc
compiler.S.flags=-c -g -x assembler-with-cpp
compiler.cpp.cmd=avr-g++
compiler.cpp.flags=-c -g -Os -w -fno-exceptions -ffunction-sections -fdata-sections -MMD
compiler.ar.cmd=avr-ar
compiler.ar.flags=rcs
compiler.objcopy.cmd=avr-objcopy
compiler.objcopy.eep.flags=-O ihex -j .eeprom --set-section-flags=.eeprom=alloc,load --no-change-warnings --change-section-lma .eeprom=0
compiler.elf2hex.flags=-O ihex -R .eeprom
compiler.elf2hex.cmd=avr-objcopy
compiler.ldflags=
compiler.size.cmd=avr-size
# this can be overriden in boards.txt
build.extra_flags=

# AVR compile patterns
# --------------------

## Compile c files
recipe.c.o.pattern="{compiler.path}{compiler.c.cmd}" {compiler.c.flags} -mmcu={build.mcu} -DF_CPU={build.f_cpu} -DARDUINO={runtime.ide.version} -DARDUINO_{build.board} -DARDUINO_ARCH_{build.arch} {build.extra_flags} {includes} "{source_file}" -o "{object_file}"

## Compile c++ files
recipe.cpp.o.pattern="{compiler.path}{compiler.cpp.cmd}" {compiler.cpp.flags} -mmcu={build.mcu} -DF_CPU={build.f_cpu} -DARDUINO={runtime.ide.version} -DARDUINO_{build.board} -DARDUINO_ARCH_{build.arch} {build.extra_flags} {includes} "{source_file}" -o "{object_file}"

## Compile S files
recipe.S.o.pattern="{compiler.path}{compiler.c.cmd}" {compiler.S.flags} -mmcu={build.mcu} -DF_CPU={build.f_cpu} -DARDUINO={runtime.ide.version} -DARDUINO_{build.board} -DARDUINO_ARCH_{build.arch} {build.extra_flags} {includes} "{source_file}" -o "{object_file}"

## Create archives
recipe.ar.pattern="{compiler.path}{compiler.ar.cmd}" {compiler.ar.flags} "{archive_file_path}" "{object_file}"

## Combine gc-sections, archives, and objects
recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {compiler.c.elf.flags} -mmcu={build.mcu} -o "{build.path}/{build.project_name}.elf" {object_files} "{archive_file_path}" "-L{build.path}" -lm

## Create eeprom
recipe.objcopy.eep.pattern="{compiler.path}{compiler.objcopy.cmd}" {compiler.objcopy.eep.flags} "{build.path}/{build.project_name}.elf" "{build.path}/{build.project_name}.eep"

## Create hex
recipe.objcopy.hex.pattern="{compiler.path}{compiler.elf2hex.cmd}" {compiler.elf2hex.flags} "{build.path}/{build.project_name}.elf" "{build.path}/{build.project_name}.hex"

## Compute size
recipe.size.pattern="{compiler.path}{compiler.size.cmd}" -A "{build.path}/{build.project_name}.elf"
recipe.size.regex=^(?:\.text|\.data|\.bootloader)\s+([0-9]+).*
recipe.size.regex.data=^(?:\.data|\.bss|\.noinit)\s+([0-9]+).*
recipe.size.regex.eeprom=^(?:\.eeprom)\s+([0-9]+).*


# Micronucleus Loader
# -------------------
tools.micronucleus.cmd.path={runtime.hardware.path}/../tools
tools.micronucleus.upload.params.verbose=-verbose
tools.micronucleus.upload.params.quiet=
tools.micronucleus.upload.pattern="{cmd.path}/micronucleus" --timeout 60 "{build.path}/{build.project_name}.hex"
#tools.micronucleus.upload.pattern="{cmd.path}/micronucleus" --run --timeout 60 "{build.path}/{build.project_name}.hex"
#tools.micronucleus.upload.pattern="{cmd.path}" -cdigispark --timeout 60 -Uflash:w:{build.path}/{build.project_name}.hex:i

# USB Default Flags
# Default blank usb manufacturer will be filled it at compile time
# - from numeric vendor ID, set to Unknown otherwise
build.usb_manufacturer=
build.usb_flags=

Pin Definitions

At this point, we need to create a custom pin definitions file. Create a directory in avr with the name variants:

Create another directory in variants named tiny14. In tiny14, create a file named pins_arduino.h.

Copy the following code into pins_arduino.h. Note that the original contents of this file come from the ATtiny cores for Arduino project.

language:c
/*
  pins_arduino.c - pin definitions for the Arduino board
  Part of Arduino / Wiring Lite

  Copyright (c) 2005 David A. Mellis

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General
  Public License along with this library; if not, write to the
  Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  Boston, MA  02111-1307  USA

  $Id: pins_arduino.c 565 2009-03-25 10:50:00Z dmellis $

  Modified 28-08-2009 for attiny84 R.Wiersma
  Modified 09-10-2009 for attiny45 A.Saporetti
*/

#ifndef Pins_Arduino_h
#define Pins_Arduino_h

#include <avr/pgmspace.h>

// ATMEL ATTINY84 / ARDUINO
//
//                           +-\/-+
//                     VCC  1|    |14  GND
//             (D 10)  PB0  2|    |13  AREF (D  0)
//             (D  9)  PB1  3|    |12  PA1  (D  1) 
//                     PB3  4|    |11  PA2  (D  2) 
//  PWM  INT0  (D  8)  PB2  5|    |10  PA3  (D  3) 
//  PWM        (D  7)  PA7  6|    |9   PA4  (D  4) 
//  PWM        (D  6)  PA6  7|    |8   PA5  (D  5)        PWM
//                           +----+

const static uint8_t A0 = 0;
const static uint8_t A1 = 1;
const static uint8_t A2 = 2;
const static uint8_t A3 = 3;
const static uint8_t A4 = 4;
const static uint8_t A5 = 5;
const static uint8_t A6 = 6;
const static uint8_t A7 = 7;

#define digitalPinToPCICR(p)    ( ((p) >= 0 && (p) <= 10) ? (&GIMSK) : ((uint8_t *)0) )
#define digitalPinToPCICRbit(p) ( ((p) <= 7) ? PCIE0 : PCIE1 )
#define digitalPinToPCMSK(p)    ( ((p) <= 7) ? (&PCMSK0) : (((p) <= 10) ? (&PCMSK1) : ((uint8_t *)0)) )
#define digitalPinToPCMSKbit(p) ( ((p) <= 7) ? (p) : (10 - (p)) )

#ifdef ARDUINO_MAIN

// these arrays map port names (e.g. port B) to the
// appropriate addresses for various functions (e.g. reading
// and writing)
const uint16_t PROGMEM port_to_mode_PGM[] = 
{
  NOT_A_PORT,
  (uint16_t)&DDRA,
  (uint16_t)&DDRB,
};

const uint16_t PROGMEM port_to_output_PGM[] = 
{
  NOT_A_PORT,
  (uint16_t)&PORTA,
  (uint16_t)&PORTB,
};

const uint16_t PROGMEM port_to_input_PGM[] = 
{
  NOT_A_PORT,
  (uint16_t)&PINA,
  (uint16_t)&PINB,
};

const uint8_t PROGMEM digital_pin_to_port_PGM[] = 
{
  PA, /* 0 */
  PA,
  PA,
  PA,
  PA,
  PA,
  PA,
  PA,
  PB, /* 8 */
  PB,
  PB,
};

const uint8_t PROGMEM digital_pin_to_bit_mask_PGM[] = 
{
  _BV(0), /* port A */
  _BV(1),
  _BV(2),
  _BV(3),
  _BV(4),
  _BV(5), 
  _BV(6),
  _BV(7),
  _BV(2), /* port B */
  _BV(1),
  _BV(0),
};

const uint8_t PROGMEM digital_pin_to_timer_PGM[] = 
{
  NOT_ON_TIMER,
  NOT_ON_TIMER,
  NOT_ON_TIMER,
  NOT_ON_TIMER, 
  NOT_ON_TIMER,
  TIMER1B, /* OC1B */
  TIMER1A, /* OC1A */
  TIMER0B, /* OC0B */
  TIMER0A, /* OC0A */
  NOT_ON_TIMER,
  NOT_ON_TIMER,
};

#endif

#endif

If you look through the platform.txt file, you'll see that the loader tool is micronucleus and not avrdude. Because Arduino does not come with the micronucleus loader tool, we need to build it or copy it from the micronucleus project directory.

Build the Micronucleus Loader (Mac)

First, you'll need to make sure you have Homebrew installed. Then, open a command terminal and enter:

cd <micronucleus Directory>/commandline
brew install libusb-compat
make

Navigate to \/commandline. Copy the micronucleus executable in the commandline directory to \/hardware/tools.

Build the Micronucleus Loader (Linux)

Navigate to the micronucleus project directory and make the loader:

cd <micronucleus Directory>/commandline
sudo apt-get install libusb-dev
make

Navigate to \/commandline. Copy the micronucleus executable in the commandline directory to \/hardware/tools.

Copy the Micronucleus Executable (Windows)

Navigate to \/commandline. In Windows, copy builds/Windows/micronucleus.exe (or copy the micronucleus executable in the current directory in Linux and OS X) to \/hardware/tools.