The bootloader source code is available.

• bootloader.atmega8.lock_bits (default value: 0x0F) is the value to write to the ATmega8 lock byte to lock the bootloader section (so it doesn't get accidently overwritten when you upload a sketch).

What's a bootloader?

See this page for an explanation of what a bootloader is and why we're using one.

Bootloader Development

See Bootloader for an explanation of what a bootloader is and why we're using one.

The "Burn Bootloader" commands in the Arduino environment use an open-source tool, avrdude. There are four steps: unlocking the bootloader section of the chip, setting the the fuses on the chip, uploading the bootloader code to the chip, and locking the bootloader section of the chip. These are controlled by a number of preferences in the Arduino preferences file.

When you reset the Arduino board, it runs the bootloader (if present). The bootloader pulses digital pin 13 (you can connect an LED to make sure that the bootloader is installed). The bootloader then listens for commands or data to arrive from the the computer. Usually, this is a sketch that the bootloader writes to the flash memory on the ATmega168 or ATmega8 chip. Then, the bootloader launches the newly-uploaded program. If, however, no data arrives from the computer, the bootloader launches whatever program was last uploaded onto the chip. If the chip is still "virgin" the bootloader is the only program in memory and will start itself again.

To burn the bootloader, you'll need to buy an AVR-ISP (in-system programmer), USBtinyISP or build a ParallelProgrammer. The programmer should be connected to the ICSP pins (the 2 by 3 pin header) - make sure you plug it in the right way. The board must be powered by an external power supply or the USB port.

Make sure you have the right item selected in the Tools | Board menu. Then, just launch the appropriate command from the Tools > Burn Bootloader menu of the Arduino environment. Burning the bootloader may take 15 seconds or more, so be patient.

Bootloading an Arduino Mini

Here are some instructions on bootloading the Mini, thanks to Gian Pablo Vilamil.

The bootloader source code is available.

Third parties have also worked on the bootloader. This page is link to some other bootloader development

Third parties have also worked on the bootloader. This page is link to some other bootloader development?

Third parties have also worked on the bootloader. This page is link to some other bootloader development?

Third parties have also worked on the bootloader. This page is link to some other bootloader development?

Third parties have also worked on the bootloader. This page is link to some other bootloader development?

Third parties have also worked on the bootloader. This page is link to some other bootloader development?

The bootloader source code is available: ATmega8, ATmega168

Versions of the bootloader

There are different versions of the bootloader - both in order to work on different hardware and because it has changed over time.

The current bootloaders (i.e. the ones included in Arduino 0009) are almost identical for the Diecimila and NG (with ATmega168). They both run at 19200 baud and take up 2 KB of flash memory on the ATmega168. The only differences is the time the bootloader waits for a new program to arrive and the number of times it flashes the pin 13 LED when it starts. Because of the automatic reset on the Diecimila, its bootloader needs only wait a very short amount of time (less than a second) - to save time, it also flashes the pin 13 LED only once. The NG bootloader waits about 6-8 seconds and flashes the LED three times.

The bootloader that actually shipped on the Arduino NG is slightly different. It enables the internal pullup resistor on pin 6, and doesn't enable the internal pullup on the RX pin. Nor does it timeout upon receiving invalid data, so if you send data to it immediately after it resets, your sketch will never start.

The Arduino BT bootloader does some initial configuration of the bluetooth module.

The ATmega8 bootloader only takes up 1 KB of flash. It does not timeout when it receives invalid data, you need to make sure that no data is sent to the board during the 6-8 seconds when the bootloader is running.

Some ancient versions of the bootloader run at 9600 baud (instead of 19200). In order to successfully upload sketches to boards with this bootloader, you'll need to change the serial.download_rate in your preferences file to 9600.

The "Burn Bootloader" commands in the Arduino environment use an open-source tool, avrdude. There are four steps: unlocking the bootloader section of the chip, setting the the fuses on the chip, uploading the bootloader code to the chip, and locking the bootloader section of the chip. These are controlled by a number of preferences in the Arduino [[Preferences | preferences file].

Make sure you have the right item selected in the Tools | Microcontroller menu (it should match the chip on your Arduino board). Then, just launch the appropriate command from the Tools menu of the Arduino environment. Burning the bootloader may take 15 seconds or more, so be patient.

A precompiled bootloader (.hex file) comes with the Arduino environment; it communicates at 19200 baud (but see the note for older boards above). The "Burn Bootloader" commands in the Arduino environment use an open-source tool, avrdude. There are four steps: unlocking the bootloader section of the chip, setting the the fuses on the chip, uploading the bootloader code to the chip, and locking the bootloader section of the chip. These are controlled by a number of preferences in the Arduino [[Preferences | preferences file].

For the ATmega8 bootloader, these are:

• bootloader.atmega8.programmer (default value: stk500) is the protocal used by the bootloader.

• bootloader.atmega8.unlock_bits (default value: 0xFF) is the value to write to the ATmega8 lock byte to unlock the bootloader section.

• bootloader.atmega8.high_fuses (default value: 0xca) is the value to write to the high byte of the ATmega8 fuses.

• bootloader.atmega8.low_fuses (default value: 0xdf) is the value to write to the low byte of the ATmega8 fuses.

• bootloader.atmega8.path (default value: bootloader) is the path (relative to the Arduino application directory) containing the precompiled bootloader.

• bootloader.atmega8.file (default value: ATmegaBOOT.hex) is the name of the file containing the precompiled bootloader code (in bootloader.path).

• bootloader.atmega8.lock_bits (default value: 0xCF) is the value to write to the ATmega8 lock byte to lock the bootloader section (so it doesn't get accidently overwritten when you upload a sketch).

For the ATmega168, these are (where <BOARD> is either "diecimila" or "ng"):

• bootloader.atmega168-<BOARD>.programmer (default value: avrispmkii) is the protocal used by the bootloader.

• bootloader.atmega168-<BOARD>.unlock_bits (default value: 0x3F) is the value to write to the ATmega168 lock byte to unlock the bootloader section.

• bootloader.atmega168-<BOARD>.extended_fuses (default value: 0x00) is the value to write to the high byte of the ATmega168 fuses.

• bootloader.atmega168-<BOARD>.high_fuses (default value: 0xdd) is the value to write to the high byte of the ATmega168 fuses.

• bootloader.atmega168-<BOARD>.low_fuses (default value: 0xff) is the value to write to the low byte of the ATmega168 fuses.

• bootloader.atmega168-<BOARD>.path (default value: bootloader168) is the path (relative to the Arduino application directory) containing the precompiled bootloader.

• bootloader.atmega168-<BOARD>.file (default value: ATmegaBOOT_168_<BOARD>.hex) is the name of the file containing the precompiled bootloader code (in bootloader.path).

• bootloader.atmega168-<BOARD>.lock_bits (default value: 0x0F) is the value to write to the ATmega168 lock byte to lock the bootloader section (so it doesn't get accidently overwritten when you upload a sketch).

The bootloader source code is available: ATmega8, ATmega168

Newer versions of the bootloader communicate with the computer at 19200 baud; older versions use 9600 baud. In order to successfully upload programs to the board, this rate needs to match the serial.download_rate in your preferences file (which defaults to 19200).

A precompiled bootloader (.hex file) comes with the Arduino environment; it communicates at 19200 baud (but see the note for older boards above). The "Burn Bootloader" commands in the Arduino environment use an open-source tool, uisp. There are four steps (each a separate call to uisp): unlocking the bootloader section of the chip, setting the the fuses on the chip, uploading the bootloader code to the chip, and locking the bootloader section of the chip. These are controlled by a number of preferences in the Arduino preferences file:

Bootloader

The bootloader is a small piece of software that we've burned onto the chips that come with your Arduino boards. It allows you to upload sketches to the board without external hardware.

When you reset the Arduino board, it runs the bootloader (if present). The bootloader pulses digital pin 13 (you can connect an LED to make sure that the bootloader is installed). The bootloader then waits a few seconds for commands or data to arrive from the the computer. Usually, this is a sketch that the bootloader writes to the flash memory on the ATmega8 chip. A few seconds later, the bootloader launches the newly-uploaded program. If no data arrives from the computer, the bootloader launches whatever program was last uploaded onto the chip. If the chip is still "virgin" the bootloader is the only program in memory and will start itself again.

Why are we using a bootloader?

The use of a bootloader allows us to avoid the use of external hardware programmers. (Burning the bootloader onto the chip, however, requires one of these external programmers.)

Not using a bootloader

If you want to use the full program space (flash) of the chip or avoid the bootloader delay, you can burn your sketches using an external programmer.

Burning the Bootloader

To burn the bootloader, you'll need to buy an AVR-ISP (in-system programmer) or build a ParallelProgrammer. The programmer should be connected to the ICSP pins (the 2 by 3 pin header) - make sure you plug it in the right way. The board must be powered by an external power supply or the USB port.

Then, just launch the "Burn Bootloader" (for AVR-ISP) or "Burn Bootloader Parallel" command from the Tools menu of the Arduino environment. Burning the bootloader may take 15 seconds or more, so be patient.

It still doesn't work! (parallel programmer on Windows XP)

Windows XP may be polling your parallel port and disrupting the bootloader burning process. You'll need this registry patch:

 
[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Parport\Parameters]
"DisableWarmPoll"=dword:00000001

See this forum thread for details.

Note for older boards.

Newer versions of the bootloader communicate with the computer at 19200 baud; older versions use 9600 baud. In order to successfully upload programs to the board, this rate needs to match the serial.download_rate in your preferences.txt file (which defaults to 19200). See the FAQ? for instructions on changing it.

How does it work?

A precompiled bootloader (.hex file) comes with the Arduino environment; it communicates at 19200 baud (but see the note for older boards above). The "Burn Bootloader" commands in the Arduino environment use an open-source tool, uisp. There are four steps (each a separate call to uisp): unlocking the bootloader section of the chip, setting the the fuses on the chip, uploading the bootloader code to the chip, and locking the bootloader section of the chip. These are controlled by a number of preferences in the Arduino preferences file:

• bootloader.programmer (default value: stk500) is the protocal used by the bootloader.

• bootloader.unlock_bits (default value: 0xFF) is the value to write to the ATmega8 lock byte to unlock the bootloader section.

• bootloader.high_fuses (default value for an ATmega8 on an Arduino board: 0xca) is the value to write to the high byte of the ATmega8 fuses.

• bootloader.low_fuses (default value for an ATmega8 on an Arduino board: 0xdf) is the value to write to the low byte of the ATmega8 fuses.

• bootloader.path (default value: bootloader) is the path (relative to the Arduino application directory) containing the precompiled bootloader.

• bootloader.file (default value: ATmegaBOOT.hex) is the name of the file containing the precompiled bootloader code (in bootloader.path).

• bootloader.lock_bits (default value: 0xCF) is the value to write to the ATmega8 lock byte to lock the bootloader section (so it doesn't get accidently overwritten when you upload a sketch).

Source Code

The bootloader source code is available.

For historical reasons we maintain the following link, that will give you access to the release of the bootloader's source code we used in the first prototype we made, it is including two batch files to do the compilation and download of it under windows.