Atmel DFU Bootloader ABI wrapper

What it is

This project consists of one header file and one source file and it includes wrapper functions which allow to access the flash and fuse-bit programming functions in the stock bootloader on some of the Atmel's USB-enabled AVR chips. It also provides a convenient function which writes a whole page to the flash memory.

Why I wrote it

While developing my mechanical keyboard project, the GH60, I came across the need to program the flash memory during runtime. The avr-gcc compiler has the necessary headers to write your own bootloader code, which would allow me to achieve exactly what I needed, but since the chip I was using (ATmega32u4) already had a stock bootloader, I wanted to use it instead.

Unfortunately, I couldn't find any libraries to use the functions it provided, so I decided to write my own.

Check out the original article, where I describe how it works.


The library provides static inlines for all the bootloader's functions:

The meaning of arguments should be self-explanatory. Further documentation can be found in Atmel's datasheet.

Except for those functions, there are two higher-level functions:

The first one performs a jump to the bootloader section and gets the chip into DFU mode and the second one writes a whole flash page (at address addr) with provided data.


The code was tested on the following devices:

  • ATmega32u4,
  • ATmega32u2.

It should also work on the those chips, though compatibility hasn't been verified:

  • ATmega16u4,
  • ATmega8u4,
  • ATmega16u2,
  • ATmega8u2,
  • AT90USB128x,
  • AT90USB64x,
  • AT90USB162,
  • AT90USB82.

If you have succesfully run the code on any of those devices or made modifications which allowed it to run, please let me know in the comments.


You can download the files from my github repository.

4 thoughts on “Atmel DFU Bootloader ABI wrapper”

  1. Hi,

    Slightly off topic question. Do you know if it is feasible to do the oposite, wire/configure the Atmel to not allow flashing unless physical switch is pressed?


  2. Hi Alex,

    normally the atmega32u4 will run the bootloader only when reset while the HWB is low. So you can connect HWB to ground through a switch and then you can run the bootloader if you press this button, hold it and then reset (probably by pressing another button).

    Except for that, you can disable the bootloader by disabling the HWBE fuse bit or even remove the bootloader code completely while programming via SPI.

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