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.
Using
The library provides static inlines for all the bootloader's functions:
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static inline void flash_page_erase_and_write(uint32_t addr); static inline uint8_t flash_read_sig(uint32_t addr); static inline uint8_t flash_read_fuse(uint32_t addr); static inline void flash_fill_temp_buffer(uint16_t data, uint16_t addr); static inline void flash_prg_page(uint32_t addr); static inline void flash_page_erase(uint32_t addr); static inline void flash_lock_wr_bits(uint8_t bits); |
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:
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static inline void run_bootloader(); void flash_write_page(uint32_t addr, const uint8_t *data); |
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.
Compatibility
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.
Download
You can download the files from my github repository.
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?
Thanks,
Alx
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.
Nice!
Hi,
Can I know if it works for ATmega 8A PU ?