How do I implement a userspace bootloader on Arduino Due?

Question

Is it possible to use a custom bootloader, that loads and executes a main program stored for example on an SD card? The idea is to make it possible to update the Arduino remotely.

I tried this with a bootloader, which writes the program into the flash storage with a 32KB offset and then uses a function pointer with that address (0x88000) to continue execution there. The 0x80000 is as far as I am informed the address offset of the flash storage. It can be written on Due boards with this library: https://github.com/sebnil/DueFlashStorage. The problem was that this just hasn't worked, the Arduino simply stopped responding after the function pointer being executed. I would appreciate any information or hints on this topic.

• Chris Stratton: A solution of this type should be possible - but was your loaded program linked to execute at that address? And did you come up with a scheme for handling interrupt vectors? I believe on the ARM cortex you can change the address of the vector table.

Answer 1

The guys at Phoenard did just that with an AVR2560. They wrote a bootloader that loads and saves FLASH memory from/to the Micro-SD card. You can save HEX files on an SD card and then load one of them in the FLASH memory and run it.

Answer 2

Not sure if you could get the bootloader to support SD, but I have little experience with bootloader code, so the way I would go about it would be to make the sketch load content from the SD that then affects the sketch process.

• Chris Stratton: That sounds like what the poster already did. To be an answer, this would need to provide a path around the fact that it didn't work - by being more than just a vague idea.