Is the source code for this available somewhere? I need to boot from external flash on a custom board, and I was hoping to get a look at this code for a starting point. I could not find it on github so either I need to look harder or it is not released for some reason.
Is this what your looking for ?
https://github.com/LowPowerLab/DualOptiboot (https://github.com/LowPowerLab/DualOptiboot)
That seems to only have the AVR bootloaders. I'm looking for the samd version that ships with the Moteino M0.
No source was released.
You may use the binary that ships with it, it's included in the Moteino SAMD boards package.