As I have been experimenting with the samd21 I have noticed that on occasion openocd combined with the at91samd commands would cause the samd21 to go into a state where I could no longer program with my atmel-ice. Further experimentation with a samd21 xplained board where I was writing a short program to modify the fuses resulted in a similar problem where I was no longer able to program the board. Looking closely at the fuse settings and you have the following for a couple of the reserved fuse settings (24:17 and 41):
Voltage Regulator Internal BOD (BOD12) configuration. These bits are written in production and must not be changed.
Through my experimentation I have found the fuses to be set to 0xFFFFFFFF and I have had to set them back to default configuration (such as 0xD8E0C7FF and 0xFFFFFC5D). Now I am wondering if blinding setting them without masking those reserved bits is causing my issues?
Anyone have some insight on these reserved bits, the damage that can be done by changing them, and methods for being able to program boards again? I have tried programming with atmel studio after they become unresponsive to programming via openocd and I still can not program.