The Boot Section Read Protection (BOOTRP) and the Application Code Section Write Protection (APPCODEWP) are located in the NVMCTRL.CTRLB register and are used for run-time write protection.
BOOTRP prevents read access and code execution from the BOOT section. This
bit can only be written from the BOOT section, and it can only be cleared by a Reset.
When BOOTRP is set, any attempt to read from the BOOT section will return
‘0’, and any instruction fetch from the BOOT section will return a
NOP instruction. The read protection will only take effect when the
BOOT section is exited after the bit is written.
APPCODEWP controls the write access to the Application code section. When set, any attempt to update this section will be ignored, even if this is executed from the BOOT section. This bit is cleared only by a Reset.