When non-secure region erase is enabled, a non-secure flash page can be erased by writing 0xFFFFFFFF into the first 32-bit word of the flash page.
Page erase is only applicable to the code area in the flash and does not work with UICR.
After erasing a flash page, all bits in the page are set to 1. The time it
takes to erase a page is specified by tERASEPAGE. The CPU is stalled if the CPU executes code from the flash while
the NVMC performs the erase operation.