25.6.8.1 Principle of Operation

The SmartEEPROM feature is provided through the AHB2 interface and makes a portion of the NVM appear like a RAM. 8-bit, 16-bit, 32-bit access is supported.

The SmartEEPROM concept relies on the following NVM physical property: It is always possible to write a '0' in a NVM word, even if this word has been previously programmed - but it is not possible to write a '1' to a bit already programmed (holding a '0').

The algorithm consists of virtually mapping physical portions of the NVM to logical addresses with an indirection mechanism. A physical page is assigned to a virtual page address and is kept as long as no bit has to be flipped from '0' to '1', as this operation requires a full block erase. In case such a transition is required, a new physical page is assigned to the modified virtual page (placed in the Flash area reserved for the SmartEEPROM). Writing the virtual page affects the cycling endurance of the SmartEEPROM.

A region can overlap the SmartEEPROM region (depending on the allocated space for the SmartEEPROM), but SmartEEPROM is independent of the Region Lock Bits.

If NVMCTRL.STATUS.AFIRST contains '1', BANKA is mapped to the NVM main address space base address (0x0000). In this case, SmartEEPROM will be in BANKB. Conversely, when BANKB is mapped to the NVM main address space base address, SmartEEPROM will be in BANKA. Thus, the CPU is not halted when accessing the SmartEEPROM.