Wear leveling in EEPROM emulator formed of flash memory cells
The present invention relates to systems and methods for implementing wear leveling in a flash memory device that emulates an EEPROM. The embodiments utilize an index array, which stores an index word for each logical address in the emulated EEPROM. Each bit in each index word is associated with a physical address for a physical word in the emulated EEPROM, and the index word keeps track of which physical word is the current word for a particular logical address. The use of the index word enables a wear leveling algorithm that allows for a programming command to a logical address to result in: (i) skipping the programming operation if the data stored in the current word does not contain a “1” that corresponds to a “0” in the data to be stored, (ii) reprogramming one or more bits of the current word in certain situations, or (iii) shifting to and programming the next physical word in certain situations.
1. An EEPROM emulated system with wear leveling, comprising:
an EEPROM emulated array comprising an array of non-volatile memory cells; and
a wear leveling module coupled to the array of non-volatile memory cells and configured to:
receive a program command, write data, and a logical address;
read a current word within a sector of physical words of non-volatile memory cells in the array of non-volatile memory cells based on the logical address and an index bit, the sector of words corresponding to the logical address and comprising a first physical word, a last physical word, and one or more physical words between the first physical word and the last physical word;
when the write data does not contain a “0” for a bit that is a “1” in the current word, skipping the programming operation;
when the write data does contain a “0” for a bit that is a “1” in the current word, and the current word is the last physical word in the sector, programming the write data in the current word; and
when the write data does contain a “0” for a bit that is a “1” in the current word, and the current word is not the last physical word in the sector, programming the write data in the next word.
2. The system of claim 1 , wherein the index bit is a bit in an index word.
3. The system of claim 2 , wherein the index word comprises a set of bits, wherein each bit in the index word corresponds to a physical word in the array.
4. The system of claim 3 , wherein each bit in the index word indicates whether a corresponding physical word in the array is used or not used.
5. The system of claim 1 , wherein the sector comprises two rows of non-volatile memory cells in the array of non-volatile memory cells.
6. The system of claim 1 , wherein each of the non-volatile memory cells comprises a bit line terminal, a source line terminal, a word line terminal, and a floating gate.
7. The system of claim 6 , wherein each of the non-volatile memory cells further comprises a control gate.
8. The system of claim 7 , wherein each of the non-volatile memory cells further comprises an erase gate.