XC2000 datasheet(110/647 Pages) INFINEON

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XC2000 Derivatives

System Units (Vol. 1 of 2)

Memory Organization

Preliminary

User’s Manual

3-48

V1.0, 2007-06

MemoryX2K, V1.1

In order to find the current data after boot-up every entry must be marked. Either it

contains a counter (from 0 to 2*N-1) or the old entries are invalidated by erasing the page

after programming the new one.

After boot-up the emulation driver software must recover this mapping information1). The

same must happen in case of power-down modes that shut-down the main memory.

As all involved pages are re-used cyclically the endurance from customer perspective is

increased by the factor N. N must be chosen high enough to fulfill endurance and

retention requirements. Disturbs in the group of N pages are no issue because they incur

at most N-1 disturbs before they get written with new data. Care must be taken however

if one sector accommodates different groups of pages with different update behavior. In

this case the updates of one group of pages could exceed the disturb limits of the other

group. So generally one sector should be used only by one such EEPROM cyclic buffer.

The algorithm keeps the old data until the new data is verified so power failure during

programming can only destroy the last update but the older data is still available. There

are still some issues with power failure that need special treatment:

•

Power is cut during programming: the following boot-up might find an apparently

correctly programmed page. However the cells might be not fully programmed and

thus have a much lower retention. The algorithm must detect this situation and

finalize the programming, e.g. with margin reads.

•

Power is cut during erase: the same as above can happen. Data may appear as

erased but the retention is lowered.

The algorithm can be improved to cover these cases as well. The easiest solution is to

use margin reads to verify the program or erase steps.

The main deficiency of the described algorithm is that the software designer is required

to plan the use of the flash memory thoroughly. The user has to choose the correct value

of N. Then all data has to be allocated to pages. Data sharing one page should have a

similar or better identical update pattern (otherwise unchanged data is unnecessarily

written). If one set of data does not fill a complete sector the available pages must be

possibly left unused because they might incur too many drain disturbs.

There are other algorithms that try to alleviate these efforts by monitoring the flash usage

and adapt automatically the assignment of data to flash cells.

This time must be taken into account for calculating the startup duration.

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