4 Software limitations

AN2244

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4

Software limitations

Data or sector headers corruption is possible in the case of power loss during variables

update or sectors erase or transfer.

To detect this corruption and recover it, a routine EEPROM_INIT( ) must be written and

called immediately after power on.

This routine is not implemented in this version of this application note. This section is limited

to the description of its principle.

The routine must use the sector status to check integrity and to perform repair if necessary.

After power loss, the EEPROM_INIT( ) routine is used to check sector header status. There

are 16 possible status combinations, half of which are invalid. The following table shows the

actions that should be taken based on the sectors states upon power up.

Table 1.

Status combinations and actions to be taken

ERASED

RECEIVE_DATA

VALID_DATA

TRANSFER

COMPLETE

ERASED

Invalid state: erase

both sectors and

format sector 1

Invalid state: erase

both sectors and

format sector 1

Use sector 1 as

valid sector and

erase

sector 2

Invalid state:

erase both sectors

and format sector 1

RECEIVE_DATA

Invalid state: erase

both sectors and

format sector 1

Invalid state: erase

both sectors and

format sector 1

Use sector 1 as

valid sector and

erase sector 2 and

transfer data from 1

to 2

Use sector 2 as

valid sector and

erase sector 1

VALID_DATA

Use sector 2 as

valid sector and

erase sector 1

Use sector 2 as

valid sector and

erase sector 1 and

transfer data from 2

to 1

Invalid state:

erase both sectors

and format sector 1

Use sector 2 as

valid sector and

erase sector 1

TRANSFER

COMPLETE

Invalid state: erase

both sectors and

format sector 1

Use sector 1 as

valid sector and

erase

sector 2

Use sector 1 as

valid sector and

erase

sector 2

Invalid state:

erase both sectors

and format sector 1

Sector 1

Sector 2