AN2244

3 Application example: EEPROM emulation using ST10F27x Flash library

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If the data to be written is different from 0xFFFFFFFF, we look for the last data equal to

0xFFFFFFFh (the following location should not contain 0x00000000) and the data is written

at this location.

The following diagram summarizes the write operation and treats the cases where written

data is equal to or different from 0xFFFFFFFF. This routine will return 0 on success,

VARIABLE_FULL if there isn’t enough memory for a variable update, or a Flash error code

indicating an operation failure (erase or program).

Figure 6.

WriteVerifyVariableFull routine flowchart

EepromSectorTransfer( ) routine

This routine transfers the most recent data (Last variable updates) plus the new one from a

full sector to an empty one. At the beginning, it determines the active sector which is the

sector that we want to transfer from. The new sector header field is defined and written (new

sector status is RECEIVE_DATA given that it is in the process of receiving data). When, the

data transfer is complete, the new sector header is marked VALID_SECTOR and the old

one TRANSFER_COMPLETE. At the end, the old sector is erased.

The transfer process is shown in the following figure:

Find Valid sector

Data=

0xFFFFFFFF?

status = FlashVerifyWord (address,0xFFFFFFFF)

Calculate the base address of the

status1 = FlashVerifyWord (address+4,0xFFFFFFFF)

status2 = FlashVerifyWord (address+4,0x00000000)

address=address+8

address=address+4

FlashProgramWord(address+4,0)

return 0

Write_request

status=0?

&&

status1=0?

Yes

No

No

status=0?

&&

status2=0?

Yes

Yes

No

variable in the valid sector address

FlashProgramWord(address, Data)

return 0