AN2540 - Application note

Embedded application aspects

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Figure 8.

WriteOnebyte function description

The above function is used to write the "FMI_Data" data byte to the "FMI_Address" address.

4.2

Wear-leveling: Flash endurance improvement

In the STR91xFxx on-chip Flash memory, each sector can be programmed or erased

reliably over 100 000 times.

For write-intensive applications that use more than two sectors (3 or 4) for the emulated

EEPROM, it is recommended to implement a wear-leveling algorithm to monitor and

distribute the number of write cycles among the sectors.

When no wear-leveling algorithm is used, the sectors are not used at the same rate. Sectors

with long-lived data do not endure as many write cycles as sectors that contain frequently

updated data. The wear-leveling algorithm ensures that equal use is made of all the

available write cycles for each sector.

4.2.1

Application example

In this example, in order to enhance the emulated EEPROM capacity, four sectors will be

used.

following: when sector n is full, switch to sector n+1. Sector n is then garbage-collected. Let

us consider the four sectors of the example: when sector3 is full, the device goes back to

sector0, then sector 3 is garbage-collected and so on (refer to Figure 9.).

void WriteVariable(u32 FMI_Address,u8 FMI_Data)

{

if (FMI_Address &1)

{

FMI_WriteHalfWord(FMI_Address,((FMI_Data << 8) | 0xFF));

FMI_WaitForLastOperation(FMI_BANK_1);

}

else

{

FMI_WriteHalfWord(FMI_Address,(0xFF00 |FMI_Data));

FMI_WaitForLastOperation(FMI_BANK_1);

}

}