AN2540 - Application note

Implementing the EEPROM emulation

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3.2

Parameter records stored in EEPROM vary in size and update frequency. Users using this

method would usually know the update frequency in advance.

In this method, sector0 and sector1 in Bank1 are used. These Flash memory sectors are

write-accessed in order to store several non-volatile variables. For this purpose, they have to

be divided identically into several parts, one per variable. The size of the memory space

allocated to each variable depends on the variable update frequency. The first 16-bit value

of each variable is stored at the base address of the memory space allocated to the

variable. When the variable is updated, the new value is stored at the next available

address: Base address + 2, base address + 4 and so on until no room remains in the

allocated memory space.

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At least two boot Flash memory sectors have to be used, more if possible for wear

leveling (refer to Section 4.2)

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Minimum use of SRAM

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Simple and easily updatable code model

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User API consisting of EepromFormat, FindValidSector, WriteVariable, ReadVariable.

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Clean-up and internal data management transparent to the user

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Code in Main Flash memory, data storage in Secondary Flash memory

3.2.1

Application example

Let us assume that in sector0, three variables: A, B and C, will be stored and updated.

In a typical application, the majority of non-volatile data are seldom updated, only a few data

are updated more frequently.

A is updated more often than B. So more memory space should be allocated to C than to A

and B, and A should have more space than B (refer to Figure 2).