Embedded application aspects

AN2540 - Application note

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4

Embedded application aspects

This section gives some advice on how to overcome software limitations in embedded

applications and to fulfill the needs of different applications.

4.1

Data granularity management

The emulated EEPROM can be used in embedded applications where non-volatile storage

of data updated with a byte, half-word or word granularity is required. It generally depends

on the user requirements and Flash architecture, such as stored data length, write access,

etc.

The STR91xFxx on-chip Flash memory allows 16-bit, half-word programming. Data can

however be programmed by bytes or words by using some software techniques.

4.1.1

Programming on a word-by-word basis

To write 32 bits of data "FMI_Data" to the desired Flash memory address "FMI_Address" in

Bank1 for example, the process is the following:

incremented twice.

4.1.2

Programming on a byte-by-byte basis

Writing by bytes offers the user the possibility to cover the entire memory space and,

therefore, to store more data. The performance may however be reduced.

A simple example can be useful to understand how to implement such a feature.

Let us assume for example that we want to write one byte of data "0xDD" into Bank1 at the

FMI_Address. This can be achieved as follows:

If FMI_Address is even, then 0xFFDD is written. If FMI_Address is odd, 0xDDFF is written.

The generic scheme is shown in Figure 8.

u16 LSB=FMI_Data;

u16

MSB= FMI_Data >>16;

FMI_WriteHalfWord ( FMI_Address,

LSB);

FMI_WaitForLastOperation(FMI_BANK_1);

FMI_WriteHalfWord ( FMI_Address+2,

MSB);FMI_WaitForLastOperation(FMI_BANK_1);