Reserve Flash for user data

[federico.massimi]

Posted on May 09, 2018 at 12:28

Hello,

    I would like to save some data in the internal flash memory of an STM32L476. I found examples and guides and I was able to write and read data from flash. But I have a question: is the internal flash memory the same used to store the program? if yes, how can I be sure that my data will not overwrite the program? Are there any flash locations reserved for user data? Is there a way to compiler (Use Atolic Truestudio) without put the program in some areas of the flash?

Thanks in advance.

[Nesrine M_O]

Posted on May 09, 2018 at 12:35

Hi

Massimi.Federico

,

you can protect your memory area using Proprietary Code Read-Out Protection (PCROP): protection against read and write operations on Flash and SRAM memories.

For more details about PCROB, I rocommend you to have a look to

http://www.st.com/content/ccc/resource/technical/document/application_note/group0/1f/99/ef/d6/24/8d/44/08/DM00226247/files/DM00226pdf/jcr:content/translations/en.DM00226pdf

Application note.

-Nesrine-

[AvaTar]

Posted on May 09, 2018 at 13:00

is the internal flash memory the same used to store the program?

Yes.

if yes, how can I be sure that my data will not overwrite the program?

Totally up to you.

Are there any flash locations reserved for user data?

Check the memory map and the Datasheet/Reference Manual. I don't know your MCU variant, but I guess not.

Such 'user data locations' use to be implemented with byte erase/program capabilities, and named 'EEPROM'.

Is there a way to compiler (Use Atolic Truestudio) without put the program in some areas of the flash?

Yes.

Create a separate linker section with your desired size, while you 'carve' it out of the code section (Flash).

You might want to consult the Atollic manuals/help for details about it, I don't work with this toolchain.

Be aware that 'normal' code Flash is not designed for frequent erase/programm, and will wear out quicky (e.g. weeks or month). Consider an external NV memory option.

[federico.massimi]

Posted on May 09, 2018 at 13:29

I dont have to do frequent write/read cycles, I just have to be able to load parameters at startup.

so what I should do is choose a flash page to use (maybe the last one) and set the compiler to not use that page.Do you know how I can do it with Atolic Truestudio?

[AvaTar]

Posted on May 09, 2018 at 14:32

Do you know how I can do it with Atolic Truestudio?

Not really, sorry. Just tried Atollic a bit a few month ago.

You would have modify the linker script for your project.

As said, reduce the size of the code segment, and declare the carved-out segment as a new section.

The Atollic IDE help should cover this, else try a search here or elsewhere - this method is specific for Atollic, but not STM32.

I dont have to do frequent write/read cycles, I just have to be able to load parameters at startup.

That would be ok.

I have witnessed over-zealous project managers forcing periodic write functionality into code Flash, to reduce BOM costs.

This cost reduction was more then compensated by broken field returns.

[federico.massimi]

Posted on May 10, 2018 at 00:41

in my project i've found this file: STM32L476RG_FLASH.ld

where i can read this lines:

MEMORY

{RAM (xrw) : ORIGIN = 0x20000000, LENGTH = 96KRAM2 (xrw) : ORIGIN = 0x10000000, LENGTH = 32KFLASH (rx) : ORIGIN = 0x8000000, LENGTH = 1024K}

from the reference manual i know that every memory page have a size of 2k,so i can simply modify the flash memory lenght from 1024K to 1022K in this file to avoid that compiler/linker use the last page of the flash? It's that simple?