Howto saving Data in Flash in Cortex M3/M4

[hoppel]

Hello,

today, i have a question about the flash. We had a project, where we can save data into flash, using it like an eeprom.
Therefor we had a linkerscript.
Here is the beginning code:

Code: Select all

ENTRY(Reset_Handler)

MEMORY {
   RAM      (RWX) : ORIGIN = 0x20000000     , LENGTH = 20K
   EXTSRAM  (RWX) : ORIGIN = 0x68000000     , LENGTH = 0
   FLASH    (RX)  : ORIGIN = 0x08000000     , LENGTH = 126K /* adjust to Device -- Flash Size -2k*/
   EEMUL    (RWX) : ORIGIN = 0x08000000+510K, LENGTH = 2K
}

_estack         = ORIGIN(RAM)+LENGTH(RAM);      /* end of the stack */
_seemul         = ORIGIN(EEMUL);                /* start of the eeprom emulation area */
_min_stack      = 0x100;                        /* minimum stack space to reserve for the user app */

We found that script in www, it works fine. But i have no experience about that script language.
Now we switched to use Chibios, because we likes the idea behind a RT.
So my Question is, how i have to change the Chibios Linker scripts to use the flash for storage.

Regards,
Andre

[Giovanni]

Hi Andre,

The linker script in ChibiOS is very similar, you have to reserve some flash space for the EEPROM emulator, something like:

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MEMORY
{
    flash : org = 0x08000000, len = 112K
    EEMUL: org = 0x08000000 + 112K, len = 16K
    ram : org = 0x20000000, len = 20k
}

I think it would work like in your example.

Giovanni

[hoppel]

Ok, thank you. I will test it.

[alex31]

On 1024k flash device, the pages at beginning of address space are 16Ko long and can be erased in relatively short time.

the pages at the end of address space are 128ko long and can take 1 second to be erased, so if i want to use a 16ko page, is it possible
to reserve page 0 for EEPROM emulator, then put the program on page 1 and subsequent ?

Thanks
Alexandre

[barthess]

Yes, it is possible. But in 0 sector you must place bootloader loading your program from proper sector.
EEMUL must reside in 1st (or any not 0th) sector.
Here you can find some discussion viewtopic.php?f=2&t=229

[alex31]

Thanks for pointing this thread.

Did you resolve all the problem mentioned in the thread to make your program began at an offseted address ?

Alexandre

[barthess]

Sure.

[jeremie.delaitre]

Hi,

I'm trying to save data (app settings) in flash too on the STM32P407 board.
I've changed my linker script with:

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MEMORY
{
    flash : org = 0x08000000, len = 500k
    persistentdata : org = 0x08000000 + 500k, len = 128k
    ram : org = 0x20000000, len = 112k
    ethram : org = 0x2001C000, len = 16k
    ccmram : org = 0x10000000, len = 64k
}

...

SECTIONS
{
...
    .persistentdata :
    {
        *(.persistentdata)
        KEEP(*(.persistentdata))
    } > persistentdata
...

Then, I've declared some variable with:

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__attribute__ ((section (".persistentdata")))
__IO uint32_t persistentValue;
__attribute__ ((section (".persistentdata")))
__IO uint32_t persistentValue2;

Everything compile as expected but when print persistentValue, then change its value and reprint it, I always got 0.

Do you have any hint?

I've read on the Internet that I should maybe erase the NAND page/sector before writing the new value (like when I flash my program with openocd) but how can I do that?

Saving app settings in flash seems to be a quiet common requirement so I'm wondering if it makes sense to have some helper in ChibiOS to do that?

[mabl]

I've not much time now. But for writing flash pages, I've once hacked this together:
https://github.com/mabl/ARMCM3-STM32F10 ... ADER/flash

[jeremie.delaitre]

Awesome! I'll give it a try when time permits (probably next week).