Proper way to keep values after reset

Mbed OS Best practice
1

Hi there,

I would like to ask for best practice how it shall be use non-volatile data.

For example, keep data of integer or array type after reset.

I found way how to create txt file in USB mass storage, but this is quite overengineered solution, I think so.

Any idea for rookies like me ?

Thanks a lot.

MK.

2

Hi,

Just as an idea, most STM32 devices I know have backup registers that are kept as long as V_BAT is on. However there are not many registers usually. They can be found in the reference manuals under the tamper sections.

Best,
Chris

3

Hello,

use SD card or if you want it without external hardware try this - KVStore - API references and tutorials | Mbed OS 6 Documentation

BR, Jan

4

Thanks a lot.

is there any simpler than 200line example for KVStore?
MK

5

I don’t know about something official.
But you can try a simple code below.

For example click HERE 
#include "mbed.h" //MbedOS 6.9 Nucleo-F303RE
#include "KVStore.h"
#include "kvstore_global_api.h"
#include <string>
/*A serial monitor is required (tested with Termite 3.4)*/
#define DEBUG 1

int main()
{
    debug_if(DEBUG, "Hello from Mbed OS version %d.%d.%d\n\n", MBED_MAJOR_VERSION, MBED_MINOR_VERSION, MBED_PATCH_VERSION);
    thread_sleep_for(500);
    char str[5];  
    char kv_key[] = {"/kv/key"};
    char kv_value[5];
    kv_info_t info;
                
    while(true){
        debug_if(DEBUG, "Please, enter a value! - five-digit \n");
        scanf("%5s",str); 
        debug_if(DEBUG, "Your value is %s!\n", str);
        kv_get_info(kv_key, &info);
        kv_get(kv_key, kv_value, info.size, 0);
        bool check = true;
        for(int i=0;str[i]!='\0';i++){
            if(str[i]!=kv_value[i]) check = false; 
        }
        if(check){
            debug_if(DEBUG, "This value is already stored!\n");
        }else{
            debug_if(DEBUG, "Saving new value\n");
            kv_set(kv_key, str, strlen(str), 0);
        } 
    }
}

BR, Jan