PIC32 data storage in flash change / corrupt

Question

I have some random issue with data saved in flash on PIC32MX470F512L.

Since there is no EEPROM, part of the flash storage is used to save configuration and some statistics (ie.: reboots reason, errors on serial communication, etc).

Over about 50+ units, randomly part of configuration change, the cause is not found but some hypothesis for the moment :

• No capacitor on MCLR
• Reading of the configuration in flash before VDD fully stabilized
• Power off during flash write

I am sure there is not enought writes to go beyond limit, somewhere between 1 and 25 writes per day.

Yet I've not been able to reproduce the issue periodically.

Here are some relevant parts of the code...

Main

int main()
{
    /* Variables defines */

    //Configure l'horloge systeme
    SYSTEMConfig(GetSystemClock(),SYS_CFG_WAIT_STATES | SYS_CFG_PCACHE);


    //Active le watchdog (periode de timeout de 8sec)
    EnableWDT();

    //Initialisation de la configuration non volatile
    config_init();

    /* Other init stuff */

    //Gestion des statistiques de demarrage.
    if(mGetWDTOFlag())
    {      //Reset par watchdog
        mClearWDTOFlag();
        g_stConfiguration.stats[STAT_REBOOT_WATCHDOG]++;
        config_saveStats();
    }
    else if(mGetPORFlag())
    {  //Reset par switch
        mClearPORFlag();
        g_stConfiguration.stats[STAT_REBOOT_NO_POWER]++;
        config_saveStats();
    }
    else if(mGetBORFlag())
    {  //Reset par mauvaise alimentation
        mClearBORFlag();
        g_stConfiguration.stats[STAT_REBOOT_NO_POWER]++;
        config_saveStats();
    }
    else if(mGetMCLRFlag())
    { //Reset par mclr (bouton reset)
        mClearMCLRFlag();
        g_stConfiguration.stats[STAT_REBOOT_OTHER]++;
        config_saveStats();
    }
    else if(mGetSWRFlag())
    {  //Reset software (non implemente encore)
        mClearSWRFlag();
        g_stConfiguration.stats[STAT_REBOOT_OTHER]++;
        config_saveStats();
    }

    /* Going to main loop */
}

Flash utility functions

void config_init() {
    // Lecture de la configuration presente en memoire
    nvm_lireConfig(&g_stConfiguration,NVM_PAGE_CONFIG);

    /*
     * Si le numero d'ordinateur est zero c'est parce qu'il n'y a rien dans la
    * flash, on va charger les valeurs par defaut.
    */
    if(g_stConfiguration.numero_ordinateur == 0)
    {
        config_defaut(&g_stConfiguration);
        nvm_ecrireConfig(&g_stConfiguration,NVM_PAGE_CONFIG);
        nvm_ecrireConfig(&g_stConfiguration,NVM_PAGE_CFG_BKP);
    }
}

void config_saveStats()
{
    nvm_ecrireConfig(&g_stConfiguration,NVM_PAGE_CONFIG);
}

void nvm_lireConfig(void *dataAdr, int pageNumber) {
    memcpy(dataAdr,(void*)eedata_addr[pageNumber],sizeof(ComputerConfiguration));
}

int nvm_ecrireConfig(void * dataAdr, int pageNumber) {
    int pagebuff[1024]; //Buffer d'une page, necessaire pour la fonction NVProgram

    // On efface la page avant d'ecrire dedans
    if(nvm_effacer(pageNumber) == NVM_SUCCESS) {
        // Ecriture des donnees dans la NVM
        if(NVMProgram((void*)eedata_addr[pageNumber],dataAdr,sizeof(ComputerConfiguration),(void*)pagebuff) == 0) {
            // Verification des donnees ecrits
            if(nvm_verifier(dataAdr,pageNumber) == NVM_SUCCESS) {
                return NVM_SUCCESS;
            } else {
                return NVM_VERIFY_ERROR;
            }
        } else {
            return NVM_WRITE_ERROR;
        }
    } else {
        return NVM_ERASE_ERROR;
    }
}

int nvm_effacer(int pageNumber) {
    if(pageNumber < NVM_NUM_PAGES) {
        if(NVMErasePage((void*) eedata_addr[pageNumber]) == 0) {
            return NVM_SUCCESS;
        } else {
            return NVM_ERASE_ERROR;
        }
    } else {
        return NVM_PAGE_OUT_OF_RANGE;
    }
}

Answer 1

After further investivation and tests, it looks like Erik Friesen was right, there was too much erase/write cycles into the flash memory.

The chip used (PIC32MX470) have a minimal cell endurance of 20000 E/W cycle (found in the datasheet page 292).

In the program I found multiple calls to the configuration write that could happen many dozens of times a day, also the erace was used twice, one manually and one into NVMProgram.

To confirm the issue, I've changed the pages used in the program and read / write were working perfectly (as those pages were not used before).

The final solution was :

• Cleaning the code, removing all unnecessary configuration save
• Removing the double erase
• Integrate the Data EEPROM Emulation library from MicroChip to extend duration even more