How to store data in flash memory of STM32F401CCU6?

[MihirJ]

My STM32F401CCU6 has 256K flash memory, and I want to use it to store some data. 

Trying to create a user kept pausing the program at the hardfault handler when I tried debugging. Where am I going wrong? Are there any good resources for this microcontroller regarding using the flash memory to store data?  

#include "user.h"
#include <string.h>
#include <stdio.h>
#include "stm32f4xx_hal.h"
#include "stm32f4xx_hal_flash.h"

#define ADDR_FLASH_SECTOR_6   ((uint32_t)0x08040000)
#define FLASH_USER_START_ADDR   ADDR_FLASH_SECTOR_6
#define USER_SIZE sizeof(User)

void createUser(const char* userID, const char* password, uint8_t tier) {
    if (userExists(userID)) {
        return;
    }

    User newUser;
    strncpy(newUser.userID, userID, USER_ID_LENGTH);
    newUser.userID[USER_ID_LENGTH] = '\0';
    strncpy(newUser.password, password, PASSWORD_LENGTH);
    newUser.password[PASSWORD_LENGTH] = '\0';
    newUser.tier = tier;

    HAL_FLASH_Unlock();

    FLASH_Erase_Sector(6, VOLTAGE_RANGE_3);

    for (uint32_t address = FLASH_USER_START_ADDR; address < FLASH_USER_START_ADDR + MAX_USERS * USER_SIZE; address += USER_SIZE) {
        User tempUser;
        memcpy(&tempUser, (void *)address, USER_SIZE);
        if (strlen(tempUser.userID) == 0) {
            for (uint32_t i = 0; i < USER_SIZE; i += 4) {
                uint32_t dataToWrite = *(uint32_t *)((uint8_t *)&newUser + i);
                HAL_FLASH_Program(FLASH_TYPEPROGRAM_WORD, address + i, dataToWrite);
            }
            break;
        }
    }

    HAL_FLASH_Lock();
}

bool userExists(const char* userID) {
    User tempUser;
    for (uint32_t address = FLASH_USER_START_ADDR; address < FLASH_USER_START_ADDR + MAX_USERS * USER_SIZE; address += USER_SIZE) {
        memcpy(&tempUser, (void *)address, USER_SIZE);
        if (strcmp(tempUser.userID, userID) == 0) {
            return true;
        }
    }
    return false;
}

void getUserPassword(const char* userID, char* outPassword) {
    User tempUser;
    for (uint32_t address = FLASH_USER_START_ADDR; address < FLASH_USER_START_ADDR + MAX_USERS * USER_SIZE; address += USER_SIZE) {
        memcpy(&tempUser, (void *)address, USER_SIZE);
        if (strcmp(tempUser.userID, userID) == 0) {
            strncpy(outPassword, tempUser.password, PASSWORD_LENGTH + 1);
            return;
        }
    }
}

[Tesla DeLorean]

There should be FLASH examples in the CubeF4 trees for assorted boards, review those.

Check what's actually faulting, the addresses involved. Isn't 0x40000 at the 256KB limit?

Check address alignments.

Not sure how you can memcpy() from current content, and write back.

Look at the error codes from the functions, rather than ignore.

Instrument code so you can observe what's going on without the debugger stepping on everything.

You can write once to locations previously erased.