MCU Flash Memory programming in C

Question

Newbie here. I am currently working on a project that involves saving password on MCU(NUC200LE3AN) Flash memory.

These codes works just fine. After writing it I am able to read the exact value of user_password1 even after the MCU restarts.

FMC_Erase(PASSWORD1_LOCATION); //u32addr 
if (*(uint32_t *)(PASSWORD1_LOCATION) == 0xffffffff)
{
    uint32_t user_password1 = "1234";
    FMC_Write(PASSWORD1_LOCATION,user_password1);
}

uint32_t ReadPass1 = *(uint32_t *)(PASSWORD1_LOCATION);

UART_Write(UART0,ReadPass1,4); //4 -> string length 
_UART_SENDBYTE(UART0,0x0D);

But I will be using uint8_t array of 5(including the terminating '\0') as a source in changing my password. Example:

FMC_Erase(PASSWORD1_LOCATION);    

uint8_t new_password[5];
new_password[0] = '1';
new_password[1] = '2';
new_password[2] = '3';
new_password[3] = '4';
new_password[4] = '\0';

if (*(uint32_t *)(PASSWORD1_LOCATION) == 0xffffffff)
{
  user_password1 = (uint32_t *)(new_password);
  FMC_Write(PASSWORD1_LOCATION,user_password1);
}

uint32_t ReadPass1 = *(uint32_t *)(PASSWORD1_LOCATION);

UART_Write(UART0,ReadPass1,4); //4 -> string length 
_UART_SENDBYTE(UART0,0x0D);

With this, I can write the password and read it as long as those fix values are there and those fix values are just for default password. After I changed my password as long as i don't turn off the MCU it could still be read which is not acceptable due to the MCU needs to be turned on/off. If I apply this and then restart the MCU, reading PASSWORD1_LOCATION returns garbage/null.

Is there a way to turn this:

uint8_t new_password[5];     
new_password[0] = '1';
new_password[1] = '2';
new_password[2] = '3';
new_password[3] = '4';
new_password[4] = '\0';

Into This:

uint32_t user_password1 = "1234";

I hope you know what I mean. Thank you.

first of all *(uint32_t *) probably does not work since it's not volatile so all those reads and writes that uses it would very likely fail. Also your uint8_t new_password[5]; uses 8 bit big endian ASCII encoding, but uint32_t user_password1 = "1234"; (BTW should be 1234 not "1234") is 32 bit unsigned binary integer, native endian. Those two representations are not compatible with each other. — user3528438
– user3528438, Commented Dec 1, 2016 at 15:56
Seriously, you are provided with library function like FMC_Write() FMC_Read() FMC_Erase() and yet you wrote your own "read" function with regular pointer deference, and then ask people why it doesn't work? Why do you think it could work? — user3528438
– user3528438, Commented Dec 1, 2016 at 16:02
uint32_t user_password1 = "1234"; --> uint32_t user_password1 = 0x31323334; and FMC_Write(PASSWORD1_LOCATION,user_password1); --> FMC_Write(PASSWORD1_LOCATION, &user_password1); — LPs
– LPs, Commented Dec 1, 2016 at 16:24
@user3528438 I made it "1234" because its a password which normally is a char. I mean I can change my password to "12AB". Thanks for your answers! — khelogram
– khelogram, Commented Dec 1, 2016 at 17:14

LPs · Accepted Answer · 2016-12-01 16:28:56Z

1

If you really want to store ascii values, you can simply translate it to its value in hex:

"1234" will be 0x31 0x32 0x33 0x34 0x00

To store it into a uint32_t, get rid of the null terminator and

FMC_Erase(PASSWORD1_LOCATION); //u32addr 
if (*(uint32_t *)(PASSWORD1_LOCATION) == 0xffffffff)
{
    uint32_t user_password1 = 0x31323334;
    FMC_Write(PASSWORD1_LOCATION, &user_password1);
}

uint32_t ReadPass1 = *(uint32_t *)(PASSWORD1_LOCATION);

UART_Write(UART0,ReadPass1,4); //4 -> string length 
_UART_SENDBYTE(UART0,0x0D);

answered Dec 1, 2016 at 16:28

LPs

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2 Comments

khelogram Over a year ago

how about if its in an array? can i do this? uint8_t new_pass1[4]; new_pass1[0] = 0x31000000; new_pass1[1] = 0x00320000; new_pass1[2] = 0x00003300; new_pass1[3] = 0x00000034; then uint32_t user_password1 = new_pass[0] + new_pass[1] + . . . .

LPs Over a year ago

No. You can do uint8_t new_array [4] = { 0x31, 0x32, 0x33, 0x34 };

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