Storing variable in Flash memory

[mani s]

I can store variables in flash memory location successfully but what is happening is updating that variable in main.c file not happening.I'm posted code what i have done below. 

Linker script file :

MEMORY

{

RAM (xrw) : ORIGIN = 0x20000000, LENGTH = 320K

FLASH (rx) : ORIGIN = 0x8000000, LENGTH = 153

MY_VARS (xrw) : ORIGIN = 0x08005000, LENGTH = 1K // storing in flash memory

}

.my_vars :

{

*(.MY_VARS*);

} >MY_VARS

In main.c file :

__attribute__((section(".MY_VARS"),myvars)) uint32_t *value=8;

int main()

{

int a =sum(); //i have a sum function of two numbers and storing in variable 'a'

value =&a; // value should updated to sum but it is not updating

readaddress=(const volatile uint32_t *)0x08005000;// reading flash memory 

printf("Read flash address %lu\n",*readaddress);// printing the data which is stored in value ,it is printing everytime 8 but it should print variable data which stored in 'a'.

}

int sum(int a)

{

int a=1, b= 34 ;

a=a+b;

return a;

}

Can anybody help me to figure this out,i hope u understood what im asking.

Thank you

[AvaTar]

> __attribute__((section(".MY_VARS"),myvars)) uint32_t *value=8;

Simply using:

const uint32_t value = 8;

will usually do the trick.

[mani s]

thanks avatar but my concern is below,

1.lets say i want to store in 0x08005000 location in flash.

2.i initilazed some data to value ,value = 8.

3.i have a function called sum() doing addition of two numbers ,this number should be stored in value and should be updated in flash.(see above for ref)

[Tesla DeLorean]

Look at the examples for writing values in to FLASH. They are more complicated than a simple assignment. You will need to enable access to the FLASH and erase prior to a write.

[mani s]

yes i have read some references to store in flash,below is the link i followed blog.atollic.com/using-gnu-gcc-on-arm-cortex-devices-placing-code-and-data-on-special-memory-addresses-using-the-gnu-ld-linker

[Tesla DeLorean · Accepted solution]

Ok, but you've got some super weird C syntax, and assignment

__attribute__((section(".MY_VARS"),myvars)) uint32_t *value=8;

value =&a; // value should updated to sum but it is not updating

I'm talking about methods to actually write FLASH from an application, ie

STM32Cube_FW_F7_V1.11.0\Projects\STM32746G-Discovery\Examples\FLASH\FLASH_EraseProgram

[mani s]

ok thanks for that

Is that method im doing wrong approach?

[Piranha]

You can read flash memory like a simple variable, but You can't write it that way. For understanding how a flash memory works, read a FLASH section in Your MCUs reference manual. For understanding how to use FLASH for some data saving, read AN3969.

P.S. Independent of flash Your assignments among value, a and readaddress are logically wrong.

[mani s]

thank you Piranha , will do that and update

[mani s]

can we call a function from flash from another project?

lets say i have created two projects project-1 and project-2. i have stored a function called Sum(

) in the flash memory,so i want to call same Sum() function from the project-2.

I have stored project-1 in 0x08002000 and project-2 in 0x08004000,i stored Sum() function is stored in 0x08003000.

I'm using stm32f413zh board,total flash memory size is 1Mbytes.

Linker script file :

MEMORY

{

RAM (xrw)   : ORIGIN = 0x20000000, LENGTH = 320K

FLASH (rx)   : ORIGIN = 0x8000000, LENGTH = 1536K

MYFUNCTION (xr)  : ORIGIN = 0x08004000 , LENGTH = 1k

}

/* Define output sections */

SECTIONS

{

 /* The startup code goes first into FLASH */

 .isr_vector :

 {

  . = ALIGN(4);

  KEEP(*(.isr_vector)) /* Startup code */

  . = ALIGN(4);

 } >FLASH

/*myfunction memeory section start address is 0x08004000 */

.myfunction :

{

*(.MYFUNCTION*);

} > MYFUNCTION

In main.c file :

 __attribute__((section(".MYFUNCTION"))) int sum(int data);

int main()

{

sum(); //i have a sum function of two numbers and storing in variable 'a'

}

int sum(int a)

{

int a=1, b= 34 ;

a=a+b;

return a;

}