Accessing typedef struct elements

Question

I have declared a tydef struct as shown below.

#define START_ADDR 0xXXXXX
typedef struct{
     uint32_t checksum;
     uint16_t index[len];
} block;

I changed the memory allocation of block using the below statement:

block *value = (block*) START__ADDR;

I verified the change in memory allocation as well and no issue with it. Now i am trying to update the value of checksum using

value->checksum=0xa5a5a5a5;

But the value of checksum is 0x00000000 and not getting updated to 0xa5a5a5a5 . Can anyone please tell me how can i change the value of checksum.

Thanks in advance.

Regards Vybhav

Answer 1

You can't write to flash memory as if it was RAM and that's it. Flash being ROM. This would be why all your variables allocated in flash is/must be const qualified, meaning read-only.

It is possible to change flash and your part could have dedicated data flash/eeprom for this purpose. But writing to such parts of the memory isn't something a compiler will do for you. You need to write a flash programming driver yourself. As in, you have to study the flash programming part in the manual + app notes.