Flash and data

[SGian.1]

Hi there !

I have a quick question about where the data are save. If i create one const array [1024] the data inside the array (because i write the word const in front) are save inside the falsh ? and this give to me more space in the ram  right ? and is the same if i create one struct and i acces with pointer ?  and please some one can help me and show where i can find all this kind of information like book tutorial website youtube ect

Thank you 

Sergio

[Khaled_DHIF]

Hello ​@SGian.1 ,

Yes, in embedded C, const data is usually placed in flash, so it saves RAM. But this depends on the compiler/linker, so it’s not guaranteed by const alone.

A struct is different: where it is stored depends on how you declare it, not on whether you access it with a pointer. A pointer only gives access to the data; it does not move it to flash or RAM.

A good rule of thumb:

• const data → often flash
• non-const data → usually RAM
• pointer → only an address

If you want to learn more, search for:

• Memory layout (per MCU in the corresponding STM32 RM) 
• linker script .data .bss .rodata (per compiler)

Kind regards, 

DHIF Khaled

[SGian.1]

Thank you soo much , have a nice day 

 

Sergio