Force Variable to be Stored in FLASH in C Using ARM Processor

Question

I know I can force an array into FLASH in ARM by declaring it "const". But this is not truly an array of consts: I want to be able to write to it regularly. I have three large arrays that take up ~50k of the 128kB of SRAM I have available, but I have an order of magnitude more FLASH than I need. How can I force these three arrays into FLASH without declaring them const? Using IAR, BTW.

Tried using the __no_init keyword; according to the linker map files this had no effect.

Answer 1

To answer the original question, you can write a linker script to force any variable to reside in a predetermined area of memory (declaring them const does not force the compiler to put it in FLASH, it is merely a strong suggestion).

On the other hand, overabundance of FLASH is not in itself a good reason to keep a non-const array in flash. Among the reasons are: 1) depending on the chip, the access to FLASH memory can be much slower than RAM access (especially for writing) 2) FLASH can only be rewritten a limited number of times: it is not a problem for an occasional rewrite but if your code constantly rewrites FLASH memory, you can ruin it rather quicky. 3) There are special procedures to write to FLASH (ARM makes it easy but it is still not as simple as writing to RAM).