Linker

FLASH and RAM are defined in the linker (.ld) file.

§Syntax to keep mind

. = ALIGN(4) Alignment will move the current location counter (.) to the next 4-bytes boundary. Why 4 bytes? because Cortex-M is 32bit and prefers word alignment. one word is 32bits or 4 bytes. This will just move the address cursor to next byte memory divisible by 4. For example if current address is 0x20002, it would become 0x20004. For example if current address is 0x20008 it would remain the same at 0x2008.

_sdata = .; Creates a linker symbol marking where .data begins in RAM. Startup code uses this.

*(.data) or *(.data*) This tells the linker to place all .data sections from all object files and place them here.

§Patterns

*(.data) matches all input section named .data *(.data*) matches all input section named .data, .data.foo, .data123, etc .data means output section name *(.data) means input section to pull in. The apostrophe in front is a wild card. For instance, if you have file1.o(.data), it means from input object file file1.o, pull its .data section and include it here in the final image. file1.o would be a file created as a result of compiling. > RAM means run address (VMA) is in RAM. Run address is runtime data AT> FLASH means Load Address (LMA) is in FLASH. Load address is the initial bytes >RAM AT> FLASH means run from RAM and load from FLASH. In other words, i am loading data from FLASH to RAM and running it

__attribute ((section("..."))) section attribute allows compiler to place annotated function or variable. It is a placement directive. unsigned char __attribute__((section(".myBufSectionRAM"))) buf_ram[128]; will allow the compiler to generate an object file entry like: buf_ram -> input section ".myBufSectionRAM" This entry is what the linker script uses to places buf_ram from object file into .myBufSectionRAM