Memory

Code in RAM

SoCs that need code to run while flash is unavailable select CONFIG_RAMFUNC, which adds a .ramfunc output section loaded from flash and copied to RAM at boot. Code gets there in one of three ways:

• a function marked PBL_SECTION_RAM, or a constant marked PBL_SECTION_RAM_RODATA (pbl/kernel/section.h);

• whole source files, with pbl_library_ramfunc(file.c ...) next to the library’s pbl_library_sources();

• input section patterns registered against the ramfunc linker hook, for vendor code annotated its own way.

Without CONFIG_RAMFUNC all three are no-ops and the code stays in flash.

Layout

The linker scripts document the memory map. kernel/pebbleos.ld explains the sections, their load and run addresses, and the kernel’s data, stack and heap; kernel/linker/memory.ld how SRAM is divided between the kernel, the app and the worker; and, on ARM, kernel/arch/arm/linker/regions.ld the alignment the MPU imposes on those regions.