Iterable Sections

This page contains the reference documentation for the iterable sections APIs, which can be used for defining iterable areas of equally-sized data structures, that can be iterated on using STRUCT_SECTION_FOREACH.

Usage

Iterable section elements are typically used by defining the data structure and associated initializer in a common header file, so that they can be instantiated anywhere in the code base.

struct my_data {
         int a, b;
};

#define DEFINE_DATA(name, _a, _b) \
         STRUCT_SECTION_ITERABLE(my_data, name) = { \
                 .a = _a, \
                 .b = _b, \
         }

...

DEFINE_DATA(d1, 1, 2);
DEFINE_DATA(d2, 3, 4);
DEFINE_DATA(d3, 5, 6);

Then the linker has to be setup to place the place the structure in a contiguous segment using one of the linker macros such as ITERABLE_SECTION_RAM or ITERABLE_SECTION_ROM. Custom linker snippets are normally declared using one of the zephyr_linker_sources() CMake functions, using the appropriate section identifier, DATA_SECTIONS for RAM structures and SECTIONS for ROM ones.

# CMakeLists.txt
zephyr_linker_sources(DATA_SECTIONS iterables.ld)

# iterables.ld
ITERABLE_SECTION_RAM(my_data, 4)

The data can then be accessed using STRUCT_SECTION_FOREACH.

STRUCT_SECTION_FOREACH(my_data, data) {
        printk("%p: a: %d, b: %d\n", data, data->a, data->b);
}

Note

The linker is going to place the entries sorted by name, so the example above would visit d1, d2 and d3 in that order, regardless of how they were defined in the code.

API Reference

Iterable Sections APIs