RT-Thread RTOS
An open source embedded real-time operating system
OFW raw FDT helpers

Raw FDT editing (<tt>raw.c</tt>)

Optional in-place libfdt helpers for firmware, loaders, or tools that modify the blob before **rt_fdt_unflatten**. Runtime drivers normally use OFW nodes and properties after unflatten.

Header: **drivers/ofw_raw.h**. Source: **components/drivers/ofw/raw.c**.

When to use

Use raw API Use rt_ofw_*
Patch DTB in RAM pre-boot Driver **probe** on live tree
Add **/chosen** properties from bootloader Read **reg / interrupts**
Install initrd nodes Platform enumeration

API highlights

API / macro Role
**fdt_add_subnode_possible** Add child if space in blob
**fdt_add_mem_rsv_possible** Add memory reserve entry
**fdt_setprop_cstring** Set string property
**fdt_setprop_cells**, **fdt_appendprop_cells** U32 cell arrays (endian-safe)
**fdt_setprop_uxx** 8/16/32/64-bit property
**fdt_getprop_u8 … fdt_getprop_s32** Typed read on blob offset
**fdt_io_addr_cells**, **fdt_io_size_cells** Cells on raw node offset
**fdt_install_initrd** Add **linux,initrd-*** under **chosen**

**FDT_SIZE_MAX**, **FDT_PADDING_SIZE** — growth limits when expanding tree.

Pitfalls

Issue Mitigation
Blob too small Reserve padding at build time; check return codes
Edit after unflatten Tree and blob may diverge — rebuild or only edit pre-unflatten
Endianness Use **fdt_setprop_cells**, not raw **fdt_setprop** for integers

See also