RT-Thread RTOS
An open source embedded real-time operating system
Open Firmware (OFW)

Open Firmware (OFW) overview

RT-Thread OFW parses the boot DTB into **struct rt_ofw_node**, then exposes property I/O, addressing, interrupts, and platform device enumeration. Implementation mirrors **components/drivers/ofw/** source layout.

Source / header Documentation
**base.c**, **ofw.c** — ofw.h OFW nodes and properties
**fdt.c** — ofw_fdt.h OFW boot and FDT
**io.c** — ofw_io.h OFW addressing and MMIO
**irq.c** — ofw_irq.h OFW interrupts
**raw.c** — ofw_raw.h OFW raw FDT helpers
**core/platform_ofw.c** OFW platform enumeration
Build DTS → DTB Devicetree Compiler

Kconfig

Option Role
**RT_USING_OFW** OFW + libfdt; requires **RT_USING_DM**
**RT_USING_BUILTIN_FDT** Link **RT_BUILTIN_FDT_PATH** (default rtthread.dtb)
**RT_FDT_EARLYCON_MSG_SIZE** Early console ring (KB, default 128)
**RT_USING_OFW_BUS_RANGES_NUMBER** Cached **ranges** slots (4 or 8)

Typical driver flow

Bootloader DTB
→ rt_fdt_prefetch / scan_memory / unflatten (@ref page_device_ofw_boot)
→ INIT_PLATFORM_EXPORT(platform_ofw_device_probe) (@ref page_device_ofw_platform)
→ driver probe(np): reg/irq/phandles
rt_ofw_get_address + rt_dm_dev_iomap (@ref page_device_ofw_io)
rt_ofw_get_irq / rt_ofw_map_irq (@ref page_device_ofw_irq)
rt_ofw_parse_phandle_cells + rt_platform_ofw_request (@ref page_device_ofw_base)

Phandle consumer pattern

Most DM subsystems share the same parse sequence:

  1. **rt_ofw_parse_phandle_cells(np, "clocks", "#clock-cells", index, &args)**
  2. **provider_np = args.data**; if **!rt_ofw_data(provider_np)** → **rt_platform_ofw_request(provider_np)**
  3. Use subsystem API (**rt_clk_get_by_index**, **rt_mbox_request_channel**, …)
Property #*-cells See also
**clocks** **#clock-cells** Clock framework (CLK)
**resets** **#reset-cells** reset DM
**mboxes** **#mbox-cells** Mailbox device model (DM)
**io-channels** **#io-channel-cells** IIO device model (DM)
**nvmem-cells** **#nvmem-cell-cells** NVMEM device model (DM)

**rt_ofw_parse_object(np, obj_name, "#clock-cells")** resolves composite objects in **rt_ofw_data** when one node exports multiple controllers.

Driver quick notes

Topic Guidance
**status** Use **rt_ofw_node_is_available** before attaching hardware
**reg** Use **rt_ofw_io_*** / **rt_ofw_get_address** — never hard-code parent **#address-cells**
IRQ Direct **interrupts** vs bridge **interrupt-map** — see OFW interrupts
Refs Pair **rt_ofw_node_get** / **rt_ofw_node_put** when caching **np**
**compatible** Most specific string first in DTS and **rt_ofw_node_id** table

Normative references

See also