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menuconfig RT_USING_OFW
bool "Using Open Firmware (OFW)"
select RT_USING_ADT
select RT_USING_ADT_REF
select RT_USING_ADT_BITMAP
select RT_USING_MEMBLOCK
depends on RT_USING_DM
default n
help
Enable Open Firmware (Device Tree) support.
OFW/Device Tree provides hardware description separate from code:
- Flattened Device Tree (FDT/DTB) parsing
- Hardware discovery and configuration
- Platform-independent device drivers
- Runtime hardware detection
Features:
- Standard device tree bindings
- Property parsing and access
- Node traversal and searching
- Phandle reference resolution
- Address translation
- Interrupt mapping
Benefits:
- Single kernel binary for multiple boards
- Easier board porting (just change DTB)
- Better hardware abstraction
- Industry-standard hardware description
Use cases:
- ARM/RISC-V systems with complex hardware
- Supporting multiple board variants
- Dynamic hardware configuration
- PCI, USB, network device enumeration
Requires:
- RT_USING_DM (Device Model)
- Memory block allocator
- Abstract Data Types (ADT) support
Essential for modern ARM Cortex-A and RISC-V systems.
Enable for device tree-based hardware discovery.
config RT_USING_BUILTIN_FDT
bool "Using builtin fdt in kernel"
depends on RT_USING_OFW
default n
help
Embed Flattened Device Tree (FDT) binary into kernel image.
When enabled:
- DTB file linked into kernel binary
- No need for bootloader to pass DTB
- DTB always available at boot
Advantages:
+ Simpler boot process
+ No DTB location dependencies
+ Guaranteed DTB availability
Disadvantages:
- Larger kernel image
- Must rebuild kernel to change DTB
- Less flexible than bootloader-provided DTB
Typical use:
- Systems without proper bootloader
- Debugging and development
- Single-board configurations
Alternative: Have bootloader pass DTB address to kernel.
Enable for embedded DTB in kernel image.
config RT_BUILTIN_FDT_PATH
string "Builtin fdt path, will rebuild if have dts"
depends on RT_USING_BUILTIN_FDT
default "rtthread.dtb"
help
Path to the compiled Device Tree Blob (DTB) file to embed.
Default: "rtthread.dtb"
This file is included in the kernel binary during linking.
Workflow:
1. Write device tree source (.dts file)
2. Compile to DTB: dtc -I dts -O dtb -o rtthread.dtb rtthread.dts
3. Set this path to the DTB location
4. Rebuild kernel (DTB will be embedded)
Path can be:
- Relative to build directory
- Absolute path
Kernel will automatically rebuild if DTS changes (if build system configured).
config RT_FDT_EARLYCON_MSG_SIZE
int "Earlycon message buffer size (KB)"
depends on RT_USING_OFW
default 128
help
Size of early console message buffer in kilobytes.
Default: 128 KB
Early console (earlycon) provides debug output before full console initialization:
- Available during early boot
- Before full UART driver loads
- Critical for debugging boot failures
Buffer stores messages when:
- Console not yet available
- Output faster than transmission
Larger buffer:
+ More boot messages captured
+ Better for verbose debugging
- More memory usage
Smaller buffer:
+ Less memory overhead
- May lose early messages
Increase for detailed boot debugging.
Decrease to save memory if earlycon not critical.
config RT_USING_OFW_BUS_RANGES_NUMBER
int "Max bus ranges number"
depends on RT_USING_OFW
default 8 if ARCH_CPU_64BIT
default 4
help
Maximum number of bus address ranges for device tree translation.
Default:
- 64-bit systems: 8 ranges
- 32-bit systems: 4 ranges
Bus ranges define address space mappings:
- CPU address to device bus address
- PCI memory/IO spaces
- Different bus protocols (AHB, APB, AXI)
Each range describes a memory window mapping.
Typical usage:
- PCI: 2-3 ranges (prefetchable mem, non-prefetchable mem, I/O)
- Complex SoCs: 4-8 ranges for different buses
Increase for:
- Complex bus hierarchies
- Multiple PCI buses
- Systems with many address spaces
Each range uses ~32-48 bytes of memory.
Set based on your SoC's bus complexity.
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