依linux community的要求，从linux-3.5后，新提交的code必须对device tree进行支持。下面介绍如何使u-boot支持device tree，以及fdt命令的使用。
1. u-boot对fdt(flattened device tree)的支持。
实现：只要加入
#define CONFIG_OF_LIBFDT /* Device Tree support */
重新编译u-boot，就可以实现对device tree的支持。
2. u-boot下的fdt命令使用
2.1 首先查看fdt的帮助信息。
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U-Boot> fdt
fdt - flattened device tree utility commands
Usage:
fdt addr <addr> [<length>] - Set the fdt location to <addr>
fdt move <fdt> <newaddr> <length> - Copy the fdt to <addr> and make it active
fdt resize - Resize fdt to size + padding to 4k addr
fdt print <path> [<prop>] - Recursive print starting at <path>
fdt list <path> [<prop>] - Print one level starting at <path>
fdt set <path> <prop> [<val>] - Set <property> [to <val>]
fdt mknode <path> <node> - Create a new node after <path>
fdt rm <path> [<prop>] - Delete the node or <property>
fdt header - Display header info
fdt bootcpu <id> - Set boot cpuid
fdt memory <addr> <size> - Add/Update memory node
fdt rsvmem print - Show current mem reserves
fdt rsvmem add <addr> <size> - Add a mem reserve
fdt rsvmem delete <index> - Delete a mem reserves
fdt chosen [<start> <end>] - Add/update the /chosen branch in the tree
<start>/<end> - initrd start/end addr
NOTE: Dereference aliases by omiting the leading '/', e.g. fdt print ethernet0.
U-Boot>
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2.2 使用fdt命令把device tree blob (dtb)文件下载到内存里。
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U-Boot> tftpboot 0x71000000 bshen/test-ek.dtb
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设置fdt的地址
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U-Boot> fdt addr 0x71000000
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然后就可以使用其余的命令参数了
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U-Boot> fdt header
magic: 0xd00dfeed
totalsize: 0x1887 (6279)
off_dt_struct: 0x38
off_dt_strings: 0x1648
off_mem_rsvmap: 0x28
version: 17
last_comp_version: 16
boot_cpuid_phys: 0x0
size_dt_strings: 0x23f
size_dt_struct: 0x1610
number mem_rsv: 0x0
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fdt print 不跟参数时，打印出整颗树
fdt print加path参数，则打path内容，如下(其中/memory是path)：
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U-Boot> fdt print /memory
memory {
device_type = "memory";
reg = <0x70000000 0x4000000>;
};
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