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为AM335x移植Linux内核主线代码

四、booting-without-of.txt学习笔记（上）

以下是摘抄的Linux内核的Documentation的内容，一边学一边做笔记。
所以以下内容可直接忽略，看源代码更方便～

linux-3.16.1/Documentation/devicetree/booting-without-of.txt
==========================================
I) - Introduction
========================
1)Entry point for arch/arm
---------------------------

a) ATAGS interface.
b) Entry with a flattened device-tree block. Firmware loads
the physical address of the flattened device tree block (dtb)
into r2, r1 is not used, but it is considered good practice
to use a valid machine number as described in
Documentation/arm/Booting.

The kernel will differentiate between ATAGS and device tree
booting by reading the memory pointed to by r2 and looking for
either the flattened device tree block magic value (0xd00dfeed)
or ATAG_CORE value at offset 0x4 from r2 (ox54410001).

        ***********************************************
        练习题：使用od -x命令查看生成的xx.dtb文件，会发现神马呢？

        [maria@localhost dts]$ od -x maria_am335x.dtb
        0000000 0dd0 edfe 0000 fd6c 0000 3800 0000 a467
        0000020 0000 2800 0000 1100 0000 1000 0000 0000
        0000040 0000 5905 0000 6c67 0000 0000 0000 0000
        0000060 0000 0000 0000 0000 0000 0100 0000 0000
        0000100 0000 0300 0000 0400 0000 0000 0000 0100
        0000120 0000 0300 0000 0400 0000 0f00 0000 0100
        0000140 0000 0300 0000 1a00 0000 1b00 6974 6d2c
        0000160 7261 6169 615f 336d 3533 0078 6974 612c
        0000200 336d 7833 0078 0000 0000 0300 0000 0400
        0000220 0000 2600 0000 0100 0000 0300 0000 1700
        
        答：可观察到前4个字节就是0xd00dfeed。
        ***********************************************
        
II) - The DT block format
========================

This chapter defines the actual format of the flattened
device-tree passed to the kernel. It is expected that a
bootloader like uboot provides a bot more support.

Note: The block has to be in main memory. It has to be
accessible in both real mode and virtual mode with no mapping
other than main memory. If you are writing a simple flash
bootloader, it should copy the block to RAM before passing
it to the kernel.

1) Header
---------

The kernel is passed the physical address pointing to an area
of memory that is roughly described in include/linux/of_fdt.h
by the structure boot_param_header:

struct boot_param_header {
        u32 magic;              /* magic work OF_DT_HEADER */
        u32 totalsize;          /* total size of DT block */
        u32 off_dt_struct;      /* offset to structure */
        u32 off_dt_strings;     /* offset to strings */
        u32 off_mem_rsvmap;     /* offset to memory reserve
                                   map */
        u32 version;            /* format version */
        u32 last_comp_version;  /* last compatible version */
        
        /* version 2 fields below */
        u32 boot_cpuid_phys;    /* Which physical CPU id we're
                                booting on */
        /* version 3 fields below */
        u32 size_dt_strings;    /* size of the strings block */

        /* version 17 fields below */
        u32 size_dt_struct;     /* size of the DT structure block */
};

/* Definitions used by the flattened device tree */
#define OF_DT_HEADER            0xd00dfeed      /* 4: version
                                                   4: total size */
#define OF_DT_BEGIN_NODE        0x1             /* Start mode: full
                                                   name */
#define OF_DT_END_NODE          0x2             /* End node */
#define OF_DT_PROP              0x3             /* Property: name off,
                                                   size, content */
#define OF_DT_END               0x9

(文章转载自edn博客 作者：MariannaZhu )

http://forum.eepw.com.cn/thread/262788/1