U-Boot與Linux內核的交互

說明：本文所使用的U-Boot的版本是1.1.6，平台是S3C2440。

U-Boot源代碼下載地址 http://www.linuxidc.com/Linux/2011-07/38897.htm

目錄

一、簡介
1.1標記列表
二、設置標記存放的地址
2.1相關的結構體定義
2.2標記存放地址的設定
三、標記的設置
3.1設置標記ATAG_CORE
3.2設置內存標記ATAG_MEM
3.3設置命令行標記ATAG_CMDLINE
3.4設置ATAG_NONE

一、簡介

U-Boot與Linux內核的交互是單向的，U-Boot將各類參數傳遞給讷河。由於他們不能同時運行，傳遞辦法只能有一個個：U-Boot將參數放在某個約定的地方之後，在啟動內核，內核啟動後從這個地方獲得參數。

1.1標記列表

除了約定好參數存放的地方外，還要規定參數的結構。Linux2.4.x以後的內核都以標記列表（tagged list）的形式來傳遞參數。標記就是一種數據結構；標記列表就是挨著存放的多個標記。標記列表以標記ATAG_CORE開始，以ATAGE_NONE結束。

標記的數據結構為tag，它是偶一個tag_header結構和一個聯合體（union）組成。tag_header結構體表示標記的類型及長度，比如是表示內存還是表示命令行參數等。對於不同類型的標記使用不同的聯合體，比如表示內存=時使用tag_men32，表示命令行時使用tag_cmdline。其定定義在include/asm-arm/setup.c文件中。

1. /*
2. * The new way of passing information: a list of tagged entries
3. */
5. /* The list ends with an ATAG_NONE node. */
6. #define ATAG_NONE 0x00000000
8. struct tag_header {
9. u32 size;
10. u32 tag;
11. };
13. /* The list must start with an ATAG_CORE node */
14. #define ATAG_CORE 0x54410001
16. struct tag_core {
17. u32 flags; /* bit 0 = read-only */
18. u32 pagesize;
19. u32 rootdev;
20. };
22. /* it is allowed to have multiple ATAG_MEM nodes */
23. #define ATAG_MEM 0x54410002
25. struct tag_mem32 {
26. u32 size;
27. u32 start; /* physical start address */
28. };
30. /* VGA text type displays */
31. #define ATAG_VIDEOTEXT 0x54410003
33. struct tag_videotext {
34. u8 x;
35. u8 y;
36. u16 video_page;
37. u8 video_mode;
38. u8 video_cols;
39. u16 video_ega_bx;
40. u8 video_lines;
41. u8 video_isvga;
42. u16 video_points;
43. };
45. /* describes how the ramdisk will be used in kernel */
46. #define ATAG_RAMDISK 0x54410004
48. struct tag_ramdisk {
49. u32 flags; /* bit 0 = load, bit 1 = prompt */
50. u32 size; /* decompressed ramdisk size in _kilo_ bytes */
51. u32 start; /* starting block of floppy-based RAM disk image */
52. };
54. /* describes where the compressed ramdisk image lives (virtual address) */
55. /*
56. * this one accidentally used virtual addresses - as such,
57. * its depreciated.
58. */
59. #define ATAG_INITRD 0x54410005
61. /* describes where the compressed ramdisk image lives (physical address) */
62. #define ATAG_INITRD2 0x54420005
64. struct tag_initrd {
65. u32 start; /* physical start address */
66. u32 size; /* size of compressed ramdisk image in bytes */
67. };
69. /* board serial number. "64 bits should be enough for everybody" */
70. #define ATAG_SERIAL 0x54410006
72. struct tag_serialnr {
73. u32 low;
74. u32 high;
75. };
77. /* board revision */
78. #define ATAG_REVISION 0x54410007
80. struct tag_revision {
81. u32 rev;
82. };
84. /* initial values for vesafb-type framebuffers. see struct screen_info
85. * in include/linux/tty.h
86. */
87. #define ATAG_VIDEOLFB 0x54410008
89. struct tag_videolfb {
90. u16 lfb_width;
91. u16 lfb_height;
92. u16 lfb_depth;
93. u16 lfb_linelength;
94. u32 lfb_base;
95. u32 lfb_size;
96. u8 red_size;
97. u8 red_pos;
98. u8 green_size;
99. u8 green_pos;
100. u8 blue_size;
101. u8 blue_pos;
102. u8 rsvd_size;
103. u8 rsvd_pos;
104. };
106. /* command line: \0 terminated string */
107. #define ATAG_CMDLINE 0x54410009
109. struct tag_cmdline {
110. char cmdline[1]; /* this is the minimum size */
111. };
113. /* acorn RiscPC specific information */
114. #define ATAG_ACORN 0x41000101
116. struct tag_acorn {
117. u32 memc_control_reg;
118. u32 vram_pages;
119. u8 sounddefault;
120. u8 adfsdrives;
121. };
123. /* footbridge memory clock, see arch/arm/mach-footbridge/arch.c */
124. #define ATAG_MEMCLK 0x41000402
126. struct tag_memclk {
127. u32 fmemclk;
128. };
130. struct tag {
131. struct tag_header hdr;
132. union {
133. struct tag_core core;
134. struct tag_mem32 mem;
135. struct tag_videotext videotext;
136. struct tag_ramdisk ramdisk;
137. struct tag_initrd initrd;
138. struct tag_serialnr serialnr;
139. struct tag_revision revision;
140. struct tag_videolfb videolfb;
141. struct tag_cmdline cmdline;
143. /*
144. * Acorn specific
145. */
146. struct tag_acorn acorn;
148. /*
149. * DC21285 specific
150. */
151. struct tag_memclk memclk;
152. } u;
153. };
155. #define tag_next(t)<span > </span>((struct tag *)((u32 *)(t) + (t)->hdr.size))
156. #define tag_size(type)<span > </span>((sizeof(struct tag_header) + sizeof(struct type)) >> 2) //???