Contents of /alx-src/trunk/kernel26-alx/linux/Documentation/arm/Booting
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Wed Mar 4 10:48:58 2009 UTC (15 years, 6 months ago) by niro
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Wed Mar 4 10:48:58 2009 UTC (15 years, 6 months ago) by niro
File size: 4705 byte(s)
import linux sources based on 2.6.12-alx-r9: -using linux-2.6.12.6 -using 2.6.12-ck6 patch set -using fbsplash-0.9.2-r3 -using vesafb-tng-0.9-rc7 -using squashfs-2.2 -added cddvd-cmdfilter-drop.patch as ck dropped it -added via-epia-dri (cle266) patch -added zd1211-svn-32 wlan driver (http://zd1211.ath.cx/download/) -added debian patches to zd1211 for wep256 etc
1 | Booting ARM Linux |
2 | ================= |
3 | |
4 | Author: Russell King |
5 | Date : 18 May 2002 |
6 | |
7 | The following documentation is relevant to 2.4.18-rmk6 and beyond. |
8 | |
9 | In order to boot ARM Linux, you require a boot loader, which is a small |
10 | program that runs before the main kernel. The boot loader is expected |
11 | to initialise various devices, and eventually call the Linux kernel, |
12 | passing information to the kernel. |
13 | |
14 | Essentially, the boot loader should provide (as a minimum) the |
15 | following: |
16 | |
17 | 1. Setup and initialise the RAM. |
18 | 2. Initialise one serial port. |
19 | 3. Detect the machine type. |
20 | 4. Setup the kernel tagged list. |
21 | 5. Call the kernel image. |
22 | |
23 | |
24 | 1. Setup and initialise RAM |
25 | --------------------------- |
26 | |
27 | Existing boot loaders: MANDATORY |
28 | New boot loaders: MANDATORY |
29 | |
30 | The boot loader is expected to find and initialise all RAM that the |
31 | kernel will use for volatile data storage in the system. It performs |
32 | this in a machine dependent manner. (It may use internal algorithms |
33 | to automatically locate and size all RAM, or it may use knowledge of |
34 | the RAM in the machine, or any other method the boot loader designer |
35 | sees fit.) |
36 | |
37 | |
38 | 2. Initialise one serial port |
39 | ----------------------------- |
40 | |
41 | Existing boot loaders: OPTIONAL, RECOMMENDED |
42 | New boot loaders: OPTIONAL, RECOMMENDED |
43 | |
44 | The boot loader should initialise and enable one serial port on the |
45 | target. This allows the kernel serial driver to automatically detect |
46 | which serial port it should use for the kernel console (generally |
47 | used for debugging purposes, or communication with the target.) |
48 | |
49 | As an alternative, the boot loader can pass the relevant 'console=' |
50 | option to the kernel via the tagged lists specifying the port, and |
51 | serial format options as described in |
52 | |
53 | Documentation/kernel-parameters.txt. |
54 | |
55 | |
56 | 3. Detect the machine type |
57 | -------------------------- |
58 | |
59 | Existing boot loaders: OPTIONAL |
60 | New boot loaders: MANDATORY |
61 | |
62 | The boot loader should detect the machine type its running on by some |
63 | method. Whether this is a hard coded value or some algorithm that |
64 | looks at the connected hardware is beyond the scope of this document. |
65 | The boot loader must ultimately be able to provide a MACH_TYPE_xxx |
66 | value to the kernel. (see linux/arch/arm/tools/mach-types). |
67 | |
68 | |
69 | 4. Setup the kernel tagged list |
70 | ------------------------------- |
71 | |
72 | Existing boot loaders: OPTIONAL, HIGHLY RECOMMENDED |
73 | New boot loaders: MANDATORY |
74 | |
75 | The boot loader must create and initialise the kernel tagged list. |
76 | A valid tagged list starts with ATAG_CORE and ends with ATAG_NONE. |
77 | The ATAG_CORE tag may or may not be empty. An empty ATAG_CORE tag |
78 | has the size field set to '2' (0x00000002). The ATAG_NONE must set |
79 | the size field to zero. |
80 | |
81 | Any number of tags can be placed in the list. It is undefined |
82 | whether a repeated tag appends to the information carried by the |
83 | previous tag, or whether it replaces the information in its |
84 | entirety; some tags behave as the former, others the latter. |
85 | |
86 | The boot loader must pass at a minimum the size and location of |
87 | the system memory, and root filesystem location. Therefore, the |
88 | minimum tagged list should look: |
89 | |
90 | +-----------+ |
91 | base -> | ATAG_CORE | | |
92 | +-----------+ | |
93 | | ATAG_MEM | | increasing address |
94 | +-----------+ | |
95 | | ATAG_NONE | | |
96 | +-----------+ v |
97 | |
98 | The tagged list should be stored in system RAM. |
99 | |
100 | The tagged list must be placed in a region of memory where neither |
101 | the kernel decompressor nor initrd 'bootp' program will overwrite |
102 | it. The recommended placement is in the first 16KiB of RAM. |
103 | |
104 | 5. Calling the kernel image |
105 | --------------------------- |
106 | |
107 | Existing boot loaders: MANDATORY |
108 | New boot loaders: MANDATORY |
109 | |
110 | There are two options for calling the kernel zImage. If the zImage |
111 | is stored in flash, and is linked correctly to be run from flash, |
112 | then it is legal for the boot loader to call the zImage in flash |
113 | directly. |
114 | |
115 | The zImage may also be placed in system RAM (at any location) and |
116 | called there. Note that the kernel uses 16K of RAM below the image |
117 | to store page tables. The recommended placement is 32KiB into RAM. |
118 | |
119 | In either case, the following conditions must be met: |
120 | |
121 | - Quiesce all DMA capable devicess so that memory does not get |
122 | corrupted by bogus network packets or disk data. This will save |
123 | you many hours of debug. |
124 | |
125 | - CPU register settings |
126 | r0 = 0, |
127 | r1 = machine type number discovered in (3) above. |
128 | r2 = physical address of tagged list in system RAM. |
129 | |
130 | - CPU mode |
131 | All forms of interrupts must be disabled (IRQs and FIQs) |
132 | The CPU must be in SVC mode. (A special exception exists for Angel) |
133 | |
134 | - Caches, MMUs |
135 | The MMU must be off. |
136 | Instruction cache may be on or off. |
137 | Data cache must be off. |
138 | |
139 | - The boot loader is expected to call the kernel image by jumping |
140 | directly to the first instruction of the kernel image. |
141 |