1 ARM Linux 2.6
2 =============
3
4 Please check <ftp://ftp.arm.linux.org.uk/pub/armlinux> for
5 updates.
6
7Compilation of kernel
8---------------------
9
10 In order to compile ARM Linux, you will need a compiler capable of
11 generating ARM ELF code with GNU extensions. GCC 3.3 is known to be
12 a good compiler. Fortunately, you needn't guess. The kernel will report
13 an error if your compiler is a recognized offender.
14
15 To build ARM Linux natively, you shouldn't have to alter the ARCH = line
16 in the top level Makefile. However, if you don't have the ARM Linux ELF
17 tools installed as default, then you should change the CROSS_COMPILE
18 line as detailed below.
19
20 If you wish to cross-compile, then alter the following lines in the top
21 level make file:
22
23 ARCH = <whatever>
24 with
25 ARCH = arm
26
27 and
28
29 CROSS_COMPILE=
30 to
31 CROSS_COMPILE=<your-path-to-your-compiler-without-gcc>
32 eg.
33 CROSS_COMPILE=arm-linux-
34
35 Do a 'make config', followed by 'make Image' to build the kernel
36 (arch/arm/boot/Image). A compressed image can be built by doing a
37 'make zImage' instead of 'make Image'.
38
39
40Bug reports etc
41---------------
42
43 Please send patches to the patch system. For more information, see
44 http://www.arm.linux.org.uk/developer/patches/info.php Always include some
45 explanation as to what the patch does and why it is needed.
46
47 Bug reports should be sent to linux-arm-kernel@lists.arm.linux.org.uk,
48 or submitted through the web form at
49 http://www.arm.linux.org.uk/developer/
50
51 When sending bug reports, please ensure that they contain all relevant
52 information, eg. the kernel messages that were printed before/during
53 the problem, what you were doing, etc.
54
55
56Include files
57-------------
58
59 Several new include directories have been created under include/asm-arm,
60 which are there to reduce the clutter in the top-level directory. These
61 directories, and their purpose is listed below:
62
63 arch-* machine/platform specific header files
64 hardware driver-internal ARM specific data structures/definitions
65 mach descriptions of generic ARM to specific machine interfaces
66 proc-* processor dependent header files (currently only two
67 categories)
68
69
70Machine/Platform support
71------------------------
72
73 The ARM tree contains support for a lot of different machine types. To
74 continue supporting these differences, it has become necessary to split
75 machine-specific parts by directory. For this, the machine category is
76 used to select which directories and files get included (we will use
77 $(MACHINE) to refer to the category)
78
79 To this end, we now have arch/arm/mach-$(MACHINE) directories which are
80 designed to house the non-driver files for a particular machine (eg, PCI,
81 memory management, architecture definitions etc). For all future
82 machines, there should be a corresponding arch/arm/mach-$(MACHINE)/include/mach
83 directory.
84
85
86Modules
87-------
88
89 Although modularisation is supported (and required for the FP emulator),
90 each module on an ARM2/ARM250/ARM3 machine when is loaded will take
91 memory up to the next 32k boundary due to the size of the pages.
92 Therefore, is modularisation on these machines really worth it?
93
94 However, ARM6 and up machines allow modules to take multiples of 4k, and
95 as such Acorn RiscPCs and other architectures using these processors can
96 make good use of modularisation.
97
98
99ADFS Image files
100----------------
101
102 You can access image files on your ADFS partitions by mounting the ADFS
103 partition, and then using the loopback device driver. You must have
104 losetup installed.
105
106 Please note that the PCEmulator DOS partitions have a partition table at
107 the start, and as such, you will have to give '-o offset' to losetup.
108
109
110Request to developers
111---------------------
112
113 When writing device drivers which include a separate assembler file, please
114 include it in with the C file, and not the arch/arm/lib directory. This
115 allows the driver to be compiled as a loadable module without requiring
116 half the code to be compiled into the kernel image.
117
118 In general, try to avoid using assembler unless it is really necessary. It
119 makes drivers far less easy to port to other hardware.
120
121
122ST506 hard drives
123-----------------
124
125 The ST506 hard drive controllers seem to be working fine (if a little
126 slowly). At the moment they will only work off the controllers on an
127 A4x0's motherboard, but for it to work off a Podule just requires
128 someone with a podule to add the addresses for the IRQ mask and the
129 HDC base to the source.
130
131 As of 31/3/96 it works with two drives (you should get the ADFS
132 *configure harddrive set to 2). I've got an internal 20MB and a great
133 big external 5.25" FH 64MB drive (who could ever want more :-) ).
134
135 I've just got 240K/s off it (a dd with bs=128k); thats about half of what
136 RiscOS gets; but it's a heck of a lot better than the 50K/s I was getting
137 last week :-)
138
139 Known bug: Drive data errors can cause a hang; including cases where
140 the controller has fixed the error using ECC. (Possibly ONLY
141 in that case...hmm).
142
143
1441772 Floppy
145-----------
146 This also seems to work OK, but hasn't been stressed much lately. It
147 hasn't got any code for disc change detection in there at the moment which
148 could be a bit of a problem! Suggestions on the correct way to do this
149 are welcome.
150
151
152CONFIG_MACH_ and CONFIG_ARCH_
153-----------------------------
154 A change was made in 2003 to the macro names for new machines.
155 Historically, CONFIG_ARCH_ was used for the bonafide architecture,
156 e.g. SA1100, as well as implementations of the architecture,
157 e.g. Assabet. It was decided to change the implementation macros
158 to read CONFIG_MACH_ for clarity. Moreover, a retroactive fixup has
159 not been made because it would complicate patching.
160
161 Previous registrations may be found online.
162
163 <http://www.arm.linux.org.uk/developer/machines/>
164
165Kernel entry (head.S)
166--------------------------
167 The initial entry into the kernel is via head.S, which uses machine
168 independent code. The machine is selected by the value of 'r1' on
169 entry, which must be kept unique.
170
171 Due to the large number of machines which the ARM port of Linux provides
172 for, we have a method to manage this which ensures that we don't end up
173 duplicating large amounts of code.
174
175 We group machine (or platform) support code into machine classes. A
176 class typically based around one or more system on a chip devices, and
177 acts as a natural container around the actual implementations. These
178 classes are given directories - arch/arm/mach-<class> and
179 arch/arm/mach-<class> - which contain the source files to/include/mach
180 support the machine class. This directories also contain any machine
181 specific supporting code.
182
183 For example, the SA1100 class is based upon the SA1100 and SA1110 SoC
184 devices, and contains the code to support the way the on-board and off-
185 board devices are used, or the device is setup, and provides that
186 machine specific "personality."
187
188 For platforms that support device tree (DT), the machine selection is
189 controlled at runtime by passing the device tree blob to the kernel. At
190 compile-time, support for the machine type must be selected. This allows for
191 a single multiplatform kernel build to be used for several machine types.
192
193 For platforms that do not use device tree, this machine selection is
194 controlled by the machine type ID, which acts both as a run-time and a
195 compile-time code selection method. You can register a new machine via the
196 web site at:
197
198 <http://www.arm.linux.org.uk/developer/machines/>
199
200 Note: Please do not register a machine type for DT-only platforms. If your
201 platform is DT-only, you do not need a registered machine type.
202
203---
204Russell King (15/03/2004)
205
