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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 2.95.1, EGCS
12 1.1.2, and GCC 3.3 are known to be good compilers. Fortunately, you
13 needn't guess. The kernel will report an error if your compiler is
14 a recognized offender.
15
16 To build ARM Linux natively, you shouldn't have to alter the ARCH = line
17 in the top level Makefile. However, if you don't have the ARM Linux ELF
18 tools installed as default, then you should change the CROSS_COMPILE
19 line as detailed below.
20
21 If you wish to cross-compile, then alter the following lines in the top
22 level make file:
23
24 ARCH = <whatever>
25 with
26 ARCH = arm
27
28 and
29
30 CROSS_COMPILE=
31 to
32 CROSS_COMPILE=<your-path-to-your-compiler-without-gcc>
33 eg.
34 CROSS_COMPILE=arm-linux-
35
36 Do a 'make config', followed by 'make Image' to build the kernel
37 (arch/arm/boot/Image). A compressed image can be built by doing a
38 'make zImage' instead of 'make Image'.
39
40
41Bug reports etc
42---------------
43
44 Please send patches to the patch system. For more information, see
45 http://www.arm.linux.org.uk/patches/info.html Always include some
46 explanation as to what the patch does and why it is needed.
47
48 Bug reports should be sent to linux-arm-kernel@lists.arm.linux.org.uk,
49 or submitted through the web form at
50 http://www.arm.linux.org.uk/forms/solution.shtml
51
52 When sending bug reports, please ensure that they contain all relevant
53 information, eg. the kernel messages that were printed before/during
54 the problem, what you were doing, etc.
55
56
57Include files
58-------------
59
60 Several new include directories have been created under include/asm-arm,
61 which are there to reduce the clutter in the top-level directory. These
62 directories, and their purpose is listed below:
63
64 arch-* machine/platform specific header files
65 hardware driver-internal ARM specific data structures/definitions
66 mach descriptions of generic ARM to specific machine interfaces
67 proc-* processor dependent header files (currently only two
68 categories)
69
70
71Machine/Platform support
72------------------------
73
74 The ARM tree contains support for a lot of different machine types. To
75 continue supporting these differences, it has become necessary to split
76 machine-specific parts by directory. For this, the machine category is
77 used to select which directories and files get included (we will use
78 $(MACHINE) to refer to the category)
79
80 To this end, we now have arch/arm/mach-$(MACHINE) directories which are
81 designed to house the non-driver files for a particular machine (eg, PCI,
82 memory management, architecture definitions etc). For all future
83 machines, there should be a corresponding include/asm-arm/arch-$(MACHINE)
84 directory.
85
86
87Modules
88-------
89
90 Although modularisation is supported (and required for the FP emulator),
91 each module on an ARM2/ARM250/ARM3 machine when is loaded will take
92 memory up to the next 32k boundary due to the size of the pages.
93 Therefore, modularisation on these machines really worth it?
94
95 However, ARM6 and up machines allow modules to take multiples of 4k, and
96 as such Acorn RiscPCs and other architectures using these processors can
97 make good use of modularisation.
98
99
100ADFS Image files
101----------------
102
103 You can access image files on your ADFS partitions by mounting the ADFS
104 partition, and then using the loopback device driver. You must have
105 losetup installed.
106
107 Please note that the PCEmulator DOS partitions have a partition table at
108 the start, and as such, you will have to give '-o offset' to losetup.
109
110
111Request to developers
112---------------------
113
114 When writing device drivers which include a separate assembler file, please
115 include it in with the C file, and not the arch/arm/lib directory. This
116 allows the driver to be compiled as a loadable module without requiring
117 half the code to be compiled into the kernel image.
118
119 In general, try to avoid using assembler unless it is really necessary. It
120 makes drivers far less easy to port to other hardware.
121
122
123ST506 hard drives
124-----------------
125
126 The ST506 hard drive controllers seem to be working fine (if a little
127 slowly). At the moment they will only work off the controllers on an
128 A4x0's motherboard, but for it to work off a Podule just requires
129 someone with a podule to add the addresses for the IRQ mask and the
130 HDC base to the source.
131
132 As of 31/3/96 it works with two drives (you should get the ADFS
133 *configure harddrive set to 2). I've got an internal 20MB and a great
134 big external 5.25" FH 64MB drive (who could ever want more :-) ).
135
136 I've just got 240K/s off it (a dd with bs=128k); thats about half of what
137 RiscOS gets; but it's a heck of a lot better than the 50K/s I was getting
138 last week :-)
139
140 Known bug: Drive data errors can cause a hang; including cases where
141 the controller has fixed the error using ECC. (Possibly ONLY
142 in that case...hmm).
143
144
1451772 Floppy
146-----------
147 This also seems to work OK, but hasn't been stressed much lately. It
148 hasn't got any code for disc change detection in there at the moment which
149 could be a bit of a problem! Suggestions on the correct way to do this
150 are welcome.
151
152
153CONFIG_MACH_ and CONFIG_ARCH_
154-----------------------------
155 A change was made in 2003 to the macro names for new machines.
156 Historically, CONFIG_ARCH_ was used for the bonafide architecture,
157 e.g. SA1100, as well as implementations of the architecture,
158 e.g. Assabet. It was decided to change the implementation macros
159 to read CONFIG_MACH_ for clarity. Moreover, a retroactive fixup has
160 not been made because it would complicate patching.
161
162 Previous registrations may be found online.
163
164 <http://www.arm.linux.org.uk/developer/machines/>
165
166Kernel entry (head.S)
167--------------------------
168 The initial entry into the kernel is via head.S, which uses machine
169 independent code. The machine is selected by the value of 'r1' on
170 entry, which must be kept unique.
171
172 Due to the large number of machines which the ARM port of Linux provides
173 for, we have a method to manage this which ensures that we don't end up
174 duplicating large amounts of code.
175
176 We group machine (or platform) support code into machine classes. A
177 class typically based around one or more system on a chip devices, and
178 acts as a natural container around the actual implementations. These
179 classes are given directories - arch/arm/mach-<class> and
180 include/asm-arm/arch-<class> - which contain the source files to
181 support the machine class. This directories also contain any machine
182 specific supporting code.
183
184 For example, the SA1100 class is based upon the SA1100 and SA1110 SoC
185 devices, and contains the code to support the way the on-board and off-
186 board devices are used, or the device is setup, and provides that
187 machine specific "personality."
188
189 This fine-grained machine specific selection is controlled by the machine
190 type ID, which acts both as a run-time and a compile-time code selection
191 method.
192
193 You can register a new machine via the web site at:
194
195 <http://www.arm.linux.org.uk/developer/machines/>
196
197---
198Russell King (15/03/2004)