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/Documentation/arm/README

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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)