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  1                            ARM Linux 2.6
  2                            =============
  4     Please check <> for
  5     updates.
  7 Compilation of kernel
  8 ---------------------
 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.
 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.
 20   If you wish to cross-compile, then alter the following lines in the top
 21   level make file:
 23     ARCH = <whatever>
 24         with
 25     ARCH = arm
 27         and
 30         to
 31     CROSS_COMPILE=<your-path-to-your-compiler-without-gcc>
 32         eg.
 33     CROSS_COMPILE=arm-linux-
 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'.
 40 Bug reports etc
 41 ---------------
 43   Please send patches to the patch system.  For more information, see
 44 Always include some
 45   explanation as to what the patch does and why it is needed.
 47   Bug reports should be sent to,
 48   or submitted through the web form at
 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.
 56 Include files
 57 -------------
 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:
 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)
 70 Machine/Platform support
 71 ------------------------
 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   $(MACHINE) to refer to the category)
 79   To this end, we now have arch/arm/mach-$(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.
 86 Modules
 87 -------
 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?
 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.
 99 ADFS Image files
100 ----------------
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.
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.
110 Request to developers
111 ---------------------
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.
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.
122 ST506 hard drives
123 -----------------
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.
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 :-) ).
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 :-)
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).
144 1772 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.
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.
161   Previous registrations may be found online.
163     <>
165 Kernel 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.
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.
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.
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."
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.
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:
198     <>
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.
203 ---
204 Russell King (15/03/2004)

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