linux/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 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  This fine-grained machine specific selection is controlled by the machine
 189  type ID, which acts both as a run-time and a compile-time code selection
 190  method.
 191
 192  You can register a new machine via the web site at:
 193
 194    <http://www.arm.linux.org.uk/developer/machines/>
 195
 196---
 197Russell King (15/03/2004)
 198
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