linux/Documentation/arm/arm.rst
<<
>>
Prefs
   1=======================
   2ARM Linux 2.6 and upper
   3=======================
   4
   5    Please check <ftp://ftp.arm.linux.org.uk/pub/armlinux> for
   6    updates.
   7
   8Compilation of kernel
   9---------------------
  10
  11  In order to compile ARM Linux, you will need a compiler capable of
  12  generating ARM ELF code with GNU extensions.  GCC 3.3 is known to be
  13  a good compiler.  Fortunately, you needn't guess.  The kernel will report
  14  an error if your compiler is 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
  26  with::
  27
  28    ARCH = arm
  29
  30  and::
  31
  32    CROSS_COMPILE=
  33
  34  to::
  35
  36    CROSS_COMPILE=<your-path-to-your-compiler-without-gcc>
  37
  38  eg.::
  39
  40    CROSS_COMPILE=arm-linux-
  41
  42  Do a 'make config', followed by 'make Image' to build the kernel
  43  (arch/arm/boot/Image).  A compressed image can be built by doing a
  44  'make zImage' instead of 'make Image'.
  45
  46
  47Bug reports etc
  48---------------
  49
  50  Please send patches to the patch system.  For more information, see
  51  http://www.arm.linux.org.uk/developer/patches/info.php Always include some
  52  explanation as to what the patch does and why it is needed.
  53
  54  Bug reports should be sent to linux-arm-kernel@lists.arm.linux.org.uk,
  55  or submitted through the web form at
  56  http://www.arm.linux.org.uk/developer/
  57
  58  When sending bug reports, please ensure that they contain all relevant
  59  information, eg. the kernel messages that were printed before/during
  60  the problem, what you were doing, etc.
  61
  62
  63Include files
  64-------------
  65
  66  Several new include directories have been created under include/asm-arm,
  67  which are there to reduce the clutter in the top-level directory.  These
  68  directories, and their purpose is listed below:
  69
  70  ============= ==========================================================
  71   `arch-*`     machine/platform specific header files
  72   `hardware`   driver-internal ARM specific data structures/definitions
  73   `mach`       descriptions of generic ARM to specific machine interfaces
  74   `proc-*`     processor dependent header files (currently only two
  75                categories)
  76  ============= ==========================================================
  77
  78
  79Machine/Platform support
  80------------------------
  81
  82  The ARM tree contains support for a lot of different machine types.  To
  83  continue supporting these differences, it has become necessary to split
  84  machine-specific parts by directory.  For this, the machine category is
  85  used to select which directories and files get included (we will use
  86  $(MACHINE) to refer to the category)
  87
  88  To this end, we now have arch/arm/mach-$(MACHINE) directories which are
  89  designed to house the non-driver files for a particular machine (eg, PCI,
  90  memory management, architecture definitions etc).  For all future
  91  machines, there should be a corresponding arch/arm/mach-$(MACHINE)/include/mach
  92  directory.
  93
  94
  95Modules
  96-------
  97
  98  Although modularisation is supported (and required for the FP emulator),
  99  each module on an ARM2/ARM250/ARM3 machine when is loaded will take
 100  memory up to the next 32k boundary due to the size of the pages.
 101  Therefore, is modularisation on these machines really worth it?
 102
 103  However, ARM6 and up machines allow modules to take multiples of 4k, and
 104  as such Acorn RiscPCs and other architectures using these processors can
 105  make good use of modularisation.
 106
 107
 108ADFS Image files
 109----------------
 110
 111  You can access image files on your ADFS partitions by mounting the ADFS
 112  partition, and then using the loopback device driver.  You must have
 113  losetup installed.
 114
 115  Please note that the PCEmulator DOS partitions have a partition table at
 116  the start, and as such, you will have to give '-o offset' to losetup.
 117
 118
 119Request to developers
 120---------------------
 121
 122  When writing device drivers which include a separate assembler file, please
 123  include it in with the C file, and not the arch/arm/lib directory.  This
 124  allows the driver to be compiled as a loadable module without requiring
 125  half the code to be compiled into the kernel image.
 126
 127  In general, try to avoid using assembler unless it is really necessary.  It
 128  makes drivers far less easy to port to other hardware.
 129
 130
 131ST506 hard drives
 132-----------------
 133
 134  The ST506 hard drive controllers seem to be working fine (if a little
 135  slowly).  At the moment they will only work off the controllers on an
 136  A4x0's motherboard, but for it to work off a Podule just requires
 137  someone with a podule to add the addresses for the IRQ mask and the
 138  HDC base to the source.
 139
 140  As of 31/3/96 it works with two drives (you should get the ADFS
 141  `*configure` harddrive set to 2). I've got an internal 20MB and a great
 142  big external 5.25" FH 64MB drive (who could ever want more :-) ).
 143
 144  I've just got 240K/s off it (a dd with bs=128k); thats about half of what
 145  RiscOS gets; but it's a heck of a lot better than the 50K/s I was getting
 146  last week :-)
 147
 148  Known bug: Drive data errors can cause a hang; including cases where
 149  the controller has fixed the error using ECC. (Possibly ONLY
 150  in that case...hmm).
 151
 152
 1531772 Floppy
 154-----------
 155  This also seems to work OK, but hasn't been stressed much lately.  It
 156  hasn't got any code for disc change detection in there at the moment which
 157  could be a bit of a problem!  Suggestions on the correct way to do this
 158  are welcome.
 159
 160
 161`CONFIG_MACH_` and `CONFIG_ARCH_`
 162---------------------------------
 163  A change was made in 2003 to the macro names for new machines.
 164  Historically, `CONFIG_ARCH_` was used for the bonafide architecture,
 165  e.g. SA1100, as well as implementations of the architecture,
 166  e.g. Assabet.  It was decided to change the implementation macros
 167  to read `CONFIG_MACH_` for clarity.  Moreover, a retroactive fixup has
 168  not been made because it would complicate patching.
 169
 170  Previous registrations may be found online.
 171
 172    <http://www.arm.linux.org.uk/developer/machines/>
 173
 174Kernel entry (head.S)
 175---------------------
 176  The initial entry into the kernel is via head.S, which uses machine
 177  independent code.  The machine is selected by the value of 'r1' on
 178  entry, which must be kept unique.
 179
 180  Due to the large number of machines which the ARM port of Linux provides
 181  for, we have a method to manage this which ensures that we don't end up
 182  duplicating large amounts of code.
 183
 184  We group machine (or platform) support code into machine classes.  A
 185  class typically based around one or more system on a chip devices, and
 186  acts as a natural container around the actual implementations.  These
 187  classes are given directories - arch/arm/mach-<class> - which contain
 188  the source files and include/mach/ to support the machine class.
 189
 190  For example, the SA1100 class is based upon the SA1100 and SA1110 SoC
 191  devices, and contains the code to support the way the on-board and off-
 192  board devices are used, or the device is setup, and provides that
 193  machine specific "personality."
 194
 195  For platforms that support device tree (DT), the machine selection is
 196  controlled at runtime by passing the device tree blob to the kernel.  At
 197  compile-time, support for the machine type must be selected.  This allows for
 198  a single multiplatform kernel build to be used for several machine types.
 199
 200  For platforms that do not use device tree, this machine selection is
 201  controlled by the machine type ID, which acts both as a run-time and a
 202  compile-time code selection method.  You can register a new machine via the
 203  web site at:
 204
 205    <http://www.arm.linux.org.uk/developer/machines/>
 206
 207  Note: Please do not register a machine type for DT-only platforms.  If your
 208  platform is DT-only, you do not need a registered machine type.
 209
 210---
 211
 212Russell King (15/03/2004)
 213