Documentation/arm/arm.rst

   1 =======================
   2 ARM Linux 2.6 and upper
   3 =======================
   4
   5     Please check <ftp://ftp.arm.linux.org.uk/pub/armlinux> for
   6     updates.
   7
   8 Compilation 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
  47 Bug 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
  63 Include 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
  79 Machine/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
  95 Modules
  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
 108 ADFS 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
 119 Request 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
 131 ST506 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
 153 1772 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
 174 Kernel 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
 212 Russell King (15/03/2004)