205 lines
7.6 KiB
Plaintext
205 lines
7.6 KiB
Plaintext
ARM Linux 2.6
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=============
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Please check <ftp://ftp.arm.linux.org.uk/pub/armlinux> for
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updates.
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Compilation of kernel
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---------------------
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In order to compile ARM Linux, you will need a compiler capable of
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generating ARM ELF code with GNU extensions. GCC 3.3 is known to be
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a good compiler. Fortunately, you needn't guess. The kernel will report
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an error if your compiler is a recognized offender.
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To build ARM Linux natively, you shouldn't have to alter the ARCH = line
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in the top level Makefile. However, if you don't have the ARM Linux ELF
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tools installed as default, then you should change the CROSS_COMPILE
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line as detailed below.
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If you wish to cross-compile, then alter the following lines in the top
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level make file:
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ARCH = <whatever>
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with
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ARCH = arm
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and
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CROSS_COMPILE=
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to
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CROSS_COMPILE=<your-path-to-your-compiler-without-gcc>
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eg.
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CROSS_COMPILE=arm-linux-
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Do a 'make config', followed by 'make Image' to build the kernel
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(arch/arm/boot/Image). A compressed image can be built by doing a
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'make zImage' instead of 'make Image'.
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Bug reports etc
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---------------
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Please send patches to the patch system. For more information, see
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http://www.arm.linux.org.uk/developer/patches/info.php Always include some
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explanation as to what the patch does and why it is needed.
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Bug reports should be sent to linux-arm-kernel@lists.arm.linux.org.uk,
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or submitted through the web form at
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http://www.arm.linux.org.uk/developer/
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When sending bug reports, please ensure that they contain all relevant
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information, eg. the kernel messages that were printed before/during
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the problem, what you were doing, etc.
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Include files
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-------------
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Several new include directories have been created under include/asm-arm,
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which are there to reduce the clutter in the top-level directory. These
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directories, and their purpose is listed below:
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arch-* machine/platform specific header files
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hardware driver-internal ARM specific data structures/definitions
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mach descriptions of generic ARM to specific machine interfaces
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proc-* processor dependent header files (currently only two
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categories)
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Machine/Platform support
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------------------------
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The ARM tree contains support for a lot of different machine types. To
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continue supporting these differences, it has become necessary to split
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machine-specific parts by directory. For this, the machine category is
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used to select which directories and files get included (we will use
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$(MACHINE) to refer to the category)
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To this end, we now have arch/arm/mach-$(MACHINE) directories which are
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designed to house the non-driver files for a particular machine (eg, PCI,
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memory management, architecture definitions etc). For all future
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machines, there should be a corresponding arch/arm/mach-$(MACHINE)/include/mach
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directory.
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Modules
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-------
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Although modularisation is supported (and required for the FP emulator),
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each module on an ARM2/ARM250/ARM3 machine when is loaded will take
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memory up to the next 32k boundary due to the size of the pages.
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Therefore, is modularisation on these machines really worth it?
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However, ARM6 and up machines allow modules to take multiples of 4k, and
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as such Acorn RiscPCs and other architectures using these processors can
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make good use of modularisation.
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ADFS Image files
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----------------
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You can access image files on your ADFS partitions by mounting the ADFS
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partition, and then using the loopback device driver. You must have
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losetup installed.
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Please note that the PCEmulator DOS partitions have a partition table at
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the start, and as such, you will have to give '-o offset' to losetup.
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Request to developers
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---------------------
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When writing device drivers which include a separate assembler file, please
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include it in with the C file, and not the arch/arm/lib directory. This
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allows the driver to be compiled as a loadable module without requiring
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half the code to be compiled into the kernel image.
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In general, try to avoid using assembler unless it is really necessary. It
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makes drivers far less easy to port to other hardware.
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ST506 hard drives
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-----------------
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The ST506 hard drive controllers seem to be working fine (if a little
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slowly). At the moment they will only work off the controllers on an
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A4x0's motherboard, but for it to work off a Podule just requires
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someone with a podule to add the addresses for the IRQ mask and the
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HDC base to the source.
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As of 31/3/96 it works with two drives (you should get the ADFS
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*configure harddrive set to 2). I've got an internal 20MB and a great
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big external 5.25" FH 64MB drive (who could ever want more :-) ).
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I've just got 240K/s off it (a dd with bs=128k); thats about half of what
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RiscOS gets; but it's a heck of a lot better than the 50K/s I was getting
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last week :-)
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Known bug: Drive data errors can cause a hang; including cases where
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the controller has fixed the error using ECC. (Possibly ONLY
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in that case...hmm).
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1772 Floppy
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-----------
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This also seems to work OK, but hasn't been stressed much lately. It
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hasn't got any code for disc change detection in there at the moment which
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could be a bit of a problem! Suggestions on the correct way to do this
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are welcome.
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CONFIG_MACH_ and CONFIG_ARCH_
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-----------------------------
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A change was made in 2003 to the macro names for new machines.
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Historically, CONFIG_ARCH_ was used for the bonafide architecture,
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e.g. SA1100, as well as implementations of the architecture,
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e.g. Assabet. It was decided to change the implementation macros
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to read CONFIG_MACH_ for clarity. Moreover, a retroactive fixup has
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not been made because it would complicate patching.
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Previous registrations may be found online.
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<http://www.arm.linux.org.uk/developer/machines/>
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Kernel entry (head.S)
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--------------------------
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The initial entry into the kernel is via head.S, which uses machine
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independent code. The machine is selected by the value of 'r1' on
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entry, which must be kept unique.
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Due to the large number of machines which the ARM port of Linux provides
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for, we have a method to manage this which ensures that we don't end up
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duplicating large amounts of code.
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We group machine (or platform) support code into machine classes. A
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class typically based around one or more system on a chip devices, and
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acts as a natural container around the actual implementations. These
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classes are given directories - arch/arm/mach-<class> and
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arch/arm/mach-<class> - which contain the source files to/include/mach
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support the machine class. This directories also contain any machine
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specific supporting code.
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For example, the SA1100 class is based upon the SA1100 and SA1110 SoC
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devices, and contains the code to support the way the on-board and off-
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board devices are used, or the device is setup, and provides that
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machine specific "personality."
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For platforms that support device tree (DT), the machine selection is
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controlled at runtime by passing the device tree blob to the kernel. At
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compile-time, support for the machine type must be selected. This allows for
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a single multiplatform kernel build to be used for several machine types.
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For platforms that do not use device tree, this machine selection is
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controlled by the machine type ID, which acts both as a run-time and a
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compile-time code selection method. You can register a new machine via the
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web site at:
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<http://www.arm.linux.org.uk/developer/machines/>
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Note: Please do not register a machine type for DT-only platforms. If your
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platform is DT-only, you do not need a registered machine type.
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---
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Russell King (15/03/2004)
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