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manual: rework introduction.txt and add embedded-basics.txt

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Split and rephrasing of introduction.txt.

Cross-toolchain explainations moved from introduction.txt into
embedded-basics.txt.

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
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Samuel Martin 2012-11-11 03:14:43 +00:00 committed by Peter Korsgaard
parent 5e84b8b73c
commit 0119ef3778
3 changed files with 126 additions and 60 deletions
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docs/manual/embedded-basics.txt Normal file
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// -*- mode:doc; -*-
Embedded system basics
----------------------
When developing an embedded system, there are a number of choices to
do:
* the cross-toolchain: target architecture/C library/...
* the bootloader
* kernel options
* the device management
* the init system
* the package selection (busybox vs. "real" programs, ...)
* ...
Some of them may be influenced by the target hardware.
Some of them may also add some constraints when you will develop the
final application for what your target is designed (e.g. some
functions may be provided by soem C libraries and missing in some
others, ...). So, these choices should be carefully done.
Buildroot allows to set most of these options to fit your needs.
Moreover, Buildroot provides an infrastructure for reproducing the
build process of your kernel, cross-toolchain, and embedded root
filesystem. Being able to reproduce the build process will be useful
when a component needs to be patched or updated or when another person
is supposed to take over the project.
[[cross-compilation-and-cross-toolchain]]
Cross-compilation & cross-toolchain
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A compilation toolchain is the set of tools that allows you to compile
code for your system. It consists of a compiler (in our case, +gcc+),
binary utils like assembler and linker (in our case, +binutils+) and a
C standard library (for example
http://www.gnu.org/software/libc/libc.html[GNU Libc],
http://www.uclibc.org/[uClibc] or
http://www.fefe.de/dietlibc/[dietlibc]).
The system installed on your development station certainly already has
a compilation toolchain that you can use to compile an application
that runs on your system. If you're using a PC, your compilation
toolchain runs on an x86 processor and generates code for an x86
processor. Under most Linux systems, the compilation toolchain uses
the GNU libc (glibc) as the C standard library. This compilation
toolchain is called the "host compilation toolchain". The machine on
which it is running, and on which you're working, is called the "host
system".
The compilation toolchain is provided by your distribution, and
Buildroot has nothing to do with it (other than using it to build a
cross-compilation toolchain and other tools that are run on the
development host).
As said above, the compilation toolchain that comes with your system
runs on and generates code for the processor in your host system. As
your embedded system has a different processor, you need a
cross-compilation toolchain - a compilation toolchain that runs on
your _host system_ but generates code for your _target system_ (and
target processor). For example, if your host system uses x86 and your
target system uses ARM, the regular compilation toolchain on your host
runs on x86 and generates code for x86, while the cross-compilation
toolchain runs on x86 and generates code for ARM.
Even if your embedded system uses an x86 processor, you might be
interested in Buildroot for two reasons:
* The compilation toolchain on your host certainly uses the GNU Libc
which is a complete but huge C standard library. Instead of using
GNU Libc on your target system, you can use uClibc which is a tiny C
standard library. If you want to use this C library, then you need a
compilation toolchain to generate binaries linked with it. Buildroot
can do that for you.
* Buildroot automates the building of a root filesystem with all
needed tools like busybox. That makes it much easier than doing it
by hand.
You might wonder why such a tool is needed when you can compile +gcc+,
+binutils+, +uClibc+ and all the other tools by hand. Of course doing
so is possible but, dealing with all of the configure options and
problems of every +gcc+ or +binutils+ version is very time-consuming
and uninteresting. Buildroot automates this process through the use
of Makefiles and has a collection of patches for each +gcc+ and
+binutils+ version to make them work on most architectures.
Buildroot offers a number of options and settings that can be tuned
when defining the cross-toolchain (refer to xref:toolchain-custom[]).
[[bootloader]]
Bootloader
~~~~~~~~~~
TODO
[[device-management]]
Device management
~~~~~~~~~~~~~~~~~
TODO
[[init-system]]
Init system
~~~~~~~~~~~
TODO

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docs/manual/going-further.txt
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// -*- mode:doc; -*-
Going further in Buildroot's innards
====================================
include::embedded-basics.txt[]
include::how-buildroot-works.txt[]
include::advanced.txt[]

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docs/manual/introduction.txt
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// -*- mode:doc; -*-
About Buildroot
===============
Buildroot is a set of Makefiles and patches that allows you to easily
generate a cross-compilation toolchain, a root filesystem and a Linux
kernel image for your target. Buildroot can be used for one, two or
all of these options, independently.
Buildroot provides a full featured environment for cross-development.
Buildroot is able to generate a cross-compilation toolchain, a root
filesystem, a Linux kernel image and a bootloader for your target.
Buildroot can be used for any combinaison of these options,
independently.
Buildroot is useful mainly for people working with embedded systems.
Embedded systems often use processors that are not the regular x86
processors everyone is used to having in his PC. They can be PowerPC
processors, MIPS processors, ARM processors, etc.
A compilation toolchain is the set of tools that allows you to compile
code for your system. It consists of a compiler (in our case, +gcc+),
binary utils like assembler and linker (in our case, +binutils+) and a
C standard library (for example
http://www.gnu.org/software/libc/libc.html[GNU Libc],
http://www.uclibc.org/[uClibc] or
http://www.fefe.de/dietlibc/[dietlibc]). The system installed on your
development station certainly already has a compilation toolchain that
you can use to compile an application that runs on your system. If
you're using a PC, your compilation toolchain runs on an x86 processor
and generates code for an x86 processor. Under most Linux systems, the
compilation toolchain uses the GNU libc (glibc) as the C standard
library. This compilation toolchain is called the "host compilation
toolchain". The machine on which it is running, and on which you're
working, is called the "host system". The compilation toolchain is
provided by your distribution, and Buildroot has nothing to do with it
(other than using it to build a cross-compilation toolchain and other
tools that are run on the development host).
As said above, the compilation toolchain that comes with your system
runs on and generates code for the processor in your host system. As
your embedded system has a different processor, you need a
cross-compilation toolchain - a compilation toolchain that runs on
your host system but generates code for your target system (and target
processor). For example, if your host system uses x86 and your target
system uses ARM, the regular compilation toolchain on your host runs on
x86 and generates code for x86, while the cross-compilation toolchain
runs on x86 and generates code for ARM.
Even if your embedded system uses an x86 processor, you might be
interested in Buildroot for two reasons:
* The compilation toolchain on your host certainly uses the GNU Libc
which is a complete but huge C standard library. Instead of using
GNU Libc on your target system, you can use uClibc which is a tiny C
standard library. If you want to use this C library, then you need a
compilation toolchain to generate binaries linked with it. Buildroot
can do that for you.
* Buildroot automates the building of a root filesystem with all
needed tools like busybox. That makes it much easier than doing it
by hand.
You might wonder why such a tool is needed when you can compile +gcc+,
+binutils+, +uClibc+ and all the other tools by hand. Of course doing
so is possible but, dealing with all of the configure options and
problems of every +gcc+ or +binutils+ version is very time-consuming
and uninteresting. Buildroot automates this process through the use
of Makefiles and has a collection of patches for each +gcc+ and
+binutils+ version to make them work on most architectures.
Moreover, Buildroot provides an infrastructure for reproducing the
build process of your kernel, cross-toolchain, and embedded root
filesystem. Being able to reproduce the build process will be useful
when a component needs to be patched or updated or when another person
is supposed to take over the project.
Buildroot supports numerous processors and their variants; it also
comes with default configuration for several boards available
off-the-shelf. Besides, a number of third-party projects are based on
or develop their BSP footnote:[BSP: Board Software Package] or
SDK footnote:[SDK: Standard Development Kit] on top of Buildroot.