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diff --git a/docs/manual/embedded-basics.txt b/docs/manual/embedded-basics.txt new file mode 100644 index 000000000..27dda37a0 --- /dev/null +++ b/docs/manual/embedded-basics.txt @@ -0,0 +1,110 @@ +// -*- 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 |