Difference between revisions of "The Linux kernel"

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= How to cross compile the linux kernel  =
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=What is Linux?=
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[[Image:tux.png|left]][http://www.kernel.org The Linux Kernel Archives]Linux is a clone of the operating system Unix, written from scratch by Linus Torvalds with assistance from a loosely-knit team of hackers across the Net. It aims towards POSIX and Single UNIX Specification compliance.
  
Embedded Linux is the use of a Linux operating system in embedded computer systems such as mobile phones, personal digital assistants, media players, set-top boxes, and other consumer electronics devices, networking equipment, machine control, industrial automation, navigation equipment and medical instruments.  
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It has all the features you would expect in a modern fully-fledged Unix, including true multitasking, virtual memory, shared libraries, demand loading, shared copy-on-write executables, proper memory management, and multistack networking including IPv4 and IPv6.
  
Unlike desktop and server versions of Linux, embedded versions of Linux are designed for devices with relatively limited resources, such as cell phones and set-top boxes. Due to concerns such as cost and size, embedded devices usually have much less RAM and secondary storage than desktop computers, and are likely to use flash memory instead of a hard drive. Since embedded devices serve specific rather than general purposes, developers optimize their embedded Linux distributions to target specific hardware configurations and usage situations. These optimizations can include reducing the number of device drivers and software applications, and modifying the Linux kernel to be a real-time operating system.  
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Although originally developed first for 32-bit x86-based PCs (386 or higher), today Linux also runs on a multitude of other processor architectures, in both 32- and 64-bit variants.
  
== Overview of How-To ==
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=Overview of How-To=
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This How-To is meant to be a starting point for people to learn build a kernel image for IGEP Processor Boards as quickly and easily as possible.
  
This How-To is meant to be a starting point for people to learn build a kernel image for IGEP v2 devices as quickly and easily as possible.  
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=How to cross compile the linux kernel=
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In order to build the Linux Kernel for IGEP PROCESSOR BOARDS it's recommended to cross-compile the kernel, that's, build the kernel in your HOST machine for a target architecture.
  
This How-To works with the Ubuntu 8.04 IGEP v2.0 SDK Virtual Machine but most of the contents are valid also for other GNU/Linux distributions. We do not issue any guarantee that this will work on other distributions.  
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To [[Ubuntu 16.04 LTS Toolchain|setup the cross-compiling]] there are two fundamental variables that the kernel uses to select the target architecture. Normally these values are guessed based on your build environment, but of course that environment here does not match our target embedded system, so we'll need to override them. The variables in question are ARCH and CROSS_COMPILE.
  
== IGEP platforms ==
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The ARCH variable is the architecture you're targetting as the kernel knows it. For IGEP PROCESSOR BOARDS you'll set to "arm" architecture.
  
* IGEP0020 is also know as IGEP v2 platform.
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Hopefully the CROSS_COMPILE variable is pretty self-explanatory. Set this to the prefix of your toolchain (including the trailing dash "-"). So if your toolchain is invoked as say arm-linux-gnueabihf-gcc, just chop off that trailing gcc and that's what you use: arm-linux-gnueabihf-.
* IGEP0030 is also know as IGEP COM MODULE.
 
* IGEP0032 is also know as IGEP COM PROTON.
 
  
=== Linux OMAP v2.6.37 series ===
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There is an additional variable, INSTALL_MOD_PATH, which defines where the /lib directory will be created, and all the modules stored. While you don't have to transfer the kernel sources to your target device, if you build any modules, you'll want this directory.
  
See the [[Linux Kernel 2.6.37.y]] article
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As example, once you've downloaded the kernel source, you should follow these steps:
  
=== Linux OMAP v2.6.35 series ===
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make ARCH=arm CROSS_COMPILE=[cross compiler] [defconfig]
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make ARCH=arm CROSS_COMPILE=[cross compiler] zImage modules
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Newest kernels can require build the dtbs too as:
  
See the [[Linux Kernel 2.6.35.y]] article
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make ARCH=arm CROSS_COMPILE=[cross compiler] zImage modules dtbs
  
=== Linux mainline tree (development)  ===
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The result will be a zImage file in <code>${KERNEL_SOURCES}/arch/arm/boot</code>
  
<span style="color: rgb(255, 0, 0);">'''Note:''' The 'master' branch is where the development work takes place and you should use this if you're after to work with the latest cutting edge developments. It is possible trunk can suffer temporary periods of instability while new features are developed and if this is undesirable we recommend using one of the release branches. '''Use ONLY for development purposes.'''</span>  
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And dabs will be in <code>${KERNEL_SOURCES}/arch/arm/boot/dts</code>
  
Additional patches can be found at http://patchwork.kernel.org/project/linux-omap/list
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At last you can install the kernel modules to your target rootfs using this command
  
This Linux kernel is also considered as a downstream of tmlind's Linux kernel. The main difference between this tree and the linux-omap tree is that the igep OMAP tree has unpublished patches for IGEP v2 support.
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make ARCH=arm CROSS_COMPILE=[cross compiler] modules_install INSTALL_MOD_PATH=[path to your target rootfs]
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Example:
  
Clone GIT repository from git.igep.es
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make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- omap2plus_defconfig<br>make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- zImage modules dtbs<br>make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- modules_install INSTALL_MOD_PATH=/media/user/rootfs
  
git clone git://git.igep.es/pub/scm/linux-omap-2.6.git
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==Linux kernels==
cd linux-omap-2.6
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===IGEP Boards based on Texas Instruments  Processors===
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* [[Linux Kernel 2.6.37.y]] (OMAP35xx and DM3730) processor board based.
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* [[Linux Kernel 4.9.y]] (OMAP35xx, DM3730, AM335x) processor board based.
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* [[Linux Kernel 3.8.y]] (OMAP5432) processor board based.
  
and build with
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===IGEP Boards based on NXP-Freescale Processors===
 
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* [[Linux Kernel 3.14.28.y]] (iMX6) processor board based.
make ARCH=arm CROSS_COMPILE=[cross compiler] omap2plus_defconfig
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* [[Linux Kernel 4.9.y]] (iMX6) processor board based.
make ARCH=arm CROSS_COMPILE=[cross compiler] uImage modules
 
 
 
The result will be an uImage file in arch/arm/boot directory. You can install the kernel modules to your target rootfs
 
 
 
make ARCH=arm CROSS_COMPILE=[cross compiler] modules_install INSTALL_MOD_PATH=[path to your target rootfs]
 
  
=See also=
 
*[[How to setup a cross compiler]]
 
  
[[Category:Software|Kernel]]
 
 
[[Category:Linux Kernel]]
 
[[Category:Linux Kernel]]
[[Category:Tutorials]]
 
[[Category:Software applications]]
 

Latest revision as of 13:46, 12 March 2018

What is Linux?

tux.png
The Linux Kernel ArchivesLinux is a clone of the operating system Unix, written from scratch by Linus Torvalds with assistance from a loosely-knit team of hackers across the Net. It aims towards POSIX and Single UNIX Specification compliance.

It has all the features you would expect in a modern fully-fledged Unix, including true multitasking, virtual memory, shared libraries, demand loading, shared copy-on-write executables, proper memory management, and multistack networking including IPv4 and IPv6.

Although originally developed first for 32-bit x86-based PCs (386 or higher), today Linux also runs on a multitude of other processor architectures, in both 32- and 64-bit variants.

Overview of How-To

This How-To is meant to be a starting point for people to learn build a kernel image for IGEP Processor Boards as quickly and easily as possible.

How to cross compile the linux kernel

In order to build the Linux Kernel for IGEP PROCESSOR BOARDS it's recommended to cross-compile the kernel, that's, build the kernel in your HOST machine for a target architecture.

To setup the cross-compiling there are two fundamental variables that the kernel uses to select the target architecture. Normally these values are guessed based on your build environment, but of course that environment here does not match our target embedded system, so we'll need to override them. The variables in question are ARCH and CROSS_COMPILE.

The ARCH variable is the architecture you're targetting as the kernel knows it. For IGEP PROCESSOR BOARDS you'll set to "arm" architecture.

Hopefully the CROSS_COMPILE variable is pretty self-explanatory. Set this to the prefix of your toolchain (including the trailing dash "-"). So if your toolchain is invoked as say arm-linux-gnueabihf-gcc, just chop off that trailing gcc and that's what you use: arm-linux-gnueabihf-.

There is an additional variable, INSTALL_MOD_PATH, which defines where the /lib directory will be created, and all the modules stored. While you don't have to transfer the kernel sources to your target device, if you build any modules, you'll want this directory.

As example, once you've downloaded the kernel source, you should follow these steps:

make ARCH=arm CROSS_COMPILE=[cross compiler] [defconfig]
make ARCH=arm CROSS_COMPILE=[cross compiler] zImage modules

Newest kernels can require build the dtbs too as:

make ARCH=arm CROSS_COMPILE=[cross compiler] zImage modules dtbs

The result will be a zImage file in ${KERNEL_SOURCES}/arch/arm/boot

And dabs will be in ${KERNEL_SOURCES}/arch/arm/boot/dts

At last you can install the kernel modules to your target rootfs using this command

make ARCH=arm CROSS_COMPILE=[cross compiler] modules_install INSTALL_MOD_PATH=[path to your target rootfs]

Example:

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- omap2plus_defconfig
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- zImage modules dtbs
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- modules_install INSTALL_MOD_PATH=/media/user/rootfs

Linux kernels

IGEP Boards based on Texas Instruments  Processors

IGEP Boards based on NXP-Freescale Processors