Cross compilation for ARM based Linux systems

This steps are tested on Ubuntu Linux 12.04, but should work for other Linux distributions. I case of other distributions package names and names of cross compilation tools may differ. There are several popular EABI versions that are used on ARM platform. This tutorial is written for gnueabi and gnueabihf, but other variants should work with minimal changes.

Prerequisites

• Host computer with Linux;

• Git;

• CMake 2.6 or higher;

• Cross compilation tools for ARM: gcc, libstc++, etc. Depending on target platform you need to choose gnueabi or gnueabihf tools. Install command for gnueabi :

  sudo apt-get install gcc-arm-linux-gnueabi
  

  Install command for gnueabihf :

  sudo apt-get install gcc-arm-linux-gnueabihf
  

• pkgconfig;

• Python 2.6 for host system;

• [optional] ffmpeg or libav development packages for armeabi(hf): libavcodec-dev, libavformat-dev, libswscale-dev;

• [optional] GTK+2.x or higher, including headers (libgtk2.0-dev) for armeabi(hf);

• [optional] libdc1394 2.x;

• [optional] libjpeg-dev, libpng-dev, libtiff-dev, libjasper-dev for armeabi(hf).

Getting OpenCV Source Code

You can use the latest stable OpenCV version available in sourceforge or you can grab the latest snapshot from our Git repository.

Getting the Latest Stable OpenCV Version

• Go to our page on Sourceforge;
• Download the source tarball and unpack it.

Getting the Cutting-edge OpenCV from the Git Repository

Launch Git client and clone OpenCV repository

In Linux it can be achieved with the following command in Terminal:

cd ~/<my_working _directory>
git clone https://github.com/opencv/opencv.git

Building OpenCV

1. Create a build directory, make it current and run the following command:

   cmake [<some optional parameters>] -DCMAKE_TOOLCHAIN_FILE=<path to the OpenCV source directory>/platforms/linux/arm-gnueabi.toolchain.cmake <path to the OpenCV source directory>
   

   Toolchain uses gnueabihf EABI convention by default. Add -DSOFTFP=ON cmake argument to switch on softfp compiler.

   cmake [<some optional parameters>] -DSOFTFP=ON -DCMAKE_TOOLCHAIN_FILE=<path to the OpenCV source directory>/platforms/linux/arm-gnueabi.toolchain.cmake <path to the OpenCV source directory>
   

   For example:

   cd ~/opencv/platforms/linux
   mkdir -p build_hardfp
   cd build_hardfp
   
   cmake -DCMAKE_TOOLCHAIN_FILE=../arm-gnueabi.toolchain.cmake ../../..
   

2. Run make in build (<cmake_binary_dir>) directory:

   make
   

Optionally you can strip symbols info from the created library via install/strip make target. This option produces smaller binary ( twice smaller) but makes further debugging harder.

Enable hardware optimizations

Depending on target platform architecture different instruction sets can be used. By default compiler generates code for armv5l without VFPv3 and NEON extensions. Add -DENABLE_VFPV3=ON to cmake command line to enable code generation for VFPv3 and -DENABLE_NEON=ON for using NEON SIMD extensions.

TBB is supported on multi core ARM SoCs also. Add -DWITH_TBB=ON and -DBUILD_TBB=ON to enable it. Cmake scripts download TBB sources from official project site http://threadingbuildingblocks.org/ and build it.