diving-meta-ros

This repository shows how to create a bitbake recipe for a ROS package and cross-compile it using the meta-ros project.

(For this tutorial the Angstrom Distribution was used. Refer to this instructions to set up an Angstrom workspace).

Building blocks:

• Angstrom distribution: Linux distribution for a variety of embedded devices. The distribution is the result of a unification of developers from the OpenZaurus, OpenEmbedded, and OpenSIMpad projects.
• meta-ros project: layer to provide ROS Groovy Galapagos in an OpenEmbedded Linux system.
• beginner_tutorials: Simple talker/listerner ROS package written in python.

The following sections will dive into the process of creating a recipe for the beginner_tutorials ROS package and cross-compile it:

The ROS package

The package selected for this example is the beginner_tutorials, a simple package written in python that creates a listener and a talker (subscriber and publisher). The package file structure is presented below:

├── CMakeLists.txt
├── README.md
├── ipkg 
│   └── beginner-tutorials_1.0.0+gitrAUTOINC+529536a8d19371beeae62eb89b6611aa02737629-r0_armv7a-vfp-neon.ipk
├── msg
│   └── Num.msg
├── package.xml
├── scripts
│   ├── listener.py
│   └── talker.py
└── srv
    └── AddTwoInts.srv

If you decide to create your own ROS package, your file structure shouldn't be much different.

(Note: Do not worry about the ipkg directory. It contains the cross-compiled version of this package ready-to-install in the beaglebone).

(Tip: Before going into the embedded system it might be wise to build and test your package in a ROS desktop-installation)

The bitbake recipe

Once we have the package tested, we need to create a bitbake recipe that will fetch the source, cross-compile it and generate an output that meet our needs. In this example the bitbake recipe will fetch the source from a git repository. Take a look at the OpenEmbedded User Manual before starting with the recipe.

The source for the recipe:

  1 DESCRIPTION = "Beginner_tutorials, talker/listener ROS package"
  2 SECTION = "devel"
  3 LICENSE = "MIT"
  4 LIC_FILES_CHKSUM = "file://package.xml;;beginline=16;endline=16;md5=05c8b019cf5b0834bc5e547a14f26ca3"
  5 
  6 DEPENDS = "roscpp catkin rospy std-msgs"
  7 RDEPENDS = "roscpp rospy std-msgs"
  8 
  9 SRC_URI = "git://github.com/vmayoral/beginner_tutorials.git"
 10 
 11 SRCREV = "${AUTOREV}"
 12 PV = "1.0.0+gitr${SRCPV}"
 13 
 14 S = "${WORKDIR}/git"
 15 
 16 inherit catkin

Let's analyze the recipe:

  1 DESCRIPTION = "Beginner_tutorials, talker/listener ROS package"
  2 SECTION = "devel"
  3 LICENSE = "MIT"

Description of the package, section and the license of it.

  4 LIC_FILES_CHKSUM = "file://package.xml;;beginline=16;endline=16;md5=05c8b019cf5b0834bc5e547a14f26ca3"

The checksum of the license line in the package.xml file of the package.

  6 DEPENDS = "roscpp catkin rospy std-msgs"
  7 RDEPENDS = "roscpp rospy std-msgs"

Build and run dependencies which can be identified directly from the package.xml (lines 42-48).

---

Note that std_msgs is written in the recipe as std-msgs. This is because open-embedded package names are with hyphen instead of underscores (which is the convention used in ROS packages)

---

  9 SRC_URI = "git://github.com/vmayoral/beginner_tutorials.git"

Source of the package to cross-compile. In this case the source is fetched from a git repository. It's also common to specify the branch using branch=hydro-devel.

 11 SRCREV = "${AUTOREV}"
 12 PV = "1.0.0+gitr${SRCPV}"

Source revision and package version.

 14 S = "${WORKDIR}/git"

Directory where the source files are located.

 16 inherit catkin

Inherit the catkin bbclass.

Cross-compiling

Now let's cross-compile the ROS package through the recipe we just created (it can be found in the recipes/beginner-tutorials/ directory of this repository).

• Set up an Angstrom distribution in your embedded platform. Some basic instructions about how to do to accomplish this are given at the README.md of https://github.com/vmayoral/beagle-ros.

• git clone this respository (https://github.com/vmayoral/diving-meta-ros) in some place such as /tmp

• Add recipes/* to the meta-ros/recipes-ros/: cp -r /path/to/diving-meta-ros/recipes/* /path/to/meta-ros/recipes-ros/. This step adds the recipe required to cross-compile this code inside of the meta-ros code structure.

• Cross-compile the recipe: bitbake beginner_tutorials to create an ipkg of the ROS package.

• Test the package built. Copy /path/to/the/package/beginner_tutorials*.ipkg to your embedded platform and install it using opkg install beginner_tutorials*.ipkg

• Run the package using rosrun beginner_tutorials talker.py or rosrun beginner_tutorials listerner.py

How to replicate

• Create a ROS package the usual way (catkin_create_pkg). Check this tutorial if you're not familiar.

• Edit the CMakeLists so that it'll deploy files according to your needs (check http://ros.org/wiki/catkin/CMakeLists.txt).

• ( Optional ) Upload the code of the package to a github repository.

• Create a bitbake recipe such as the one provided for this example available at recipes/beginner-tutorials/beginner-tutorials_git.bb.

• Put the recipe in the meta-ros file structure (check cross-compiling step to find an example).

• cross-compile and install the package.