Monday, October 27, 2008

Coding Eye-Candy for Portable Linux Devices

At ACCESS, I've had the opportunity to do interesting things with Linux on cell phones. Some modern ARM chips, such as the Marvell XScale and TI OMAP series, have unusual frame buffer architectures that let you do "eye candy" on the cheap, without requiring a GPU.

In July 2008, I presented a paper about this work at the Ottawa Linux Symposium. I was also supposed to give it at GUADEC in Istanbul, but wasn't able to attend, so David "Lefty" Schlesinger gave it for me there.

If you are interested, here are links to:
  • The paper itself, which is somewhat academic in tone
  • The PowerPoint presentation based on the paper, which is more informal
  • A movie showing this in action on an XScale-based Zylonite prototype system, with narration by yours truly
As of the date of this post, I'm in the middle of porting this system to an OMAP 3430-based system.

Monday, October 20, 2008

Open Source Builds For Newbies


If you build open source software, you'll run into a lot of variants of the following list of commands:
cd (some directory)
sudo make install

Some common variants replace the ./configure with ./, or add some extra stuff on the end of that line or the make line. This article explains what's going on with this kind of command sequence.


If you look at most programs and other software components whose purpose is not trivial, they're made from more than one source file. There are several ways to tell a computer how to put all those source files together to create a component, and the most common is called a makefile. (There are also various kinds of project files that are used with development systems like Microsoft's Visual Studio, or Metrowerks' CodeWarrior.)

The Bad Old Days

The problem with makefiles is that they can need different contents to account for different computers and operating systems and compiler systems. For example, you might need one makefile for Linux on an x86 computer with version 3.4 of the gcc compiler, another for the same system using gcc 4.2, yet another for a Sun workstation running Solaris, and yet another for Mac OS X.

Up through the mid 1990s, the normal way to cope with this was to supply a different makefile for each combination of hardware, operating system, and compiler. That often meant a dozen or more makefiles. And if you had an unsupported combination, you had to write your own makefile.

Also, many software components rely on other software components, mostly known as libraries. But people work on libraries, so they change over time, and it's possible to get mismatches. For instance, if you write a program that works with PNG images, you'll probably want to use the "libpng" library. But there are different versions of libpng, and in the old days, if you wrote your program to work with one version, and somebody got your source code and tried to build it with a different version of libpng, the build might have failed, or the program might not have worked right. And makefiles have no reasonable way to check to see if you have the right version of a library.

The Good New Days

Several tools solve this whole problem - these are called the GNU Autotools, and pkg-config.
  • The GNU Autotools create the configure file, which is a set of commands that builds a makefile for your particular computer, operating system, and compiler collection.
  • Then the configure file typically uses pkg-config to make sure you have the right versions of any libraries you need, and complains if you don't.
What Each Step Does
  1. cd (some directory) makes that directory the current one.
  2. ./configure runs the configure script in that directory. That checks your operating system, compiler, CPU, and what libraries you have installed. If everything is okay, it creates a makefile in that same directory.
  3. make gets information from the makefile to build your software component
  4. sudo make install takes the component you built at the make step, and installs it where it needs to go on your computer to be useful.
For more information
Here are links about: