I just got a TP-Link TL-MR3040 a few days ago, and successfully set it up as a PirateBox, which involved refreshing the firmware with OpenWrt rather than a stock image. This is actually a pretty cool little device for the $35, it’ll run Linux, and with OpenWrt, not only can it function as a router, it can act as a tiny server running off a file system attached via USB.

I’ve tried this build on multiple platforms, and documented some of that in a previous version of this posting. While I’ve successfully gotten the core of OpenWrt to build on OS X, and a number of things to build on CentOS, I’ve only gotten consistent and reliable results overall on Debian-like systems, so that’s what I’m going to be sticking to here.

In particular, I’ve had nothing but trouble trying to build an OpenWrt image for a Raspberry Pi anywhere other than on Debian or a Debian derivative. I have verified working builds for both the TL-MR3040 and the Raspberry Pi on Mint 17.

The instructions for building a firmware image on the OpenWrt wiki are a version or more out of date — they’re for building Attitude Adjustment, rather than Barrier Breaker.

The procedure for building top-of-trunk for OpenWrt developers is better documented than the Attitude Adjustment build seems to have been, but still a little bit scattered.

Additionally, the guide for setting up a build environment on OS X relies on MacPorts, and I prefer Homebrew, is similarly outdated, and there are a wrinkle or two along the way, so I figured I should document what I’ve done. I’m not recommending, at this point, that you try building this stuff directly on OS X. Use a VM running Debian or Mint instead, that’s my recommendation.

Set Up the Prerequisites

On Ubuntu 14.04 LTS “Trusty Tahr”/Debian 7.7.0/Mint 17

sudo apt-get install subversion build-essential libncurses5-dev zlib1g-dev gawk git ccache gettext libssl-dev xsltproc zip

On OS X 10.10 “Yosemite”

On OS X, we’ll want to specifically set up a case-sensitive file system to work on. We can create a .dmg file that we can use for our development with the following commands. Twenty gig is plenty of space.

hdiutil create -size 20g -fs "Case-sensitive HFS+" -volname OpenWrt OpenWrt.dmg
hdiutil attach OpenWrt.dmg

Getting the build environment set up right here is a little more ornate. If you don’t have Homebrew (and you should), you’ll need to get that installed first. You’ll also need to install Xcode and the Xcode Command Line Tools.

brew update
brew upgrade
brew install coreutils e2fsprogs ossp-uuid asciidoc binutils fastjar gtk+ gnu-getopt gnu-tar intltool openssl subversion rsync sdcc gawk wget findutils

When brew installs the gnu toolset, it doesn’t automatically link it into your path, and the build wants to use gnu-compatible tools. However, brew does create an auxiliary directory of gnu-compatible aliases at /usr/local/opt/coreutils/libexec/gnubin, and for the purposes of the build, we can set our path to preference those tools temporarily.

ln -s /usr/local/Cellar/gnu-getopt/1.1.5/bin/getopt /usr/local/opt/coreutils/libexec/gnubin/getopt
ln -s /usr/local/bin/gtar /usr/local/opt/coreutils/libexec/gnubin/tar
export PATH=/usr/local/opt/coreutils/libexec/gnubin:$PATH

Get the Sources

Get the Barrier Breaker sources from the upstream repo to build the current stable release:

git clone git://git.openwrt.org/14.07/openwrt.git

Or pull down the latest OpenWrt “Chaos Calmer” sources to build the “bleeding edge” top-of-trunk version:

git clone git://git.openwrt.org/openwrt.git

Prepare For the Build

Connect to the source directory, and update and install all the feeds. These represents the build schemes for all of the optional components that you can add to your OpenWrt system.

cd ~/openwrt
./scripts/feeds update -a
./scripts/feeds install -a

Configure the build.

make prereq

This sets up prerequisites for the build and then takes you into menuconfig, a screen-driven configuration utility based on the one used to set up builds for the Linux kernel.

For starts, you simply want to pick an appropriate “Target system” and “Target profile”. For the TP-Link TL-MR3040, the target system is “Atheros AR7xxx/9xxx”, subtarget “generic”. For a Raspberry Pi, the target system is “BRCOM947xx/953xx”, the only profile is “Raspberry Pi”.

For an initial build, I’d suggest simply picking the correct target and leaving it at that. You can start adding other options once you’ve verified that you can produce a working build and have an idea how much free space you’ve got to play with on the system. You want to start out minimal, the MR3040 only has 4MB (!) of available flash memory.

When you’re done here, select “Exit”, and save your configuration file as .config when prompted to do so.

Build that sucker!

All it takes is a make at this point. I like to use make V=s because I like to watch it do its thing.

make

Results will be in the bin/ folder, in a subfolder corresponding to the architecture you’ve built for — in my case “ar71xx”.