The FPGA+ARM Armadeus APF51 board: Buildroot notes

Scope

This post was spun off the main post regarding setting up the Armadeus board for Embedded Linux on ARM and Xilinx Spartan-6 FPGA. It covers my own little war story as I set up the Buildroot SDK, so I could have my own cross compiler and Linux kernel to work with.

As kernel.org happened to be down, this was a (forced) opportunity to look a bit deeper into how things work under the hood. These are my notes, reflecting my own experience, and isn’t a substitute for any official documentation.

Setting up the build environment

Downloaded armadeus-4.0.tar.bz2 from the SourceForge page. There are binaries there too (Linux kernel, rootfs and U-boot image). Opened the tarball, changed directory, and followed the instructions and deduced that the apf51_defconfig is valid even though not documented:

$ make apf51_defconfig

that downloaded buildroot-2010.11.tar.bz2 from http://buildroot.uclibc.org/downloads/buildroot-2010.11.tar.bz2 ran some script (a lot of patches applied) and then opened the config menu.

Config menu settings:

• Under Target Options > Armadeus Device Support > Size of a single RAM chip, change it to 512 MB (to match my board). On second thought, the kernel detects all 512MB anyhow (despite this parameter set at 256 MB) so it looks like there’s no need to change this.
• Under Build options, set Number of jobs to run simultaneously to the number of cores in the compiling computer (8 for a quadcore with hyperthreading). So it finishes today.

and then simply went “make”. The computer spits a lot of mumbo-jumbo. Loads, really.

In retrospective, I would consider running “make source” to download whatever needs to be downloaded. In my own build, this turned out to be where problems occured.

Note: Always run make from armadeus-4.0 and not from “buildroot”. Doing the latter will work properly for several components, but will fail every now and then with weird errors. It’s very easy to make this mistake, in particular when kickstarting the build after download failures.

After the build finishes, the interesting stuff is in

• buildroot/output/images — Root, kernel and bootloader images.
• buildroot/output/build/staging_dir — Things to run on the host computer, such as the cross-compiler (e.g. buildroot/output/build/staging_dir/usr/arm-unknown-linux-uclibcgnueabi/bin/gcc)

Issues resulting from kernel.org being down

The build got stuck at downloading the Linux kernel. kernel.org happened to be down for maintenance, and Armadeus’ FTP site didn’t supply it. So I fetched  linux-2.6.38.1.tar.bz2 from a Linux mirror and put the file in /path/to/armadeus-4.0/buildroot/downloads and ran make again.

And then a git clone for linux-firmware.git failed, since it’s from kerner.org as well. So I went for the safe “trust anyone” strategy, and went for any repository I could find. So instead of the failed

git clone git://git.kernel.org/pub/scm/linux/kernel/git/dwmw2/linux-firmware.git /home/eli/armadeus/build/armadeus-4.0/buildroot/output/build/firmware-af5222c5ded5d944267acfbd001571409bea7eeb

I went

$ git clone https://github.com/mdamt/linux-firmware.git /home/eli/armadeus/build/armadeus-4.0/buildroot/output/build/firmware-af5222c5ded5d944267acfbd001571409bea7eeb

which wasn’t really helpful, since it didn’t satisfy some Make rule. Running “make -d” I found out that the Make rules would be happy with a tarball, so I went

$ tar -czf ../../downloads/firmware-af5222c5ded5d944267acfbd001571409bea7eeb.tar.gz firmware-af5222c5ded5d944267acfbd001571409bea7eeb

and ran “make” again after removing the directory from which I had created the tarball.

Other problems

I also needed to download iproute2-2.6.35.tar.bz2 from Fedora’s repository into armadeus-4.0/buildroot/downloads, as it couldn’t be downloaded from linuxfoundation.org. This was starting to become routine.

And then I got

/usr/bin/ld: cannot find -lc

while building host-module-init-tools-3.12. And as buildroot’s docs guessed correctly, I am using Fedora, so it was all down to a

# yum install glibc-static

and go “make” again.

Just a silly mistake

When attempting to build the kernel I got

drivers/usb/Kconfig:169: can't open file "drivers/armadeus/Kconfig"

which was a direct result of the broken link of the “armadeus” subdirectory in “output/build/linux-2.6.38.1/drivers/”.  But that was just a silly mistake: I ran “make” from “buildroot” and not from the armadeus-4.0 directory, so the Makefile setting up the necessary environment variable was never set.

Doing it all over again

The idea is to rerun everything offline, i.e. without any downloads from the internet. One can’t always rely on that servers will be up and ready… The correct way to do this is to define the download directories before starting off, but I didn’t bother.

My motivation for doing this was that after kickstarting the build so many times, it crossed my mind that I may have messed up something without noticing. So I figured it would be best to rerun it all in one go.

So first of all, move the already built directory to finished-armadeus-4.0. It’s some 3.5 GB, but we’ll need only the download directories.

$ tar -xjf armadeus-4.0.tar.bz2
$ cd armadeus-4.0
$ cp -r ../finished-armadeus-4.0/downloads/ .
$ cp -r ../finished-armadeus-4.0/buildroot/downloads/ buildroot/
$ make apf51_defconfig

Which brings us back to the configuration menu, after which a simple “make” does the work.

It’s also worth to mention, that according to the docs/README file, “make source” will download all necessary sources, which is a good starter.