Embedded System Development: QEMU + BuildRoot + Linux ARM

Here are some basic steps to get a virtual ARM Development board which will allows to practice our embedded systems skills or test code / firmware or whatever we want to do but without the need of having a physical device.

The following takes place in a Linux machine running on Virtual Box (512MB RAM), which I first thought would’ve taken much more time to compile the whole stuff but it only took ~2h.

For the whole procedure you are gonna need some development packages such as gcc, g++, bison, flex, gettext, texinfo, zlib, ncurses, uml-utilities and maybe others, just install them when the process complains.

[divider_flat] First Step: Setting up the Environment

We need to make use of tun/tap device to create a local lan in order to let the embedded linux find the NFS mount point.

$ sudo tunctl -u youruser Set 'tap0' persistent owned by 10101 $ sudo ifconfig tap0 up

Since we want this set-up for development I assume we want to add new binaries or modify configuration on-the-fly so I have created ~/root-nfs where the file system for our embedded device will reside. Update /etc/exports appropriately:

$ echo "/home/someuser/root-nfs", sync,no_root_squash)" > /etc/exports

Remember the no_root_squash method or files only accessible by root will no be exported through NFS.

Second Step: Configuring QEMU

Grab the source from www.qemu.org and compile it, or if you prefer just used some prebuilt binaries. It shouldn’t make any difference.

QEMU not only emulate CPUs but also a bunch of development boards with its attached hardware so you can run real software that interacts with the ethernet or whatever other peripheral available.

For our purpose we are going to use versatilepb which is an ARM based development board which you can physically have it but thanks to QEMU we can use a virtual one.

The only thing you need be sure when configuring/compiling/installing QEMU is that it supports ARM as target and the versatilepb machine is available.

Third Step: Getting BuildRoot

Buildroot is a great framework for crosscompiling, targeting mainly embedded systems. It is a bunch of Makefiles and configuration files which automatizes the toolchain generation for the target platform, building bootloader, kernel, libraries, binaries and preparing the appropriate images for booting a device.

The configuration is pretty similar to the Linux Kernel so if you are used to deal with menuconfig this will not show any difficult to you.

After decompressing buildroot we have to perform some minor configuration to produce the binaries we need for our target device.

Just type:

$ make menuconfig

And change the following entries:

  • Target Architecture = arm
  • Target Architecture Variant = generic_arm
  • Target ABI = EABI
  • Target Options -> Generic Serial Port Config -> serial port to run getty on (ttyAMA0)
  • Package Selection, make sure Busybox is selected
  • Target FileSystem Options -> check tar the root filesystem
  • Kernel -> set deconfig name to “versatile”
  • Kernel -> Kernel binary format to zImage

Afterwards do:

$ make linux26-menuconfig

Accept the default configurations and change anything you feel like changing

Note: I had a problem with the provided fakeroot version so I downloaded the fakeroot_1.11 from the debian repository and copied it to buildroot/dl/ (which is the place where downloaded packages are stored) and changed the verson to 1.11 in buildroot/packages/fakeroot/fakeroot.mk and then make again.

Just type:

$ make

And let the whole Makefiles produce the desired images!

They will be placed under buildroot/output/images, there you will find the zImage and the root.tar containing a whole filesystem with everything need to boot a Linux Operating System.

Final Step: Booting QEMU

Just before booting we should uncompress the root fs to the exported NFS directory as root, otherwise the special files under /dev will not be properly created which will stop our system working properly.

Now we just need to tell qemu the following parameters to run our system:

  • -M versatilepb # our target platform
  • -kernel buildroot/output/image/zImage # our generated kernel image targeting ARM
  • -net nic # so qemu emuletes a NIC interfaces as part of the versatilepb platform
  • -net tap,ifname=tap0,script=no # tell qemu to link the emulated NIC to the preconfigured tap device
  • -append “console=ttyAMA0 root=/dev/nfs rw nfsroot= ip=” # to instruct the booted linux kernel to search for the root-fs in the specified NFS server using the provided ip as its own
  • -nographic # to output everything to stdout

And all together:

qemu-system-arm -M versatilepb -kernel buildroot/output/image/zImage -net nic -net tap,ifname=tap0,script=no append "console=ttyAMA0 root=/dev/nfs rw nfsroot= ip=" -nographic

Now you should see the booting process of Linux and then the busybox login, as seen in the image above; just use root and no password to log in.

Originally published at http://www.gabrielgonzalezgarcia.com on February 21, 2011.