I wanted to do some experimental hacking on my Raspberry Pi, specifically to try a bit of fun with talking to Arduino and Spark Cores. My ultimate aim was to have a go at doing something fun with the meArm robotic arm (https://www.wevolver.com/#/project/196/parts/629/document)
I started off compiling OpenCV and OpenNI on the physical pi, but quickly realised I didn’t have a big enough SD card lying around. I momentarily thought about stealing one of my wife’s pro camera SD cards, but then thought about the consequences… I then decided to emulate the whole thing and then buy an SD card when the project was done.
First off, you need a qemu environment. I’ll assume you have a basic qemu installation going, but if not, get started with
sudo apt-get install qemu-system qemu-user-static binfmt-support
Next, you will need to download the latest raspbian release image. Make a directory to use, and then grab it
mkdir ~/qemu_vms cd ~/qemu_vms wget http://downloads.raspberrypi.org/raspbmc_latest
You also need a kernel:
XEC Design maintains a qemu kernel with the ARMhf patches already, but if you would like to build your own one, feel free to grab it at https://github.com/raspberrypi/linux
You will need to extract the zip archive that you just downloaded, and you should be left with something like:
which means you are ready to start doing cool stuff! (Remember that if you are reading this, the .img file has probably changed, so keep a note of that!)
Lets boot this thing up!
qemu-system-arm -kernel kernel-qemu -cpu arm1176 -m 256 -M versatilepb -no-reboot -serial stdio -append "root=/dev/sda2 panic=1 rootfstype=ext4 rw init=/bin/bash" -hda 2014-06-20-wheezy-raspbian.img
which should start up qemu with a command prompt. Login with the default credentials (user: pi, pass: raspberry) and have a cookie for getting this far.
Now, you will notice that not everything can be emulated by qemu, so change /etc/ld.so.preload like this
nano /etc/ld.so.preload #Comment out the libcofi_rpi object like this #/usr/lib/arm-linux-gnueabihf/libcofi_rpi.so
Now you need to edit
(This is a new file!)
Add the following to your new file:
KERNEL=="sda", SYMLINK+="mmcblk0" KERNEL=="sda?", SYMLINK+="mmcblk0p%n" KERNEL=="sda2", SYMLINK+="root"
Now you should halt/shutdown the system, and prepare for your first real boot!
Boot up again with
qemu-system-arm -kernel kernel-qemu -cpu arm1176 -m 256 -M versatilepb -no-reboot -serial stdio -append "root=/dev/sda2 panic=1 rootfstype=ext4 rw" -hda 2014-06-20-wheezy-raspbian.img
Do a df -h and notice with horror that you have almost no space to work with!
Resizing the image “disk” is pretty easy though.
First close down the emulator again, then
qemu-img resize 2014-06-20-wheezy-raspbian.img +4G
This will make your partition 6GB long (do more if you like…) which should be plenty of space and will fit onto a relatively cheap 8GB SD Card.
Now boot up your emulator again and do:
sudo ln -snf mmcblk0p2 /dev/root sudo raspi-config
Choose the first option to resize your disk, and it will tell you to reboot. Great, once everything is halted, manually restart your emulator, and do another df -h. SURPRISE! It now looks like this:
Filesystem Size Used Avail Use% Mounted on rootfs 6.6G 2.1G 4.2G 33% / /dev/root 6.6G 2.1G 4.2G 33% / devtmpfs 125M 0 125M 0% /dev tmpfs 25M 204K 25M 1% /run tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 50M 0 50M 0% /run/shm /dev/sda1 56M 9.5M 47M 17% /boot
You are done! Great job!