description of how to emulate the pi

qemu.md

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+Target Pi on Mac
+----------------
+
+So even the idea is to run software on the Pi, not everyone has a Pi (yet :-)
+
+Others, like me, prefer to develop on a laptop and not carry the Pi around. 
+
+For all those, this here explains how to emulate the Pi on a Mac.
+
+Replace the buggy llvm
+-----------------------
+
+Written April 2014: as of writing the latest and greatest llvm based gcc (5.1) on Maverick (10.9) has a bug that makes qemu hang.
+
+So type gcc -v and if the output contains "LLVM version 5.1", you must install gcc4.2. Easily donw with homebrew:
+
+brew install https://raw.github.com/Homebrew/homebrew-dupes/master/apple-gcc42.rb
+
+This will not interfere with the systems compiler as the gcc4.3 has postfixed executables (ie gcc-4.2) 
+
+Qemu 
+----
+
+Then its time to get the Qemu. There may be other emulators out there, and i have read of armulator, but this is what i found discribed and it works and is "easy enough".
+
+brew install qemu --env=std --cc=gcc-4.2
+
+For people not on Maverick it may work without the -cc option. 
+
+Pi images
+----------
+
+Create a directory for the stuff on your mac, ie pi.
+
+Get the latest Raspian image.
+
+There seems to be some chicken and egg problem, so quemu needs the kernel seperately. There is one in the links.
+
+Configure
+---------
+
+In the blog post there is some fun configuration, I did it and it works. Not sure what happens if you don't.
+The booting is described below (you may or may not need an extra init=/bin/bash in the root... quotes), so boot your Pi and then configure:
+
+nano /etc/ld.so.preload
+
+Put a # in front of the first to comment it out. Should just be one line there.
+
+Press ctrl-x then y then enter to save and exit.
+
+(Optional) Create a file /etc/udev/rules.d/90-qemu.rules with the following content:
+KERNEL=="sda", SYMLINK+="mmcblk0"
+KERNEL=="sda?", SYMLINK+="mmcblk0p%n"
+KERNEL=="sda2", SYMLINK+="root"
+
+The kernel sees the disk as /dev/sda, while a real pi sees /dev/mmcblk0. 
+This will create symlinks to be more consistent with the real pi.
+
+Boot
+-----
+
+There is quite a bit to the command line to boot the pi (i have an alias), here it is:
+
+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 raspbian.img -redir tcp:2222::22
+
+- the cpu is what braodcom precifies, ok
+- memory is unfortuantely hardcoded in the versatilepb "machine"
+- the kernel is the file name of the kernel you downloaded (or extracted)
+- raspbian.img is the image you downloaded. Renamed as it probably had the datestamp on it
+- the redir redircts the port 2222 to let you log into the pi
+
+So "ssh -p 2222 -l pi localhost" will get you "in". Ie username pi (password raspberry is the default) and port 2222
+
+Qemu bridges the network (that it emulates), and so your pi is now as connected as your mac.
+
+More Disk
+---------
+
+The image that you download has only 200Mb free. Since the gcc is included and we're developing (tiny little files of) ruby, this may be ok. If not there is a 3 step procedure to up the space.
+
+1. dd if=/dev/zero bs=1m count=2048 >> raspbian.img 
+
+The 2048 gets you 2Gb as we specified 1m (meg).
+
+2. On the pi launch "sudo fdisk /dev/sda" . This will probably only work if your do the (Optional) config above.
+
+Say p, and write down the start of the second partition (122880 for me).
+d 2 will delete the second partition
+n p 2 will create a new primary second partition
+write the number as start and just return to the end.
+p to check
+w to write and quit.
+
+3. Reboot, and run resize2fs
+
+Links
+-----
+
+Blog post: http://xecdesign.com/qemu-emulating-raspberry-pi-the-easy-way/
+Kernel: http://xecdesign.com/downloads/linux-qemu/kernel-qemu
+Rasbian file system(preferably be torrent): http://www.raspberrypi.org/downloads/