[Skiboot] [PATCH 2/3] mambo: Add README.md for skiboot.tcl

[Michael Neuling]

Stewart has a great blog post on getting started with mambo and
skiboot. It would be better to have this content here so we can keep
it in sync with the code.

Original blog post here:
  https://www.flamingspork.com/blog/2014/12/03/running-skiboot-opal-on-the-power8-simulator/

Signed-off-by: Michael Neuling <mikey at neuling.org>
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 external/mambo/README.md | 57 ++++++++++++++++++++++++++++++++++++++++++++++++
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 create mode 100644 external/mambo/README.md

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+# Running skiboot and Linux in Mambo
+
+The POWER8 Functional Simulator (aka Mambo) is free to use but not
+open source and is only supported on limited platforms.  This is a
+guide to getting started guide with it with skiboot and linux.
+
+## Getting Started
+
+From a bare x86_64 Ubuntu 16.04 install, to running skiboot and linux
+in the simulator, you can do do the following:
+
+### Steps to get Running on Ubuntu
+xterm is needed by the simulator.
+```
+apt-get install xterm
+```
+
+### Download mambo from IBM
+Download systemsim-p8..deb from:
+http://www-304.ibm.com/support/customercare/sas/f/pwrfs/home.html
+```
+dpkg -i systemsim-p8*deb
+```
+
+### Grab your skiboot, linux and initramfs images
+How to build a skiboot.lid is in the top level README file.
+
+Use a 64 bit powerpc kernel here. If compiling yourself, we suggest
+using powernv_defconfig.
+
+If you use op-build to build a full set of OpenPower images, you’ll
+likely be able to extract skiboot, zImage.epapr (or vmlinux and
+rootfs.cpio.xz) from output/images. We suggest using the
+openpower_mambo_defconfig.
+
+### Setup environment variables
+Setup environment variables to point to your images
+```
+export SKIBOOT_ZIMAGE=$HOME/src/op-build/output/images/zImage.epapr
+export SKIBOOT=$HOME/src/op-build/output/images/skiboot.lid
+export SKIBOOT_AUTORUN=1
+```
+If you want a vmlinux and separate initramfs you can also do this:
+```
+export SKIBOOT_ZIMAGE=$HOME/src/op-build/output/images/vmlinux
+export SKIBOOT_INITRD=$HOME/src/op-build/output/images/rootfs.cpio.xz
+export SKIBOOT=$HOME/src/skiboot/skiboot.lid
+export SKIBOOT_AUTORUN=1
+```
+
+### Run the simulator
+```
+/opt/ibm/systemsim-p8/run/pegasus/power8 -f $HOME/src/skiboot/external/mambo/skiboot.tcl
+```
+
+This should open an xterm and start booting.  It should take around
+20sec to get to a petitboot console.
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