From I9100XWLPT to CM9

Intro

Ok, so this is just a promt guide-through for all those that have Samsung I9100 and want to make use of Cyanogenmod 9. Which is far better (well, not in all apps, I must admit) than the stock software (version I9100XWLPT in my case). This guide is based on a real-life scenario, when my new galaxy s2 was blessed with the new software :)

Remark: This work was based on xda thread but I thought it would be nice to provide a simple and clean guide for all interested.

Download required software

You will need three software packages in order to perform the procedure:

1. rooting package (Root_SuperSU.0.95.Only-signed.zip) from root. The rooting procedure is safe, as the bootloader does not see installed software as no-brand and thus it does not (but I am not a lawyer, so still, you do it on your own risk) void the warranty
2. latest CM 9 from cm9s2
3. latest Google apps (which are proprietary and do not come with CM builds) from gapps

Put all three packages into sd card of the device

The packages will be "flashed" (which in fact is just unpacking) in a recovery mode from the external memory (sd-card).

Turn off the phone

Now we will go to recovery mode (which by the way is one of three possible bootloader operating modes).

Press VolumeUP + Home + Power for a few (>5) seconds 

Release buttons when you see the device starting. It should boot nicely into recovery mode where you can operate using VolumeUp/Down & Power buttons.

Install root package and CM

In the recovery mode, perform the following:

1. Apply update from external memory: Root_SuperSU.0.95.Only-signed.zip
2. Clear cache
3. Clear flash memory
4. Apply update form external memory: cm-9.1.0-galaxys2.zip
5. Reboot device

Right now, the device should boot up with CM working smoothly. But there are no google apps like gmail or talk.

Install google apps

Go again into recovery mode (right now you can either do VolumeUp+Home+Power procedure or simply reboot into recovery from Shutdown menu - long-press Power button when device is working).

In the recovery mode, perform the following:

1. Apply update from external memory: gapps-ics-20120317-signed.zip
2. Reboot device

You are done

Happy waiting for the official CyanogenMod 10!

Sidenote

You can always go back to stock firmware by the means of Odin and leaked Samsung Android packages. However, this post is not intended to describe how to do it.