[Xperia Arc General] Someguyfromhell:
10. Unlocking bootloader

Unlocked bootloader is needed for most custom ROMs and for ALL custom kernels. It allows the booting system to be changed.

This can be done via official way or via test point method. Official way also removes DRM keys, which cannot be restored at all.

WARNING: You will lose warranty with this!

THE OFFICIAL METHOD - You lose DRM!

Go to http://unlockbootloader.sonymobile.com.

Enter service menu, open keypad and enter *#*#7378423#*#*.

Service Info - Configuration, Bootloader Unlock Allowed: Yes/No. If it says Yes, continue. If it says No, do not continue, because it will not work.

On the website, click "Start Unlocking the bootloader".

In the text, there are instructions, what you need to do. Also there are drivers that are needed for this process. Follow the instructions.

Install the drivers, then click Continue.

Enter your IMEI, name and e-mail. Leave out the last number from the IMEI.

You get a code, leave the website open, you will need this code.

Turn off your phone, then connect USB cable to your PC, hold down Volume UP button and connect USB cable to your phone. Blue LED should light up.

You will be asked for drivers. Point to the usb_driver folder where you placed the android_winusb.inf-file, and select the Android Boot loader Interface-file.

Open command prompt, first enter this

cd C:\...\android-sdk\platform-tools

Replace C with the correct drive letter and ... with the path to the android-sdk folder. Next, enter this command

fastboot.exe -i 0x0fce oem unlock 0xKEY

Replace KEY with the key that you got from the website.

Bootloader is now unlocked.

THE TEST POINT METHOD

Go to this topic http://xdaforums.com/showthread.php?t=1285285.

Follow the instructions to patch bootloader.

11. Installing custom kernel

Most custom ROMs will require a custom kernel, some of these include it already(CM, MIUI etc), other you need to find yourself(Hybrom). Installation is done via fastboot. First, you need to find a custom kernel, that will work on your phone. You can find these from Development section.

Make sure your bootloader is unlocked, enter service menu(*#*#7378423#*#*), Service Info, Configuration, if it says Bootloader unlocked: Yes, then it is unlocked.

Make sure fastboot drivers are installed. These should come with Android SDK.

Download the kernel you want. You will need a .img file, which is mostly inside a .zip file.

From the downloads section, download kernel installation package and extract the folder.

Place the .img file inside the folder. If it's name isn't boot.img yet, rename it to boot.img.

Place your phone in fastboot. Turn it off, connect USB cable to your computer, hold Volume UP button and then connect USB cable to your phone. Blue LED should light UP.

Double-click on the flash.cmd file. It will start fastboot automatically and install the kernel.

When finished, disconnect the cable and turn on your phone.

12. Installing custom ROM

Requirements: Unlocked bootloader, ROM .zip file downloaded.

Nothing difficult here.

Place the downloaded .zip file to the root of your SDcard.

Install the custom kernel, explained in previous tutorial.

Enter Recovery(while booting, when screen gets brighter, press Volume Down button until phone enters Recovery).

Make factory reset, wipe cache partition and clear Dalvik Cache(under Advanced).

NB! Do NOT make format /system, because some ROMs require files from system folder and installation will not finish if files are not available. Then you have to install stock ROM again.

Choose install zip from sdcard, pick the downloaded .zip file on your SDcard.

Wait for it to finish and reboot your phone.

13. Relocking bootloader

When you return to stock and/or need warranty back, you will need to relock bootloader. First install stock ROM and kernel and then relock bootloader, else you will have problems. Depending on the unlocking method, there are 2 ways to relock.

TEST POINT METHOD

Start S1 Tool and click Restore button. Should relock the bootloader automatically.

OFFICIAL METHOD

Will not work on test point method, because bootloader was patched there ant not unlocked.

Make sure you have Flashtool installed.

From the downloads section, download Xperia_Relock_Bootloader.zip file.

Extract the package, there is a .ftf file.

Flash the .ftf file with Flashtool.

Bootloader is locked again

14. Preparing for Ice Cream Sandwich update

ICS update is already released. You might want to know, what you need to do to get the update. Make sure, that you have

a working Xperia 2011 device

with stock ROM and stock kernel installed(if you install via PC Companion or SEUS)

and locked bootloader(if you install via PC Companion or SEUS).

Root access doesn't matter(according to current information), whether you have or not. It is lost after update anyway.

PC Companion and/or Update Service installed on your computer.

Drivers working for your phone.

Official update will only be available via PC Companion and Update Service. But you can also use Flashtool to install ICS.

15. Overclock/undervolt/underclock guide

Want to give your phone a small performance boost? Or save battery?

WARNING! The following is done fully under your own responsibility! Overclocking is a dangerous process and doing it without knowledge will end in FULL BRICK! Be careful with what you do and proceed only if you fully understand the process!

You need root, unlocked bootloader and custom kernel, that allows OC/UC/UV, installed.

Install app to edit the CPU, for example SetCPU, SetXperia, NoFrills CPU Control or another one.

Open the application on your phone.

CPU Frequency is the clock, how fast your CPU works. The faster it works, the more power it uses, more heat is generated, info is faster calculated.

CPU voltage is how much power the CPU receives. It can affect, how CPU works. Manufacturers set it to high enough for CPU to work properly. You can set it lower to save battery, however you might occur problems with your phone!

Search on internet for more information about overclocking to know more about it.

Do everything carefully, as a small mistake could result in serious problems(for example, FULL BRICK due to motherboard damage). Repairing can cost more than phone itself.