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Since the launch of the , we have received a lot of really great feedback. The Sony Ericsson Developer Program wants to continue to build on this open dialogue with external developers.
Developers and advanced users can now unlock the boot loader, which is the first step to be able to flash your own image. Now we have seen quite a few comments in different forums like the XDA forum, where developers run into problems when building their own image, and and trying to flash the image using Fastboot. With the help of our Master Software Architect, James Jacobsson, we put together a short article on how to do this.
Before moving on, we’d like to remind you again that there is no turning back when unlocking the boot loader. You may void the warranty of the phone, and you will not be able to revert the phone to a locked or original state if you unlock it.
What is the Linux kernel? The Xperia™ line of smartphones run on the Android™, the mobile operating system based on the Linux kernel. Though it is only a small part of the operating system, the kernel ensures that all other processes in the system are synchronized to work together properly.
Why rebuild the kernel? Rebuilding the kernel enables end users to make modifications to their devices that are normally not intended by the device manufacturer, such as theming the device by changing system icons and removing/modifying system components. Please note that Sony Ericsson is not recommending this.
Considerations before building your own kernel and reflashing your device As mentioned in the beginning of this article, the first step is to unlock the boot loader. When the boot loader is unlocked, the sensitive data is removed, such as DRM certificates, and the user partition of the file system is wiped out. But all other functionality, such as the camera and other drivers, is left intact. Please note that content, like music files, that require the DRM certificate will not be accessible any more. But most importantly, you may void the warranty of your phone if you decide to unlock it. Aside from the considerations mentioned above, the functionality is there, just waiting for you to take advantage of it. So, if you’re ready, here’s how to get started.
Building the kernel It takes a few main steps to build the kernel. Below we’ll show you how to build a Linux kernel and flash it onto the device.
Step A – Download the necessary software Download the following software to get started:
Step B – Building the kernel To build the kernel, you first need to unpack the kernel. Once you’ve unpacked the kernel, you need to configure it, and then build it. The example below is based on you using the file called 3.0.A.2.181_182.tar.bz2.
1. Go into the kernel directory:
cd kernel2. Configure the kernel:
ARCH=arm CROSS_COMPILE=/opt/arm-2010q1/bin/arm-none-eabi- make semc_zeus_defconfigNote: Replace:
/opt/arm-2010q1with where you installed your cross-compiler. Also, this example is for Xperia™ PLAY. Replace:
defconfigwith the following values depending on what device you want to configure it for:
Xperia™ PLAY | semc_zeus_defconfig |
Xperia™ arc | semc_anzu_defconfig |
Xperia™ neo | semc_hallon_defconfig |
3. Build the kernel:
ARCH=arm CROSS_COMPILE=/opt/arm-2010q1/bin/arm-none-eabi- makeReplace:
/opt/arm-2010q1with where you installed your cross-compiler. Once done, you should have a compressed kernel-image in arch/arm/boot/zImage.
Step C – Getting a RAM disk The RAM disk is the initial filesystem the kernel will mount before transferring control to userspace. How you create your own root filesystem is beyond the scope of this article, but you can use the following instructions to pack/unpack the file.
Unpacking (you have ramdisk.img, and want to create a directory of files out of it):
gzip -d - < ramdisk.img > cpio -idmPacking (You have directory of files, and want to create ramdisk.img from it):
find . | cpio --quiet -H newc -o | gzip > ramdisk.imgStep D – Assembling the boot.img Now that we have all the parts we need to create a flashable file. The next stop is to package the parts. To do this, you’ll need the program mkbootimg, which is part of the standard Android tree. If you don’t feel like compiling all of Android to get this tool, it is available to download from various trusted sites on the Internet.
Once you have the tool, this is the command to combine your kernel and RAM disk into a flashable file:
mkbootimg --base 0x00200000 --kernel kernel/arch/arm/boot/zImage --ramdisk ramdisk.img -o boot.imgStep E – Flashing the file You should flash the file using Fastboot. If you’ve unlocked the boot loader on your device, you already have Fastboot.
1. To flash the boot.img file, use the following the command:
fastboot –i 0x0fce flash boot boot.img2. Now, it will prompt you to connect your device. To do so, follow these simple steps:
3. As a last step in the process, you need to reboot the device. You can either remove the USB cable and battery to power the device down. If you prefer, you can instead issue the following command (either method will work):
fastboot –i 0x0fce rebootImportant information! Sony Ericsson does not guarantee any support on this, but we will monitor the thread on the XDA Developers forum. However, we cannot guarantee an answer for every question asked in this forum.
Additional information for experienced Linux kernel experts The kernel is pretty standard, all the regular things you’re used to is there, and available to use. Things that are different are the memory config and the kernel commandline. The memory config is hardcoded (i.e., ATAGs aren’t used for this). It’s set in the board-file for your target, such as kernel/arch/arm/mach-msm/board-semc_zeus.c in the function msm7x30_fixup. The kernel commandline is also not fetched from the boot.img file, but compiled into the kernel (CONFIG_CMDLINE). Some arguments are also added from the boot loader.
Additional information if porting non-Linux format files to the device The boot loader will accept any reasonably formatted boot.img file. For example, at the , you will see the format of the boot.img file. This allows you to create a boot.img file containing two loadable files (kernel+ramdisk), which will get loaded into RAM. Once the boot loader is loaded, it passes the control to the first instruction of the loaded kernel image. After control is passed, the kernel can rely on the data contained in the RAM disk already being loaded.
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