In this chapter, we used U-Boot to demonstrate two scenarios for operating system boot-up. First, we booted Android from NOR flash using U-Boot. Even though the Android emulator doesn’t have NOR flash, we created an image to simulate it. Second, we booted Android from NAND flash. In this case, we put the kernel and RAMDISK images inside system.img and used U-Boot to boot the system.
We can build almost everything on our own to boot the Android system, except RAMDISK and the file system. To make our own RAMDISK and file system, we hacked them from the Android SDK. In next two chapters, we will go even further; that is, we will explore how to build everything, including the Android file system, from source code.