Overall analysis of Android startup
1. The overall architecture of the Android system
Android is a Linux-based open source operating system developed by Google
PowerManagement: The bottom layer of the system is power management. Only when the power is turned on, the system can be turned on
Linux kernel: The driver layer, which includes drivers for various peripherals such as Audio, Carmera, and usb.
HAL layer: Hardware abstraction layer , HAL is an abstraction layer with a standard interface for hardware vendors to implement.
The Hardware Abstraction Layer (HAL) provides a standard interface that exposes device hardware capabilities to higher-level Java API frameworks. The HAL consists of several library modules, each of which implements an interface to a specific type of hardware component, such as a camera or a Bluetooth module. When a framework API requires access to device hardware, the Android system loads library modules for that hardware component.
Android Runtime: (ART) The Java runtime environment provided by AOSP. ART translates an application's bytecode into processor-specific instructions, which are executed by the device's runtime environment.
For devices running Android 5.0 (API level 21) or higher, each app runs in its own process and has its own instance of the Android Runtime (ART). ART is written to run multiple virtual machines on low-memory devices by executing DEX files, a bytecode format designed for Android that is optimized to use very little memory. A compilation toolchain (such as Jack) compiles Java source code to DE