Hal - General

HAL

what

android Hardware abstraction layer , Simply put, yes Linux Encapsulation of kernel driver , Interface up , Shield the details of the bottom layer . Hardware divides the support for hardware into two layers , On the first floor userspace, On the first floor kernel space, The hardware abstraction layer is in the user space , The kernel driver runs in kernel space .

why

The hardware abstraction layer and the kernel driver are integrated into the kernel space , From the perspective of technology implementation , Tolerable , From a business perspective ,Linux The kernel source code follows GNU License,Android Source code follows Apache License, When the former releases products , The source code must be published , The latter does not require the release of source code , If you put all the code supported by the hardware in Linux Driver layer , It means exposing the driver source code , It means that the relevant parameters and implementation of the hardware are disclosed , Harm the interests of businesses .

how

The learning process , Learn how to write hardware drivers in kernel space , How to add interfaces in the hardware driver layer to support access to hardware , How to provide hardware access services when the system starts , How to write jni Make it possible to pass through java Interface to access hardware and so on .