How to start Android Kernel programming?

I have 6 months experience with Android, developing simple UI-based applications. Now I want to write applications targeting the Android core Kernel. For example, I want to develop a framework which is not present in Android. To achieve that, we have to write the code for the Kernel. I don't know where and how to start Android Kernel programming.

If anybody knows the way to start it please help me.

• http://www.xda-developers.com/">xda-developers</a><br />A very awesome and very active place for anything smart smart phone related.
• http://kernelnewbies.org/">kernelnewbies</a><br /> Generally good resource for starting out learning linux kernel
  (Which is what the android is built off of)
• http://source.android.com/source/building-kernels.html">Building Android Kernel
  Android Kernel Source
  
• http://lwn.net/Kernel/LDD3/">Linux kernel
  Online guide to driver development among many other related topics.
  

Update

For android source code you can check out one of the following...

https://stackoverflow.com/questions/7669329/since-android-git-kernel-org-is-down-where-do-i-get-source-code-for-android">or this question

http://source.android.com/source/downloading.html">or source.android.com

I personally dig https://chrome.google.com/webstore/detail/android-sdk-search/hgcbffeicehlpmgmnhnkjbjoldkfhoin">this chrome plugin for browsing android source code.

If you are talking about platform level programming,i.e. framework extensions, native libraries and services there are a few places to start. The first one is the new and updated official open source project page. The portions about contributing and porting provide some basic information on the platform architecture and what you need to work with the platform. The next step is to understand the build system for the platform and framework. There are some limited info available on the net if you google for it. The best way is probably to study some of the makefile templates available in the open source project in the build folder. For info on how to add your own modules using Android.mk files it is a good thing to study make files for existing projects such as the ones available in external in the open source projects.

Once you have gotten as far as the above. That is you know the basics of platform level development and how to build your own modules for the platform the next step is to study the framework extension example available in the open source project. Check out the vendor/sample/PlatformLibrary folder (edit, as of 2.2 the vendor stuff has moved to the device folder) in the open source project and read the readme file, study the code, build it and make sure you understand it. If you don't then JNI, shared libraries, the platform security model and the core framework are areas that could help you out.

I guess that since you are talking about kernel programming you are also looking for ways to hook up new hardware with the platform and expose that functionality using your framework extensions to the applications. Hardware is basically added as a standard Linux driver so getting it to work under Linux is a good first step. How to hook it into the Android framework after that depends on what type of hardware it is. You could either use a native process to control it (compare the camera service or radio daemon in the current platform) or just spawn a thread in the application that uses your framework extension. For hardware that does not require that much attention plugging it in using an Android HAL library could also be an option.

I hope that provides some initial pointers on where to look. The official mailing lists are otherwise the main source of info about platform level development. Especially Android porting and Android platform.

You should also check out http://pdk.android.com. I just found this site recently and it is extremely useful. I wish I knew about it sooner. I'm not sure how dedicated Google is to updating the site because as BMB mentioned the vendor stuff was moved to the device folder in 2.2 but there have been no changes to the PDK site to reflect that. Also, some of the links don't work but I was able to find all the pages by doing a site search in Google.