Android硬件抽象层（HAL）概要介绍和学习计划

很精练的android系统开发介绍

http://blog.csdn.net/luoshengyang/article/details/6567257

摘要如下：

app（java）

通过IService.Stub使用service提供的接口

	import android.os.IHelloService; 
	
	private IHelloService helloService;
	helloService = IHelloService.Stub.asInterface(ServiceManager.getService("hello"));
	
	helloService.setVal(val);

"hello"：            系统启动时加载HelloService时指定
IHelloService.Stub   IHelloService.aidl生成

framework service（java）（基于AIDL）

对上：提供java接口，注册service服务
对下：调用jni提供的native接口

frameworks/base/core/java/android/os

IHelloService.aidl：生成IHelloService.Stub

	interface IHelloService {  
		void setVal(int val);  
		int getVal();  
	}

frameworks/base/services/java/com/android/server

HelloService.java：实现java接口到nativa接口转换

			public class HelloService extends IHelloService.Stub {
				HelloService() {  
					init_native();  
				}  
				public void setVal(int val) {  
					setVal_native(val);  
				}     
				public int getVal() {  
					return getVal_native();  
				}  
				  
				private static native boolean init_native();  
				private static native void setVal_native(int val);  
				private static native int getVal_native();  
			};  

SystemServer.java：增加加载HelloService的代码

			ServiceManager.addService("hello", new HelloService());

framework JNI接口（c++）（基于JNI）

对上：实现、注册native接口，实现java环境变量转换
对下：调用HAL接口

frameworks/base/services/jni
com_android_server_HelloService.cpp：对应com.android.server.HelloService
java接口的本地实现（基于HAL接口）；jni注册；java变量转换

	namespace android  
	{  
		struct hello_device_t* hello_device = NULL;  
		static void hello_setVal(JNIEnv* env, jobject clazz, jint value) {  
			hello_device->set_val(hello_device, val);  
		}  
		static jint hello_getVal(JNIEnv* env, jobject clazz) {  
			hello_device->get_val(hello_device, &val);  
		}  
		static inline int hello_device_open(const hw_module_t* module, struct hello_device_t** device) {  
			return module->methods->open(module, HELLO_HARDWARE_MODULE_ID, (struct hw_device_t**)device);  
		}  
		static jboolean hello_init(JNIEnv* env, jclass clazz) {  
			hello_module_t* module;  
			if(hw_get_module(HELLO_HARDWARE_MODULE_ID, (const struct hw_module_t**)&module) == 0) {  
				if(hello_device_open(&(module->common), &hello_device) == 0) {  
		<span style="white-space:pre">	</span>	}  
	<span style="white-space:pre">	</span>	}  
		}  


		static const JNINativeMethod method_table[] = {  
			{"init_native", "()Z", (void*)hello_init},  
			{"setVal_native", "(I)V", (void*)hello_setVal},  
			{"getVal_native", "()I", (void*)hello_getVal},  
		};  


		int register_android_server_HelloService(JNIEnv *env) {  
			return jniRegisterNativeMethods(env, "com/android/server/HelloService", method_table, NELEM(method_table));  
		}  
	};  

HAL接口（c）（基于android HAL框架）

对上：实现驱动隔离（用户控件）
对下：调用驱动

hardware/libhardware/include/hardware
struct hw_module_t common
struct hw_device_t common

hardware/libhardware/modules
struct hello_module_t HAL_MODULE_INFO_SYM静态定义
hello_device_open动态设置struct hello_device_t