一、Android源码分析

在Android 系统源码中，服务的启动都是通过 SystemServer.java 这个类实现的。

1、源码位置：

2、源码部分展示：

(1)SystemServer.java (run())

private void run() {
......
// Start services.
try {
    startBootstrapServices();
    startCoreServices();
    startOtherServices();
} catch (Throwable ex) {
    Slog.e("System", "******************************************");
    Slog.e("System", "************ Failure starting system services", ex);
    throw ex;
}
......
}

通过这部分源码，我们发现，系统服务分为了三类，下边我们一一分析。

(2)startBootstrapService()

private void startBootstrapServices() {
    // Wait for installd to finish starting up so that it has a chance to
    // create critical directories such as /data/user with the appropriate
    // permissions.  We need this to complete before we initialize other services.
    Installer installer = mSystemServiceManager.startService(Installer.class);

    // Activity manager runs the show.
    mActivityManagerService = mSystemServiceManager.startService(
            ActivityManagerService.Lifecycle.class).getService();
    mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
    mActivityManagerService.setInstaller(installer);

    // Display manager is needed to provide display metrics before package manager
    // starts up.
    mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class);

    // Power manager needs to be started early because other services need it.
    // Native daemons may be watching for it to be registered so it must be ready
    // to handle incoming binder calls immediately (including being able to verify
    // the permissions for those calls).
    mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);

    // Now that the power manager has been started, let the activity manager
    // initialize power management features.
    mActivityManagerService.initPowerManagement();

    // We need the default display before we can initialize the package manager.
    mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);

    // Only run "core" apps if we're encrypting the device.
    String cryptState = SystemProperties.get("vold.decrypt");
    if (ENCRYPTING_STATE.equals(cryptState)) {
        Slog.w(TAG, "Detected encryption in progress - only parsing core apps");
        mOnlyCore = true;
    } else if (ENCRYPTED_STATE.equals(cryptState)) {
        Slog.w(TAG, "Device encrypted - only parsing core apps");
        mOnlyCore = true;
    }

    // Start the package manager.
    Slog.i(TAG, "Package Manager");
    mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
            mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
    mFirstBoot = mPackageManagerService.isFirstBoot();
    mPackageManager = mSystemContext.getPackageManager();

    Slog.i(TAG, "User Service");
    ServiceManager.addService(Context.USER_SERVICE, UserManagerService.getInstance());

    // Initialize attribute cache used to cache resources from packages.
    AttributeCache.init(mSystemContext);

    // Set up the Application instance for the system process and get started.
    mActivityManagerService.setSystemProcess();
}

通过这部分源码，我们发现，该方法负责启动系统中最重要的几个服务，PKMS,PMS,AMS等。

(3)startCoreService()

/**
 * Starts some essential services that are not tangled up in the bootstrap process.
 */
private void startCoreServices() {
    // Manages LEDs and display backlight.
    mSystemServiceManager.startService(LightsService.class);

    // Tracks the battery level.  Requires LightService.
    mSystemServiceManager.startService(BatteryService.class);

    // Tracks application usage stats.
    mSystemServiceManager.startService(UsageStatsService.class);
    mActivityManagerService.setUsageStatsManager(
            LocalServices.getService(UsageStatsManagerInternal.class));
    // Update after UsageStatsService is available, needed before performBootDexOpt.
    mPackageManagerService.getUsageStatsIfNoPackageUsageInfo();

    // Tracks whether the updatable WebView is in a ready state and watches for update installs.
    mSystemServiceManager.startService(WebViewUpdateService.class);
}

通过注释我们可以看到，这些服务都是一些和系统引导，就是启动无关的一下服务。

(4)startOtherServices()

所以说，剩下的这个方法就是我们需要添加服务的地方了

                try {
                   Slog.i(TAG, "GPIO Service");
                   ServiceManager.addService("iServerGpio", new GpioService());
                } catch (Throwable e) {
                    Slog.e(TAG, "Failure starting GpioService", e);
                }

3、服务存放位置

那么，这个存放位置是确定的吗？其实不是的。看下图：

我们可以看到，我们只要在SystemServer.java 中正确引包就可以了，但是为了代码的整洁，还是按规矩来比较好。

二、实现方法

为了阅读方便，我们以GpioService 为例：

1、将服务放置到源码中

按照上边所示放到相应位置。

2、在SystemServer.java 中添加代码

(1)引包

(2)创建对象

(3)开启服务

           try {
                   Slog.i(TAG, "GPIO Service");
                   ServiceManager.addService("iServerGpio", new GpioService());
                } catch (Throwable e) {
                    Slog.e(TAG, "Failure starting GpioService", e);
                }

三、编译方法

具体编译方法，看RK3328-CC 官网，链接如下：
http://www.t-firefly.com/doc/product/info/id/252.html