android usb相关知识总结

转载请注明出处：http://blog.csdn.net/droyon/article/details/45098027

1、android背景介绍

UsbService，在系统启动时创建，在该文件中，和usb状态息息相关的操作类是UsbDeviceManager，大部分的usb以及adb相关的逻辑，在这个类中做处理。UsbDeviceManager中，我们需要关注三部分内容。一、配置文件。二、  private final UEventObserver mUEventObserver = new UEventObserver() ，接受UEvent事件。三、UsbHandler。

其中配置文件，保存当前usb状态。UEventObserver接受usb事件，push给UsbHandler来处理。UsbHandler是用来处理Usb事件的关键类。

2、Usb默认状态从哪里获取，当前的默认状态又是什么？

Usb的当前状态保存在mCurrentFunctions成员变量中，该变量在UsbHandler的构造中进行初始化。

mDefaultFunctions = SystemProperties.get("persist.sys.usb.config", "adb");

                // Check if USB mode needs to be overridden depending on OEM specific bootmode.
                mDefaultFunctions = processOemUsbOverride(mDefaultFunctions);

                // sanity check the sys.usb.config system property
                // this may be necessary if we crashed while switching USB configurations
                String config = SystemProperties.get("sys.usb.config", "none");
                if (!config.equals(mDefaultFunctions)) {
                    Slog.w(TAG, "resetting config to persistent property: " + mDefaultFunctions);
                    SystemProperties.set("sys.usb.config", mDefaultFunctions);
                }

                mCurrentFunctions = mDefaultFunctions;

3、插入usb时，弹出adb以及Notification通知的大体流程是什么？

插入usb时，我们的UEventObserver会收到信息，最终push给UsbHandler。

UEvent信息：

04-17 14:20:03.352 V/UsbDeviceManager(  759): USB UEVENT: {USB_STATE=DISCONNECTED, SUBSYSTEM=android_usb, SEQNUM=7528, ACTION=change, DEVPATH=/devices/virtual/android_usb/android0}

private final UEventObserver mUEventObserver = new UEventObserver() {
        @Override
        public void onUEvent(UEventObserver.UEvent event) {
            if (DEBUG) Slog.v(TAG, "USB UEVENT: " + event.toString());

            String state = event.get("USB_STATE");
            String accessory = event.get("ACCESSORY");
            if (state != null) {
                mHandler.updateState(state);
            } else if ("START".equals(accessory)) {
                if (DEBUG) Slog.d(TAG, "got accessory start");
                startAccessoryMode();
            }
        }
    };

updateState方法：更新mConnection状态。

public void updateState(String state) {
            int connected, configured;

            if ("DISCONNECTED".equals(state)) {
                connected = 0;
                configured = 0;
            } else if ("CONNECTED".equals(state)) {
                connected = 1;
                configured = 0;
            } else if ("CONFIGURED".equals(state)) {
                connected = 1;
                configured = 1;
            } else {
                Slog.e(TAG, "unknown state " + state);
                return;
            }
            removeMessages(MSG_UPDATE_STATE);
            Message msg = Message.obtain(this, MSG_UPDATE_STATE);
            msg.arg1 = connected;
            msg.arg2 = configured;
            // debounce disconnects to avoid problems bringing up USB tethering
            sendMessageDelayed(msg, (connected == 0) ? UPDATE_DELAY : 0);
        }

case MSG_UPDATE_STATE:
                    mConnected = (msg.arg1 == 1);
                    mConfigured = (msg.arg2 == 1);
                    updateUsbNotification();
                    updateAdbNotification();
                    if (containsFunction(mCurrentFunctions,
                            UsbManager.USB_FUNCTION_ACCESSORY)) {
                        updateCurrentAccessory();
                    } else if (!mConnected) {
                        // restore defaults when USB is disconnected
                        setEnabledFunctions(mDefaultFunctions, false);
                    }
                    if (mBootCompleted) {
                        updateUsbState();
                        updateAudioSourceFunction();
                    }
                    break;

public static final String USB_FUNCTION_MASS_STORAGE = "mass_storage";

    /**
     * Name of the adb USB function.
     * Used in extras for the {@link #ACTION_USB_STATE} broadcast
     *
     * {@hide}
     */
    public static final String USB_FUNCTION_ADB = "adb";

    /**
     * Name of the RNDIS ethernet USB function.
     * Used in extras for the {@link #ACTION_USB_STATE} broadcast
     *
     * {@hide}
     */
    public static final String USB_FUNCTION_RNDIS = "rndis";

    /**
     * Name of the MTP USB function.
     * Used in extras for the {@link #ACTION_USB_STATE} broadcast
     *
     * {@hide}
     */
    public static final String USB_FUNCTION_MTP = "mtp";

    /**
     * Name of the PTP USB function.
     * Used in extras for the {@link #ACTION_USB_STATE} broadcast
     *
     * {@hide}
     */
    public static final String USB_FUNCTION_PTP = "ptp";

    /**
     * Name of the CHARGING USB function.
     * Used in extras for the {@link #ACTION_USB_STATE} broadcast
     *
     * {@hide}
     */
    public static final String USB_FUNCTION_CHARGING = "charging";

    /**
     * Name of the audio source USB function.
     * Used in extras for the {@link #ACTION_USB_STATE} broadcast
     *
     * {@hide}
     */
    public static final String USB_FUNCTION_AUDIO_SOURCE = "audio_source";

    /**
     * Name of the Accessory USB function.
     * Used in extras for the {@link #ACTION_USB_STATE} broadcast
     *
     * {@hide}
     */
    public static final String USB_FUNCTION_ACCESSORY = "accessory";

上层能够设定usb类型的类名叫做：UsbSettings，在其中，用户可以设定当前UsbSettings状态为mtp、ptp以及厂商定义的其他usb状态。

在用户操作时，会调用mUsbManager.setCurrentFunction(function, true);

tring function = USB_FUNCTION_DEFAULT;
        if (preference == mMtp && mMtp.isChecked()) {
            function = UsbManager.USB_FUNCTION_MTP;
        } else if (preference == mPtp && mPtp.isChecked()) {
            function = UsbManager.USB_FUNCTION_PTP;
        } else if (preference == mCharging && mCharging.isChecked()) {
            function = UsbManager.USB_FUNCTION_CHARGING;
        } else if (preference == mSDCard && mSDCard.isChecked()) {
            function = UsbManager.USB_FUNCTION_MASS_STORAGE;
        }

        operateInprogress = true;
        mUsbManager.setCurrentFunction(function, true);
        updateToggles(function);

UsbService.java

@Override
    public void setCurrentFunction(String function, boolean makeDefault) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.MANAGE_USB, null);

        // If attempt to change USB function while file transfer is restricted, ensure that
        // the current function is set to "none", and return.
        UserManager userManager = (UserManager) mContext.getSystemService(Context.USER_SERVICE);
        if (userManager.hasUserRestriction(UserManager.DISALLOW_USB_FILE_TRANSFER)) {
            if (mDeviceManager != null) mDeviceManager.setCurrentFunctions("none", false);
            return;
        }

        if (mDeviceManager != null) {
            mDeviceManager.setCurrentFunctions(function, makeDefault);
        } else {
            throw new IllegalStateException("USB device mode not supported");
        }
    }