| Mobile High-Definition Link (MHL) is an audio and video interface for connecting smart phones, mobile video players, cameras and other mobile devices to high-definition televisions, projectors, monitors and other display devices. First, the MHL sender modulates the standard signal from three Transition Minimized Differential signal (TMDS) channels of High Definition Multimedia Interface (HDMI) or Digital Visual Interface (DVI) into one TMDS channel with speed up to three times.Then the MHL sender reuses a micro-USB interface which exists in most of current mobile devices to transmit video and image that stored in the mobile device to a large screen display device, to enhance the ability of people to share information. Compared with traditional audio and video interface, MHL has many advantages such as fewer connection pins and faster transmission speed than HDMI/DVI, and so on. However, due to the short time of the developmen, many MHL technologies are not yet mature.Video and image can be only transmitted from a mobile device to a display device.People can not control the mobile device from a display device. The display device just plays a role of expanding mobile device screen.In order to solve the problem mentioned above, a reverse control transfer system of MHL will be designed and researched in this paper. The system is connected to a smart phone via MHL at one end and connected to a display device through HDMI interface at the other end. Furthermore, there is a human-computer interaction(HCI) interface for the system to receive external information. Core processor of the system is in charge of parsesing information that receives from HCI interface. After completing, the parsed data is converted into a MHL protocol format and sended to smart phone through MHL control bus. When the smart phone receives the commands and data from the reverse control transfer system, it makes corresponding changes and transmits data to the display device through MHL data bus.So the system can achieve the purpose of controlling a smart phone from a display device via MHLThe reverse control transfer system of MHL includes both hardware and software parts.The hardware part contains a ARM processor, a HCI interface and a power management unit. The ARM processor is used as the system’s central control unit. The HCI interface adopts keyboard and mouse that used in people’s daily office life as information input system. The mouse and keyboard system contains two parts of wired and wireless.The wired part uses a USB interface as a solution while bluetooth technology is adopted to realize the wireless part. Power management unit is primarily in charge of the smart charging for a smart phone and power management for the entire system. Software part of the system is based on Linux operating system.It is divided into two parts:device driver and application software. Device driver drives hardware directly, shields details of hardware implementation, and provides software interfaces to application software. Application software is responsible for the protocol parsing and transformation, and the realization of the power management strategy. It receives data that comes from device driver and send back when the data is processed.Device driver is install to Linux operating system as module, Linux will schedule it in appropriate time as information comes from application software.The last part of this paper is the test of the reverse control transfer system. Test results show that when a smart phone accesses to the system, the system works properly and can charge the smart phone.If the smart phone is in a state of playing video, through the mouse and keyboard we can make it stop, play, fast forward, rewind and so on. When disconnected smart phones from reverse control transfer system, the system turns to a low power state. |
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