还君明珠双泪垂 苏笙:emerging micro optical finger navigation module embedded system development

Module 1 Introduction to Micro-optical finger navigation
Micro-optical finger navigation module, set the optical sensor measurements, micro-mechanical and digital / analog microelectronics in one, is highly miniaturized mechatronic machine input module, the core technology is the optical finger navigation OFN (Optical Finger Navigation), also known as single-finger navigation SFN (Single Finger Navigation), optical trackpad OTP (Optical Track Pad) or optical navigation touch key ONK (Optical Navigation Key). Different manufacturers have different titles, more recognized is the "optical finger navigation OFN".
Simply put, OFN module is highly miniaturized mouse.
1.1 Work
OFN module, usually by infrared LED light source, shading touch panels, optical lenses and a photosensitive array chip processing / control chips, usually made of flexible integrated application in the easy route FPC (Flexible Printing Circuit) board. Common OFNFPC, also integrates the surface button that said "Dome Array (Metal Dome Switch)", in order to achieve a simple "click OK" function.
OFN module works as follows: finger shading touch panel, the photosensitive array detected target activities, wake-up system on chip SoC into normal operation, infrared LED light to start the detection light path, through the optical lens group of the refraction and focusing, the photosensitive get scene after scene of the image array data; SoC abstraction from different motion vector MV (Motion Vector), then according to motion vectors in time and space correlation, calculated each time the plane relative to the amount of finger movement, the formation of motion data , and promptly through the data interface to transmit out. Fingers out, the photosensitive array by testing also enables SoC into sleep mode to save power.
Shading touch panel, need to be able to respond to light radiated interference and external humidity change.
Determine the correlation between exercise and the core of computing is OFN, usually follow a simplified optical mouse mature 13 points, 9 points, 7 or 5:00 motion estimation algorithm. Can also be a series of data for further analysis and calculation, by "click", "double", "drag" and other accompanying information, so as to realize the various functions of the traditional mouse.
OFN data generally includes the formation of two types: control information and motion information. Control information indicating whether the movement, click, double click, drag, etc., sports information that is X-plane direction and Y direction of relative displacement.
1.2 Technical characteristics
To sum up from the application point of view, OFN performance characteristics are as follows:
① ultra-thin ultra-small design. Typically, the shape of area 10 mm × 10 mm or less, the effective aperture of the light-sensitive 1.5 mm × 1.5 mm or less, the thickness of 2  8 ~ 5  1 mm, 2 mm thickness have OFN launch.
② low-power design. Operating current in 2 ~ 16 mA, typically 3 mA; standby current of 80 ~ 150 μA, most of the devices to 100 μA.
③ DC power requirements. 2.6 ~ 5.0 V range, commonly used for the 2.8 V operating voltage, are moving adaptive, lower power supply development.
④ a flexible multi-interface support. By conventional digital interface I2C (InterIntegrated Circuit) or SPI (Serial Peripheral Interface) or accept the host configuration data upload, there are PS2 mouse port or USB interface; can interrupt at any time to the host prompts for information input; can be reset and Switch the form to accept the host unified.
⑤ optional or adaptive resolution of the photosensitive array, 200 ~ 1250 CPI (Dots Per Inch) is usually 800CPI.
⑥ displacement data set. Usually 8-bit complement format.
⑦ excellent EMC / EMI design, 2 kV or more of the ESD (ElectroStatic Discharge) capability.
1.3 Product applications
OFN, once launched, to be applied rapidly, especially in a wide range of mobile phones, whether it is cheaper feature phones (feature phone) or high-performance 3G (3rd  Generation) smart phones (smart phone), both the Nucleus MTK , ThreadX  rapid development, Symbian system or Windows Mobile, ARMLinux / Android, MACOSXiPhone system, such as Samsung's i329/728/780/788/908/8510, Nokia's E72/N900, BlackBerry's 8520/9700, LG's ks500 / kt500, SonyEricsson's X1/X2/X3, Sharp's SH8020C, ZTE's X60, and many others.
In addition, MID (Mobile Internet Devices) / MPC (Multimedia Personal Computer) / Internet, GPS navigation, PMP (Portable Media Player) entertainment, digital camera / video camera and other popular products, are constantly being widely used. Do not focus on cost and power consumption of the industrial and agricultural considering process control, instrumentation equipment, and other industries, is also quietly extended the application of OFN.
OFN spectacular prospect, needs to promote the application of the OFN, applications for the continuous improvement of the development of OFN.
2 Development of micro-optical finger navigation module
2.1 Application of the device selection
Many semiconductor companies OFN components and modules for the R & D and production, such as Avago's ABDSA320, ST's VD5376, ATLab the ATA2188MOF and MOA devices and FO1R/FO3R/SMID/AP33M2I/P module, CrucialTec the CT01 ~ 27 series of modules, Apexone's A2815 device and AMF813 module, Mitsumi's SFN11LE and SFN11GU and so on. It is particularly worth mentioning is SFN11GU, ultra-thin module has reached 2 mm. Many Opto Semiconductors devices using the existing production of different specifications of OFN OFN module products, such as Côte Communications, Century ISSI, HPB optoelectronics.
Select OFN components or modules, the main factors to consider are: physical size, power consumption, power supply and hardware interfaces. Physical aspects are more concerned about the thickness, the thinner the more suitable for portable consumer products, of course, the higher the cost will be. Portable consumer product applications, with particular emphasis physical, power, and power supply, usually form small, work and standby current is small and can lower voltage power supply devices or modules OFN more popular. Agricultural and industrial process control, instrumentation equipment, industrial applications, the more consideration is OFN components or modules of the stable and efficient, convenient connections and EMI / EMC / ESD capability.
The focus here OFN explain complex features finger touch navigation and real-time detection is OFN and displacement of the basic functions of a compound derived therefrom, OFN features include: click, double click, drag, scroll, flip, roll screens. OFN devices commonly used, only the basic navigation functions. Suitable for commonly used "click OK" needs to form OFN module, often under the FPC with tiny "Guozi film" mechanical keys, has been able to meet most applications, and very economical. Some OFN, then directly to the commonly used click, double click, drag and other simple integration of complex functions within the device, to scroll, flip, roll screens and other sophisticated features designed to regulate the complex API library for device or mode OFN group of users in specific applications the upper free on-demand software to add, CrucialTec OFN some CTxx series modules is the case.
2.2 Hardware system design
The introduction of embedded systems OFN, hardware circuit design needs to be done:
① digital I / O interface connection, the main consideration three aspects.
◆ I / O interfaces. Increase 10 ~ 50 Ω current limiting resistor be achieved, especially in the case of different voltage specifications.
◆ EMI suppression. Ceramic capacitor can be constituted with the current limiting resistor simple RC filter circuit to be realized.
◆ drive capability enhancements. Simple pull-up resistor can be realized.
② Power supply noise reduction filter can use tantalum capacitors and ceramic capacitors, simple to implement.
2.3 Software System Design
OFN module, as a new micro-machine interface device input, and is usually the identity of chip equipment, added to the various types of embedded microprocessor core application systems, embedded microprocessor software system must OFN modules to achieve a timely manner from the driver to get various information from the OFN.
OFN driver module includes three parts: the initial configuration, process change control and data send and receive transmissions. OFN photosensitive completed the initial configuration resolution, sleep mode, continuous interruption interval setting other items, if not the initial configuration, OFN press the default configuration. Change control process for the host of the OFN switch, reset the control parameters and its work. Send and receive data transmission is OFN conventional behavior, as long as your fingers touch, OFN a certain time interval will be interrupted in the form of notification by the host system. Can be used in real-time interrupt or query to retrieve from the OFN finger touch input information. Queries often need to use the cycle timer, the timer interrupt OFN query and obtain the necessary data. This layer sense, the way they are a class of query interrupt. External events can interrupt the host or the timer interrupt service, through I2C or SPI bus operation, the necessary OFN detection information.
OFN by detecting low-level drivers get information, there is no embedded operating system for EOS (Embedded Operatig System) software system directly, or such as RTX, μC / OSII embedded real-time operating systems such as micro-ERTOS (Embedded Real Time Operating System) of host system, the upper application directly to the on-screen instructions, operating control, or data storage, forwarding and other activities, mainly for agricultural and industrial process control, instrumentation equipment, improved device performance test applications such circumstances. For Nucleus MTK, ThreadX development fast, Symbian, Windows CE / Mobile, ARMLinux / Android, MACOSXiPhone, VxWorks and other typical EOS system of the host system and its application, but also information on OFN or control data encapsulation format in order to make the original The vast majority of the systematic application can be used directly, such as a mouse data packet format, packet format touch screen, direction, format and other key information. This information package or transform, the operation simple to implement directly in the driver to operate the complex is required at the application layer through the message queue communication or synchronization mechanism and other software to do "two pass" or "three pass" to be realized.
Software system with the EOS, OFN drivers need to follow the appropriate procedures for the preparation EOS utility driver, debugging, add / unloading requirements, such as Windows CE / Mobile, single / double, local / stream interface driver, dynamic library form, ARMLinux characters device drivers, dynamically add / unloading, VxWorks for I / O device drivers and so on. OFN driver is a common system transmitted human-computer interaction input information, the driver must be for the public. EOS drivers can be divided into specific driver or utility drivers into two categories, the public demanding the driver software, you need according to the specific characteristics and requirements of EOS, serious writing, debugging and testing.
3 Application of micro-optical finger navigation module Practice
Systems in various embedded applications development using OFN modules, hardware and software system design is the realization of OFN drivers, the key is OFN real-time data collection and public information under the specific formation of EOS. The following OFN for some of the most common application development and design practices, to articulate. Involving the I2C, SPI, UART, LCD (Liquid Crystal Display), timer (Timer), GPIO (General Port Input / Output) operations such as software drivers, limited space, this is no longer highlighted.
3.1 The industrial measurement and control / instrumentation equipment applications
Agricultural and industrial process control, instrumentation equipment, device performance testing and other software systems or micro ERTOS OFN under the application of external events can interrupt or timer queries the way, in its operation of the interrupt service routine I2C or SPI bus directly and efficiently OFN get the finger from the touch information and the on-screen instructions, operating control, or data storage, forwarding and other activities.
The following example code (see online version) shows the S3C2440 ARM926T microprocessor core module A2815 OFN platform performance test case. The interrupt service routine for I2C or SPI bus operation, finger-touch access to information, the LCD screen to the "mouse" in the form with the action shown, and through the UART interface to upload data to the PC.
3.2 Nucleus MTK mobile phone applications
MediaTek MediaTek launch a variety of styles feature phones to high price has a very high market share, and its core is ARM7EJS or ARM9EJS microprocessors, in MentorATI priority preemptive scheduling and rotation of the multi-tasking time slice ERTOS - Nucleus, based on the formation of a complete human-machine interface MMI (Man Machine Interface) application system, commonly known as "MTK". Nucleus MTK most cases can be managed by one level interrupt mechanism: low-level interrupt LISR (Lower ISR) → Advanced Interrupt HISR (High ISR) → interrupt tasking ISR (Interrupt Serve Routine). ISR can communicate with other tasks or synchronous interaction.
Nucleus MTK system does not support the mouse, but support for keyboard and touch screen operation, touch screen and comes down on the keyboard. Therefore, under the application of OFN Nucleus MTK module, need to OFN's "touch" information into a "direction of action" information, and then to the public broadcasting as the "direction keys" information, so as to most existing and future applications shared. Not be overlooked is the frequent need to achieve a high degree of information and slow OFN directional buttons reasonable match between, you can average filter algorithm and logic analysis for this purpose choice.
Note that, Nucleus MTK software system-level and grade are more stringent, between high and low levels in addition to communication, synchronization and information transfer, generally does not allow function calls to each other; the same time, to ensure the timeliness of interrupt response, should not interrupt service routine stay in for too much, so traditional device drivers and analytical processing needs on different levels, according to priorities, respectively, to be achieved.
Nucleus MTK accordance with the above specifications and OFN device drivers use the information mechanism, design OFN Nucleus MTK software application modules as follows: the definition of OFN specific message structure, format and distribution interrupt bus interface; real-time mobile information access OFN, choice treatment, packaging OFN message into packets, upload MMI application processing layer; MMI application processing layer unpacking analysis, transformed into the direction of the button "Press" and "release" message, then broadcast to the entire system. The key program development related to the following:
① basic settings. Constant increase in global operations MSG_ID_MMI_OFN_MOVE_REQ, defines the message structure OFN ofn_hdr_ind_struct {LOCAL_PARA_HDR, kal_uint8 Direction}, and the custom device driver in the system initialization file, add a call to the initialization function of OFN.
② the underlying driver design. Due to space limitations, this list only query timer interrupt I2C interface implementation.
③ Public Information form. The main program file in the upper MMITask.c add code.
3.3 Windows CE / Mobile applications
Windows CE / Mobile is an embedded system, especially smart phones, the widespread application of the EOS. Windows CE / Mobile in accordance with the "physical interrupt IRQ (Interrupt ReQuest) → logical interrupt SYSINTR (System Interrupt) → interrupt service thread IST (Interrupt Serve Thread)" The layers of mapping the interrupt handling, the device drivers to user mode under DLL (Dynamic Link Library) file exists, divided into local and stream interface driver, independence and double-layer drive, can be loaded automatically at boot time or dynamically loaded. The driver load at startup, you need to add a special configuration of the registry.
OFN characteristics of the decision module and its application in the Windows CE / Mobile, its driver should be designed to form independent local drive, and when the system starts automatically loaded. Windows CE / Mobile supports mouse operation, a mouse, the system defines the message structure can be used to simplify the OFN drivers. OFN module of Windows CE / Mobile software applications can be fully implemented in the driver interrupt service routine of writing and the configuration of the system registry to add a OFN module Windows CE / Mobile Driver key. The I2C bus interface, external interrupt event trigger module that OFN Windows CE / Mobile Driver concrete realization, for the ARM926T microprocessor core kernel S3C2440.
3.4 ARMLinux / Android Applications
ARMLinux / Android is an open-source, audio / video performance, network of powerful, easy to expand the development of EOS and its application system, once introduced to the portable mobile communications, micro notebook computers, has been widely used in many fields. The bottom number is based on the CortexA8/A9, ARM1176, ARM9EJS other core microprocessor. Linux device driver specification is under the device as a file operation, known as the "device file", the application is very convenient. The device driver is divided into character, block-based and network-based categories, the majority of embedded system peripherals or interfaces can be used as character device driver. Depending on the application characteristics, Linux all the input devices can be classified as a linked list data structure of the character buffer input subclass (Input), including mouse, keyboard, touch screen, etc., in which the mouse class driver (mousedev) architecture system is complete. ARMLinux / Android system, these features make the drive module OFN a lot of easy application development: the mouse class driver can follow the example of a way to quickly achieve OFN driver design. Linux drivers can be dynamically loaded, you can also load at startup; OFN equipment frequently, should choose to load at startup. Here to launch CortexA8 common core TI OMAP3530 processor platform as an example, the key code slightly - Editor's Note.
4 Conclusion
Optical finger navigation module, performance, highly integrated, low cost, small form, favored the system in embedded applications. Just follow all the specific characteristics of embedded application system, follow the various types of embedded system and its operating system-driven software development rules, and local conditions, specific conditions, can be seamlessly integrated into all existing embedded application software and hardware system, and expand into new embedded applications products. Steadily improved micro-optical finger navigation module, excellent prospects, and promote the human-machine interface of the far-reaching changes in the input and rapid development.LCD module distributors China, LCD module graphic