Development Of The Embedded System With USB Host Interface

In PC filed, the USB interface has already become one of the universal device interfaces. It has got very broad application and development. At the same time, in embedded system filed, with the actualization of the digital home concept and the development of the digital information home appliances, consumer electronic products and communication electronic products have become the tow main kinds of embedded products. People hope that these embedded products can operate mutually and share content with each other. Besides, they can make full use of the available USB devices to shake off PC. Consequently, satisfy people's demand to the mobile and portable feature of the data exchange. That proves that the embedded USB host technology will be one of the very reasonable schemes. It is the developing trend of USB interface.The embedded USB host technology is to introduce USB host controller into embedded products in order to make them able to communicate with all kinds of USB devices, such as USB mouse, USB keypad, USB storage etc, just like PC. In recent years, with the rapid development of semiconductor technology, the bus width, working frequency and arithmetic ability have got incessant improvement. The bus width has got 64 bits. The working frequency has got 1 GHz. Not only that, the embedded processor is developing towards multi-core and multi-thread direction. That will make the embedded processor more and more power. Simultaneously, in company with the development of the IC manufacture technology and the popularization of USB, many chip manufacture companies have produced out the USB host controller chip, such as Philips'ISP1161A1. These progresses provide the fine hardware base for the embedded USB host technology. In software aspect, the rapid development of the embedded operation system relieves the difficulty of developing the embedded USB host controller driver to a great extent. Take Linux OS as example. Linux OS has included the USB Core subsystem since version 2.4 and supports USB host controller driver. Therefore, it is time to develop the embedded system with USB host interface. The software and hardware environment is fine.This embedded system adopts the Intel PXA255 processor as the core of the hardware system. PXA255 is designed for the multi-media communication .Its bus width is 32 bits. Its working frequency can reach 400 MHz. Besides, it has manykinds of device interface. In order to satisfy application demand, the following function modules are extend, including Flash & SDRAM Storage Module, Ethernet Communication Module, USB Host Interface Module, LCD Display Module, Audio I/O Module, Touch Screen Module, JTAG Download Module and 232 Serial Communication Module. Among these modules, the Flash Storage Module contains two chips of Intel'E28F128J3A-150 to construct 32MB flash storage space. The SDRAM Storage Module is made up of two chips of Samsung's K4S181632C to construct 64MB memory space. The Ethernet Communication Module adopts CS8900A as 10M Ethernet controller. The CS8900A realizes the MAC with hardware to save processor resource. The USB Host Interface Module adopts Philips'ISP1161A1 as the USB host controller. ISP1161A1 integrates one USB host controller and one device controller on a chip. Its host controller accords with USB2.0 and supports full speed (12Mb/s) and low speed (1.5Mb/s). In addition, it supports PIO (Programmable Input Output) mode to interface with the embedded processor conveniently. The LCD Display Module contains one TFT LCD with 640x480 pixel which interfaces with PXA255's LCD controller. The Audio I/O Module is made up of CS4297A audio codec and PXA255's AC97 controller unit. The Touch Screen Module adopts ADS7843 to construct touch screen input circuit.After researching on the circuit principle of every function module, this design makes use of Protel 99 SE CAD software to finish the schematic design and PCB (Printing Circuit Board) design of this embedded system hardware platform. Finally, finish this embedded system development board through board fabrication and surface mounting.This embedded system adopts Linux2.4.18 as the EOS (Embedded Operation System). Linux is organized with layer structure and opens its source code. Its network is power. And it supports many kinds of file system and can operation on many kinds of embedded processor, including PXA255 processor. Besides, this system uses U-boot1.1.2 as the boot loader and makes JFFS2 (Journaling Flash File System) to be root file system. In software development, NFS (Network File System) is used to share file with PC. The above parts construct the basic embedded system software platform for software development and debug.USB (Universal Serial Bus) is a device interface standard published by Intel, Microsoft, Compaq, IBM, NEC etc. USB has many features, such as low-powerconsumption, plug & play, multi-kind transfer mod, bus power, tri-kind data transfer speed etc. So USB is applied very broadly. By now the number of available USB device has been more than 100 million. Because USB protocol does get the simplification and universalization of hardware through the complexity of software, so research on USB protocol is necessary for developing the embedded USB host. This design explains the following content in detail.⑴The data packet format in USB, transaction and transfer;⑵The concept of endpoint, pipe, interface and setup in USB device. The data transfer flow between USB host and USB device;⑶The structure and definition of the standard descriptors;⑷The functions of USB host controller and the software structure in USB host.This design adopts ISP1161A1 as the USB host controller and makes the Linux2.4.18 to be the EOS. By researching on the USB subsystem in Linux2.4.18 and the transfer flow of URB, find out and explain the API for HCD (Host Controller Driver). Make the structure of HCD clear. Developed the ISP1161A1 hardware initialization module, register reading/write module, USB Core interface API, interrupt handling module, data transfer handling module and root hub module by studying ISP1161A1. Consequently finish the ISP1161A1 host controller driver. Finally, register the driver into the Linux2.4.18 kernel and finish the USB host interface design to make this embedded system platform have USB interface function.The testing indicates that the embedded system works stably. The bus frequency can reach 100MHz and can play audio and video simultaneously. Besides, the system can interface with USB storage, USB keypad and OV2000 USB camera and work well. The system can be applied in the occasion where the USB host interface is necessary. And it is able to communication with the available USB device in order to expand its function. Therefore, the system has the very good application prospect.