| USB(universal serial bus) is the serial bus with the merits of data dependable transaction, convenience of extension and low cost solution, which can realize the Plug&Play connection for PC peripherals. Meanwhile it is now moving into the embedded field widely. The system of USB HOST in this paper is designed to the application of embedded system, broadening the field of microprocessor application.The system of USB HOST designed in the paper can support the communication between USB memory device and SEP3203 GARFIELD which is a microprocessor developed using an ARM7TDMI core and including the following component EMI, INTC, TIMER, GPIO and so on. The EPSON S1R72005 is selected as the main controller of USB HOST module, which connects to the EMI, one of the SEP3203 GARFIELD' s module. And the interrupt service of USB HOST is handled via GPIO.The scheme of hardware design is firstly solved by the analysis of implementation of SEP3203 GARFIELD and EPSON S1R72005 based on USB protocol. As to the software, the FAT16 file system is supported using the platform of ASIX OS real-time operation system in view of frequent communication in lite mass-storage USB memory device. Then the system of software driver is presented through the reference of Linux USB subsystem, and the code of USBD layer and HCD layer is described in detail. In the last the flow of implementation for software code is expatiated. Since the control transmission and bulk transmission are in common use in USB mass-storage devices, the system of software in USB HOST in this paper was simplified for the improvement of performance in data transmission.The USB system designed in the paper is working stably under the ASIX OS real-time operation system on hardware platform constituted by SEP3203 GARFIELD and EPSON S1R72005, which makes communication with USB mass-storage device, including recognition of Plug&Pull, emulation of device, loading driver, creation of directory, data read / write and so on for USB mass-storage device. |
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