A Research And Realization Of USB Device Protocol Stack Based On Freescale MCU

Nowadays, more and more digital devices use USB as the interface to communicate with the HOST. We can see these devices around us from needing only to transmit small amount data devices, such as mouse, keyboard and so on,to needing to transmit large amount data devices, such as digital camera, digital video and any other storage devices.The USB Interface has almost been used in every type of computer peripheral.This is because of that USB specification is been perfected constantly and USB interface has many advantages. In the current USB application, PC always plays the role of USB Host, and the USB drive in PC is available without any other operation. Many operation systems of PC have included almost USB Device classes’ driver program. But various USB devices need to be programed according to the USB specification. So this paper points to design a common USB device protocol based on FreeScale S08JS16MCU. The user only needs to call some API functions to realize USB transmission without knowing how to process the data in the bottom. Therefore, using this protocol stack can greatly reduce the developers’working capacity, effectively shorten the development time, reduce development risk and guarantee quality development.Firstly, this article introduces the current application of USB interface, and elaborates the theory of USB interface. It includes the Bus Topology, USB data flow model, and four transfer types and so on.Secondly, the article introduces the protocol’s framework, and then start to elaborate how to realize every function module, how to transfer the data between every module, how to transfer information by call-back function between every level, what data structures need to be established, what global variable needs to be set and the user of this protocol how to operate every function.At last, the article analyzes how to manage the memory of USB controller. And then we start to check the protocol by tracing the USB Bus enumeration process that is necessary and important for all USB devices.At the end of this article, detailed description about the disadvantages and improvement of this protocol is mentioned and the foreground of USB interface is prospected.