Design And Implementation A Software Of The Arm-Based Instrument System

Virtual instrument is a new type of intelligent instrument with the development of computer technology and modern measurement technology. It puts forward the idea that the software replaces the hardware, and uses the computer software to cooperate with the data acquisition module to replace the traditional instrument and meter, which represents the latest development direction of the test instrument. With the rapid development of mobile computing and wearable technology, this structure has been unable to meet the needs of users for the miniaturized portable instrument. But in recent years the ARM architecture processor widely used in embedded system and mobile intelligent terminal with the advantages of low power consumption, low cost, high performance. It makes the virtual instrument system based on ARM platform to be a new idea to construct the future instrument system.NI provides NI-VISA library functions which integrated various types of interface drivers, and also a software development kit which allows users to program through graphical software development. But it’s hard to implement on ARM platform. Faced the present situation, we use Python scripting language to achieve a virtual instrument software system based on ARM mobile computing platform and Linux system, and achieve a virtual oscilloscope software with the data acquisition card which is support USBTMC protocol. This paper mainly includes the following four aspects.1. Programming of USBTMC class driver: In this paper, we design the driver layer software for different interfaces of the instrument include USB, Ethernet, Serial, and we focus on the implementation of the USBTMC class interface driver. We achieve the operation and control of the USB interface for the python program by using the PyUSB. On this basis, combined with the principle of USBTMC protocol implementation of the class interface device driver, including device initialization, find device, open device and block data read and write operations, to provide the underlying support for the VISA session resources.2. Implementation of VISA Library Based on Python: Because the NI-VISA library can not work under the ARM architecture, this paper combined with the PyVISA project, achieve a pure Python VISA library to provide interface functions for the virtual instrument top-level software under the Linux operating system. Include resource manager, resource template method and session resources software interface, wherein the session resources we focused on the realization of the USBInstrSession class resources. Finally implement the communication between the virtual instrument software and the data acquisition card.3. Software design and implementation of virtual oscilloscope: This paper designs and realizes five kinds of function modules of virtual oscilloscope based on the VISA library which is designed by ourselves, including equipment management module, file management module, function module, acquisition and display module and parameter measurement module. At the same time, using the python GUI Graphical expansion pack we implement the oscilloscope interface, including waveform display area, a vertical channel setting zone, horizontal channel setup area, triggering channel setting parameter area and display area.