Implementation Of LXI Interface In Arbitrary Waveform Generator

The test bus standard plays an important role in the field of test and measurement,which promotes the development of test system,LXI(LAN eXtension for instrumentation)is a modular test platform standard based on Ethernet.It is a new generation test bus standard after GPIB,VXI and PXI.LXI standard makes full use of the advantages of LAN and extends the testing system from laboratory to anywhere connected to the Internet.As the basic general equipment in electronic measurement,signal generator is widely used in various kinds of tests.There is no doubt that a signal generator with LXI interface plays an important role in the formation of automatic test system.Firstly,this thesis introduces LXI protocol.According to the LXI specification and the hardware platform resources of arbitrary waveform generator,it implements the network interface by connecting the Ethernet physical layer chip and transplanting the light weight TCP/IP protocol stack LwIP.On this basis,the hardware of arbitrary waveform generator is upgraded to meet the resource requirements of LXI interface.Then,the hardware circuit design is given,including the FPGA circuit,DAC circuit,waveform output channels and LAN interface circuit.At the end of this thesis,the transplantation method of LwIP,LAN configuration and network discovery mechanism based on mDNS are described,and the design and implementation of embedded Web server,built-in Web page and SCPI instruction set are discussed.The main research work of this thesis is as follows:(1)The control unit of arbitrary waveform generator is upgraded to meet the hardware resource requirements of LXI protocol.The MCU controller of original arbitrary waveform generator cannot meet the LXI protocol expansion requirements in speed,memory and on-chip storage,and there is no Ethernet interface controller.The upgraded MCU is STM32F429ZGT6,which has Ethernet controller inside already and has doubled processing speed,storage and on-chip resources.The new MCU meets the LXI protocol requirements and almost does not increase the cost at the same time.(2)With the low-cost hardware resources,the lightweight protocol stack LwIP is transplanted and the basic functions of LXI protocol are realized.LXI needs the support of TCP/IP protocols.Because of the complexity of TCP/IP protocols,normally they are difficult to implement on low-end embedded platforms.This thesis transplants the lightweight protocol stack LwIP to complete the network protocol tailoring as LXI protocol required,and realizes the basic functions of LXI protocol,including three LAN configuration modes,the discovery mechanism based on mDNS and the design of embedded Web server and built-in Web page.(3)The standardized SCPI instruction set is designed and the command parsing is completed to realize the remote control of arbitrary waveform generator.LXI protocol supports unified and compatible drivers and control commands.According to the functional characteristics of arbitrary waveform generator,SCPI remote contrrol commands are designed,and the commands are parsed by traversing binary tree,and finally the function of remote control of arbitrary waveform generator with standard instrument control language is realized.After testing,the LXI arbitrary waveform generator designed in this thesis conforms to the content of LXI protocol specification version 1.5.It realizes the basic functions of class C instrument.The device can be searched through LXI instrument discovery tool and the basic information of the equipment can be accessed through browser.Also,the equipment can be controlled by LXI standard-compliant software.The sampling rate of this arbitrary waveform generator is 200 MSa/s,the vertical resolution is 14 bits,and the maximum output sinusoidal frequency is 60MHz.It can output various kinds of conventional waveform.