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The trigger bus, star trigger bus and system reference clock of PXI (PCI eXtension for Instrumentation) bus provide a low-cost and convenient solution for test and measurement system; On the other hand, characteristics such as real-time, smart and embedded in an object by controlled of embedded system provide an outstanding supervisory flat. In this paper, an external clock is provided to the four data acquisition modules with the same function by using the system reference clock of PXI bus, and solve timing and synchronization problems among the modules by using its trigger bus when an internal reference clock is used, thereby, an almost zero delay parallel synchronization system is realized. Every data acquisition module is made up of an analog board with amplifier, anti-aliasing filter, ADC and a digital board with high performance DSP, FPGA, SRRAM, DPRAM, PCI interface chip, and there is a real time operating system kernel (DSP/BIOS) that is embedded in the DSP to control data acquisition and storage, produce and set the sampling clock, control the length of sampling data, feed back the status of system running, and exchange data with host and do preprocessing arithmetic for sampling data. The preprocessing arithmetic in the DSP includes wave algorithm (plus, subtract, integral and differential coefficient, etc.) and wave filter (limiting amplifier, jitter elimination, median value and smoothing etc.) in time domain and FFT, IIR filter (high-pass, low-pass, band-pass and band-stop.) and FIR (high-pass, low-pass, band-pass and band-stop.) filter in frequency domain.
The PXI chassis exchange DSP code, control or status information and data (including raw data and processed data) by using MXI-3 bus, and a DDK driver is designed in order to improve data storage speed to SCSI hard disk, which makes the data escape the file system of operating system. In order to decrease the velocity of refreshing screen and weaken the effect of glittering in the screen, the data from PXI chassis is displayed in the memory first in the form of bitmap and then paste it to screen wholly, which greatly increases the speed and quality of real time plot.
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