Today's electronic systems require an ever-increasing amount of data, including analog and digital data. So for researchers and system developers, the biggest challenge is how to integrate, test and maintain a faster and more accurate test system to handle the ever-increasing amount of data. For some application types, such as video signal analysis, the need is for continuous acquisition of high-speed analog and digital information for real-time analysis. Therefore, when designing or selecting this type of measurement system, if you can clearly understand the data flow and possible problems, you can reduce development costs, speed up time to market, and avoid expensive system redesign costs.
Applications such as spectrum monitoring, signal analysis, optical signal acquisition, fiber testing, radar and satellite signal collection are typical high-speed and high-accuracy data acquisition applications. The biggest challenge for these applications for engineers is how to meet the high bandwidth system requirements. This article will share the details of the PXI Express platform when building a high-bandwidth system, such as the onboard memory of a digitizer or waveform generator, the PCIe signal architecture in a PXI Express chassis, computer operating system, memory, and storage. select.
Introduction The data transfer interface of traditional desktop instruments is GPIB, RS-232 or LAN. The advantages of these interfaces are that they are very easy to operate, but they are not efficient when transferring large amounts of data. When a large amount of continuous data is to be collected, the data length is limited by the size of the internal memory. The new advanced instruments on the market, such as oscilloscopes, wave generators or logic analyzers, use x86 architecture, so there is basically no limit on the speed of high-speed, large-scale data acquisition. However, it is a difficult and complicated task to achieve multi-channel acquisition by synchronizing across instruments.
Since the first version of the PXI specification was introduced in 1998, the PXI platform and its modules have been widely used in military, electronics manufacturing and scientific research applications. The first version of the PXI specification uses the high-speed transfer characteristics of the PCI bus, while the subsequent PXI specification uses the PCI Express bus, inheriting its low Latency, high bandwidth and point-to-point transmission characteristics, plus The interface for triggering and timing synchronization makes the PXI platform and PXI module particularly suitable for high-speed data transmission.
When designing systems for high-speed data logging on the PXI platform, whether it is continuously transferring data from modular instruments to system memory or storage, or vice versa, PXI Express's high-speed bus, point-to-point transmission characteristics, and Unique trigger and timing signals make it easy to implement. The following article will further discuss several points and directions that need to be considered in the process of designing and implementing a data recording system.
The architecture of the data logging system and its considerations Figure 1 briefly illustrates the flow of data in a set of PXI Express platforms. The components consist of a PXI Express chassis, a PXI Express controller, and a modular instrument, including digitizers and waveform generation. Device. Taking a high-speed digitizer as an example, after the analog signal is converted into digital data by the ADC, it is moved to the on-board memory for temporary storage, and then transferred to the system memory of the PXI Express controller via the bus controller and the PCI Express interface. On, do the subsequent calculations and processing. If the flow of data to the destination is a storage device, it will be moved directly to the storage device without any processing calculations to maintain high-speed, continuous data recording. On the PXI Express backplane, the PCIe switch is used to allow the system to expand into more slots. Since different PXI Express chassis have different slot types, each PCIe switch has different winding methods, which affects data transmission efficiency. For example, a modular instrument-waveform generator whose data flow operates in the opposite direction.
Figure 1. Simplified diagram of the overall architecture of the PXI Express platform and modular instrument, showing the direction of data record transmission of the PXI Express system.
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