Using PCIe & intelligent DMA to achieve blazing data rates in real-time recording instruments
Integration into a larger system
While the API would be used by the GUI to communicate with the server, the engineer can also utilize the API to allow the recorder to be integrated into a larger system.
By providing a user API, the recorder becomes more than a stand-alone instrument, serving as a user development platform as well. This allows different types of users the flexibility they may desire, while providing the out-of-the-box experience of an instrument all in one product.
In order to define an API that can be easily integrated into a larger application, it is important to define the API routines in a simple and straightforward manner. These routines should abstract the user from details of the message building, the socket interface and other intricacies of the recording architecture. Error checking should be included in the recording server, allowing the user to receive error codes in response to failed messages.
The API should not only contain routines that control the interface, but should contain routines that obtain general status information, perform built-in-test (BIT) facilities and allow the user to view snapshots of the data prior to and during recording. Combining these facilities provides the user with the ability to create a well-featured recorder application as part of a bigger system.
Post processing and analysis
One of the problems engineers often have to deal with after recording data in the field is the issue of offloading the mission data to a system that will perform the analysis, post-processing and archiving. This process should be made simple and quick, minimizing the down-time that field engineers have during the offload process.
The use of a non-proprietary file system (NTFS) to record data provides the ability to avoid the offload process, required by systems that use a proprietary file system. In this situation, the user can instantly access recordings as standard files on the recording device itself without the need for a lengthy conversion process.
In addition, by utilizing hot-swappable SATA drives, field engineers can simply swap out disks filled with mission data for fresh ones and transport only the data disks to their analysis system.
By adding a RAID controller to the analysis system data can be instantly accessible on the analysis machine, avoiding the offload process completely. The recorder is then immediately available to collect new data as soon as the disk swap is made, allowing for almost no down-time in the field.
Keep in mind the data files that are provided to the analysis system must contain critical information related to the recording event itself. This can be accomplished by adding a small header to the beginning of each data file.
The parameters stored in this header should be well-defined, containing all of the critical information about the recording, including time-stamping, I/O module settings and general information about the recording session itself. Additionally, user-settable fields should be reserved, allowing the user to add any information that he wishes to the file header.
The information stored in the file header can be used by system analysis and signal visualization tools. Integrating these tools into the recorder provides a robust product; one that allows field engineers the ability to verify their signal integrity prior to, during and after a recording session.
Example real-time control application
Combining all of the techniques described will help the system developer create a highly dependable real-time recorder, capable of recording and playing data at very high sustained data rates.
Figure 3 – Real-Time Recording and Playback Instrument (COTS and Rugged Versions)
An example control application is silicon lithography inspection, which uses a Model 2706 Real-Time recording instrument (Figure 3 above), along with its SystemFlow Recording Software, to inspect silicon wafers. The RTS 2706 recording instrument records silicon wafer data via a sensor and the data can be used for quality control and inspection purposes.
Chris Tojeira is the Technical Director and Chief Architect of the Recording Systems Product Line at Pentek, Inc. Chris has over 15 years experience in the electronics industry and has held positions as a Strategic Account Engineer and Applications Engineering Manager for Pentek. He holds a BS degree in Electrical Engineering from Rutgers University in NJ.
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