The TAXI Direct-to-Disk interface is a special-purpose interface circuit for demultiplexing of data from a Racal Storeplex (or equivalent) multichannel recorder onto one or more hard disks that reside in, and/or are controlled by, a personal computer (PC). [The name “TAXI” as used here is derived from the acronym TAXI, which signifies transparent asynchronous transceiver interface.] The TAXI Direct-to-Disk interface was developed for original use in capturing data from instrumentation on a test stand in a NASA rocket-testing facility. The control, data-recording, and datapostprocessing equipment of the facility are located in a control room at a safe distance from the test stand. Heretofore, the transfer of data from the instrumentation to the postprocessing equipment has entailed post-test downloading via software, requiring many hours to days of post-test reduction before the data could be viewed in a channelized format. The installation of the TAXI Directto- Disk interface, in conjunction with other modifications, causes the transfer of data to take place in real time, so that the data are immediately available for review during or after the test.
The instrumentation is connected to the input terminals of the signal-processing unit of multichannel recorder by standard coaxial cables. The coaxial output of the signal-processing unit is converted to fiber-optic output by means of a commercial coaxial-cable/fiber-optic converter (that is, a fiber-optic transceiver) designed specifically for this application. The fiber-optic link carries the data signals to an identical fiber-optic transceiver in the control room. On the way to the TAXI Direct-to-Disk interface that is the focus of this article, the data signals are processed through a companion special-purpose circuit denoted by the similar name “parallel TAXI interface” (see figure).
The TAXI Direct-to-Disk interface is implemented by means of field-programmable gate arrays (FPGAs), memory chips, and other integrated circuits on a printed-circuit board that conforms to the peripheral component interface (PCI) standard and is denoted the TAXI-100 card. The TAXI-100 card performs real-time demultiplexing of the data signals from the parallel TAXI Direct- to-Disk interface to individual chan- nel files within the host PC. The data are provided in a layered interface that consists of the TAXI physical layer with the Racal proprietary data format contained in the application layer. The application layer is stripped off by the parallel TAXI Direct-to-Disk interface. Parallel clock and data signals containing the Racal proprietary data format are received by the TAXI-100 card in the parallel format and demultiplexed, according to formats extracted from within the data, into channel buffers in the form of firstin/ first-out (FIFO) memory chips. Other proprietary programmable logic chips provide for the management and buffering of the channel blocks until they are presented to the host PC across a PCI bus interface. Real-time software drivers running under the Microsoft NT 4.0 operating system provide for realtime handling of interrupts and buffering onto small computer systems interface (SCSI) disks in individual channel files. A host graphical user interface enables the user to select recorder channels.
This work was done by Bruce G. Newnan of Integrated Systems Consultants and Steven F. Ahlport of Pacific Custom Systems, Inc., for Stennis Space Center.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to Integrated Systems Consultants 1282 Shasta Ave. Suite 1 San Jose, CA 95126 Refer to SSC-00141, volume and number of this NASA Tech Briefs issue, and the page number.