Tru Test Software has developed a unique approach to utilizing the Talon SR192 test instrument. The SR192 is a versatile, high performance VXI based digital I/O module. We have developed a set of drivers for the SR192 that can be customized to provide high performance and ease of use in most Bus Emulation and other applications. Most older applications use Word Serial Commands to control the SR192. Word Serial Commands are a relatively slow method of controlling the instrument. Our approach was to exclusively use A16 and A32 register based commands to provide the fastest possible access to the instrument for both loading vectors and instrument control.

SR192 DEMO

A new SR192 demo is available that illustrates the speed and ease of using the SR192 instrument with customized drivers. To obtain the self extracting demo file for your system, select SRDEMO16 for Windows 3.11 or SRDEMO32 for Windows 95, 98 or NT. When the self extracting EXE file is run, a SRDEMO16 or SRDEMO32 directory is created that contains a setup file for the demo. Running the setup file creates all the necessary files for the demo, along with a text file with complete demo instructions.

The following is a benchmark of a SR192 application that illustrates the reduction in system development and application development time, and enhanced performance of the instrument that was achieved using this approach with high level drivers.
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Benchmark of the Talon SR192 as a Bus Emulator using register commands

SR192 Project Requirements
The project requirements were to develop a set of high level bus emulation drivers to take advantage of all the resources of the SR192, use A32 accesses to achieve fastest possible setup and execution times, and structure the drivers as a set of easy to use functions to be called directly from the test application.

SR192 Results
The results were that the maximum number of SR192 stimulus/response vectors (128K) could be loaded onto the hardware in 15 seconds. The setup and configuration time was under 1 second. Execution time for 128K vectors was 130ms. Evaluation of the response was under 1 second. Application development time was under 1 day for a set of known stimulus/response vectors.

SR192 configuration
The SR192 was configured to emulate a 10 Mhz, 24 bit address, 16 bit data bus, 8 interrupt lines and 9 control lines. Three SR105's were used to emulate the address, data, and interrupt lines. A fourth SR105 was used to dynamically monitor the control lines during bus cycles. A SR107 was used to emulate the static control lines and a SR101 was used to drive the dynamic control lines, provide bus timing, and control stimulus/response sequencing.

SR192 System configuration
The SR192 was driven by an external PC running a Pentium II 166Mhz processor. The VXIbus was connected to the processor through a MXIbus controller. The operating system was Windows 3.11.

SR192 Software configuration
All SR192 commands and data transfers were done through A16, and A32 VXI accesses using VISA Memory based I/O (high level) functions. The development system was CVI.

SR192 Software Functionality
Software functions were provided to configure the SR192, load stimulus/response vectors, setup the test sequences, setup and monitor the control lines, execute the test sequences, read individual responses from each bus cycle, and evaluate the real time compare results from the entire test sequence. Each function had built in unit test capability to simulate all outputs and inputs so applications could be 100% unit tested offline before being run on the hardware. Functions also provided input parameter limit checking and error reporting.

SR192 Application structure
The applications were structured so that configuration of the instrument, loading of stimulus/response vectors, and loading of test sequences needed to only be done once. This typically took about 130us per vector. Several sets of test vectors and test sequences up to 128K of each could all be loaded at once and then be individually invoked by the application as needed. Once invoked, application of the vectors was a factor of bus cycle time. Typically this was about 1us per vector (bus cycle).

SR192 Evaluation of Test Results
Test results could be evaluated in 2 ways.

For results where an exact match could not be guaranteed, response vectors could be read back individually and then compared for maximums and minimums through a test executive. This involved more time because evaluation of individual results now became a factor of the test executive.

The second evaluation method involved loading the expected response vectors so that the hardware could do a real time result evaluation as the bus cycles were executing. The cumulative results for up to 128K response vectors could now be done with a maximum of 3 test executive compares.

SR192 Application Development
Application development time was kept to a minimum by the structure and ease of use of the drivers. The drivers were set up so that the stimulus and response information were transferred to the instrument at the same time through 1 invocation of the function. The SR192 structure is such that only 1 subsequence of write data or read data can be programmed at 1 time. However up to 128K of different subsequences can be strung together in a sequence to achieve execution of any combination of bus cycles desired. The drivers provided made the building of subsequences and sequences relatively easy such that a large series of read/write (or other) vectors could be built in a short amount of time.

Another benefit of the drivers was the fact that they removed the need for the application developer to have any knowledge of the inner workings of the SR192. The application developer is able to concentrate on the task of providing the necessary stimulus/response information for the application.

SR192 Summary
The SR192 proved to be an excellent choice for the bus emulation project because of its powerful set of hardware resources and configurability options. The SR192 loaded with the proper set of I/O and timing modules can be software configured to emulate almost any bus type structure. This in combination with a set of high level bus emulation functions results in a high performance bus emulation device that is easily programmable in the application environment.

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