Tru Test Software has developed a unique approach to utilizing the Talon BE64 test instrument. The BE64 is a versatile, high performance VXI based digital I/O module that is primarily designed for use in test systems that require bus emulation capabilities. We have developed a set of drivers for the BE64 that can be customized to provide high performance and ease of use in most Bus Emulation applications. Most older applications use Word Serial Commands to control the BE64. Word Serial Commands are a relatively slow method of controlling the instrument. Our approach was to use A16 and A24 register based commands whenever possible and cache word serial commands to provide the fastest possible access to the instrument for both loading vectors and instrument control.

The following is a benchmark of a BE64 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.

Benchmark of the Talon BE64 using register commands and word serial cache

BE64 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 BE64, use A16 and A24 accesses whenever possible 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.

BE64 Results
The drivers provided performance for the BE64 that rivals that of the SR192. For instance the drivers can create the vector tables, write a 16K pattern to the UUT, read it back and compare the results in about 6 seconds total. A test program to achieve the above results could be written in about 15 minutes. This was done using the BE64 in conjunction with the Talon 386 POD to write and read a block of RAM on the UUT. Note that the table vectors (address and data) can now be totally random and are not subject to the former restrictive address and data patterns imposed by the BE64 hardware and SCPI commands. Also note that there is absolutely no file I/O involved with these drivers. All timing, stimulus, and compare information is wholly contained within the application calling the drivers. The compare function which exists for the BE64 hardware using word serial commands, is now offloaded to the software driver making it easier to use, faster and more versatile.

BE64 Software Functionality
It takes 6 basic driver functions (create read table, create write table, setup sequence, execute sequence, read table data, and compare table data) to accomplish the above performance. Some other minor driver functions may be needed to manipulate the control bits depending on the application. The compare table data function automatically finds and compares all read tables in a sequence, even if they are non-contiguous and contain random vectors. This function was written to duplicate in software the real time hardware compare functionality of the SR192.

Many onboard functions of the BE64 such as memory management, table management, byte and word alignment, and compare tables are now offloaded to the software drivers. This vastly reduces the number of word serial commands needed to control the instrument and gives a major boost in versatility and performance while reducing the complexity of use.

The BE64 drivers are exact duplicates of what was developed for the SR192 in terms of functionality and parameters. So again, the application programmer can rapidly develop tests for the UUT with little or no knowledge of the BE64 once the drivers are in place.

The BE64 timing sets and field memories are loaded using A24 commands, and most of the states set by SCPI commands now use cache. This results in fast initialization and low overhead during execution.

BE64 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 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 2us per vector (bus cycle).

BE64 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 software drivers could seek out the response vectors for all results in a sequence and deliver a pass/fail result similar to the realtime compare function in the SR192. The cumulative results for up to 32K response vectors could now be done with a maximum of 2 test executive compares.

BE64 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 information was transferred to the instrument at the same time through 1 invocation of the function. The BE64 structure is such that only 1 subsequence of write data or read data can be programmed at 1 time. However up to 16 different subsequences can be strung together in a sequence to achieve execution of any combination of bus cycles desired. The drivers provide storage for a many sequences as needed 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 BE64. The application developer is able to concentrate on the task of providing the necessary stimulus/response information for the application.

BE64 Summary
The BE64 proved to be an excellent choice for the bus emulation project because of its powerful set of hardware resources and configurability options. The BE64 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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