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Since the CMC digital tutorial contains a step by step procedure of how to use the Test Fixturing Software, a description will not be given here.
Both test benches use a similar approach which imports the stimulus test vectors in a 74ks165 and the simulation results are written to an output file. The gate-level simulation uses the output file from the functional simulation as input file. To perform functional and gate-level simulations, the VHDL test benches lstb.
74LS – 8-Bit Shift Register Para In/Ser Out
Since this is a very simple circuit, there is no expected output included in the test vector generation program. These setup files are different from those of the CMC tutorials as a generic technology has been used for the example. The output file from the Test Fixturing Software can be used to make the jumper connections on the test head and to connect the timing and pattern pods from the VXI mainframe to the test head.
For the 74LS, the Perl script topcf. This can be done with a C program or with a Perl script.
74LS165 – 8-Bit Shift Register Para In/Ser Out
For this example, the gate-level simulation output file is to be used for the physical test. The implementation is very simple and a novice VHDL designer should be able to understand. The rest of this section describes the steps on Figure 5 for the 74LS The expected outputs are actually generated by the functional simulation.
In general, physical testing takes much less time than simulation in Synopsys so a more exhaustive set of test vectors can be used for the physical test.
All source files are included so that the reader can download the files and try to setup the test on his or her own. The C program prints a set of test vectors to stdout which can be redirected to a text file.
The functional test vectors are generated with a simple C program lstv. However, for a more complicated circuit, the expected outputs should be generated and used for functional simulation. Synopsys is used to synthesize the VHDL code to a gate-level circuit using the Synopsys’ Class library as the target library. This file contains not only the stimulus, but also the expected responses. After gate-level simulation, the design can be exported to Cadence to finish the rest of the design flow as described in the Design Flow section.
Each line of the file consists of one vector of stimulus data that the VHDL test bench reads. The test bench uses a clock to output the stimulus data in a periodic manner. To perform functional simulation, synthesis, and gate-level simulation with these files, the following Synopsys setup files should be used: To be able to use the test vectors for physical testing, the test vector file needs to be converted to HP PCF format.
The gate-level simulation test bench compares the expected responses with actual responses from the circuit and outputs error messages if they do not match.