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How can we write a test bench for a design in Vivado-HLS? Here, I am going to explain the structure of

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a test bench in Vivado-HLS and how to use that to perform design simulation and debugging.

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The C top-level function, called main(), is also the test bench top-function.

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That means a testbench should start with the main() function.

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The test bench functions won’t be synthesised. Therefore, it can call any types of function in C or 

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use any features in C language. It can accept a few arguments, and it should return an integer value. 

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While the name of the design top-function should be defined in the Vivado-HLS project settings, the name of 

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the test bench top-function is always main().

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Any function under the design top function should be synthesisable. 

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The test bench should call the design top function along with its execution.

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Self-checking is one of the test bench requirements. The test bench should check the design correctness

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and report that through the main function return statement.

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If the results are correct, the test bench should return the value of 0. 

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Otherwise, the test bench should return any non-zero values.

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Let’s consider this simple design which transfers an 8-bit date from its input to its output without 

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any changes.

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The test bench of this design consists of five stages:

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1-The C main() function is the top function and should return an integer value.

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2-Then the design inputs should be generated. As it receives an 8-bit input which can have 

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256 different cases. We use a for-loop to generate all the possible values for the input.

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3- Then the test bench should call the design top-function, pass the input and receive the output.

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4- The received output should be compared against the golden model (or known good results) which in this 

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case is very simple, and it is the original input value. 

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In the case of any discrepancy, a non-zero value should be written into the return variable, which 

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is status in this code.

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5- Then a proper message can be written to the output to report the status of the design. 

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In addition, the function returns the success of the design verification by the return status. 

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You are responsible for ensuring that the test bench checks the results. If the test bench does not check 

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the results but returns zero, Vivado HLS indicates that the simulation test has been successful 

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even though the results were not actually checked. Even if the output data is correct and valid,

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Vivado HLS reports a simulation failure if the test bench does not return the value

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zero in function main().

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The Vivado HLS GUI does not have a command console and cannot accept user inputs during the test bench execution. 

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So, using scanf C-function and similar functions are not allowed. 

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After getting familiar with the testbench concept and its coding style, we should explore its development 

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in the Vivado-HLS IDE.

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The next lecture will cope with this challenge. 

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This is our takeaway message. A test bench top-function of a design consists of four main parts: Generating 

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the design inputs. Calling the design top-function using the generated inputs. Comparing the design

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outputs with the golden model outputs. Returning the success of the design verification.

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Now the quiz of this lecture. Write a testbench function for the following design.