Writing a good test bench in vhdl

In this FPGA Verilog projectsome simple processing operations are implemented in Verilog such as inversion, brightness control and threshold operations. The image processing operation is selected by a "parameter.

Writing a good test bench in vhdl

A practical example - part 3 - VHDL testbench First, let's pull writing a good test bench in vhdl of the pieces of the prior design together into a single listing. This gives us a great overview of the design and helps us to layout a testing stratagy.

Here is the entire design for our data acquisition engine: This article is available in PDF format for easy printing From the above code, the Xilinx ISE environment makes is simple to build the basic framework for the testbench code. To start the process, select "New Source" from the menu items under "Project".

This launches the "New Source Wizard". The "New Source Wizard" then allows you to select a source to associate to the new source in this case 'acpeng' from the above VHDL codethen click on 'Next'.

The Wizard then creates the necessary framework for a test bench module see below. The framework above includes much of the code necessary for our test bench. It includes a component declaration section linesInput signal declarations and initializations linesOutput declarations lines and the test component instantiation lines This framework gives us a good starting point, from which to build our complete test bench.

I like to start my test bench design working through the fundamentals and then extending the stimulus generation until we have adequately exercised our design. My first steps are usually focused on clock generation. To this end, we will need to tweak some of the constants to match our target clock rates, as well as some minor changes so that we can suppress the SPI clock Sclk to times when we are transmitting or receiving data from SPI devices.

This is simple enough. Now we need to do a little modification to the SPI clock generation logic. First we need to create two signals to assist in the gating logic.

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Now we need to create a process to generate simulated ADC data for our design. OK, now we need to connect all the pieces together and start to make something happen, but first, let's have a plan of attack on how to test the device. Next we should send a SPI command to set the sample size and start the collection sequence.

The rest is just waiting around until the collection burst is run.

writing a good test bench in vhdl

This is about all that is needed to verify the basic functionality of the device. Sure, we could add additional test to exercise all of the sample size counts from 1 tobut for the time being this should be sufficient.

As planned, we have a short reset and hold sequence lines and a SPI command sequence to set the sample count to one and to set the 'Run' flag lines Now we can start looking at the simulation data.

Running the simulation and capturing the first 2. Good, so far we got one right.

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For now, this is what we want. Now, let's look at how the design is effected by the reset line. In the tracings above, the reset signal starts out asserted lowns later it is released, re-asserted another ns later and then final released.

This show us two things, first that reset had no real effect, there was no difference between our power up state and our reset state. Then ns later, the SPI data line sdi is set high. After the Sclk signal has gone high then low lineswe clear the SDI signal, preparing to send six zeros to the SPI peripheral latch the high bits of CycleCnt.

The testbench then waits through six Sclk cycles lineslatching in the high bits of CycleCnt. To finish off the SPI write sequence, we wait ns and re-assert the CS lines to 'no select' state, or '11' lines 2.

Looking over the traces so far, there are a couple of things to note: Neither of these are real issues. Another note worthy thing is occurring right before we are entering the 'no select' state on the CS lines, at 2.You can practice this by treating VHDL as an ordinary software language, writing subprograms that carry out tasks without consideration for hardware necessities.

You can then build a testbench that operates much like a software unit test. International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research.

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Write File Test Bench Architecture In VHDL, there are predefined libraries that allow the user to write to an output ASCII file in a simple way. The TextIO library is a standard library that provides all the procedure to read from or write to a file. International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research.

The material references the Intel ® Stratix ® 10 device architecture as well as aspects of the Intel ® Quartus ® Prime software and third-party tools that you might use in your design. The guidelines presented in this document can improve productivity and avoid common design pitfalls.

Contents • Purpose of test benches • Structure of simple test bench – Side note about delay modeling in VHDL • Better test benches – .

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