We declare two integer variables called num_checks and num_errors and initialize them to zero. Then, we will perform the comparison between the expected output and the actual output. The first thing to do is to generate the expected result, which will be simply the switch variable delayed by one clock cycle. We will now add a check to the test bench to compare the led outputs with an expected result. This is to be expected, since the led values are captured in flip-flops on the rising edge of clk. However, notice how the led values lag behind the switch values by one clock cycle. The waveform below shows the last few clock cycles of my simulation. Here is what I have for my top.v file `timescale 1ns / 1nsĪnd here is my bench.v file `timescale 1ns / 1ns You should take the time now to modify your existing top.v and bench.v files to use the nonblocking assignment operator where appropriate. Likewise, always use a blocking assignment when assigning the output of a combinational always block. It is critically important that you always use long blocking assignments when assigning to output values in sequential always blocks. When the simulator encounters a nonblocking assignment, it evaluates the right hand side of the expression and schedules that value to be assigned to the left hand side of the expression once all other always blocks are evaluated. module top(input clk, output reg a, output reg b) ![]() The example below shows the same code with nonblocking assignments. Verilog also supports a different assignment operator called a nonblocking assignment. The sequential assignments above are called blocking assignments. If you elaborate the RTL design and look at the schematic, you’ill see the correct implementation: a and b are both 1 for the entire simulation. When I simulate this a is set to 1 right away, and then nothing ever changes. Consider the code below: module top(input clk, output reg a, output reg b) Furthermore, it is actually impossible because sometimes, two blocks might both need to go first. You would be spending all of your time trying to keep track of which block goes before which other block. Even if it were possible to know, this situation is so common that making a working simulation with a real-life design would be just about impossible. And which one is executed first has an impact on the simulation’s behavior. It’s unclear ahead of time which one will execute first. So, which goes first? The answer is, quite simply, we don’t know. ![]() So the question is, which of these events happens first in the simulation? In real hardware, it is possible for them to happen simultaneously, but in the simulator this is not possible. In our test bench module, we drove the switch values to random values on the rising edge of clk as well. ![]() Here is the code: always clk) led = switch In our FPGA, we had an assignment which set the value of the the led outputs to be the same as the switch inputs on the rising edge of clk. The very observant reader of the last tutorial might have noticed there is an ambiguity in what the simulator needs to be doing. In addition, we’ll discuss an important subject that causes some confusion. I downloaded a few additional viewers which are handily imported via the BCFormats.bcpkg file C:\Program Files (x86)\Beyond Compare 3\Helpers>dir /b /sĬ:\Program Files (x86)\Beyond Compare 3\Helpers\HtmlTidyĬ:\Program Files (x86)\Beyond Compare 3\Helpers\PdfToText.exeĬ:\Program Files (x86)\Beyond Compare 3\Helpers\XLS_to_TAB_Single.vbsĬ:\Program Files (x86)\Beyond Compare 3\Helpers\HtmlTidy\HtmlTidy.exeĬ:\Program Files (x86)\Beyond Compare 3\Helpers\HtmlTidy\XML_tidied_sorted.batĬ:\Program Files (x86)\Beyond Compare 3\Helpers\HtmlTidy\XML_tidied_sorted_config.In this tutorial, we are going to cover a little bit more on simulation. I see that BeyondCompare can be extended to include additional file formats, as in Additional File Viewer Rules for Beyond Compare 2 and also Additional file format downloads for version 3 but after a quick initial search I don't see how user's develop these special viewers.
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