#GENERATE A TEST BENCH WITH MODELSIM PE SOFTWARE#
#GENERATE A TEST BENCH WITH MODELSIM PE CODE#

When we define a period using the time type we must give both a number and a time unit. We use a special pre-defined type in VHDL to specify time. We can also use the wait statement but this is only valid within processes and is slightly more complex to understand. The most basic method is the VHDL after statement which we can either use concurrently or within processes. There are two main constructs in VHDL which we use to consume time. Infact, this is crucial for creating test stimulus.

#GENERATE A TEST BENCH WITH MODELSIM PE CODE#

One of the key differences between testbench code and design code is that we don't need to synthesize the testbench.ДЄs a result of this, we can use special constructs which consume time. In the example above, we use a library called вЂњworkвЂќ and an architecture called вЂњrtlвЂќ.

There are two additional requirements for this type of instantiation вЂ“ the library and the architecture must also be specified. Likewise, the names of the ports are on the left and the name of the signals are on the right. The code snippet below shows the syntax for doing this.ДЄnd_gate_instance: entity work.and_gate(rtl)ДЄs with the component instantiation technique, each instantiation must have a unique name. However, as the testbench has no inputs or outputs, we create an empty VHDL entity. We use the entity to define the inputs and outputs to our design. The first step in writing a testbench is creating a VHDL component which acts as the top level of the test.ДЄs we discussed in a previous post, we need to write a VHDL entity architecture pair in order to create a VHDL component.

#GENERATE A TEST BENCH WITH MODELSIM PE SOFTWARE#

The freely available software packages from Xilinx ( Vivado) and Intel ( Quartus) both offer this capability and are recommendedВ as tools for learning VHDL. Instead, we can use a simulation tool which allows for waveforms to be viewed directly. Therefore, we don't diccuss the output checking block as it adds unnecessary complexity. The main purpose of this post is to introduce the skills which will allow us to test our solutions to the exercises on this site.

It is also possible to include all of these different elements in a single file. The stimulus and output checker will be in separate files for larger designs. The stimulus block generates the inputs to the FPGA design and a separate block checks the outputs. The diagram below shows the typical architecture of a simple testbench. Testbenches consist of non-synthesizable VHDL code which generate inputs to the design and checks that the outputs are correct. If you are interested in learning more about testbench design using either VHDL or SystemVerilog, then there are several excellent courses paid course available on sites such as udemy. This allows us to test designs while working through the VHDL tutorials on this site. If you are hoping to design FPGAs professionally, then it will be important to learn this skill at some point.ДЄs it is better to focus on one language as a time, this blog post introduces basic VHDL testbench principles. System Verilog is widely adopted in industry and is probably the most common language to use. We can write testbenches using a variety of languages, with VHDL, Verilog and System Verilog being the most popular. When using VHDL to design digital circuits, we normally also create a testbench to stimulate the code and ensure that the functionality is correct. Finally, we go through a complete test bench example.

We then look at some key concepts such as the time type and time consuming constructs. We start by looking at the architecture of a VHDL test bench. In this post we look at how we use VHDL to write a basic testbench.

Generate a test bench with modelsim pe