How to use the command ghdl (with examples)
The ghdl command is an open-source simulator for the VHDL (VHSIC Hardware Description Language) language. It is used to analyze, elaborate, run, and check VHDL source files.
Use case 1: Analyze a VHDL source file and produce an object file
Code:
ghdl -a filename.vhdl
Motivation: When working with VHDL, it is necessary to analyze the source code before further processing. The -a option in the ghdl command is used to analyze a VHDL source file and produce an object file. This object file can then be used for further processing.
Explanation:
ghdl: The command to run the GHDL simulator.-a: The option to analyze a VHDL source file.filename.vhdl: The name of the VHDL source file to analyze.
Example output:
No output is generated when analyzing a VHDL source file. However, if there are any syntax errors in the file, they will be displayed in the console.
Use case 2: Elaborate a design
Code:
ghdl -e design
Motivation: After analyzing the VHDL source code, the next step is to elaborate the design. Elaboration is the process of resolving references and binding entities to configurations and architectures. The -e option in the ghdl command is used to elaborate a design.
Explanation:
ghdl: The command to run the GHDL simulator.-e: The option to elaborate a design.design: The name of the configuration unit, entity unit, or architecture unit to elaborate.
Example output:
No output is generated when elaborating a design. However, if there are any errors or warnings during the elaboration process, they will be displayed in the console.
Use case 3: Run an elaborated design
Code:
ghdl -r design
Motivation: Once the design has been elaborated, it can be executed. The -r option in the ghdl command is used to run an elaborated design.
Explanation:
ghdl: The command to run the GHDL simulator.-r: The option to run an elaborated design.design: The name of the elaborated design to run.
Example output:
The output generated when running an elaborated design depends on the design itself. It could be the expected output of the VHDL testbench or any other output specified in the design.
Use case 4: Run an elaborated design and dump output to a waveform file
Code:
ghdl -r design --wave=output.ghw
Motivation: When debugging a VHDL design, it can be helpful to visualize the signals and waveforms during the simulation. The --wave option in the ghdl command is used to specify the waveform file to generate during the simulation.
Explanation:
ghdl: The command to run the GHDL simulator.-r: The option to run an elaborated design.design: The name of the elaborated design to run.--wave: The option to specify the waveform file to generate.output.ghw: The name of the waveform file to generate.
Example output:
The output generated is a waveform file (output.ghw) that can be opened and visualized using waveform viewer tools compatible with GHDL.
Use case 5: Check the syntax of a VHDL source file
Code:
ghdl -s filename.vhdl
Motivation: It is important to check the syntax of VHDL source files before further processing or analyzing them. The -s option in the ghdl command is used to check the syntax of a VHDL source file.
Explanation:
ghdl: The command to run the GHDL simulator.-s: The option to check the syntax of a VHDL source file.filename.vhdl: The name of the VHDL source file to check the syntax of.
Example output:
If the syntax of the VHDL source file is correct, no output is generated. However, if there are any syntax errors, they will be displayed in the console.
Use case 6: Display the help page
Code:
ghdl --help
Motivation: When using a new command or needing a reminder of the available options and syntax, it can be helpful to access the help page. The --help option in the ghdl command is used to display the help page.
Explanation:
ghdl: The command to run the GHDL simulator.--help: The option to display the help page.
Example output:
The output generated is the help page for the ghdl command, which provides information about the available options, usage examples, and more.
