compile

ghdl -a adder.vhd

run

ghdl -r adder

test

same analyze & run: ghdl -a adder_tb.vhd ghdl -r adder_tb

produce wavefile

ghdl -r adder --wave=adder.ghw or ghdl -r adder --vcd=adder_wave.vcd

view wavefile

gtkwave adder.ghw or gtkwave adder_wave.vcd

Quick Start Guide

VHDL-2008

if using

use std.env.all;

we must add --std=08 to our -a, -r commands:

ghdl -a --std=08 debounce_filter.vhd
ghdl -a --std=08 debounce_filter_tb.vhd
ghdl -e --std=08 debounce_filter_tb
ghdl -r --std=08 debounce_filter_tb --vcd=debounce.vcd

VHDL-2008 is a significant revision of the VHDL (VHSIC Hardware Description Language) standard that was released in 2008. It introduced several important improvements over the previous versions (like VHDL-93 and VHDL-2002).

Key features introduced in VHDL-2008 include:

1. Enhanced type system:

   • Fixed-point and floating-point packages
   • Better support for mixed-language simulation
   • Enhanced array types and operations

2. Improved design and verification capabilities:

   • Force/release statements for debugging
   • Enhanced generic types
   • Better package generics
   • The std.env package (which we used with finish in our testbench)

3. Simplified coding:

   • Direct entity instantiation (without needing component declarations)
   • Enhanced file I/O capabilities
   • Better support for PSL (Property Specification Language)
   • External names

4. Better tool support:

   • Standardized VHDL PSL integration
   • Enhanced synthesis packages
   • Improved error handling

For example, in VHDL-93 you would need to write:

-- VHDL-93 style
component Debounce_Filter is
  generic (DEBOUNCE_LIMIT : integer);
  port (...);
end component;

-- Then instantiate
UUT: Debounce_Filter 
  generic map (...)
  port map (...);

While in VHDL-2008 you can directly write:

-- VHDL-2008 style
UUT: entity work.Debounce_Filter
  generic map (...)
  port map (...);

The newer standard makes the code more concise and easier to maintain, which is why many modern designs prefer using VHDL-2008 when the tools support it.