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-- A testbench has no ports.
entity adder_tb is
end adder_tb;
architecture behav of adder_tb is
-- Declaration of the component that will be instantiated.
component adder
port (i0, i1 : in bit; ci : in bit; s : out bit; co : out bit);
end component;
-- Specifies which entity is bound with the component.
for adder_0: adder use entity work.adder;
signal i0, i1, ci, s, co : bit;
begin
-- Component instantiation.
adder_0: adder port map (i0 => i0, i1 => i1, ci => ci,
s => s, co => co);
-- This process does the real job.
process
type pattern_type is record
-- The inputs of the adder.
i0, i1, ci : bit;
-- The expected outputs of the adder.
s, co : bit;
end record;
-- The patterns to apply.
type pattern_array is array (natural range <>) of pattern_type;
constant patterns : pattern_array :=
(('0', '0', '0', '0', '0'),
('0', '0', '1', '1', '0'),
('0', '1', '0', '1', '0'),
('0', '1', '1', '0', '1'),
('1', '0', '0', '1', '0'),
('1', '0', '1', '0', '1'),
('1', '1', '0', '0', '1'),
('1', '1', '1', '1', '1'));
begin
-- Check each pattern.
for i in patterns'range loop
-- Set the inputs.
i0 <= patterns(i).i0;
i1 <= patterns(i).i1;
ci <= patterns(i).ci;
-- Wait for the results.
wait for 1 ns;
-- Check the outputs.
assert s = patterns(i).s
report "bad sum value" severity error;
assert co = patterns(i).co
report "bad carry out value" severity error;
end loop;
assert false report "end of test" severity note;
-- Wait forever; this will finish the simulation.
wait;
end process;
end behav;
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