format/move code a little for consistency

2 files changed, 62 insertions, 65 deletions

diff --git a/full-adder/full-adder.srcs/sim_1/add4b_tb.vhd b/full-adder/full-adder.srcs/sim_1/add4b_tb.vhd
index 2999486..312cf22 100644
--- a/full-adder/full-adder.srcs/sim_1/add4b_tb.vhd
+++ b/full-adder/full-adder.srcs/sim_1/add4b_tb.vhd
@@ -1,52 +1,52 @@
-LIBRARY ieee;
-USE ieee.std_logic_1164.ALL;
-USE ieee.numeric_std.ALL;
-LIBRARY UNISIM;
-USE UNISIM.Vcomponents.ALL;
-ENTITY add4b_tb IS
-END add4b_tb;
-ARCHITECTURE behavioral OF add4b_tb IS 
-   COMPONENT add4b
-	Port (
-    A: in std_logic_vector(3 downto 0);
-    B: in std_logic_vector(3 downto 0);
-    Cin: in std_logic;
-    X: out std_logic_vector(3 downto 0);
-    Cout: out std_logic);
-   END COMPONENT;
+library ieee;
+library unisim;
 
-   SIGNAL A: std_logic_vector(3 downto 0);
-   SIGNAL B: std_logic_vector(3 downto 0);
-   SIGNAL S: std_logic_vector(3 downto 0);
-   SIGNAL C_out	:	STD_LOGIC;
-   SIGNAL C_in  :	STD_LOGIC;
-    Signal Test_case: STD_LOGIC_VECTOR (7 downto 0):= (others =>'0');
-	signal OK: boolean := true;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+use unisim.vcomponents.all;
 
-BEGIN
-   UUT: add4b PORT MAP(
-        A => A,
-        B => B,
-        X => S,
-        Cout => C_out,
-        Cin => C_in);
+entity add4b_tb is
+end add4b_tb;
 
--- *** Test Bench - User Defined Section ***
-   tb : PROCESS
-			variable S0_t	:	STD_LOGIC;
-			variable S1_t	:	STD_LOGIC;
-			variable S2_t	:	STD_LOGIC;
-			variable S3_t	:	STD_LOGIC;
-			variable C_out_t	:	STD_LOGIC;
-			variable A_t : integer;
-			variable B_t : integer;
-			variable sum : integer;
+architecture behavioral of add4b_tb is component add4b
+	port (
+		A: in std_logic_vector(3 downto 0);
+		B: in std_logic_vector(3 downto 0);
+		Cin: in std_logic;
+		X: out std_logic_vector(3 downto 0);
+		Cout: out std_logic);
+end component;
 
+signal A: std_logic_vector(3 downto 0);
+signal B: std_logic_vector(3 downto 0);
+signal S: std_logic_vector(3 downto 0);
+signal C_out	:	STD_LOGIC;
+signal C_in  :	STD_LOGIC;
+signal Test_case: STD_LOGIC_VECTOR (7 downto 0):= (others =>'0');
+signal OK: boolean := true;
 
-	BEGIN
+begin
+	UUT: add4b port map(
+		A => A,
+		B => B,
+		X => S,
+		Cout => C_out,
+		Cin => C_in);
+
+	tb: process
+		variable S0_t	:	STD_LOGIC;
+		variable S1_t	:	STD_LOGIC;
+		variable S2_t	:	STD_LOGIC;
+		variable S3_t	:	STD_LOGIC;
+		variable C_out_t	:	STD_LOGIC;
+		variable A_t : integer;
+		variable B_t : integer;
+		variable sum : integer;
+
+	begin
 		C_in <= '0'; -- C_in is ignored in this test
 		for I in 0 to 255 loop
-			
+
 			Test_case <= Std_logic_vector(to_unsigned(I,8));
 			A(0) <= Test_case(0);
 			A(1) <= Test_case(1);
@@ -56,49 +56,35 @@ BEGIN
 			B(1) <= Test_case(5);
 			B(2) <= Test_case(6);
 			B(3) <= Test_case(7);
-			
-			
+
 			A_t := To_integer(unsigned(test_case(3 downto 0)));
 			B_t := To_integer(unsigned(test_case(7 downto 4)));
 			sum := A_t+B_t;
-			
+
 			S0_t := to_unsigned(sum,5)(0);
 			S1_t := to_unsigned(sum,5)(1);
 			S2_t := to_unsigned(sum,5)(2);
 			S3_t := to_unsigned(sum,5)(3);
 			C_out_t := to_unsigned(sum,5)(4);
-			
+
 			wait for 5 ns;
-				
 			If S(0) /= S0_t then
 				OK <= false;
 			end if;
-			
 			if S(1) /= S1_t then
 				OK <= false;
 			end if;
-			
 			if S(2) /= S2_t then
 				OK <= false;
 			end if;
-			
 			if S(3) /= S3_t then
 				OK <= false;
 			end if;
-			
 			if C_out /= C_out_t then
 				OK <= false;
 			end if;
-			
 			wait for 5 ns;
-			
-		
 		end loop;
-		
-		
-		
-      WAIT; -- will wait forever
-   END PROCESS;
--- *** End Test Bench - User Defined Section ***
-
-END;
\ No newline at end of file
+		wait; -- stop for simulator
+	end process;
+end;
diff --git a/full-adder/full-adder.srcs/sources_1/add4b.vhd b/full-adder/full-adder.srcs/sources_1/add4b.vhd
index 28c2c24..e70862b 100644
--- a/full-adder/full-adder.srcs/sources_1/add4b.vhd
+++ b/full-adder/full-adder.srcs/sources_1/add4b.vhd
@@ -2,6 +2,7 @@ LIBRARY ieee;
 USE ieee.std_logic_1164.ALL;
 USE ieee.numeric_std.ALL;
 
+-- half adder entity
 entity half_add is
   port (
     A: in std_logic;
@@ -16,10 +17,13 @@ begin
   X <= (A XOR B);
 end Behavioral;
 
+
+
 LIBRARY ieee;
 USE ieee.std_logic_1164.ALL;
 USE ieee.numeric_std.ALL;
 
+-- full adder entity
 entity add1b is
   port (
     A: in std_logic;
@@ -34,25 +38,31 @@ architecture Behavioral of add1b is
   signal s1: std_logic;
   signal s2: std_logic;
 begin
+	-- first add A and B with HA
   add0: entity work.half_add
     port map (
       A => A,
       B => B,
       X => s0,
       Cout => s1);
+	-- then add first result with Cin to get final result
   add1: entity work.half_add
     port map (
       A => Cin,
       B => s0,
       X => X,
       Cout => s2);
+	-- calculate Cout by OR-ing the Cout of both half adders
   Cout <= (s2 OR s1);
 end Behavioral;
 
+
+
 LIBRARY ieee;
 USE ieee.std_logic_1164.ALL;
 USE ieee.numeric_std.ALL;
 
+-- full 4-bit adder entity
 entity add4b is
   port (
     A: in std_logic_vector(3 downto 0);
@@ -63,10 +73,11 @@ entity add4b is
 end add4b;
 
 architecture Behavioral of add4b is
-  signal C0: std_logic;
-  signal C1: std_logic;
-  signal C2: std_logic;
+  signal C0: std_logic; -- Cout0 -> Cin1
+  signal C1: std_logic; -- Cout1 -> Cin2
+  signal C2: std_logic; -- Cout2 -> Cin3
 begin
+	-- full adder ladder (e.g. Cin -> Cin0, Cout0 -> Cin1, ..., Cout3 -> Cout)
   add0: entity work.add1b
     port map (
       A => A(0),