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Query regarding 32bits ALU design
von NIDHI K. (Company: STUDENT) (n_khanna)

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I want to implement 32bits alu on nexys4 ddr fpga board but there is an 
issue regarding I/O pins number board has total 16 input pins so i was 
tring to write the code as follow- but i am not getting the simulation 
results outputs are coming as unsigned

1
ibrary IEEE;

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use IEEE.STD_LOGIC_1164.ALL;

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use IEEE.STD_LOGIC_ARITH.ALL;

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use IEEE.STD_LOGIC_UNSIGNED.ALL;

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entity alu_32 is

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port ( clk,reset : in std_logic;

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          sel : in std_logic_vector(2 downto 0);

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       a,b : in std_logic_vector(31 downto 0);

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       y : out std_logic_vector(31 downto 0) );

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end alu_32;

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architecture Behavioral of alu_32 is

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  --signal a : std_logic_vector(31 downto 0) ;

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  --signal  a,b : std_logic_vector(31 downto 0);

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  signal count1,count2 : std_logic_vector (1 downto 0);

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  signal atemp, btemp ,atemp1, btemp1: std_logic_vector(15 downto 0);

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  signal y1,y2  :std_logic_vector(31 downto 0);

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  begin

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process(clk)

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begin

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      if (reset='1')then

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     y<="00000000000000000000000000000000";

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     end if;

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    if (rising_edge(clk)) then 

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      if count1 ="11" then

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      count1 <= "00";

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      else 

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      count1 <= count1 + 1;

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      end if;

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    end if;

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        if  count1 = "00" then

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       atemp <= y1(31 downto 16);

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       elsif 

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       count1 = "01" then

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       btemp <= y1(15 downto 0);

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       elsif

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       count1 ="10" then

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       a<= atemp & btemp;

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     end if;

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      if  count2 = "00" then

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       atemp1 <= y2(31 downto 16);

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       elsif 

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       count2 = "01" then 

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       btemp1 <= y2(15 downto 0);

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       elsif 

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       count2 ="10" then

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       b<= atemp1 & btemp1;

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     end if;   

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end process;

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PROCESS (sel)

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begin

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 case sel is

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 when "001" => y <=  (a - b) ;

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 when "010" => y <=  not (a) ;

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 when "011" => y <=  (a xor  b) ;

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 when "100" => y <=  (a + b) ;

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 when "101" => y <=(a and b) ;

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 when "110" => y <=  (a or b) ;

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 when others => y <=  (a nand  b) ;

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 End case ;

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 end process ;

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end Behavioral;

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----------------------------------------------------------------

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TESTBENCH 

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LIBRARY ieee;

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USE ieee.std_logic_1164.ALL;

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USE ieee.std_logic_unsigned.all;

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USE ieee.numeric_std.ALL;

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ENTITY test32bit_vhd IS

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END test32bit_vhd;

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ARCHITECTURE behavior OF test32bit_vhd IS 

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  -- Component Declaration for the Unit Under Test (UUT)

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  COMPONENT alu32

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  PORT(

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    clk ,reset: IN std_logic;

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    sel : IN std_logic_vector(2 downto 0);    

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    a : INOUT std_logic_vector(31 downto 0);

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    b : INOUT std_logic_vector(31 downto 0);      

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    y : OUT std_logic_vector(31 downto 0)

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    );

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  END COMPONENT;

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  --Inputs

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  SIGNAL clk :  std_logic := '0';

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  SIGNAL reset :  std_logic := '0';

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  SIGNAL sel :  std_logic_vector(2 downto 0) := (others=>'0');

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  --BiDirs

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  SIGNAL a :  std_logic_vector(31 downto 0);

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  SIGNAL b :  std_logic_vector(31 downto 0);

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  --Outputs

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  SIGNAL y :  std_logic_vector(31 downto 0);

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  constant clkperiod : time := 100 ns;

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BEGIN

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  -- Instantiate the Unit Under Test (UUT)

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  uut: alu32 PORT MAP(

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    clk => clk,

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    reset => reset,

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    sel => sel,

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    a => a,

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    b => b,

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    y => y

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  );

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  clk_process : process

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  BEGIN

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clk <= '0';

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wait for clkperiod/2 ;

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clk <= '1';

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wait for clkperiod/2;

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end process;

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stimproces : process

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begin 

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    wait for 100 ns;

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    wait for 50 ns;

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    reset <= '1';

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    wait for 100 ns;

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    reset <= '0' ;

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    wait for 100 ns;

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    a <= "01011101010100111110000101100010";

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    b <= "00111100101011111100111001100111";

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    --enable <= '1';

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    sel <= "001";

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    wait for 200 ns;

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    sel <= "010";

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    wait for 200 ns;

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    wait; -- will wait forever

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  END PROCESS;

149
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END;


PLZ tell me the mistake i am doing in writing the codes

  


  



  

  
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    Re: Query regarding 32bits ALU design
  


  

    

      von
      
        Lothar M.
            (Company: Titel)
        (lkmiller)
        (Moderator)
      
      


      
    


    

      
    

    

    

  
  


  

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NIDHI K. wrote:
> i was tring to write the code as follow
Pls read and follow the instructions above every edit box. Here a 
summary:
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NIDHI K. wrote:
> PLZ tell me the mistake i am doing in writing the codes
What simulation result do you get and what did you expect?

>    if (reset='1')then
>       y<="00000000000000000000000000000000";
>    end if;
>    if (rising_edge(clk)) then ...
It is not possible to synthesize this, because its some kind of "clock 
sensitive despite reset" construct. I'm pretty sure you will not find 
such a piece of code elsewhere...

> but i am not getting the simulation results outputs are coming as
> unsigned
Do you 1. not get a result or 2. do you get an unsigned result?

> a : INOUT std_logic_vector(31 downto 0);
> b : INOUT std_logic_vector(31 downto 0);
Why the heck an inout here?
The components port must fit the entitys port.

> USE ieee.std_logic_unsigned.all;
> USE ieee.numeric_std.ALL;
Never ever use both of the packages together, because you may encouter 
strange errors due to double type definitions. I urge you to use only 
the numeric_std.

> PROCESS (sel)
> begin
In ths process sensitivity list the signals a and b are missing. That 
means your simulation is 1. wrong and 2. does not match the reality.


>        if  count1 = "00" then
>        atemp <= y1(31 downto 16);
>        elsif
>        count1 = "01" then
>        btemp <= y1(15 downto 0);
>        elsif
>        count1 ="10" then
>        a <= atemp & btemp;
This is kind of nonsense: splitting up a vector y1 and then 
concatenating it in three steps to the previous value. What is it good 
for?

> entity alu_32 is
> port ( clk,reset : in std_logic;
An Arithmetic Logic Unit usually does NOT have or need a clock. Why does 
yours?

  


  




  

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