Source-Code » VHDL » Barrel Shifter VHDL Code and Test Bench

Barrel Shifter VHDL Code and Test Bench

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barrel shifter
test bench
modelsim
synthesis

This document provides VHDL code for a Barrel Shifter, along with a corresponding test bench. It also presents the simulated and synthesized outputs obtained using ModelSIM and Leonardo Spectrum tools, respectively.

The Barrel Shifter’s primary functions are:

  • Rotating or shifting input data.
  • Rotating the data by a specified number of bits in a combinational manner.

Barrel Shifter VHDL Code

This VHDL model implements a Barrel Shifter that rotates the input data by a specified number of bits.

-- Develop a VHDL model for a Barrel shifter that rotates
-- the input data by the specified number of bits.
library ieee;
use ieee.std_logic_1164.all;

entity Barrel is
    port (
        clk,reset,load :in std_logic;
        data_in:in std_logic_vector (7 downto 0);
        data_out:out std_logic_vector (7 downto 0)
    );
end Barrel;

architecture Barrel of Barrel is
begin
    process (reset,clk,data_in)
        variable d: std_logic_vector (7 downto 0);
    begin
        if (reset = '0') then
            d:=(others => '0');
        elsif (clk'event and clk = '1') then
            if (load ='1') then
                d:=data_in;
            else
                d:= d(0) & d(7 downto 1) ;
            end if;
        end if;
        data_out<= d;
    end process;
end Barrel;

Barrel Shifter Test Bench in VHDL

The following code provides a test bench for the Barrel Shifter.

--test bench for barrel shifter
library ieee;
use ieee.std_logic_1164.all;

entity tb_Barrel is
end tb_Barrel;

architecture tb_Barrel of tb_Barrel is
    component Barrel
        port (
            clk,reset,load :in std_logic;
            data_in:in std_logic_vector (7 downto 0);
            data_out:out std_logic_vector (7 downto 0)
        );
    end component;

    signal clk,res,load : std_logic;
    signal d_in,d_out : std_logic_vector (7 downto 0);
begin
    br: Barrel port map (clk,res,load,d_in,d_out);

    process
    begin
        res <= '1';
        load <= '1';
        wait for 5 ns;
        load <= '1';
        clk<='0';
        d_in<="11111101";
        wait for 5 ns;
        clk<='1';
        d_in<="11111111";
        wait for 5 ns;
        res <= '1';
        d_in <= "01100101";
        load <= '1';
        wait for 5 ns;
        load <= '0';
        wait;
    end process;
end tb_Barrel;

Simulated Output

The simulated output of the Barrel Shifter, obtained using ModelSIM, is shown below:

Barrel Shifter simulated output

Figure 1: Simulated output of Barrel Shifter using ModelSim.

Synthesized Output

The synthesized output of the Barrel Shifter, obtained using Leonardo Spectrum Tool, is shown below:

Barrel Shifter synthesized output

Figure 2: Synthesized output of Barrel Shifter using Leonardo Spectrum Tool.

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