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--##############################################################################

--

--  aluBOpSelector

--      ALU B-operand selector

--

--      This multiplexer brings the proper data on the B-input of the ALU.

--

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

--

--  Versions / Authors

--      1.0 Francois Corthay    first implementation

--

--  Provided under GNU LGPL licence: <http://www.gnu.org/copyleft/lesser.html>

--

--  by the electronics group of "HES-SO//Valais Wallis", in Switzerland:

--  <http://www.hevs.ch/en/rad-instituts/institut-systemes-industriels/>.

--

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--

--  Hierarchy

--      Used by "nanoblaze/nanoProcessor/aluAndRegs".

--

--##############################################################################

LIBRARY ieee;

  USE ieee.std_logic_1164.all;

  USE ieee.numeric_std.all;

ENTITY aluBOpSelector IS

  GENERIC(

    registerBitNb : positive := 8

  );

  PORT(

      instrData       : IN  signed(registerBitNb-1 DOWNTO 0);

      instrDataSel    : IN  std_ulogic;

      portIn          : IN  signed(registerBitNb-1 DOWNTO 0);

      portInSel       : IN  std_ulogic;

      registerFileIn  : IN  signed(registerBitNb-1 DOWNTO 0);

      registerFileSel : IN  std_ulogic;

      scratchpadSel   : IN  std_ulogic;

      spadIn          : IN  signed(registerBitNb-1 DOWNTO 0);

      opB             : OUT signed (registerBitNb-1 DOWNTO 0)

  );

END aluBOpSelector ;

--==============================================================================

ARCHITECTURE RTL OF aluBOpSelector IS

BEGIN

  selectDataSource: process(

    registerFileSel, registerFileIn,

    scratchpadSel,   spadIn,

    portInSel,       portIn,

    instrDataSel,    instrData

  )

  begin

    if registerFileSel = '1' then

      opB <= registerFileIn;

    elsif scratchpadSel = '1' then

      opB <= spadIn;

    elsif portInSel = '1' then

      opB <= portIn;

    elsif instrDataSel = '1' then

      opB <= instrData;

    else

      opB <= (others => '-');

    end if;

  end process selectDataSource;

END ARCHITECTURE RTL;