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

--

--  programCounter

--      Program counter

--

--      Addresses the instruction ROM.

--      Capable of incrementation, jump and function return

--

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

--

--  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/>.

--

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

--

--  Hierarchy

--      Used by "nanoblaze/nanoProcessor".

--

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

LIBRARY ieee;

  USE ieee.std_logic_1164.all;

  USE ieee.numeric_std.all;

ENTITY programCounter IS

  GENERIC(

    programCounterBitNb : positive := 10

  );

  PORT(

    reset             : IN  std_ulogic;

    clock             : IN  std_ulogic;

    instrAddress      : IN  unsigned(programCounterBitNb-1 DOWNTO 0);

    storedProgCounter : IN  unsigned(programCounterBitNb-1 DOWNTO 0);

    incPC             : IN  std_ulogic;

    loadInstrAddress  : IN  std_ulogic;

    loadStoredPC      : IN  std_ulogic;

    progCounter       : OUT unsigned(programCounterBitNb-1 DOWNTO 0)

  );

END programCounter ;

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

ARCHITECTURE RTL OF programCounter IS

  signal pCounter: unsigned(progCounter'range);

BEGIN

  updateProgramCounter: process(reset, clock)

  begin

    if reset = '1' then

      pCounter <= (others => '0');

    elsif rising_edge(clock) then

      if incPC = '1' then

        pCounter <= pCounter + 1;

      elsif loadInstrAddress = '1' then

        pCounter <= instrAddress;

      elsif loadStoredPC = '1' then

        pCounter <= storedProgCounter;

      end if;

    end if;

  end process updateProgramCounter;

  progCounter <= pCounter;

END ARCHITECTURE RTL;