-- /*Copyright (c) 2015, Adam Taylor
-- All rights reserved.

-- Redistribution and use in source and binary forms, with or without
-- modification, are permitted provided that the following conditions are met:

-- 1. Redistributions of source code must retain the above copyright notice, this
   -- list of conditions and the following disclaimer. 
-- 2. Redistributions in binary form must reproduce the above copyright notice,
   -- this list of conditions and the following disclaimer in the documentation
   -- and/or other materials provided with the distribution.

-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
-- ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
-- WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
-- DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
-- ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
-- (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
-- LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
-- ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
-- SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

-- The views and conclusions contained in the software and documentation are those
-- of the authors and should not be interpreted as representing official policies, 
-- either expressed or implied, of the FreeBSD Project*/
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity Adams_Perihperal_v1_0 is
	generic (
		-- Users to add parameters here

		-- User parameters ends
		-- Do not modify the parameters beyond this line


		-- Parameters of Axi Slave Bus Interface S00_AXI
		C_S00_AXI_DATA_WIDTH	: integer	:= 32;
		C_S00_AXI_ADDR_WIDTH	: integer	:= 4
	);
	port (
		-- Users to add ports here
        interrupt : out std_logic;
		-- User ports ends
		-- Do not modify the ports beyond this line
        

		-- Ports of Axi Slave Bus Interface S00_AXI
		s00_axi_aclk	: in std_logic;
		s00_axi_aresetn	: in std_logic;
		s00_axi_awaddr	: in std_logic_vector(C_S00_AXI_ADDR_WIDTH-1 downto 0);
		s00_axi_awprot	: in std_logic_vector(2 downto 0);
		s00_axi_awvalid	: in std_logic;
		s00_axi_awready	: out std_logic;
		s00_axi_wdata	: in std_logic_vector(C_S00_AXI_DATA_WIDTH-1 downto 0);
		s00_axi_wstrb	: in std_logic_vector((C_S00_AXI_DATA_WIDTH/8)-1 downto 0);
		s00_axi_wvalid	: in std_logic;
		s00_axi_wready	: out std_logic;
		s00_axi_bresp	: out std_logic_vector(1 downto 0);
		s00_axi_bvalid	: out std_logic;
		s00_axi_bready	: in std_logic;
		s00_axi_araddr	: in std_logic_vector(C_S00_AXI_ADDR_WIDTH-1 downto 0);
		s00_axi_arprot	: in std_logic_vector(2 downto 0);
		s00_axi_arvalid	: in std_logic;
		s00_axi_arready	: out std_logic;
		s00_axi_rdata	: out std_logic_vector(C_S00_AXI_DATA_WIDTH-1 downto 0);
		s00_axi_rresp	: out std_logic_vector(1 downto 0);
		s00_axi_rvalid	: out std_logic;
		s00_axi_rready	: in std_logic
	);
end Adams_Perihperal_v1_0;

architecture arch_imp of Adams_Perihperal_v1_0 is

	-- component declaration
	component Adams_Perihperal_v1_0_S00_AXI is
		generic (
		C_S_AXI_DATA_WIDTH	: integer	:= 32;
		C_S_AXI_ADDR_WIDTH	: integer	:= 4
		);
		port (
		-- Adam Interface
        Reg0 : OUT std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
        Reg1 : OUT std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
        Reg2 : OUT std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
        Reg3 : IN std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
        
		-- AXI Interface
		S_AXI_ACLK	: in std_logic;
		S_AXI_ARESETN	: in std_logic;
		S_AXI_AWADDR	: in std_logic_vector(C_S_AXI_ADDR_WIDTH-1 downto 0);
		S_AXI_AWPROT	: in std_logic_vector(2 downto 0);
		S_AXI_AWVALID	: in std_logic;
		S_AXI_AWREADY	: out std_logic;
		S_AXI_WDATA	: in std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
		S_AXI_WSTRB	: in std_logic_vector((C_S_AXI_DATA_WIDTH/8)-1 downto 0);
		S_AXI_WVALID	: in std_logic;
		S_AXI_WREADY	: out std_logic;
		S_AXI_BRESP	: out std_logic_vector(1 downto 0);
		S_AXI_BVALID	: out std_logic;
		S_AXI_BREADY	: in std_logic;
		S_AXI_ARADDR	: in std_logic_vector(C_S_AXI_ADDR_WIDTH-1 downto 0);
		S_AXI_ARPROT	: in std_logic_vector(2 downto 0);
		S_AXI_ARVALID	: in std_logic;
		S_AXI_ARREADY	: out std_logic;
		S_AXI_RDATA	: out std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
		S_AXI_RRESP	: out std_logic_vector(1 downto 0);
		S_AXI_RVALID	: out std_logic;
		S_AXI_RREADY	: in std_logic
		);
	end component Adams_Perihperal_v1_0_S00_AXI;



CONSTANT c : signed(16 DOWNTO 0) := to_signed(-577,17);
CONSTANT b : signed(16 DOWNTO 0) := to_signed(57910,17);
CONSTANT a : signed(16 DOWNTO 0) := to_signed(33610,17);

SIGNAL squared : signed(33 DOWNTO 0); -- register holds input squared.
SIGNAL cx2 : signed(50 DOWNTO 0); --register used to hold Cx2
SIGNAL bx : signed(33 DOWNTO 0); -- register used to hold bx
SIGNAL res_int : signed(16 DOWNTO 0); --register holding the temporary result


SIGNAL result : std_logic_vector(31 DOWNTO 0);
SIGNAL reg0   : std_logic_vector(31 DOWNTO 0);
SIGNAL reg1   : std_logic_vector(31 DOWNTO 0);
SIGNAL reg2   : std_logic_vector(31 DOWNTO 0);
SIGNAL reg3   : std_logic_vector(31 DOWNTO 0):=(OTHERS=>'0');

begin

-- Instantiation of Axi Bus Interface S00_AXI
Adams_Perihperal_v1_0_S00_AXI_inst : Adams_Perihperal_v1_0_S00_AXI
	generic map (
		C_S_AXI_DATA_WIDTH	=> C_S00_AXI_DATA_WIDTH,
		C_S_AXI_ADDR_WIDTH	=> C_S00_AXI_ADDR_WIDTH
	)
	port map (
	
	    reg0            => reg0,
	    reg1            => reg1,
	    reg2            => reg2,
	    reg3            => reg3,
	    
		S_AXI_ACLK	    => s00_axi_aclk,
		S_AXI_ARESETN	=> s00_axi_aresetn,
		S_AXI_AWADDR	=> s00_axi_awaddr,
		S_AXI_AWPROT	=> s00_axi_awprot,
		S_AXI_AWVALID	=> s00_axi_awvalid,
		S_AXI_AWREADY	=> s00_axi_awready,
		S_AXI_WDATA	    => s00_axi_wdata,
		S_AXI_WSTRB	    => s00_axi_wstrb,
		S_AXI_WVALID	=> s00_axi_wvalid,
		S_AXI_WREADY	=> s00_axi_wready,
		S_AXI_BRESP	    => s00_axi_bresp,
		S_AXI_BVALID	=> s00_axi_bvalid,
		S_AXI_BREADY	=> s00_axi_bready,
		S_AXI_ARADDR	=> s00_axi_araddr,
		S_AXI_ARPROT	=> s00_axi_arprot,
		S_AXI_ARVALID	=> s00_axi_arvalid,
		S_AXI_ARREADY	=> s00_axi_arready,
		S_AXI_RDATA	=> s00_axi_rdata,
		S_AXI_RRESP	=> s00_axi_rresp,
		S_AXI_RVALID	=> s00_axi_rvalid,
		S_AXI_RREADY	=> s00_axi_rready
	);

	-- Add user logic here
PROCESS(s00_axi_aclk)
BEGIN
    IF rising_edge(s00_axi_aclk) THEN
      squared <= signed( '0'& reg1(15 DOWNTO 0)) * signed('0'& reg1(15 DOWNTO 0)); 
      cx2 <= (squared * c);
      bx <= (signed('0'& reg1(15 DOWNTO 0))* b);
      res_int <= a + cx2(48 DOWNTO 32) + ("000"& bx(32 DOWNTO 19));
      result(15 downto 0) <= std_logic_vector(res_int(res_int'high -1 DOWNTO 0));
    END IF;
END PROCESS;

--PROCESS(s00_axi_aclk)
--BEGIN
--    IF rising_edge(s00_axi_aclk) THEN     
--      bx <= (signed('0'& reg1(15 DOWNTO 0))* b);
--    END IF;
--END PROCESS;

interrupt <= '0';
reg3 <= x"0000"& std_logic_vector(result(15 DOWNTO 0));	 
	-- User logic ends

end arch_imp;

File Two Adams_Perihperal_v1_0_S00_AXI.vhd
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

entity Adams_Perihperal_v1_0_S00_AXI is
	generic (
		-- Users to add parameters here

		-- User parameters ends
		-- Do not modify the parameters beyond this line

		-- Width of S_AXI data bus
		C_S_AXI_DATA_WIDTH	: integer	:= 32;
		-- Width of S_AXI address bus
		C_S_AXI_ADDR_WIDTH	: integer	:= 4
	);
	port (
		-- Users to add ports here
		Reg0 : OUT std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
        Reg1 : OUT std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
        Reg2 : OUT std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
        Reg3 : IN std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);

        
		-- User ports ends
		-- Do not modify the ports beyond this line

		-- Global Clock Signal
		S_AXI_ACLK	: in std_logic;
		-- Global Reset Signal. This Signal is Active LOW
		S_AXI_ARESETN	: in std_logic;
		-- Write address (issued by master, acceped by Slave)
		S_AXI_AWADDR	: in std_logic_vector(C_S_AXI_ADDR_WIDTH-1 downto 0);
		-- Write channel Protection type. This signal indicates the
    -- privilege and security level of the transaction, and whether
    -- the transaction is a data access or an instruction access.
		S_AXI_AWPROT	: in std_logic_vector(2 downto 0);
		-- Write address valid. This signal indicates that the master signaling
    -- valid write address and control information.
		S_AXI_AWVALID	: in std_logic;
		-- Write address ready. This signal indicates that the slave is ready
    -- to accept an address and associated control signals.
		S_AXI_AWREADY	: out std_logic;
		-- Write data (issued by master, acceped by Slave) 
		S_AXI_WDATA	: in std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
		-- Write strobes. This signal indicates which byte lanes hold
    -- valid data. There is one write strobe bit for each eight
    -- bits of the write data bus.    
		S_AXI_WSTRB	: in std_logic_vector((C_S_AXI_DATA_WIDTH/8)-1 downto 0);
		-- Write valid. This signal indicates that valid write
    -- data and strobes are available.
		S_AXI_WVALID	: in std_logic;
		-- Write ready. This signal indicates that the slave
    -- can accept the write data.
		S_AXI_WREADY	: out std_logic;
		-- Write response. This signal indicates the status
    -- of the write transaction.
		S_AXI_BRESP	: out std_logic_vector(1 downto 0);
		-- Write response valid. This signal indicates that the channel
    -- is signaling a valid write response.
		S_AXI_BVALID	: out std_logic;
		-- Response ready. This signal indicates that the master
    -- can accept a write response.
		S_AXI_BREADY	: in std_logic;
		-- Read address (issued by master, acceped by Slave)
		S_AXI_ARADDR	: in std_logic_vector(C_S_AXI_ADDR_WIDTH-1 downto 0);
		-- Protection type. This signal indicates the privilege
    -- and security level of the transaction, and whether the
    -- transaction is a data access or an instruction access.
		S_AXI_ARPROT	: in std_logic_vector(2 downto 0);
		-- Read address valid. This signal indicates that the channel
    -- is signaling valid read address and control information.
		S_AXI_ARVALID	: in std_logic;
		-- Read address ready. This signal indicates that the slave is
    -- ready to accept an address and associated control signals.
		S_AXI_ARREADY	: out std_logic;
		-- Read data (issued by slave)
		S_AXI_RDATA	: out std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
		-- Read response. This signal indicates the status of the
    -- read transfer.
		S_AXI_RRESP	: out std_logic_vector(1 downto 0);
		-- Read valid. This signal indicates that the channel is
    -- signaling the required read data.
		S_AXI_RVALID	: out std_logic;
		-- Read ready. This signal indicates that the master can
    -- accept the read data and response information.
		S_AXI_RREADY	: in std_logic
	);
end Adams_Perihperal_v1_0_S00_AXI;

architecture arch_imp of Adams_Perihperal_v1_0_S00_AXI is

	-- AXI4LITE signals
	signal axi_awaddr	: std_logic_vector(C_S_AXI_ADDR_WIDTH-1 downto 0);
	signal axi_awready	: std_logic;
	signal axi_wready	: std_logic;
	signal axi_bresp	: std_logic_vector(1 downto 0);
	signal axi_bvalid	: std_logic;
	signal axi_araddr	: std_logic_vector(C_S_AXI_ADDR_WIDTH-1 downto 0);
	signal axi_arready	: std_logic;
	signal axi_rdata	: std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
	signal axi_rresp	: std_logic_vector(1 downto 0);
	signal axi_rvalid	: std_logic;

	-- Example-specific design signals
	-- local parameter for addressing 32 bit / 64 bit C_S_AXI_DATA_WIDTH
	-- ADDR_LSB is used for addressing 32/64 bit registers/memories
	-- ADDR_LSB = 2 for 32 bits (n downto 2)
	-- ADDR_LSB = 3 for 64 bits (n downto 3)
	constant ADDR_LSB  : integer := (C_S_AXI_DATA_WIDTH/32)+ 1;
	constant OPT_MEM_ADDR_BITS : integer := 1;
	------------------------------------------------
	---- Signals for user logic register space example
	--------------------------------------------------
	---- Number of Slave Registers 4
	signal slv_reg0	:std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
	signal slv_reg1	:std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
	signal slv_reg2	:std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
	signal slv_reg3	:std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
	signal slv_reg_rden	: std_logic;
	signal slv_reg_wren	: std_logic;
	signal reg_data_out	:std_logic_vector(C_S_AXI_DATA_WIDTH-1 downto 0);
	signal byte_index	: integer;

begin
	-- I/O Connections assignments

	S_AXI_AWREADY	<= axi_awready;
	S_AXI_WREADY	<= axi_wready;
	S_AXI_BRESP	<= axi_bresp;
	S_AXI_BVALID	<= axi_bvalid;
	S_AXI_ARREADY	<= axi_arready;
	S_AXI_RDATA	<= axi_rdata;
	S_AXI_RRESP	<= axi_rresp;
	S_AXI_RVALID	<= axi_rvalid;
	-- Implement axi_awready generation
	-- axi_awready is asserted for one S_AXI_ACLK clock cycle when both
	-- S_AXI_AWVALID and S_AXI_WVALID are asserted. axi_awready is
	-- de-asserted when reset is low.

        Reg0 <= slv_reg0;
        Reg1 <= slv_reg1;
        Reg2 <= slv_reg2;
        slv_reg3 <= Reg3;

	process (S_AXI_ACLK)
	begin
	  if rising_edge(S_AXI_ACLK) then 
	    if S_AXI_ARESETN = '0' then
	      axi_awready <= '0';
	    else
	      if (axi_awready = '0' and S_AXI_AWVALID = '1' and S_AXI_WVALID = '1') then
	        -- slave is ready to accept write address when
	        -- there is a valid write address and write data
	        -- on the write address and data bus. This design 
	        -- expects no outstanding transactions. 
	        axi_awready <= '1';
	      else
	        axi_awready <= '0';
	      end if;
	    end if;
	  end if;
	end process;

	-- Implement axi_awaddr latching
	-- This process is used to latch the address when both 
	-- S_AXI_AWVALID and S_AXI_WVALID are valid. 

	process (S_AXI_ACLK)
	begin
	  if rising_edge(S_AXI_ACLK) then 
	    if S_AXI_ARESETN = '0' then
	      axi_awaddr <= (others => '0');
	    else
	      if (axi_awready = '0' and S_AXI_AWVALID = '1' and S_AXI_WVALID = '1') then
	        -- Write Address latching
	        axi_awaddr <= S_AXI_AWADDR;
	      end if;
	    end if;
	  end if;                   
	end process; 

	-- Implement axi_wready generation
	-- axi_wready is asserted for one S_AXI_ACLK clock cycle when both
	-- S_AXI_AWVALID and S_AXI_WVALID are asserted. axi_wready is 
	-- de-asserted when reset is low. 

	process (S_AXI_ACLK)
	begin
	  if rising_edge(S_AXI_ACLK) then 
	    if S_AXI_ARESETN = '0' then
	      axi_wready <= '0';
	    else
	      if (axi_wready = '0' and S_AXI_WVALID = '1' and S_AXI_AWVALID = '1') then
	          -- slave is ready to accept write data when 
	          -- there is a valid write address and write data
	          -- on the write address and data bus. This design 
	          -- expects no outstanding transactions.           
	          axi_wready <= '1';
	      else
	        axi_wready <= '0';
	      end if;
	    end if;
	  end if;
	end process; 

	-- Implement memory mapped register select and write logic generation
	-- The write data is accepted and written to memory mapped registers when
	-- axi_awready, S_AXI_WVALID, axi_wready and S_AXI_WVALID are asserted. Write strobes are used to
	-- select byte enables of slave registers while writing.
	-- These registers are cleared when reset (active low) is applied.
	-- Slave register write enable is asserted when valid address and data are available
	-- and the slave is ready to accept the write address and write data.
	slv_reg_wren <= axi_wready and S_AXI_WVALID and axi_awready and S_AXI_AWVALID ;

	process (S_AXI_ACLK)
	variable loc_addr :std_logic_vector(OPT_MEM_ADDR_BITS downto 0); 
	begin
	  if rising_edge(S_AXI_ACLK) then 
	    if S_AXI_ARESETN = '0' then
	      slv_reg0 <= (others => '0');
	      slv_reg1 <= (others => '0');
	      slv_reg2 <= (others => '0');
	     -- slv_reg3 <= (others => '0');
	    else
	      loc_addr := axi_awaddr(ADDR_LSB + OPT_MEM_ADDR_BITS downto ADDR_LSB);
	      if (slv_reg_wren = '1') then
	        case loc_addr is
	          when b"00" =>
	            for byte_index in 0 to (C_S_AXI_DATA_WIDTH/8-1) loop
	              if ( S_AXI_WSTRB(byte_index) = '1' ) then
	                -- Respective byte enables are asserted as per write strobes                   
	                -- slave registor 0
	                slv_reg0(byte_index*8+7 downto byte_index*8) <= S_AXI_WDATA(byte_index*8+7 downto byte_index*8);
	              end if;
	            end loop;
	          when b"01" =>
	            for byte_index in 0 to (C_S_AXI_DATA_WIDTH/8-1) loop
	              if ( S_AXI_WSTRB(byte_index) = '1' ) then
	                -- Respective byte enables are asserted as per write strobes                   
	                -- slave registor 1
	                slv_reg1(byte_index*8+7 downto byte_index*8) <= S_AXI_WDATA(byte_index*8+7 downto byte_index*8);
	              end if;
	            end loop;
	          when b"10" =>
	            for byte_index in 0 to (C_S_AXI_DATA_WIDTH/8-1) loop
	              if ( S_AXI_WSTRB(byte_index) = '1' ) then
	                -- Respective byte enables are asserted as per write strobes                   
	                -- slave registor 2
	                slv_reg2(byte_index*8+7 downto byte_index*8) <= S_AXI_WDATA(byte_index*8+7 downto byte_index*8);
	              end if;
	            end loop;
	          when b"11" =>
	            for byte_index in 0 to (C_S_AXI_DATA_WIDTH/8-1) loop
	              if ( S_AXI_WSTRB(byte_index) = '1' ) then
	                -- Respective byte enables are asserted as per write strobes                   
	                -- slave registor 3
	                -- slv_reg3(byte_index*8+7 downto byte_index*8) <= S_AXI_WDATA(byte_index*8+7 downto byte_index*8);
	              end if;
	            end loop;
	          when others =>
	            slv_reg0 <= slv_reg0;
	            slv_reg1 <= slv_reg1;
	            slv_reg2 <= slv_reg2;
	          --  slv_reg3 <= slv_reg3;
	        end case;
	      end if;
	    end if;
	  end if;                   
	end process; 

	-- Implement write response logic generation
	-- The write response and response valid signals are asserted by the slave 
	-- when axi_wready, S_AXI_WVALID, axi_wready and S_AXI_WVALID are asserted.  
	-- This marks the acceptance of address and indicates the status of 
	-- write transaction.

	process (S_AXI_ACLK)
	begin
	  if rising_edge(S_AXI_ACLK) then 
	    if S_AXI_ARESETN = '0' then
	      axi_bvalid  <= '0';
	      axi_bresp   <= "00"; --need to work more on the responses
	    else
	      if (axi_awready = '1' and S_AXI_AWVALID = '1' and axi_wready = '1' and S_AXI_WVALID = '1' and axi_bvalid = '0'  ) then
	        axi_bvalid <= '1';
	        axi_bresp  <= "00"; 
	      elsif (S_AXI_BREADY = '1' and axi_bvalid = '1') then   --check if bready is asserted while bvalid is high)
	        axi_bvalid <= '0';                                 -- (there is a possibility that bready is always asserted high)
	      end if;
	    end if;
	  end if;                   
	end process; 

	-- Implement axi_arready generation
	-- axi_arready is asserted for one S_AXI_ACLK clock cycle when
	-- S_AXI_ARVALID is asserted. axi_awready is 
	-- de-asserted when reset (active low) is asserted. 
	-- The read address is also latched when S_AXI_ARVALID is 
	-- asserted. axi_araddr is reset to zero on reset assertion.

	process (S_AXI_ACLK)
	begin
	  if rising_edge(S_AXI_ACLK) then 
	    if S_AXI_ARESETN = '0' then
	      axi_arready <= '0';
	      axi_araddr  <= (others => '1');
	    else
	      if (axi_arready = '0' and S_AXI_ARVALID = '1') then
	        -- indicates that the slave has acceped the valid read address
	        axi_arready <= '1';
	        -- Read Address latching 
	        axi_araddr  <= S_AXI_ARADDR;           
	      else
	        axi_arready <= '0';
	      end if;
	    end if;
	  end if;                   
	end process; 

	-- Implement axi_arvalid generation
	-- axi_rvalid is asserted for one S_AXI_ACLK clock cycle when both 
	-- S_AXI_ARVALID and axi_arready are asserted. The slave registers 
	-- data are available on the axi_rdata bus at this instance. The 
	-- assertion of axi_rvalid marks the validity of read data on the 
	-- bus and axi_rresp indicates the status of read transaction.axi_rvalid 
	-- is deasserted on reset (active low). axi_rresp and axi_rdata are 
	-- cleared to zero on reset (active low).  
	process (S_AXI_ACLK)
	begin
	  if rising_edge(S_AXI_ACLK) then
	    if S_AXI_ARESETN = '0' then
	      axi_rvalid <= '0';
	      axi_rresp  <= "00";
	    else
	      if (axi_arready = '1' and S_AXI_ARVALID = '1' and axi_rvalid = '0') then
	        -- Valid read data is available at the read data bus
	        axi_rvalid <= '1';
	        axi_rresp  <= "00"; -- 'OKAY' response
	      elsif (axi_rvalid = '1' and S_AXI_RREADY = '1') then
	        -- Read data is accepted by the master
	        axi_rvalid <= '0';
	      end if;            
	    end if;
	  end if;
	end process;

	-- Implement memory mapped register select and read logic generation
	-- Slave register read enable is asserted when valid address is available
	-- and the slave is ready to accept the read address.
	slv_reg_rden <= axi_arready and S_AXI_ARVALID and (not axi_rvalid) ;

	process (slv_reg0, slv_reg1, slv_reg2, slv_reg3, axi_araddr, S_AXI_ARESETN, slv_reg_rden)
	variable loc_addr :std_logic_vector(OPT_MEM_ADDR_BITS downto 0);
	begin
	  if S_AXI_ARESETN = '0' then
	    reg_data_out  <= (others => '1');
	  else
	    -- Address decoding for reading registers
	    loc_addr := axi_araddr(ADDR_LSB + OPT_MEM_ADDR_BITS downto ADDR_LSB);
	    case loc_addr is
	      when b"00" =>
	        reg_data_out <= slv_reg0;
	      when b"01" =>
	        reg_data_out <= slv_reg1;
	      when b"10" =>
	        reg_data_out <= slv_reg2;
	      when b"11" =>
	        reg_data_out <= slv_reg3;
	      when others =>
	        reg_data_out  <= (others => '0');
	    end case;
	  end if;
	end process; 

	-- Output register or memory read data
	process( S_AXI_ACLK ) is
	begin
	  if (rising_edge (S_AXI_ACLK)) then
	    if ( S_AXI_ARESETN = '0' ) then
	      axi_rdata  <= (others => '0');
	    else
	      if (slv_reg_rden = '1') then
	        -- When there is a valid read address (S_AXI_ARVALID) with 
	        -- acceptance of read address by the slave (axi_arready), 
	        -- output the read dada 
	        -- Read address mux
	          axi_rdata <= reg_data_out;     -- register read data
	      end if;   
	    end if;
	  end if;
	end process;


	-- Add user logic here

	-- User logic ends

end arch_imp;