Subversion Repositories wb_vga

--

--  Wishbone bus toolkit.

--

--  (c) Copyright Andras Tantos <andras_tantos@yahoo.com> 2001/03/31

--  This code is distributed under the terms and conditions of the GNU General Public Lince.

--

--

-- ELEMENTS:

--   wb_io_reg: A slightly modified version of the wb_out_reg component

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

--

--  wb_io_reg. A slightly modified version of the wb_out_reg component

--

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

library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.STD_LOGIC_UNSIGNED.all;

library wb_tk;

use wb_tk.technology.all;

entity wb_io_reg is

        generic (

                width : positive := 8;

                bus_width: positive := 8;

                offset: integer := 0

        );

        port (

                clk_i: in std_logic;

                rst_i: in std_logic;

                rst_val: std_logic_vector(width-1 downto 0) := (others => '0');

        cyc_i: in std_logic := '1';

                stb_i: in std_logic;

        sel_i: in std_logic_vector ((bus_width/8)-1 downto 0) := (others => '1');

                we_i: in std_logic;

                ack_o: out std_logic;

                ack_oi: in std_logic := '-';

                adr_i: in std_logic_vector (size2bits((width+offset+bus_width-1)/bus_width)-1 downto 0) := (others => '0');

                dat_i: in std_logic_vector (bus_width-1 downto 0);

                dat_oi: in std_logic_vector (bus_width-1 downto 0) := (others => '-');

                dat_o: out std_logic_vector (bus_width-1 downto 0);

                q: out std_logic_vector (width-1 downto 0);

                ext_d: in std_logic_vector (width-1 downto 0) := (others => '-');

                ext_we: in std_logic := '0'

        );

end wb_io_reg;

architecture wb_io_reg of wb_io_reg is

        signal content : std_logic_vector (width-1 downto 0);

begin

        -- output bus handling with logic

        gen_dat_o: process is

                variable rd_sel: std_logic;

            variable adr: integer;

            variable reg_i: integer;

        begin

                wait on dat_oi, we_i, stb_i, content, adr_i, cyc_i, sel_i;

                rd_sel := cyc_i and stb_i and not we_i;

            for i in dat_i'RANGE loop

                adr := CONV_INTEGER(adr_i);

                reg_i := i-offset+adr*bus_width;

                if ((reg_i >= 0) and (reg_i < width) and (sel_i(i/8) = '1')) then

                                dat_o(i) <= (dat_oi(i) and not rd_sel) or (content(reg_i) and rd_sel);

                        else

                                dat_o(i) <= dat_oi(i);

                        end if;

                end loop;

        end process;

        -- this item never generates any wait-states unless an external write is under process

--      ack_o <= (stb_i or ack_oi) and (not (ext_we and we_i));

        ack_o <= (ack_oi and not stb_i) or ((not (ext_we and we_i)) and stb_i);

--      ack_o <= (stb_i or ack_oi);

        reg: process is

            variable adr: integer;

            variable reg_i: integer;

        begin

                wait until clk_i'EVENT and clk_i='1';

                if (rst_i = '1') then

                        content <= rst_val;

                else

                        if (ext_we = '1') then

                        content <= ext_d;

                        else

                                if (stb_i = '1' and cyc_i = '1' and we_i = '1') then

                                    for i in dat_i'RANGE loop

                                        adr := CONV_INTEGER(adr_i);

                                        reg_i := i-offset+adr*bus_width;

                                        if ((reg_i >= 0) and (reg_i < width) and (sel_i(i/8) = '1')) then

                                                content(reg_i) <=  dat_i(i);

                                            end if;

                                        end loop;

                                end if;

                        end if;

                end if;

        end process;

        q <= content;

end wb_io_reg;