-- MIPS I system
-- Copyright 2011-2012 Stefan Schuermans <stefan@schuermans.info>
-- Copyleft GNU public license V2 or later
--          http://www.gnu.org/copyleft/gpl.html

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.NUMERIC_STD.ALL;
USE work.io_lcd_pins.all;

ENTITY e_io_lcd IS
    PORT (
        rst:       IN  std_logic;
        clk:       IN  std_logic;
        o_rd_data: OUT std_logic_vector(31 DOWNTO 0);
        i_wr_data: IN  std_logic_vector(31 DOWNTO 0);
        i_wr_en:   IN  std_logic_vector( 3 DOWNTO 0);
        pin_o_lcd: OUT t_io_lcd_pins
    );
END ENTITY e_io_lcd;

ARCHITECTURE a_io_lcd OF e_io_lcd IS

    SIGNAL n_lcd: t_io_lcd_pins;
    SIGNAL r_lcd: t_io_lcd_pins := (data => (OTHERS => '0'),
                                    e => '0', rs => '0', rw => '0');

BEGIN

    p_next: PROCESS(r_lcd, i_wr_data, i_wr_en)
    BEGIN
        IF i_wr_en(0) = '1' THEN
            n_lcd.data <= i_wr_data(7 DOWNTO 0);
        ELSE
            n_lcd.data <= r_lcd.data;
        END IF;
        IF i_wr_en(1) = '1' THEN
            n_lcd.e <= i_wr_data(8);
        ELSE
            n_lcd.e <= r_lcd.e;
        END IF;
        IF i_wr_en(2) = '1' THEN
            n_lcd.rs <= i_wr_data(16);
        ELSE
            n_lcd.rs <= r_lcd.rs;
        END IF;
        IF i_wr_en(3) = '1' THEN
            n_lcd.rw <= i_wr_data(24);
        ELSE
            n_lcd.rw <= r_lcd.rw;
        END IF;
    END PROCESS p_next;

    p_sync: PROCESS(rst, clk)
    BEGIN
        IF rst = '1' THEN
            r_lcd.data <= (OTHERS => '0');
            r_lcd.e    <= '0';
            r_lcd.rs   <= '0';
            r_lcd.rw   <= '0';
        ELSIF rising_edge(clk) THEN
            r_lcd <= n_lcd;
        END IF;
    END PROCESS p_sync;

    p_read: PROCESS(rst, clk)
    BEGIN
        IF rst = '1' THEN
            o_rd_data <= (OTHERS => '0');
        ELSIF rising_edge(clk) THEN
            o_rd_data( 7 DOWNTO  0) <= r_lcd.data;
            o_rd_data( 8)           <= r_lcd.e;
            o_rd_data(15 DOWNTO  9) <= (OTHERS => '0');
            o_rd_data(16)           <= r_lcd.rs;
            o_rd_data(23 DOWNTO 17) <= (OTHERS => '0');
            o_rd_data(24)           <= r_lcd.rw;
            o_rd_data(31 DOWNTO 25) <= (OTHERS => '0');
        END IF;
    END PROCESS p_read;

    pin_o_lcd <= r_lcd;

END ARCHITECTURE a_io_lcd;