path: root/lab4/KBD_ENC.vhd

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-- KBD ENC
-- Anders Nilsson
-- 16-feb-2016
-- Version 1.1


-- library declaration
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;            -- basic IEEE library
use IEEE.NUMERIC_STD.ALL;               -- IEEE library for the unsigned type
                                        -- and various arithmetic operations

-- entity
entity KBD_ENC is
  port ( clk	                : in std_logic;			-- system clock (100 MHz)
	 rst		        : in std_logic;			-- reset signal
         PS2KeyboardCLK	        : in std_logic; 		-- USB keyboard PS2 clock
         PS2KeyboardData	: in std_logic;			-- USB keyboard PS2 data
         data			: out std_logic_vector(7 downto 0);		-- tile data
         addr			: out unsigned(10 downto 0);	-- tile address
         we			: out std_logic);		-- write enable
end KBD_ENC;

-- architecture
architecture behavioral of KBD_ENC is
  signal PS2Clk			: std_logic;			-- Synchronized PS2 clock
  signal PS2Data		: std_logic;			-- Synchronized PS2 data
  signal PS2Clk_Q1, PS2Clk_Q2 	: std_logic;			-- PS2 clock one pulse flip flop
  signal PS2Clk_op 		: std_logic;			-- PS2 clock one pulse 
	
  signal PS2Data_sr 		: std_logic_vector(10 downto 0);-- PS2 data shift register
	
  signal PS2BitCounter	        : unsigned(3 downto 0);		-- PS2 bit counter
  signal make_Q			: std_logic;			-- make one pulselse flip flop
  signal make_op		: std_logic;			-- make one pulse

  type state_type is (IDLE, MAKE, BREAK);			-- declare state types for PS2
  signal PS2state : state_type;					-- PS2 state

  signal ScanCode		: std_logic_vector(7 downto 0);	-- scan code
  signal TileIndex		: std_logic_vector(7 downto 0);	-- tile index
  
  type curmov_type is (FORWARD, BACKWARD, NEWLINE);		-- declare cursor movement types
  signal curMovement : curmov_type;				-- cursor movement
	
  signal curposX		: unsigned(5 downto 0);		-- cursor X position
  signal curposY		: unsigned(4 downto 0);		-- cursor Y position
	
  type wr_type is (STANDBY, WRINDEX, WRCUR);			-- declare state types for write cycle
  signal WRstate : wr_type;					-- write cycle state

begin

  -- Synchronize PS2-KBD signals
  process(clk)
  begin
    if rising_edge(clk) then
      PS2Clk <= PS2KeyboardCLK;
      PS2Data <= PS2KeyboardData;
    end if;
  end process;

	
  -- Generate one cycle pulse from PS2 clock, negative edge

  process(clk)
  begin
    if rising_edge(clk) then
      if rst='1' then
        PS2Clk_Q1 <= '1';
        PS2Clk_Q2 <= '0';
      else
        PS2Clk_Q1 <= PS2Clk;
        PS2Clk_Q2 <= not PS2Clk_Q1;
      end if;
    end if;
  end process;
	
  PS2Clk_op <= (not PS2Clk_Q1) and (not PS2Clk_Q2);
	

  
  -- PS2 data shift register

  -- ***********************************
  -- *                                 *
  -- *  VHDL for :                     *
  -- *  PS2_data_shift_reg             *
  -- *                                 *
  -- ***********************************




  ScanCode <= PS2Data_sr(8 downto 1);
	
  -- PS2 bit counter
  -- The purpose of the PS2 bit counter is to tell the PS2 state machine when to change state

  -- ***********************************
  -- *                                 *
  -- *  VHDL for :                     *
  -- *  PS2_bit_Counter                *
  -- *                                 *
  -- ***********************************

	
	

  -- PS2 state
  -- Either MAKE or BREAK state is identified from the scancode
  -- Only single character scan codes are identified
  -- The behavior of multiple character scan codes is undefined

  -- ***********************************
  -- *                                 *
  -- *  VHDL for :                     *
  -- *  PS2_State                      *
  -- *                                 *
  -- ***********************************

	
	

  -- Scan Code -> Tile Index mapping
  with ScanCode select
    TileIndex <= x"00" when x"29",	-- space
                 x"01" when x"1C",	-- A
                 x"02" when x"32",	-- B
		 x"03" when x"21",	-- C
		 x"04" when x"23",	-- D
		 x"05" when x"24",	-- E
		 x"06" when x"2B",	-- F
		 x"07" when x"34",	-- G
		 x"08" when x"33",	-- H
		 x"09" when x"43",	-- I
		 x"0A" when x"3B",	-- J
		 x"0B" when x"42",	-- K
		 x"0C" when x"4B",	-- L
		 x"0D" when x"3A",	-- M
		 x"0E" when x"31",	-- N
		 x"0F" when x"44",	-- O
		 x"10" when x"4D",	-- P
		 x"11" when x"15",	-- Q
		 x"12" when x"2D",	-- R
		 x"13" when x"1B",	-- S
		 x"14" when x"2C",	-- T
		 x"15" when x"3C",	-- U
		 x"16" when x"2A",	-- V
		 x"17" when x"1D",	-- W
		 x"18" when x"22",	-- X
		 x"19" when x"35",	-- Y
		 x"1A" when x"1A",	-- Z
                 x"1B" when x"54",      -- Å
                 x"1C" when x"52",      -- Ä
                 x"1D" when x"4C",      -- Ö
		 x"00" when others;
						 
						 
  -- set cursor movement based on scan code
  with ScanCode select
    curMovement <= NEWLINE when x"5A",	        -- enter scancode (5A), so move cursor to next line
                   BACKWARD when x"66",	        -- backspace scancode (66), so move cursor backward
                   FORWARD when others;	        -- for all other scancodes, move cursor forward


  -- curposX
  -- update cursor X position based on current cursor position (curposX and curposY) and cursor
  -- movement (curMovement)
  process(clk)
  begin
    if rising_edge(clk) then
      if rst='1' then
        curposX <= (others => '0');
      elsif (WRstate = WRINDEX) then
        if (curMovement = FORWARD) then
          if (curposX = 19) then
            curposX <= (others => '0');
          else
            curposX <= curposX + 1;
          end if;
        elsif (curMovement = BACKWARD) then
          if ((curposX = 0) and (curposY >= 0)) then
            curposX <= to_unsigned(19, curposX'length);
          else
            curposX <= curposX - 1;
          end if;
        elsif (curMovement = NEWLINE) then
          curposX <= (others => '0');
        end if;
      end if;
    end if;
  end process;
	

  -- curposY
  -- update cursor Y position based on current cursor position (curposX and curposY) and cursor
  -- movement (curMovement)
  process(clk)
  begin
    if rising_edge(clk) then
      if rst='1' then
        curposY <= (others => '0');
      elsif (WRstate = WRINDEX) then
        if (curMovement = FORWARD) then
          if (curposX = 19) then
            if (curposY = 14) then
              curposY <= (others => '0');
            else
              curposY <= curposY + 1;
            end if;
          end if;
        elsif (curMovement = BACKWARD) then
          if (curposX = 0) then
            if (curposY = 0) then
              curposY <= to_unsigned(14, curposY'length);
            else
              curposY <= curposY - 1;
            end if;
          end if;
        elsif (curMovement = NEWLINE) then
          if (curposY = 14) then
            curposY <= (others => '0');
          else
            curposY <= curposY + 1;
          end if;
        end if;
      end if;
    end if;
  end process;


  -- write state
  -- every write cycle begins with writing the character tile index at the current
  -- cursor position, then moving to the next cursor position and there write the
  -- cursor tile index
  process(clk)
  begin
    if rising_edge(clk) then
      if rst='1' then
        WRstate <= STANDBY;
      else
        case WRstate is
          when STANDBY =>
            if (PS2state = MAKE) then
              WRstate <= WRINDEX;
            else
              WRstate <= STANDBY;
            end if;
          when WRINDEX =>
            WRstate <= WRCUR;
          when WRCUR =>
            WRstate <= STANDBY;
          when others =>
            WRstate <= STANDBY;
        end case;
      end if;
    end if;
  end process;
	

  -- we will be enabled ('1') for two consecutive clock cycles during WRINDEX and WRCUR states
  -- and disabled ('0') otherwise at STANDBY state
  we <= '0' when (WRstate = STANDBY) else '1';


  -- memory address is a composite of curposY and curposX
  -- the "to_unsigned(20, 6)" is needed to generate a correct size of the resulting unsigned vector
  addr <= to_unsigned(20, 6)*curposY + curposX;

  
  -- data output is set to be x"1F" (cursor tile index) during WRCUR state, otherwise set as scan code tile index
  data <= x"1F" when (WRstate =  WRCUR) else TileIndex;

  
end behavioral;