kbd.vhd

--------------------------------------------------------------------------------
--
--    FileName:         kbd.vhd
--    Dependencies:     debounce.vhd
--    Design Software:  Quartus II 32-bit Version 12.1 Build 177 SJ Full Version
--
--    HDL CODE is PROVIDED "AS IS."  DIGI-KEY EXPRESSLY DISCLAIMS ANY
--    WARRANTY OF ANY KIND, WHETHER EXPRESS OR IMPLIED, INCLUDING BUT NOT
--    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
--    PARTICULAR PURPOSE, OR NON-INFRINGEMENT. IN NO EVENT SHALL DIGI-KEY
--    BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT OR CONSEQUENTIAL
--    DAMAGES, LOST PROFITS OR LOST DATA, HARM TO YOUR EQUIPMENT, COST OF
--    PROCUREMENT OF SUBSTITUTE GOODS, TECHNOLOGY OR SERVICES, ANY CLAIMS
--    BY THIRD PARTIES (INCLUDING BUT NOT LIMITED TO ANY DEFENSE THEREOF),
--    ANY CLAIMS FOR INDEMNITY OR CONTRIBUTION, OR OTHER SIMILAR COSTS.
--
--    Version History
--    Version 1.0 11/29/2013 Scott Larson
--      Initial Public Release
--
--  See https://eewiki.net/pages/viewpage.action?pageId=28279002
--
--  @note This file has been renamed and updated from the original.
--------------------------------------------------------------------------------
library ieee;
use ieee.std_logic_1164.all;
use work.util.common_generics;

package kbd_pkg is

	component ps2_kbd_top is
		generic(
			clock_frequency:           integer := 50000000; -- system clock frequency in Hz
			ps2_debounce_counter_size: integer := 8);       -- set such that 2^size/clock_frequency = 5us (size = 8 for 50MHz)
		port(
			clk:        in  std_ulogic;                     -- system clock input
			ps2_clk:    in  std_ulogic;                     -- clock signal from PS2 keyboard
			ps2_data:   in  std_ulogic;                     -- data signal from PS2 keyboard
			ascii_new:  out std_ulogic := '0';              -- output flag indicating new ascii value
			ascii_code: out std_ulogic_vector(6 downto 0)); -- ASCII value
	end component;

	component ps2_kbd_core is
	generic(
		clock_frequency: integer := 50000000;  -- system clock frequency in Hz
		debounce_counter_size: integer := 8);  -- set such that (2^size)/clock_frequency = 5us (size = 8 for 50MHz)
	port(
		clk:          in  std_ulogic; -- system clock
		ps2_clk:      in  std_ulogic; -- clock signal from PS/2 keyboard
		ps2_data:     in  std_ulogic; -- data signal from PS/2 keyboard
		ps2_code_new: out std_ulogic; -- flag that new PS/2 code is available on ps2_code bus
		ps2_code:     out std_ulogic_vector(7 downto 0)); -- code received from PS/2
	end component;

	component ps2_debounce is
		generic(counter_size:  integer := 19); --counter size (19 bits gives 10.5ms with 50MHz clock)
		port(
			clk:    in  std_ulogic;
			button: in  std_ulogic;  --input signal to be debounced
			result: out std_ulogic := '0'); --debounced signal
	end component;

	component keyboard is
		generic(
			g: common_generics;
			ps2_debounce_counter_size: integer := 8);       -- set such that 2^size/clock_frequency = 5us (size = 8 for 50MHz)
		port(
			clk:              in  std_ulogic;        -- system clock input
			rst:              in  std_ulogic;        -- system reset

			ps2_clk:          in  std_ulogic;        -- clock signal from PS2 keyboard
			ps2_data:         in  std_ulogic;        -- data signal from PS2 keyboard

			kbd_char_re:      in  std_ulogic;        -- acknowledge kbd_char_buf_new
			kbd_char_buf_new: out std_ulogic := '0'; -- output flag indicating new ascii value
			kbd_char_buf:     out std_ulogic_vector(6 downto 0)); -- ASCII value
	end component;
end package;

------ Keyboard ----------------------------------------------------------------
library ieee, work;
use ieee.std_logic_1164.all;
use work.kbd_pkg.all;
use work.util.common_generics;

entity keyboard is
	generic(
		g: common_generics;
		ps2_debounce_counter_size: integer := 8);       -- set such that 2^size/clock_frequency = 5us (size = 8 for 50MHz)
	port(
		clk:              in  std_ulogic;        -- system clock input
		rst:              in  std_ulogic;        -- system reset

		ps2_clk:          in  std_ulogic;        -- clock signal from PS2 keyboard
		ps2_data:         in  std_ulogic;        -- data signal from PS2 keyboard

		kbd_char_re:      in  std_ulogic;        -- acknowledge kbd_char_buf_new
		kbd_char_buf_new: out std_ulogic := '0'; -- output flag indicating new ascii value
		kbd_char_buf:     out std_ulogic_vector(6 downto 0)); -- ASCII value
end entity;

architecture rtl of keyboard  is
	signal kbd_new_c, kbd_new_n:  std_ulogic := '0';
	signal kbd_new_edge: std_ulogic := '0';
	signal kbd_new:      std_ulogic := '0'; -- new ASCII char available
	signal kbd_char:     std_ulogic_vector(kbd_char_buf'range) := (others => '0'); -- ASCII char
begin
	kbd_char_buf_new <= kbd_new_c after g.delay;

	ps2_next: process(clk, rst)
	begin
		if rst = '1' and g.asynchronous_reset then
			kbd_new_c  <= '0' after g.delay;
		elsif rising_edge(clk) then
			if rst = '1' and not g.asynchronous_reset then
				kbd_new_c <= '0' after g.delay;
			else
				kbd_new_c   <= kbd_new_n after g.delay;
			end if;
		end if;
	end process;

	new_char: entity work.reg
	generic map(g => g, N => kbd_char'length)
	port map(
		clk => clk,
		rst => rst,
		di  => kbd_char,
		we  => kbd_new_edge,
		do  => kbd_char_buf);

	ps2_proc: process(kbd_new_edge, kbd_new_c, kbd_char_re)
	begin
		if kbd_new_edge = '1' then
			kbd_new_n  <= '1' after g.delay;
		elsif kbd_char_re = '1' then
			kbd_new_n  <= '0' after g.delay;
		else
			kbd_new_n  <= kbd_new_c after g.delay;
		end if;
	end process;

	-- Process a kbd_new into a single edge for the rest of the
	-- system.
	ps2_edge_new_character_0: entity work.rising_edge_detector
	generic map(g => g)
	port map(
		clk => clk,
		rst => rst,
		di  => kbd_new,
		do  => kbd_new_edge);

	ps2_0: work.kbd_pkg.ps2_kbd_top
	generic map(
		clock_frequency => g.clock_frequency,
		ps2_debounce_counter_size => ps2_debounce_counter_size)
	port map(
		clk        => clk,
		ps2_clk    => ps2_clk,
		ps2_data   => ps2_data,
		ascii_new  => kbd_new,
		ascii_code => kbd_char);
end architecture;
------ Keyboard ----------------------------------------------------------------

------ PS2 KBD TOP -------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;
use work.kbd_pkg.all;

entity ps2_kbd_top is
	generic(
		clock_frequency:           integer := 50000000; -- system clock frequency in Hz
		ps2_debounce_counter_size: integer := 8);       -- set such that 2^size/clock_frequency = 5us (size = 8 for 50MHz)
	port(
		clk:        in  std_ulogic;                     -- system clock input
		ps2_clk:    in  std_ulogic;                     -- clock signal from PS2 keyboard
		ps2_data:   in  std_ulogic;                     -- data signal from PS2 keyboard
		ascii_new:  out std_ulogic := '0';              -- output flag indicating new ascii value
		ascii_code: out std_ulogic_vector(6 downto 0)); -- ASCII value
end entity;

architecture rtl of ps2_kbd_top is
	type machine is(ready, new_code, translate, output); -- needed states
	signal state: machine;                               -- state machine
	signal ps2_code_new: std_ulogic;                      -- new PS2 code flag from ps2_kbd_core component
	signal ps2_code:     std_ulogic_vector(7 downto 0);   -- PS2 code input form ps2_kbd_core component
	signal prev_ps2_code_new: std_ulogic := '1';          -- value of ps2_code_new flag on previous clock
	signal break:        std_ulogic := '0';               -- '1' for break code, '0' for make code
	signal e0_code:      std_ulogic := '0';               -- '1' for multi-code commands, '0' for single code commands
	signal caps_lock:    std_ulogic := '0';               -- '1' if caps lock is active, '0' if caps lock is inactive
	signal control_r:    std_ulogic := '0';               -- '1' if right control key is held down, else '0'
	signal control_l:    std_ulogic := '0';               -- '1' if left control key is held down, else '0'
	signal shift_r:      std_ulogic := '0';               -- '1' if right shift is held down, else '0'
	signal shift_l:      std_ulogic := '0';               -- '1' if left shift is held down, else '0'
	signal ascii:        std_ulogic_vector(7 downto 0) := x"FF"; -- internal value of ASCII translation

begin

	-- instantiate PS2 keyboard interface logic
	ps2_kbd_core_0: work.kbd_pkg.ps2_kbd_core
		generic map(
			clock_frequency       => clock_frequency,
			debounce_counter_size => ps2_debounce_counter_size)
		port map(
			clk                   => clk,
			ps2_clk               => ps2_clk,
			ps2_data              => ps2_data,
			ps2_code_new          => ps2_code_new,
			ps2_code              => ps2_code);

	process(clk)
	begin
	if rising_edge(clk) then
		prev_ps2_code_new <= ps2_code_new; -- keep track of previous ps2_code_new values to determine low-to-high transitions
		case state is

			-- ready state: wait for a new PS2 code to be received
			when ready =>
				if(prev_ps2_code_new = '0' AND ps2_code_new = '1') then -- new PS2 code received
					ascii_new <= '0';                               -- reset new ASCII code indicator
					state <= new_code;                              -- proceed to new_code state
				else                                                    -- no new PS2 code received yet
					state <= ready;                                 -- remain in ready state
				end if;

			-- new_code state: determine what to do with the new PS2 code
			when new_code =>
				if(ps2_code = x"F0") then    -- code indicates that next command is break
					break <= '1';        -- set break flag
					state <= ready;      -- return to ready state to await next PS2 code
				elsif(ps2_code = x"E0") then -- code indicates multi-key command
					e0_code <= '1';      -- set multi-code command flag
					state <= ready;      -- return to ready state to await next PS2 code
				else                         -- code is the last PS2 code in the make/break code
					ascii(7) <= '1';     -- set internal ascii value to unsupported code (for verification)
					state <= translate;  -- proceed to translate state
				end if;

			-- translate state: translate PS2 code to ASCII value
			when translate =>
					break <= '0';    -- reset break flag
					e0_code <= '0';  -- reset multi-code command flag

					-- handle codes for control, shift, and caps lock
					case ps2_code is
						when x"58" =>                   -- caps lock code
							if(break = '0') then    -- if make command
								caps_lock <= NOT caps_lock; -- toggle caps lock
							end if;
						when x"14" =>                   -- code for the control keys
							if(e0_code = '1') then          -- code for right control
								control_r <= NOT break; -- update right control flag
							else                            -- code for left control
								control_l <= NOT break; -- update left control flag
							end if;
						when x"12" =>                   -- left shift code
							shift_l <= NOT break;   -- update left shift flag
						when x"59" =>                   -- right shift code
							shift_r <= NOT break;   -- update right shift flag
						when others => null;
					end case;

					-- translate control codes (these do not depend on shift or caps lock)
					if(control_l = '1' OR control_r = '1') then
						case ps2_code is
							when x"1E" => ascii <= x"00"; -- ^@  NUL
							when x"1C" => ascii <= x"01"; -- ^A  SOH
							when x"32" => ascii <= x"02"; -- ^B  STX
							when x"21" => ascii <= x"03"; -- ^C  ETX
							when x"23" => ascii <= x"04"; -- ^D  EOT
							when x"24" => ascii <= x"05"; -- ^E  ENQ
							when x"2B" => ascii <= x"06"; -- ^F  ACK
							when x"34" => ascii <= x"07"; -- ^G  BEL
							when x"33" => ascii <= x"08"; -- ^H  BS
							when x"43" => ascii <= x"09"; -- ^I  HT
							when x"3B" => ascii <= x"0A"; -- ^J  LF
							when x"42" => ascii <= x"0B"; -- ^K  VT
							when x"4B" => ascii <= x"0C"; -- ^L  FF
							when x"3A" => ascii <= x"0D"; -- ^M  CR
							when x"31" => ascii <= x"0E"; -- ^N  SO
							when x"44" => ascii <= x"0F"; -- ^O  SI
							when x"4D" => ascii <= x"10"; -- ^P  DLE
							when x"15" => ascii <= x"11"; -- ^Q  DC1
							when x"2D" => ascii <= x"12"; -- ^R  DC2
							when x"1B" => ascii <= x"13"; -- ^S  DC3
							when x"2C" => ascii <= x"14"; -- ^T  DC4
							when x"3C" => ascii <= x"15"; -- ^U  NAK
							when x"2A" => ascii <= x"16"; -- ^V  SYN
							when x"1D" => ascii <= x"17"; -- ^W  ETB
							when x"22" => ascii <= x"18"; -- ^X  CAN
							when x"35" => ascii <= x"19"; -- ^Y  EM
							when x"1A" => ascii <= x"1A"; -- ^Z  SUB
							when x"54" => ascii <= x"1B"; -- ^[  ESC
							when x"5D" => ascii <= x"1C"; -- ^\  FS
							when x"5B" => ascii <= x"1D"; -- ^]  GS
							when x"36" => ascii <= x"1E"; -- ^^  RS
							when x"4E" => ascii <= x"1F"; -- ^_  US
							when x"4A" => ascii <= x"7F"; -- ^?  DEL
							when others => null;
						end case;
					else -- if control keys are not pressed

						-- translate characters that do not depend on shift, or caps lock
						case ps2_code is
							when x"29" => ascii <= x"20"; -- space
							when x"66" => ascii <= x"08"; -- backspace (BS control code)
							when x"0D" => ascii <= x"09"; -- tab (HT control code)
							when x"5A" => ascii <= x"0D"; -- enter (CR control code)
							when x"76" => ascii <= x"1B"; -- escape (ESC control code)
							when x"71" =>
								if(e0_code = '1') then  -- ps2 code for delete is a multi-key code
									ascii <= x"7F"; -- delete
								end if;
							when others => null;
						end case;

						-- translate letters (these depend on both shift and caps lock)
						if((shift_r = '0' AND shift_l = '0' AND caps_lock = '0') OR
							((shift_r = '1' OR shift_l = '1') AND caps_lock = '1')) then  -- letter is lowercase
							case ps2_code is
								when x"1C" => ascii <= x"61"; -- a
								when x"32" => ascii <= x"62"; -- b
								when x"21" => ascii <= x"63"; -- c
								when x"23" => ascii <= x"64"; -- d
								when x"24" => ascii <= x"65"; -- e
								when x"2B" => ascii <= x"66"; -- f
								when x"34" => ascii <= x"67"; -- g
								when x"33" => ascii <= x"68"; -- h
								when x"43" => ascii <= x"69"; -- i
								when x"3B" => ascii <= x"6A"; -- j
								when x"42" => ascii <= x"6B"; -- k
								when x"4B" => ascii <= x"6C"; -- l
								when x"3A" => ascii <= x"6D"; -- m
								when x"31" => ascii <= x"6E"; -- n
								when x"44" => ascii <= x"6F"; -- o
								when x"4D" => ascii <= x"70"; -- p
								when x"15" => ascii <= x"71"; -- q
								when x"2D" => ascii <= x"72"; -- r
								when x"1B" => ascii <= x"73"; -- s
								when x"2C" => ascii <= x"74"; -- t
								when x"3C" => ascii <= x"75"; -- u
								when x"2A" => ascii <= x"76"; -- v
								when x"1D" => ascii <= x"77"; -- w
								when x"22" => ascii <= x"78"; -- x
								when x"35" => ascii <= x"79"; -- y
								when x"1A" => ascii <= x"7A"; -- z
								when others => null;
							end case;
						else                                     -- letter is uppercase
							case ps2_code is
								when x"1C" => ascii <= x"41"; -- A
								when x"32" => ascii <= x"42"; -- B
								when x"21" => ascii <= x"43"; -- C
								when x"23" => ascii <= x"44"; -- D
								when x"24" => ascii <= x"45"; -- E
								when x"2B" => ascii <= x"46"; -- F
								when x"34" => ascii <= x"47"; -- G
								when x"33" => ascii <= x"48"; -- H
								when x"43" => ascii <= x"49"; -- I
								when x"3B" => ascii <= x"4A"; -- J
								when x"42" => ascii <= x"4B"; -- K
								when x"4B" => ascii <= x"4C"; -- L
								when x"3A" => ascii <= x"4D"; -- M
								when x"31" => ascii <= x"4E"; -- N
								when x"44" => ascii <= x"4F"; -- O
								when x"4D" => ascii <= x"50"; -- P
								when x"15" => ascii <= x"51"; -- Q
								when x"2D" => ascii <= x"52"; -- R
								when x"1B" => ascii <= x"53"; -- S
								when x"2C" => ascii <= x"54"; -- T
								when x"3C" => ascii <= x"55"; -- U
								when x"2A" => ascii <= x"56"; -- V
								when x"1D" => ascii <= x"57"; -- W
								when x"22" => ascii <= x"58"; -- X
								when x"35" => ascii <= x"59"; -- Y
								when x"1A" => ascii <= x"5A"; -- Z
								when others => null;
							end case;
						end if;

						-- translate numbers and symbols (these depend on shift but not caps lock)
						if(shift_l = '1' OR shift_r = '1') then  -- key's secondary character is desired
							case ps2_code is
								when x"16" => ascii <= x"21"; -- |
								when x"52" => ascii <= x"22"; -- "
								when x"26" => ascii <= x"23"; -- #
								when x"25" => ascii <= x"24"; -- $
								when x"2E" => ascii <= x"25"; -- %
								when x"3D" => ascii <= x"26"; -- &
								when x"46" => ascii <= x"28"; -- (
								when x"45" => ascii <= x"29"; -- )
								when x"3E" => ascii <= x"2A"; -- *
								when x"55" => ascii <= x"2B"; -- +
								when x"4C" => ascii <= x"3A"; -- :
								when x"41" => ascii <= x"3C"; -- <
								when x"49" => ascii <= x"3E"; -- >
								when x"4A" => ascii <= x"3F"; -- ?
								when x"1E" => ascii <= x"40"; -- @
								when x"36" => ascii <= x"5E"; -- ^
								when x"4E" => ascii <= x"5F"; -- _
								when x"54" => ascii <= x"7B"; -- {
								when x"5D" => ascii <= x"7C"; -- |
								when x"5B" => ascii <= x"7D"; -- }
								when x"0E" => ascii <= x"7E"; -- ~
								when others => null;
							end case;
						else -- key's primary character is desired
							case ps2_code is
								when x"45" => ascii <= x"30"; -- 0
								when x"16" => ascii <= x"31"; -- 1
								when x"1E" => ascii <= x"32"; -- 2
								when x"26" => ascii <= x"33"; -- 3
								when x"25" => ascii <= x"34"; -- 4
								when x"2E" => ascii <= x"35"; -- 5
								when x"36" => ascii <= x"36"; -- 6
								when x"3D" => ascii <= x"37"; -- 7
								when x"3E" => ascii <= x"38"; -- 8
								when x"46" => ascii <= x"39"; -- 9
								when x"52" => ascii <= x"27"; -- '
								when x"41" => ascii <= x"2C"; -- ,
								when x"4E" => ascii <= x"2D"; -- -
								when x"49" => ascii <= x"2E"; -- .
								when x"4A" => ascii <= x"2F"; -- /
								when x"4C" => ascii <= x"3B"; -- ;
								when x"55" => ascii <= x"3D"; -- =
								when x"54" => ascii <= x"5B"; -- [
								when x"5D" => ascii <= x"5C"; -- \
								when x"5B" => ascii <= x"5D"; -- ]
								when x"0E" => ascii <= x"60"; -- `
								when others => null;
							end case;
						end if;

					end if;

				if(break = '0') then  -- the code is a make
					state <= output;      -- proceed to output state
				else                  -- code is a break
					state <= ready;       -- return to ready state to await next PS2 code
				end if;

			-- output state: verify the code is valid and output the ASCII value
			when output =>
				if(ascii(7) = '0') then            -- the PS2 code has an ASCII output
					ascii_new <= '1';                  -- set flag indicating new ASCII output
					ascii_code <= ascii(6 downto 0);   -- output the ASCII value
				end if;
				state <= ready;                    -- return to ready state to await next PS2 code

		end case;
	end if;
	end process;

end;

--------------------------------------------------------------------------------
--
--   FileName:         ps2_kbd_core.vhd
--   Dependencies:     debounce.vhd
--   Design Software:  Quartus II 32-bit Version 12.1 Build 177 SJ Full Version
--
--   HDL CODE IS PROVIDED "AS IS."  DIGI-KEY EXPRESSLY DISCLAIMS ANY
--   WARRANTY OF ANY KIND, WHETHER EXPRESS OR IMPLIED, INCLUDING BUT NOT
--   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
--   PARTICULAR PURPOSE, OR NON-INFRINGEMENT. IN NO EVENT SHALL DIGI-KEY
--   BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT OR CONSEQUENTIAL
--   DAMAGES, LOST PROFITS OR LOST DATA, HARM TO YOUR EQUIPMENT, COST OF
--   PROCUREMENT OF SUBSTITUTE GOODS, TECHNOLOGY OR SERVICES, ANY CLAIMS
--   BY THIRD PARTIES (INCLUDING BUT NOT LIMITED TO ANY DEFENSE THEREOF),
--   ANY CLAIMS FOR INDEMNITY OR CONTRIBUTION, OR OTHER SIMILAR COSTS.
--
--   Version History
--   Version 1.0 11/25/2013 Scott Larson
--     Initial Public Release
--
--   @note This file has been modified from the original one found at
--   <https://eewiki.net/pages/viewpage.action?pageId=28279002>
--------------------------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;

entity ps2_kbd_core is
	generic(
		clock_frequency: integer := 50000000;  -- system clock frequency in Hz
		debounce_counter_size: integer := 8);  -- set such that (2^size)/clock_frequency = 5us (size = 8 for 50MHz)
	port(
		clk:          in  std_ulogic; -- system clock
		ps2_clk:      in  std_ulogic; -- clock signal from PS/2 keyboard
		ps2_data:     in  std_ulogic; -- data signal from PS/2 keyboard
		ps2_code_new: out std_ulogic; -- flag that new PS/2 code is available on ps2_code bus
		ps2_code:     out std_ulogic_vector(7 downto 0)); -- code received from PS/2
end entity;

architecture rtl of ps2_kbd_core is

	signal sync_ffs: std_ulogic_vector(1 downto 0);        -- synchronizer flip-flops for PS/2 signals
	signal ps2_clk_int: std_ulogic;                        -- debounced clock signal from PS/2 keyboard

	attribute buffer_type: string;
	attribute buffer_type of ps2_clk_int: signal is "BUFG";

	signal ps2_data_int: std_ulogic;                       -- debounced data signal from PS/2 keyboard
	signal ps2_word: std_ulogic_vector(10 downto 0);       -- stores the ps2 data word
	signal parity_error: std_ulogic;                       -- validate parity, start, and stop bits
	signal count_idle: integer range 0 to clock_frequency/18000; --counter to determine PS/2 is idle

begin

	--synchronizer flip-flops
	process(clk)
	begin
		if rising_edge(clk) then         -- rising edge of system clock
			sync_ffs(0) <= ps2_clk;  -- synchronize PS/2 clock signal
			sync_ffs(1) <= ps2_data; -- synchronize PS/2 data signal
		end if;
	end process;

	-- debounce ps2 input signals
	debounce_ps2_clk: work.kbd_pkg.ps2_debounce
	generic map(counter_size => debounce_counter_size)
	port map(clk => clk, button => sync_ffs(0), result => ps2_clk_int);

	debounce_ps2_data: work.kbd_pkg.ps2_debounce
	generic map(counter_size => debounce_counter_size)
	port map(clk => clk, button => sync_ffs(1), result => ps2_data_int);

	-- input ps2 data
	process(ps2_clk_int)
	begin
		if(ps2_clk_int'event and ps2_clk_int = '0') then          -- falling edge of ps2 clock
			ps2_word <= ps2_data_int & ps2_word(10 downto 1); -- shift in ps2 data bit
		end if;
	end process;

	-- verify that parity, start, and stop bits are all correct
	parity_error <= not (not ps2_word(0) and ps2_word(10) and (ps2_word(9) xor ps2_word(8) xor
	    ps2_word(7) xor ps2_word(6) xor ps2_word(5) xor ps2_word(4) xor ps2_word(3) xor
	    ps2_word(2) xor ps2_word(1)));

	-- determine if ps2 port is idle (i.e. last transaction is finished) and output result
	process(clk)
	begin
		if rising_edge(clk) then                           -- rising edge of system clock
			if(ps2_clk_int = '0') then                 -- low ps2 clock, PS/2 is active
				count_idle <= 0;                   -- reset idle counter
			elsif(count_idle /= clock_frequency/18_000) then  -- ps2 clock has been high less than a half clock period (<55us)
				count_idle <= count_idle + 1;      -- continue counting
			end if;

			if(count_idle = clock_frequency/18_000 and parity_error = '0') then  -- idle threshold reached and no errors detected
				ps2_code_new <= '1';                           -- set flag that new PS/2 code is available
				ps2_code <= ps2_word(8 downto 1);              -- output new PS/2 code
			else                                                   -- PS/2 port active or error detected
				ps2_code_new <= '0';                           -- set flag that PS/2 transaction is in progress
			end if;
		end if;
	end process;

end;

--------------------------------------------------------------------------------
--
--   FileName:         (originally) debounce.vhd
--   Dependencies:     none
--   Design Software:  Quartus II 32-bit Version 11.1 Build 173 SJ Full Version
--
--   HDL CODE IS PROVIDED "AS IS."  DIGI-KEY EXPRESSLY DISCLAIMS ANY
--   WARRANTY OF ANY KIND, WHETHER EXPRESS OR IMPLIED, INCLUDING BUT NOT
--   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
--   PARTICULAR PURPOSE, OR NON-INFRINGEMENT. IN NO EVENT SHALL DIGI-KEY
--   BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT OR CONSEQUENTIAL
--   DAMAGES, LOST PROFITS OR LOST DATA, HARM TO YOUR EQUIPMENT, COST OF
--   PROCUREMENT OF SUBSTITUTE GOODS, TECHNOLOGY OR SERVICES, ANY CLAIMS
--   BY THIRD PARTIES (INCLUDING BUT NOT LIMITED TO ANY DEFENSE THEREOF),
--   ANY CLAIMS FOR INDEMNITY OR CONTRIBUTION, OR OTHER SIMILAR COSTS.
--
--   Version History
--   Version 1.0 3/26/2012 Scott Larson
--     Initial Public Release
--
-- @note This file has been modified from the original one found
-- on the web from: <https://eewiki.net/pages/viewpage.action?pageId=28279002>
--
--------------------------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity ps2_debounce is
	generic(counter_size:  integer := 19); --counter size (19 bits gives 10.5ms with 50MHz clock)
	port(
		clk:    in  std_ulogic;
		button: in  std_ulogic;  --input signal to be debounced
		result: out std_ulogic := '0'); --debounced signal
end entity;

architecture rtl of ps2_debounce is
	signal flipflops:   std_ulogic_vector(1 downto 0); --input flip flops
	signal counter_set: std_ulogic;                    --sync reset to zero
	signal counter_out: unsigned(counter_size downto 0) := (others => '0'); --counter output
begin
	counter_set <= flipflops(0) xor flipflops(1);   --determine when to start/reset counter

	process(clk)
	begin
		if rising_edge(clk) then
			flipflops(0) <= button;
			flipflops(1) <= flipflops(0);
			if counter_set = '1'  then                  --reset counter because input is changing
				counter_out <= (others => '0');
			elsif counter_out(counter_size) = '0'  then --stable input time is not yet met
				counter_out <= counter_out + 1;
			else                                        --stable input time is met
				result <= flipflops(1);
			end if;
		end if;
	end process;
end;