dunkirk.sh
bouncy fpga game
www.youtube.com/watch?v=IiLWF3GbV7w
1-- ========================================================================
2-- PS2 Keyboard Decoder
3-- Receives serial data from a PS2 keyboard and outputs which
4-- WASD keys are currently held down.
5--
6-- PS2 protocol: 11 bits per key event (start, 8 data LSB first, parity, stop)
7-- Make code = key pressed, F0 + code = key released
8-- Scan codes: W=1D, A=1C, S=1B, D=23
9-- ========================================================================
10
11library IEEE;
12use IEEE.STD_LOGIC_1164.all;
13use IEEE.STD_LOGIC_UNSIGNED.all;
14
15entity ps2_decoder is
16 port(
17 ps2_clk : in std_logic; -- clock from keyboard
18 ps2_data : in std_logic; -- serial data from keyboard
19 key_w : out std_logic; -- '1' when W is held
20 key_a : out std_logic; -- '1' when A is held
21 key_s : out std_logic; -- '1' when S is held
22 key_d : out std_logic -- '1' when D is held
23 );
24end ps2_decoder;
25
26architecture behavior of ps2_decoder is
27 signal shift_reg : std_logic_vector(10 downto 0);
28 signal bit_count : std_logic_vector(3 downto 0) := (others => '0');
29 signal break_flag : std_logic := '0';
30 signal scan_code : std_logic_vector(7 downto 0);
31begin
32
33 -- Single process: shift in bits, decode when frame complete
34 ps2_receive : process(ps2_clk)
35 begin
36 if ps2_clk'event and ps2_clk = '0' then
37 -- Shift in new bit (MSB first into shift register)
38 shift_reg <= ps2_data & shift_reg(10 downto 1);
39
40 if bit_count = "1010" then
41 -- 11th bit received (stop bit), frame complete
42 -- Data byte is in shift_reg(9 downto 2) at this point:
43 -- shift_reg(10) = parity (from previous edge)
44 -- shift_reg(9) = data bit 7
45 -- shift_reg(2) = data bit 0
46 -- shift_reg(1) = start bit
47 scan_code <= shift_reg(9 downto 2);
48
49 -- Decode: F0 means next byte is a key release
50 if shift_reg(9 downto 2) = X"F0" then
51 break_flag <= '1';
52 elsif break_flag = '1' then
53 -- Key released
54 break_flag <= '0';
55 case shift_reg(9 downto 2) is
56 when X"1D" => key_w <= '0';
57 when X"1C" => key_a <= '0';
58 when X"1B" => key_s <= '0';
59 when X"23" => key_d <= '0';
60 when others => null;
61 end case;
62 else
63 -- Key pressed
64 case shift_reg(9 downto 2) is
65 when X"1D" => key_w <= '1';
66 when X"1C" => key_a <= '1';
67 when X"1B" => key_s <= '1';
68 when X"23" => key_d <= '1';
69 when others => null;
70 end case;
71 end if;
72
73 bit_count <= (others => '0');
74 else
75 bit_count <= bit_count + 1;
76 end if;
77 end if;
78 end process ps2_receive;
79
80end behavior;