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`resetall
`timescale 1ns/100ps
`define TOTAL_BITS 11
`define EXTEND_CODE 16'hE0
`define RELEASE_CODE 16'hF0
`define LEFT_SHIFT 16'h12
`define RIGHT_SHIFT 16'h59
module ps2_keyboard_interface (
clk,
reset,
ps2_clk,
ps2_data,
rx_extended,
rx_released,
rx_shift_key_on,
rx_scan_code,
rx_ascii,
rx_data_ready, // rx_read_o
rx_read, // rx_read_ack_i
tx_data,
tx_write,
tx_write_ack_o,
tx_error_no_keyboard_ack
);
// Parameters
// The timer value can be up to (2^bits) inclusive.
parameter TIMER_60USEC_VALUE_PP = 2950; // Number of sys_clks for 60usec.
parameter TIMER_60USEC_BITS_PP = 12; // Number of bits needed for timer
parameter TIMER_5USEC_VALUE_PP = 186; // Number of sys_clks for debounce
parameter TIMER_5USEC_BITS_PP = 8; // Number of bits needed for timer
parameter TRAP_SHIFT_KEYS_PP = 0; // Default: No shift key trap.
// State encodings, provided as parameters
// for flexibility to the one instantiating the module.
// In general, the default values need not be changed.
// State "m1_rx_clk_l" has been chosen on purpose. Since the input
// synchronizing flip-flops initially contain zero, it takes one clk
// for them to update to reflect the actual (idle = high) status of
// the I/O lines from the keyboard. Therefore, choosing 0 for m1_rx_clk_l
// allows the state machine to transition to m1_rx_clk_h when the true
// values of the input signals become present at the outputs of the
// synchronizing flip-flops. This initial transition is harmless, and it
// eliminates the need for a "reset" pulse before the interface can operate.
parameter m1_rx_clk_h = 1;
parameter m1_rx_clk_l = 0;
parameter m1_rx_falling_edge_marker = 13;
parameter m1_rx_rising_edge_marker = 14;
parameter m1_tx_force_clk_l = 3;
parameter m1_tx_first_wait_clk_h = 10;
parameter m1_tx_first_wait_clk_l = 11;
parameter m1_tx_reset_timer = 12;
parameter m1_tx_wait_clk_h = 2;
parameter m1_tx_clk_h = 4;
parameter m1_tx_clk_l = 5;
parameter m1_tx_wait_keyboard_ack = 6;
parameter m1_tx_done_recovery = 7;
parameter m1_tx_error_no_keyboard_ack = 8;
parameter m1_tx_rising_edge_marker = 9;
parameter m2_rx_data_ready = 1;
parameter m2_rx_data_ready_ack = 0;
// I/O declarations
input clk;
input reset;
inout ps2_clk;
inout ps2_data;
output rx_extended;
output rx_released;
output rx_shift_key_on;
output [7:0] rx_scan_code;
output [7:0] rx_ascii;
output rx_data_ready;
input rx_read;
input [7:0] tx_data;
input tx_write;
output tx_write_ack_o;
output tx_error_no_keyboard_ack;
reg rx_extended;
reg rx_released;
reg [7:0] rx_scan_code;
reg [7:0] rx_ascii;
reg rx_data_ready;
reg tx_error_no_keyboard_ack;
// Internal signal declarations
wire timer_60usec_done;
wire timer_5usec_done;
wire extended;
wire released;
wire shift_key_on;
// NOTE: These two signals used to be one. They
// were split into two signals because of
// shift key trapping. With shift key
// trapping, no event is generated externally,
// but the "hold" data must still be cleared
// anyway regardless, in preparation for the
// next scan codes.
wire rx_output_event; // Used only to clear: hold_released, hold_extended
wire rx_output_strobe; // Used to produce the actual output.
wire tx_parity_bit;
wire rx_shifting_done;
wire tx_shifting_done;
wire [11:0] shift_key_plus_code;
reg [`TOTAL_BITS-1:0] q;
reg [3:0] m1_state;
reg [3:0] m1_next_state;
reg m2_state;
reg m2_next_state;
reg [3:0] bit_count;
reg enable_timer_60usec;
reg enable_timer_5usec;
reg [TIMER_60USEC_BITS_PP-1:0] timer_60usec_count;
reg [TIMER_5USEC_BITS_PP-1:0] timer_5usec_count;
reg [7:0] ascii; // "REG" type only because a case statement is used.
reg left_shift_key;
reg right_shift_key;
reg hold_extended; // Holds prior value, cleared at rx_output_strobe
reg hold_released; // Holds prior value, cleared at rx_output_strobe
reg ps2_clk_s; // Synchronous version of this input
reg ps2_data_s; // Synchronous version of this input
reg ps2_clk_hi_z; // Without keyboard, high Z equals 1 due to pullups.
reg ps2_data_hi_z; // Without keyboard, high Z equals 1 due to pullups.
//--------------------------------------------------------------------------
// Module code
assign ps2_clk = ps2_clk_hi_z?1'bZ:1'b0;
assign ps2_data = ps2_data_hi_z?1'bZ:1'b0;
// Input "synchronizing" logic -- synchronizes the inputs to the state
// machine clock, thus avoiding errors related to
// spurious state machine transitions.
always @(posedge clk)
begin
ps2_clk_s <= ps2_clk;
ps2_data_s <= ps2_data;
end
// State register
always @(posedge clk)
begin : m1_state_register
if (reset) m1_state <= m1_rx_clk_h;
else m1_state <= m1_next_state;
end
// State transition logic
always @(m1_state
or q
or tx_shifting_done
or tx_write
or ps2_clk_s
or ps2_data_s
or timer_60usec_done
or timer_5usec_done
)
begin : m1_state_logic
// Output signals default to this value, unless changed in a state condition.
ps2_clk_hi_z <= 1;
ps2_data_hi_z <= 1;
tx_error_no_keyboard_ack <= 0;
enable_timer_60usec <= 0;
enable_timer_5usec <= 0;
case (m1_state)
m1_rx_clk_h :
begin
enable_timer_60usec <= 1;
if (tx_write) m1_next_state <= m1_tx_reset_timer;
else if (~ps2_clk_s) m1_next_state <= m1_rx_falling_edge_marker;
else m1_next_state <= m1_rx_clk_h;
end
m1_rx_falling_edge_marker :
begin
enable_timer_60usec <= 0;
m1_next_state <= m1_rx_clk_l;
end
m1_rx_rising_edge_marker :
begin
enable_timer_60usec <= 0;
m1_next_state <= m1_rx_clk_h;
end
m1_rx_clk_l :
begin
enable_timer_60usec <= 1;
if (tx_write) m1_next_state <= m1_tx_reset_timer;
else if (ps2_clk_s) m1_next_state <= m1_rx_rising_edge_marker;
else m1_next_state <= m1_rx_clk_l;
end
m1_tx_reset_timer:
begin
enable_timer_60usec <= 0;
m1_next_state <= m1_tx_force_clk_l;
end
m1_tx_force_clk_l :
begin
enable_timer_60usec <= 1;
ps2_clk_hi_z <= 0; // Force the ps2_clk line low.
if (timer_60usec_done) m1_next_state <= m1_tx_first_wait_clk_h;
else m1_next_state <= m1_tx_force_clk_l;
end
m1_tx_first_wait_clk_h :
begin
enable_timer_5usec <= 1;
ps2_data_hi_z <= 0; // Start bit.
if (~ps2_clk_s && timer_5usec_done)
m1_next_state <= m1_tx_clk_l;
else
m1_next_state <= m1_tx_first_wait_clk_h;
end
// This state must be included because the device might possibly
// delay for up to 10 milliseconds before beginning its clock pulses.
// During that waiting time, we cannot drive the data (q[0]) because it
// is possibly 1, which would cause the keyboard to abort its receive
// and the expected clocks would then never be generated.
m1_tx_first_wait_clk_l :
begin
ps2_data_hi_z <= 0;
if (~ps2_clk_s) m1_next_state <= m1_tx_clk_l;
else m1_next_state <= m1_tx_first_wait_clk_l;
end
m1_tx_wait_clk_h :
begin
enable_timer_5usec <= 1;
ps2_data_hi_z <= q[0];
if (ps2_clk_s && timer_5usec_done)
m1_next_state <= m1_tx_rising_edge_marker;
else
m1_next_state <= m1_tx_wait_clk_h;
end
m1_tx_rising_edge_marker :
begin
ps2_data_hi_z <= q[0];
m1_next_state <= m1_tx_clk_h;
end
m1_tx_clk_h :
begin
ps2_data_hi_z <= q[0];
if (tx_shifting_done) m1_next_state <= m1_tx_wait_keyboard_ack;
else if (~ps2_clk_s) m1_next_state <= m1_tx_clk_l;
else m1_next_state <= m1_tx_clk_h;
end
m1_tx_clk_l :
begin
ps2_data_hi_z <= q[0];
if (ps2_clk_s) m1_next_state <= m1_tx_wait_clk_h;
else m1_next_state <= m1_tx_clk_l;
end
m1_tx_wait_keyboard_ack :
begin
if (~ps2_clk_s && ps2_data_s)
m1_next_state <= m1_tx_error_no_keyboard_ack;
else if (~ps2_clk_s && ~ps2_data_s)
m1_next_state <= m1_tx_done_recovery;
else m1_next_state <= m1_tx_wait_keyboard_ack;
end
m1_tx_done_recovery :
begin
if (ps2_clk_s && ps2_data_s) m1_next_state <= m1_rx_clk_h;
else m1_next_state <= m1_tx_done_recovery;
end
m1_tx_error_no_keyboard_ack :
begin
tx_error_no_keyboard_ack <= 1;
if (ps2_clk_s && ps2_data_s) m1_next_state <= m1_rx_clk_h;
else m1_next_state <= m1_tx_error_no_keyboard_ack;
end
default : m1_next_state <= m1_rx_clk_h;
endcase
end
// State register
always @(posedge clk)
begin : m2_state_register
if (reset) m2_state <= m2_rx_data_ready_ack;
else m2_state <= m2_next_state;
end
// State transition logic
always @(m2_state or rx_output_strobe or rx_read)
begin : m2_state_logic
case (m2_state)
m2_rx_data_ready_ack:
begin
rx_data_ready <= 1'b0;
if (rx_output_strobe) m2_next_state <= m2_rx_data_ready;
else m2_next_state <= m2_rx_data_ready_ack;
end
m2_rx_data_ready:
begin
rx_data_ready <= 1'b1;
if (rx_read) m2_next_state <= m2_rx_data_ready_ack;
else m2_next_state <= m2_rx_data_ready;
end
default : m2_next_state <= m2_rx_data_ready_ack;
endcase
end
// This is the bit counter
always @(posedge clk)
begin
if ( reset
|| rx_shifting_done
|| (m1_state == m1_tx_wait_keyboard_ack) // After tx is done.
) bit_count <= 0; // normal reset
else if (timer_60usec_done
&& (m1_state == m1_rx_clk_h)
&& (ps2_clk_s)
) bit_count <= 0; // rx watchdog timer reset
else if ( (m1_state == m1_rx_falling_edge_marker) // increment for rx
||(m1_state == m1_tx_rising_edge_marker) // increment for tx
)
bit_count <= bit_count + 1;
end
// This signal is high for one clock at the end of the timer count.
assign rx_shifting_done = (bit_count == `TOTAL_BITS);
assign tx_shifting_done = (bit_count == `TOTAL_BITS-1);
// This is the signal which enables loading of the shift register.
// It also indicates "ack" to the device writing to the transmitter.
assign tx_write_ack_o = ( (tx_write && (m1_state == m1_rx_clk_h))
||(tx_write && (m1_state == m1_rx_clk_l))
);
// This is the ODD parity bit for the transmitted word.
assign tx_parity_bit = ~^tx_data;
// This is the shift register
always @(posedge clk)
begin
if (reset) q <= 0;
else if (tx_write_ack_o) q <= {1'b1,tx_parity_bit,tx_data,1'b0};
else if ( (m1_state == m1_rx_falling_edge_marker)
||(m1_state == m1_tx_rising_edge_marker) )
q <= {ps2_data_s,q[`TOTAL_BITS-1:1]};
end
// This is the 60usec timer counter
always @(posedge clk)
begin
if (~enable_timer_60usec) timer_60usec_count <= 0;
else if (~timer_60usec_done) timer_60usec_count <= timer_60usec_count + 1;
end
assign timer_60usec_done = (timer_60usec_count == (TIMER_60USEC_VALUE_PP - 1));
// This is the 5usec timer counter
always @(posedge clk)
begin
if (~enable_timer_5usec) timer_5usec_count <= 0;
else if (~timer_5usec_done) timer_5usec_count <= timer_5usec_count + 1;
end
assign timer_5usec_done = (timer_5usec_count == TIMER_5USEC_VALUE_PP - 1);
// Create the signals which indicate special scan codes received.
// These are the "unlatched versions."
assign extended = (q[8:1] == `EXTEND_CODE) && rx_shifting_done;
assign released = (q[8:1] == `RELEASE_CODE) && rx_shifting_done;
// Store the special scan code status bits
// Not the final output, but an intermediate storage place,
// until the entire set of output data can be assembled.
always @(posedge clk)
begin
if (reset || rx_output_event)
begin
hold_extended <= 0;
hold_released <= 0;
end
else
begin
if (rx_shifting_done && extended) hold_extended <= 1;
if (rx_shifting_done && released) hold_released <= 1;
end
end
// These bits contain the status of the two shift keys
always @(posedge clk)
begin
if (reset) left_shift_key <= 0;
else if ((q[8:1] == `LEFT_SHIFT) && rx_shifting_done && ~hold_released)
left_shift_key <= 1;
else if ((q[8:1] == `LEFT_SHIFT) && rx_shifting_done && hold_released)
left_shift_key <= 0;
end
always @(posedge clk)
begin
if (reset) right_shift_key <= 0;
else if ((q[8:1] == `RIGHT_SHIFT) && rx_shifting_done && ~hold_released)
right_shift_key <= 1;
else if ((q[8:1] == `RIGHT_SHIFT) && rx_shifting_done && hold_released)
right_shift_key <= 0;
end
assign rx_shift_key_on = left_shift_key || right_shift_key;
// Output the special scan code flags, the scan code and the ascii
always @(posedge clk)
begin
if (reset)
begin
rx_extended <= 0;
rx_released <= 0;
rx_scan_code <= 0;
rx_ascii <= 0;
end
else if (rx_output_strobe)
begin
rx_extended <= hold_extended;
rx_released <= hold_released;
rx_scan_code <= q[8:1];
rx_ascii <= ascii;
end
end
// Store the final rx output data only when all extend and release codes
// are received and the next (actual key) scan code is also ready.
// (the presence of rx_extended or rx_released refers to the
// the current latest scan code received, not the previously latched flags.)
assign rx_output_event = (rx_shifting_done
&& ~extended
&& ~released
);
assign rx_output_strobe = (rx_shifting_done
&& ~extended
&& ~released
&& ( (TRAP_SHIFT_KEYS_PP == 0)
|| ( (q[8:1] != `RIGHT_SHIFT)
&&(q[8:1] != `LEFT_SHIFT)
)
)
);
// This part translates the scan code into an ASCII value...
// Only the ASCII codes which I considered important have been included.
// if you want more, just add the appropriate case statement lines...
// (You will need to know the keyboard scan codes you wish to assign.)
// The entries are listed in ascending order of ASCII value.
assign shift_key_plus_code = {3'b0,rx_shift_key_on,q[8:1]};
always @(shift_key_plus_code)
begin
casez (shift_key_plus_code)
12'h?66 : ascii <= 8'h08; // Backspace ("backspace" key)
12'h?0d : ascii <= 8'h09; // Horizontal Tab
12'h?5a : ascii <= 8'h0d; // Carriage return ("enter" key)
12'h?76 : ascii <= 8'h1b; // Escape ("esc" key)
12'h?29 : ascii <= 8'h20; // Space
12'h116 : ascii <= 8'h21; // !
12'h152 : ascii <= 8'h22; // "
12'h126 : ascii <= 8'h23; // #
12'h125 : ascii <= 8'h24; // $
12'h12e : ascii <= 8'h25; // %
12'h13d : ascii <= 8'h26; // &
12'h052 : ascii <= 8'h27; // '
12'h146 : ascii <= 8'h28; // (
12'h145 : ascii <= 8'h29; // )
12'h13e : ascii <= 8'h2a; // *
12'h155 : ascii <= 8'h2b; // +
12'h041 : ascii <= 8'h2c; // ,
12'h04e : ascii <= 8'h2d; // -
12'h049 : ascii <= 8'h2e; // .
12'h04a : ascii <= 8'h2f; // /
12'h045 : ascii <= 8'h30; // 0
12'h016 : ascii <= 8'h31; // 1
12'h01e : ascii <= 8'h32; // 2
12'h026 : ascii <= 8'h33; // 3
12'h025 : ascii <= 8'h34; // 4
12'h02e : ascii <= 8'h35; // 5
12'h036 : ascii <= 8'h36; // 6
12'h03d : ascii <= 8'h37; // 7
12'h03e : ascii <= 8'h38; // 8
12'h046 : ascii <= 8'h39; // 9
12'h14c : ascii <= 8'h3a; // :
12'h04c : ascii <= 8'h3b; // ;
12'h141 : ascii <= 8'h3c; // <
12'h055 : ascii <= 8'h3d; // =
12'h149 : ascii <= 8'h3e; // >
12'h14a : ascii <= 8'h3f; // ?
12'h11e : ascii <= 8'h40; // @
12'h11c : ascii <= 8'h41; // A
12'h132 : ascii <= 8'h42; // B
12'h121 : ascii <= 8'h43; // C
12'h123 : ascii <= 8'h44; // D
12'h124 : ascii <= 8'h45; // E
12'h12b : ascii <= 8'h46; // F
12'h134 : ascii <= 8'h47; // G
12'h133 : ascii <= 8'h48; // H
12'h143 : ascii <= 8'h49; // I
12'h13b : ascii <= 8'h4a; // J
12'h142 : ascii <= 8'h4b; // K
12'h14b : ascii <= 8'h4c; // L
12'h13a : ascii <= 8'h4d; // M
12'h131 : ascii <= 8'h4e; // N
12'h144 : ascii <= 8'h4f; // O
12'h14d : ascii <= 8'h50; // P
12'h115 : ascii <= 8'h51; // Q
12'h12d : ascii <= 8'h52; // R
12'h11b : ascii <= 8'h53; // S
12'h12c : ascii <= 8'h54; // T
12'h13c : ascii <= 8'h55; // U
12'h12a : ascii <= 8'h56; // V
12'h11d : ascii <= 8'h57; // W
12'h122 : ascii <= 8'h58; // X
12'h135 : ascii <= 8'h59; // Y
12'h11a : ascii <= 8'h5a; // Z
12'h054 : ascii <= 8'h5b; // [
12'h05d : ascii <= 8'h5c; // \
12'h05b : ascii <= 8'h5d; // ]
12'h136 : ascii <= 8'h5e; // ^
12'h14e : ascii <= 8'h5f; // _
12'h00e : ascii <= 8'h60; // `
12'h01c : ascii <= 8'h61; // a
12'h032 : ascii <= 8'h62; // b
12'h021 : ascii <= 8'h63; // c
12'h023 : ascii <= 8'h64; // d
12'h024 : ascii <= 8'h65; // e
12'h02b : ascii <= 8'h66; // f
12'h034 : ascii <= 8'h67; // g
12'h033 : ascii <= 8'h68; // h
12'h043 : ascii <= 8'h69; // i
12'h03b : ascii <= 8'h6a; // j
12'h042 : ascii <= 8'h6b; // k
12'h04b : ascii <= 8'h6c; // l
12'h03a : ascii <= 8'h6d; // m
12'h031 : ascii <= 8'h6e; // n
12'h044 : ascii <= 8'h6f; // o
12'h04d : ascii <= 8'h70; // p
12'h015 : ascii <= 8'h71; // q
12'h02d : ascii <= 8'h72; // r
12'h01b : ascii <= 8'h73; // s
12'h02c : ascii <= 8'h74; // t
12'h03c : ascii <= 8'h75; // u
12'h02a : ascii <= 8'h76; // v
12'h01d : ascii <= 8'h77; // w
12'h022 : ascii <= 8'h78; // x
12'h035 : ascii <= 8'h79; // y
12'h01a : ascii <= 8'h7a; // z
12'h154 : ascii <= 8'h7b; // {
12'h15d : ascii <= 8'h7c; // |
12'h15b : ascii <= 8'h7d; // }
12'h10e : ascii <= 8'h7e; // ~
12'h?71 : ascii <= 8'h7f; // (Delete OR DEL on numeric keypad)
default : ascii <= 8'h2e; // '.' used for unlisted characters.
endcase
end
endmodule
//`undefine TOTAL_BITS
//`undefine EXTEND_CODE
//`undefine RELEASE_CODE
//`undefine LEFT_SHIFT
//`undefine RIGHT_SHIFT

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