default : m1_next_state <= m1_rx_clk_h;  endcaseend// State registeralways @(posedge clk)begin : m2_state_register  if (reset) m2_state <= m2_rx_data_ready_ack;  else m2_state <= m2_next_state;end// State transition logicalways @(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;  endcaseend// This is the bit counteralways @(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// 輸入輸出移位妥當(dāng)邏輯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 registeralways @(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 counteralways @(posedge clk)begin  if (~enable_timer_60usec)   	  timer_60usec_count <= 0;  else if (~timer_60usec_done) timer_60usec_count <= timer_60usec_count + 1;endassign timer_60usec_done = (timer_60usec_count == (TIMER_60USEC_VALUE_PP - 1));// This is the 5usec timer counteralways @(posedge clk)begin  if (~enable_timer_5usec) timer_5usec_count <= 0;  else if (~timer_5usec_done) timer_5usec_count <= timer_5usec_count + 1;endassign 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;  endend// 左SHIFT鍵檢測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// 右SHIFT鍵檢測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;endassign rx_shift_key_on = left_shift_key || right_shift_key;// Output the special scan code flags, the scan code and the asciialways @(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;  endend// 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.  endcaseendendmodule//`undefine TOTAL_BITS//`undefine EXTEND_CODE//`undefine RELEASE_CODE//`undefine LEFT_SHIFT//`undefine RIGHT_SHIFT