module ultrasonic_fpga #(
    parameter integer CLK_FREQ = 27_000_000  // Fréquence d'horloge en Hz
)(
    input  wire clk,
    input  wire rst,
    input  wire start,
    inout  wire sig,                // Broche bidirectionnelle vers le capteur
    output reg [15:0] distance_cm  // Distance mesurée en cm
);

    reg [2:0] state;
    reg [15:0] trig_counter;
    reg [31:0] echo_counter;
    reg sig_out;
    reg sig_dir; // 1: output, 0: input

    assign sig = sig_dir ? sig_out : 1'bz;
    wire sig_in = sig;

    localparam IDLE         = 3'd0,
               TRIG_HIGH    = 3'd1,
               TRIG_LOW     = 3'd2,
               WAIT_ECHO    = 3'd3,
               MEASURE_ECHO = 3'd4,
               DONE         = 3'd5;

    localparam integer TRIG_PULSE_CYCLES = CLK_FREQ / 100_000; // 10us pulse
    localparam integer DIST_DIVISOR = (58 * CLK_FREQ) / 1_000_000; // pour conversion us -> cm

    always @(posedge clk or posedge rst) begin
        if (rst) begin
            state <= IDLE;
            trig_counter <= 0;
            echo_counter <= 0;
            sig_out <= 0;
            sig_dir <= 0;
            distance_cm <= 0;
        end else begin
            case (state)
                IDLE: begin
                    sig_out <= 0;
                    sig_dir <= 1;
                    if (start) begin
                        state <= TRIG_HIGH;
                        trig_counter <= 0;
                    end
                end

                TRIG_HIGH: begin
                    sig_out <= 1;
                    sig_dir <= 1;
                    if (trig_counter < TRIG_PULSE_CYCLES) begin
                        trig_counter <= trig_counter + 1;
                    end else begin
                        trig_counter <= 0;
                        state <= TRIG_LOW;
                    end
                end

                TRIG_LOW: begin
                    sig_out <= 0;
                    sig_dir <= 0; // Mettre en entrée
                    state <= WAIT_ECHO;
                end

                WAIT_ECHO: begin
                    if (sig_in) begin
                        echo_counter <= 0;
                        state <= MEASURE_ECHO;
                    end
                end

                MEASURE_ECHO: begin
                    if (sig_in) begin
                        echo_counter <= echo_counter + 1;
                    end else begin
                        distance_cm <= (echo_counter * 1000) / DIST_DIVISOR;
                        state <= DONE;
                    end
                end

                DONE: begin
                    state <= IDLE;
                end
            endcase
        end
    end

endmodule