`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Elektronska brava sa sifrom - PYNQ-Z2 verzija
//
// Korisceni pinovi na ploci:
//   button0, button1, button2, button3  -> PYNQ-Z2 push buttons
//   led0, led1, led2, led3              -> PYNQ-Z2 LEDs
//
// Tacna sifra:
//   button0 -> button1 -> button2 -> button3
//
// Reset sistema:
//   press button3 
//
// Znacenje LED dioda:
//   led0 = prvi korak sifre prihvacen
//   led1 = drugi korak sifre prihvacen
//   led2 = treci korak sifre prihvacen
//   led3 = pristup dozvoljen / sistem zakljucan
//////////////////////////////////////////////////////////////////////////////////

`timescale 1ns / 1ps

module electronic_lock_pynqz2(
    input  wire clk,
    input  wire button0,
    input  wire button1,
    input  wire button2,
    input  wire button3,
    output reg  led0,
    output reg  led1,
    output reg  led2,
    output reg  led3
);

    localparam integer CLK_FREQ = 125_000_000;
    localparam integer DEBOUNCE_LIMIT = 2_500_000;
    localparam integer LOCK_TIME = 5;

    localparam S_IDLE    = 3'd0;
    localparam S_KEY1    = 3'd1;
    localparam S_KEY2    = 3'd2;
    localparam S_KEY3    = 3'd3;
    localparam S_GRANTED = 3'd4;
    localparam S_ERROR   = 3'd5;
    localparam S_LOCKED  = 3'd6;

    reg [2:0] state = S_IDLE;
    reg [1:0] attempts = 2'd0;

    reg [3:0] btn_sync_0 = 4'b0000;
    reg [3:0] btn_sync_1 = 4'b0000;

    wire [3:0] buttons_raw;
    assign buttons_raw = {button3, button2, button1, button0};

    always @(posedge clk) begin
        btn_sync_0 <= buttons_raw;
        btn_sync_1 <= btn_sync_0;
    end

    reg [3:0] btn_last = 4'b0000;
    reg [3:0] btn_stable = 4'b0000;
    reg [21:0] debounce_cnt = 0;

    reg key_event = 1'b0;
    reg [1:0] key_code = 2'd0;

    always @(posedge clk) begin
        key_event <= 1'b0;

        if (btn_sync_1 != btn_last) begin
            btn_last <= btn_sync_1;
            debounce_cnt <= 0;
        end else begin
            if (debounce_cnt < DEBOUNCE_LIMIT) begin
                debounce_cnt <= debounce_cnt + 1;
            end else begin
                if (btn_stable != btn_sync_1) begin
                    btn_stable <= btn_sync_1;

                    if (btn_sync_1 != 4'b0000) begin
                        key_event <= 1'b1;

                        if (btn_sync_1[0]) key_code <= 2'd0;
                        else if (btn_sync_1[1]) key_code <= 2'd1;
                        else if (btn_sync_1[2]) key_code <= 2'd2;
                        else if (btn_sync_1[3]) key_code <= 2'd3;
                    end
                end
            end
        end
    end

    reg [27:0] sec_cnt = 0;
    reg one_sec_tick = 1'b0;

    always @(posedge clk) begin
        one_sec_tick <= 1'b0;

        if (sec_cnt == CLK_FREQ - 1) begin
            sec_cnt <= 0;
            one_sec_tick <= 1'b1;
        end else begin
            sec_cnt <= sec_cnt + 1;
        end
    end

    reg [3:0] lock_seconds = 0;
    reg blink = 1'b0;

    always @(posedge clk) begin
        if (one_sec_tick) begin
            blink <= ~blink;
        end
    end

    always @(posedge clk) begin
        case (state)

            S_IDLE: begin
                if (key_event) begin
                    if (key_code == 2'd0)
                        state <= S_KEY1;
                    else
                        state <= S_ERROR;
                end
            end

            S_KEY1: begin
                if (key_event) begin
                    if (key_code == 2'd1)
                        state <= S_KEY2;
                    else
                        state <= S_ERROR;
                end
            end

            S_KEY2: begin
                if (key_event) begin
                    if (key_code == 2'd2)
                        state <= S_KEY3;
                    else
                        state <= S_ERROR;
                end
            end

            S_KEY3: begin
                if (key_event) begin
                    if (key_code == 2'd3) begin
                        state <= S_GRANTED;
                        attempts <= 0;
                        lock_seconds <= 0;
                    end else begin
                        state <= S_ERROR;
                    end
                end
            end

            // Kada je brava otvorena, ponovni pritisak na button3 vraca sistem na pocetak
            S_GRANTED: begin
                if (key_event && key_code == 2'd3) begin
                    state <= S_IDLE;
                    attempts <= 0;
                    lock_seconds <= 0;
                end else begin
                    state <= S_GRANTED;
                end
            end

            S_ERROR: begin
                if (attempts == 2'd2) begin
                    attempts <= attempts + 1;
                    state <= S_LOCKED;
                    lock_seconds <= 0;
                end else begin
                    attempts <= attempts + 1;
                    state <= S_IDLE;
                end
            end

            S_LOCKED: begin
                if (one_sec_tick) begin
                    if (lock_seconds == LOCK_TIME - 1) begin
                        lock_seconds <= 0;
                        attempts <= 0;
                        state <= S_IDLE;
                    end else begin
                        lock_seconds <= lock_seconds + 1;
                    end
                end
            end

            default: begin
                state <= S_IDLE;
            end

        endcase
    end

    always @(*) begin
        led0 = 1'b0;
        led1 = 1'b0;
        led2 = 1'b0;
        led3 = 1'b0;

        case (state)

            S_IDLE: begin
                led0 = attempts[0];
                led1 = attempts[1];
            end

            S_KEY1: begin
                led0 = 1'b1;
            end

            S_KEY2: begin
                led0 = 1'b1;
                led1 = 1'b1;
            end

            S_KEY3: begin
                led0 = 1'b1;
                led1 = 1'b1;
                led2 = 1'b1;
            end

            S_GRANTED: begin
                led0 = 1'b1;
                led1 = 1'b1;
                led2 = 1'b1;
                led3 = 1'b1;
            end

            S_ERROR: begin
                led3 = 1'b1;
            end

            S_LOCKED: begin
                led0 = blink;
                led1 = blink;
                led2 = blink;
                led3 = blink;
            end

            default: begin
                led0 = 1'b0;
                led1 = 1'b0;
                led2 = 1'b0;
                led3 = 1'b0;
            end

        endcase
    end

endmodule