// NII Core Surface Driver - FPGA Bitstream
// Based on Canonical Core v1 architecture
// Layer 6: Steady-State Stability (SSS) monitoring
// Layer 7: Alcubierre Information Metric
// FAMM-aware scheduling
// Topological state management
// Q16.16 fixed-point arithmetic

`timescale 1ns / 1ps

// ═══════════════════════════════════════════════════════════════════════════
// Q16.16 Fixed-Point Arithmetic
// ═══════════════════════════════════════════════════════════════════════════

module q16_16_add (
    input  [15:0] a,
    input  [15:0] b,
    output [15:0] sum
);
    assign sum = a + b;
endmodule

module q16_16_sub (
    input  [15:0] a,
    input  [15:0] b,
    output [15:0] diff
);
    assign diff = a - b;
endmodule

module q16_16_mul (
    input  [15:0] a,
    input  [15:0] b,
    output [15:0] product
);
    wire [31:0] temp;
    assign temp = a * b;
    assign product = temp[30:15];  // Extract Q16.16 result
endmodule

module q16_16_div (
    input  [15:0] numerator,
    input  [15:0] denominator,
    output [15:0] quotient
);
    wire [31:0] temp;
    assign temp = (numerator << 16) / denominator;
    assign quotient = temp[15:0];
endmodule

module q16_16_compare (
    input  [15:0] a,
    input  [15:0] b,
    output        lt,
    output        eq,
    output        gt
);
    assign lt = (a < b);
    assign eq = (a == b);
    assign gt = (a > b);
endmodule

// ═══════════════════════════════════════════════════════════════════════════
// SSS Monitor Module - Layer 6
// ═══════════════════════════════════════════════════════════════════════════

module sss_monitor (
    input  wire        clk,
    input  wire        reset_n,
    input  wire [15:0] routing_load,      // L_R
    input  wire [15:0] memory_load,       // L_M
    input  wire [15:0] extraneous_weight, // λ_E
    input  wire [15:0] engram_length,     // ℓ
    input  wire [15:0] extraneous_gradient, // ‖∇L_E‖
    input  wire [15:0] heel_dig_limit,   // σ_sys
    output wire [15:0] sss_constant,
    output wire        slip_threshold_crossed,
    output wire        mode_survival_trigger
);
    // Counter-torque: L_R + L_M
    wire [15:0] counter_torque;
    q16_16_add counter_torque_inst (
        .a(routing_load),
        .b(memory_load),
        .sum(counter_torque)
    );
    
    // Torsional term: λ_E · ℓ · ‖∇L_E‖
    wire [15:0] temp1;
    wire [15:0] torsional_term;
    q16_16_mul mul1_inst (
        .a(extraneous_weight),
        .b(engram_length),
        .product(temp1)
    );
    q16_16_mul mul2_inst (
        .a(temp1),
        .b(extraneous_gradient),
        .product(torsional_term)
    );
    
    // SSS constant: counter_torque - torsional_term
    q16_16_sub sss_inst (
        .a(counter_torque),
        .b(torsional_term),
        .diff(sss_constant)
    );
    
    // Slip threshold: Φ_sss < -σ_sys
    wire [15:0] negative_heel_dig;
    assign negative_heel_dig = -heel_dig_limit;
    wire sss_lt_threshold;
    q16_16_compare compare_inst (
        .a(sss_constant),
        .b(negative_heel_dig),
        .lt(sss_lt_threshold),
        .eq(),
        .gt()
    );
    
    // Register slip threshold crossing
    reg slip_crossed_reg;
    always @(posedge clk or negedge reset_n) begin
        if (!reset_n) begin
            slip_crossed_reg <= 1'b0;
        end else begin
            slip_crossed_reg <= sss_lt_threshold;
        end
    end
    
    assign slip_threshold_crossed = slip_crossed_reg;
    
    // MODE_SURVIVAL trigger (with hysteresis)
    reg [3:0] slip_counter;
    always @(posedge clk or negedge reset_n) begin
        if (!reset_n) begin
            slip_counter <= 4'h0;
        end else if (sss_lt_threshold) begin
            if (slip_counter < 4'hF)
                slip_counter <= slip_counter + 4'h1;
        end else begin
            slip_counter <= 4'h0;
        end
    end
    
    assign mode_survival_trigger = (slip_counter >= 4'h8);  // 8 consecutive crossings
endmodule

// ═══════════════════════════════════════════════════════════════════════════
// Sigmoid Function (Q16.16) - Piecewise Linear Approximation
// ═══════════════════════════════════════════════════════════════════════════

module sigmoid_q16_16 (
    input  wire [15:0] x,
    output wire [15:0] y
);
    // Piecewise linear approximation for sigmoid
    // sigmoid(x) ≈ 0 for x < -5, 1 for x > 5, (x+5)/10 otherwise
    wire x_lt_neg5, x_gt_pos5;
    wire [15:0] x_plus_5, x_div_10;
    
    assign x_lt_neg5 = (x < 16'h8000);  // -5.0 in Q16.16
    assign x_gt_pos5 = (x > 16'h5000);  // 5.0 in Q16.16
    
    q16_16_add add_inst (
        .a(x),
        .b(16'h5000),  // 5.0
        .sum(x_plus_5)
    );
    
    q16_16_div div_inst (
        .numerator(x_plus_5),
        .denominator(16'hA000),  // 10.0
        .quotient(x_div_10)
    );
    
    assign y = x_lt_neg5 ? 16'h0000 : (x_gt_pos5 ? 16'hFFFF : x_div_10);
endmodule

// ═══════════════════════════════════════════════════════════════════════════
// Warp Metric Module - Layer 7
// ═══════════════════════════════════════════════════════════════════════════

module virtual_warp_metric (
    input  wire        clk,
    input  wire        reset_n,
    input  wire [15:0] kappa,            // κ
    input  wire [15:0] sss_constant,
    input  wire [15:0] opcode_efficacy,  // Ω_opcode
    input  wire [15:0] local_velocity,
    input  wire [15:0] coherence,        // φ
    input  wire [15:0] proper_time,      // dτ
    input  wire [15:0] entropy_displacement, // dH
    output wire [15:0] virtual_warp_value,       // f(x_i)
    output wire [15:0] effective_velocity,
    output wire [15:0] virtual_warp_metric_value
);
    // Warp function: f(x_i) = sigmoid(-κ·Φ_sss) · Ω_opcode
    wire [15:0] neg_kappa_sss;
    q16_16_mul mul_kappa_inst (
        .a(-kappa),
        .b(sss_constant),
        .product(neg_kappa_sss)
    );
    
    sigmoid_q16_16 sigmoid_inst (
        .x(neg_kappa_sss),
        .y(virtual_warp_value)
    );
    
    wire [15:0] virtual_warp_final;
    q16_16_mul mul_warp_inst (
        .a(virtual_warp_value),
        .b(opcode_efficacy),
        .product(virtual_warp_final)
    );
    
    // Effective velocity: v_eff = v_local / (1 - φ)
    wire [15:0] one_minus_coherence;
    wire [15:0] denominator;
    q16_16_sub sub_coherence_inst (
        .a(16'hFFFF),  // 1.0
        .b(coherence),
        .diff(one_minus_coherence)
    );
    
    // Avoid division by zero
    assign denominator = (one_minus_coherence == 16'h0000) ? 16'hFFFF : one_minus_coherence;
    
    q16_16_div div_velocity_inst (
        .numerator(local_velocity),
        .denominator(denominator),
        .quotient(effective_velocity)
    );
    
    // Warp metric: dI² = -dτ² + (dH - v_eff · f · Ω · dτ)²
    wire [15:0] time_term;
    wire [15:0] space_term_inner;
    wire [15:0] space_term;
    wire [15:0] warp_coupling;  // f · Ω
    
    q16_16_mul mul_time_inst (
        .a(-proper_time),
        .b(proper_time),
        .product(time_term)
    );
    
    assign virtual_warp_coupling = virtual_warp_final;
    
    wire [15:0] v_eff_warp_dtau;
    q16_16_mul mul_space1_inst (
        .a(effective_velocity),
        .b(virtual_warp_coupling),
        .product(v_eff_warp_dtau)
    );
    
    q16_16_mul mul_space2_inst (
        .a(v_eff_warp_dtau),
        .b(proper_time),
        .product(space_term_inner)
    );
    
    q16_16_sub sub_space_inst (
        .a(entropy_displacement),
        .b(space_term_inner),
        .diff(space_term)
    );
    
    q16_16_mul mul_space_final_inst (
        .a(space_term),
        .b(space_term),
        .product(virtual_warp_metric_value)
    );
endmodule

// ═══════════════════════════════════════════════════════════════════════════
// FAMM Scheduler Module
// ═══════════════════════════════════════════════════════════════════════════

module famm_scheduler (
    input  wire        clk,
    input  wire        reset_n,
    input  wire [15:0] torsional_stress,   // Σ²
    input  wire [15:0] interlocking_energy, // I_lock
    input  wire [15:0] laplacian_energy,   // Δϕ
    output wire [15:0] famm_load,
    output wire [1:0]  schedule_decision   // 00: execute, 01: throttle, 10: defer
);
    // FAMM load: Σ² + I_lock + Δϕ
    wire [15:0] temp1;
    q16_16_add add1_inst (
        .a(torsional_stress),
        .b(interlocking_energy),
        .sum(temp1)
    );
    
    q16_16_add add2_inst (
        .a(temp1),
        .b(laplacian_energy),
        .sum(famm_load)
    );
    
    // Scheduling decision based on load thresholds
    wire load_lt_025, load_lt_050;
    assign load_lt_025 = (famm_load < 16'h4000);  // 0.25
    assign load_lt_050 = (famm_load < 16'h8000);  // 0.5
    
    // Combinational scheduling decision
    assign schedule_decision = load_lt_025 ? 2'b00 : (load_lt_050 ? 2'b01 : 2'b10);
endmodule

// ═══════════════════════════════════════════════════════════════════════════
// Topological Adapter Module
// ═══════════════════════════════════════════════════════════════════════════

module topological_adapter (
    input  wire        clk,
    input  wire        reset_n,
    input  wire [15:0] cognitive_load,
    output wire [1:0]  topology_metric  // 00: relational, 01: semantic, 10: topological, 11: minimal
);
    // Topology adaptation based on cognitive load
    wire load_lt_025, load_lt_050, load_lt_075;
    assign load_lt_025 = (cognitive_load < 16'h4000);  // 0.25
    assign load_lt_050 = (cognitive_load < 16'h8000);  // 0.5
    assign load_lt_075 = (cognitive_load < 16'hC000);  // 0.75
    
    // Combinational topology selection
    assign topology_metric = load_lt_025 ? 2'b00 : (load_lt_050 ? 2'b01 : (load_lt_075 ? 2'b10 : 2'b11));
endmodule

// ═══════════════════════════════════════════════════════════════════════════
// Complete NII Surface Driver
// ═══════════════════════════════════════════════════════════════════════════

module nii_surface_driver (
    input  wire        clk,
    input  wire        reset_n,
    
    // SSS inputs
    input  wire [15:0] routing_load,
    input  wire [15:0] memory_load,
    input  wire [15:0] extraneous_weight,
    input  wire [15:0] engram_length,
    input  wire [15:0] extraneous_gradient,
    input  wire [15:0] heel_dig_limit,
    
    // Warp metric inputs
    input  wire [15:0] kappa,
    input  wire [15:0] opcode_efficacy,
    input  wire [15:0] local_velocity,
    input  wire [15:0] coherence,
    input  wire [15:0] proper_time,
    input  wire [15:0] entropy_displacement,
    
    // FAMM inputs
    input  wire [15:0] torsional_stress,
    input  wire [15:0] interlocking_energy,
    input  wire [15:0] laplacian_energy,
    
    // Topological input
    input  wire [15:0] cognitive_load,
    
    // Outputs
    output wire [15:0] sss_constant_out,
    output wire        slip_threshold_crossed,
    output wire        mode_survival_trigger,
    output wire [15:0] virtual_warp_value_out,
    output wire [15:0] effective_velocity_out,
    output wire [15:0] virtual_warp_metric_out,
    output wire [15:0] famm_load_out,
    output wire [1:0]  schedule_decision_out,
    output wire [1:0]  topology_metric_out
);
    // SSS monitor instance
    wire [15:0] sss_constant_wire;
    sss_monitor sss_inst (
        .clk(clk),
        .reset_n(reset_n),
        .routing_load(routing_load),
        .memory_load(memory_load),
        .extraneous_weight(extraneous_weight),
        .engram_length(engram_length),
        .extraneous_gradient(extraneous_gradient),
        .heel_dig_limit(heel_dig_limit),
        .sss_constant(sss_constant_wire),
        .slip_threshold_crossed(slip_threshold_crossed),
        .mode_survival_trigger(mode_survival_trigger)
    );
    
    assign sss_constant_out = sss_constant_wire;
    
    // Warp metric instance
    wire [15:0] warp_value_wire;
    wire [15:0] effective_velocity_wire;
    wire [15:0] warp_metric_wire;
    
    virtual_warp_metric virtual_warp_inst (
        .clk(clk),
        .reset_n(reset_n),
        .kappa(kappa),
        .sss_constant(sss_constant_wire),
        .opcode_efficacy(opcode_efficacy),
        .local_velocity(local_velocity),
        .coherence(coherence),
        .proper_time(proper_time),
        .entropy_displacement(entropy_displacement),
        .virtual_warp_value(virtual_warp_value_wire),
        .effective_velocity(effective_velocity_wire),
        .virtual_warp_metric_value(virtual_warp_metric_wire)
    );
    
    assign virtual_warp_value_out = virtual_warp_value_wire;
    assign effective_velocity_out = effective_velocity_wire;
    assign virtual_warp_metric_out = virtual_warp_metric_wire;
    
    // FAMM scheduler instance
    wire [15:0] famm_load_wire;
    wire [1:0] schedule_decision_wire;
    
    famm_scheduler famm_inst (
        .clk(clk),
        .reset_n(reset_n),
        .torsional_stress(torsional_stress),
        .interlocking_energy(interlocking_energy),
        .laplacian_energy(laplacian_energy),
        .famm_load(famm_load_wire),
        .schedule_decision(schedule_decision_wire)
    );
    
    assign famm_load_out = famm_load_wire;
    assign schedule_decision_out = schedule_decision_wire;
    
    // Topological adapter instance
    wire [1:0] topology_metric_wire;
    
    topological_adapter topo_inst (
        .clk(clk),
        .reset_n(reset_n),
        .cognitive_load(cognitive_load),
        .topology_metric(topology_metric_wire)
    );
    
    assign topology_metric_out = topology_metric_wire;
endmodule

// ═══════════════════════════════════════════════════════════════════════════
// Testbench
// ═══════════════════════════════════════════════════════════════════════════

module nii_surface_driver_tb;
    reg clk;
    reg reset_n;
    
    // SSS inputs
    reg [15:0] routing_load;
    reg [15:0] memory_load;
    reg [15:0] extraneous_weight;
    reg [15:0] engram_length;
    reg [15:0] extraneous_gradient;
    reg [15:0] heel_dig_limit;
    
    // Warp metric inputs
    reg [15:0] kappa;
    reg [15:0] opcode_efficacy;
    reg [15:0] local_velocity;
    reg [15:0] coherence;
    reg [15:0] proper_time;
    reg [15:0] entropy_displacement;
    
    // FAMM inputs
    reg [15:0] torsional_stress;
    reg [15:0] interlocking_energy;
    reg [15:0] laplacian_energy;
    
    // Topological input
    reg [15:0] cognitive_load;
    
    // Outputs
    wire [15:0] sss_constant_out;
    wire slip_threshold_crossed;
    wire mode_survival_trigger;
    wire [15:0] virtual_warp_value_out;
    wire [15:0] effective_velocity_out;
    wire [15:0] virtual_warp_metric_out;
    wire [15:0] famm_load_out;
    wire [1:0] schedule_decision_out;
    wire [1:0] topology_metric_out;
    
    // Instantiate DUT
    nii_surface_driver dut (
        .clk(clk),
        .reset_n(reset_n),
        .routing_load(routing_load),
        .memory_load(memory_load),
        .extraneous_weight(extraneous_weight),
        .engram_length(engram_length),
        .extraneous_gradient(extraneous_gradient),
        .heel_dig_limit(heel_dig_limit),
        .kappa(kappa),
        .opcode_efficacy(opcode_efficacy),
        .local_velocity(local_velocity),
        .coherence(coherence),
        .proper_time(proper_time),
        .entropy_displacement(entropy_displacement),
        .torsional_stress(torsional_stress),
        .interlocking_energy(interlocking_energy),
        .laplacian_energy(laplacian_energy),
        .cognitive_load(cognitive_load),
        .sss_constant_out(sss_constant_out),
        .slip_threshold_crossed(slip_threshold_crossed),
        .mode_survival_trigger(mode_survival_trigger),
        .virtual_warp_value_out(virtual_warp_value_out),
        .effective_velocity_out(effective_velocity_out),
        .virtual_warp_metric_out(virtual_warp_metric_out),
        .famm_load_out(famm_load_out),
        .schedule_decision_out(schedule_decision_out),
        .topology_metric_out(topology_metric_out)
    );
    
    // Clock generation (50MHz)
    initial clk = 0;
    always #10 clk = ~clk;
    
    // Test stimulus
    initial begin
        // Initialize inputs
        reset_n = 0;
        routing_load = 16'h8000;  // 1.0 (assuming Q1.15 or similar)
        memory_load = 16'h6000;   // 0.75
        extraneous_weight = 16'h4000;  // 0.5
        engram_length = 16'h3000;     // 0.375
        extraneous_gradient = 16'h1000;  // 0.125
        heel_dig_limit = 16'h4000;       // 0.5
        
        kappa = 16'h8000;       // 1.0
        opcode_efficacy = 16'h7FFF;  // 1.0
        local_velocity = 16'h8000;  // 1.0
        coherence = 16'h6000;     // 0.75
        proper_time = 16'h0500;   // small dt
        entropy_displacement = 16'h1000;
        
        torsional_stress = 16'h8000;
        interlocking_energy = 16'h4000;
        laplacian_energy = 16'h2000;
        
        cognitive_load = 16'h0000;  // 0.0
        
        #20;
        reset_n = 1;
        
        #100;
        $display("SSS Constant: %h", sss_constant_out);
        $display("Slip Threshold Crossed: %b", slip_threshold_crossed);
        $display("Virtual Warp Value: %h", virtual_warp_value_out);
        $display("Effective Velocity: %h", effective_velocity_out);
        $display("Virtual Warp Metric: %h", virtual_warp_metric_out);
        $display("FAMM Load: %h", famm_load_out);
        $display("Schedule Decision: %b", schedule_decision_out);
        $display("Topology Metric: %b", topology_metric_out);
        
        #100;
        cognitive_load = 16'h8000;  // 0.5 - trigger topology change
        #100;
        $display("Topology Metric after load: %b", topology_metric_out);
        
        #100;
        $finish;
    end
endmodule