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// Copyright (c) 2019, NORDUnet A/S All rights reserved.
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//======================================================================

module modexpng_recombinator_cell
(
    clk,
    ce, clr,
    din, dout, doutw
);


    //
    // Headers
    //
    `include "modexpng_parameters.vh"
    `include "modexpng_dsp48e1.vh"
    `include "modexpng_dsp_slice_primitives.vh"

    
    //
    // Ports
    //
    input                clk;
    input                ce;
    input                clr;
    input  [ MAC_W -1:0] din;
    output [WORD_W -1:0] dout;
    output [WORD_W   :0] doutw;
    
    
    //
    // din <=> {z[13:0], y[15:0], x[15:0]}
    //
    wire [WORD_W -1:0] din_z = {2'b00, din[3 * WORD_W -3 : 2 * WORD_W]}; // [47:46][45:32]
    wire [WORD_W -1:0] din_y = {       din[2 * WORD_W -1 :     WORD_W]}; // [31:16]
    wire [WORD_W -1:0] din_x = {       din[    WORD_W -1 :          0]}; // [15: 0]

    
    //
    // Delayed Clock Enables
    //
    reg ce_dly1 = 1'b0, ce_dly2 = 1'b0, ce_dly3 = 1'b0, ce_dly4 = 1'b0, ce_dly5 = 1'b0, ce_dly6 = 1'b0; 
    always @(posedge clk) {ce_dly1, ce_dly2, ce_dly3, ce_dly4, ce_dly5, ce_dly6} <= {ce, ce_dly1, ce_dly2, ce_dly3, ce_dly4, ce_dly5};


    //
    // Delayed Clear
    //
    reg clr_dly1, clr_dly2, clr_dly3, clr_dly4;
    always @(posedge clk) {clr_dly1, clr_dly2, clr_dly3, clr_dly4} <= {clr, clr_dly1, clr_dly2, clr_dly3};
    

    //
    // Phase Flip-Flop
    //
    reg phase_ff, phase_ff_dly1, phase_ff_dly2, phase_ff_dly3, phase_ff_dly4, phase_ff_dly5;
    always @(posedge clk)
        if      (ce)  phase_ff <= ~phase_ff;
        else if (clr) phase_ff <= 1'b0;

    always @(posedge clk)
        {phase_ff_dly1, phase_ff_dly2, phase_ff_dly3, phase_ff_dly4, phase_ff_dly5} <= {phase_ff, phase_ff_dly1, phase_ff_dly2, phase_ff_dly3, phase_ff_dly4};
        
    
    //
    // Shift Registers
    //
    reg [WORD_W-1:0] din_x_dly1;
    reg [WORD_W-1:0] din_y_dly1;
    reg [WORD_W-1:0] din_z_dly1;
    reg [WORD_W-1:0] din_z_dly2;

    always @(posedge clk) begin
        //
        if      (ce)  {din_x_dly1, din_y_dly1, din_z_dly1} <= {din_x,     din_y,     din_z};
        else if (clr) {din_x_dly1, din_y_dly1, din_z_dly1} <= {WORD_ZERO, WORD_ZERO, WORD_ZERO};
        //
        if      (ce)  {din_z_dly2} <= {din_z_dly1};
        else if (clr) {din_z_dly2} <= {WORD_ZERO};
        //
    end
    

    //
    // DSP Input Registers
    //
    reg [2 * WORD_W-1:0] master_ab_reg;
    reg [2 * WORD_W-1:0] master_c_reg;

    reg [    WORD_W+1:0] slave_ab_reg;
    reg [    WORD_W+1:0] slave_ab_next_reg;


    //
    // DSP Cascade Bus
    //
    wire [DSP48E1_P_W-1:0] master_slave_p_int;


    //
    // DSP Output Buses
    //
    wire [DSP48E1_P_W-1:0] master_p_int;
    wire [DSP48E1_P_W-1:0] slave_p_int;

    
    //
    // DSP Input Mapping
    //
    wire [DSP48E1_C_W-1:0] master_ab_int = {{(DSP48E1_C_W - 2 * WORD_W){1'b0}}, master_ab_reg};
    wire [DSP48E1_C_W-1:0] master_c_int  = {{(DSP48E1_C_W - 2 * WORD_W){1'b0}}, master_c_reg};

    wire [DSP48E1_C_W-1:0] slave_ab_int = {{(DSP48E1_C_W - (WORD_W+3)){1'b0}}, slave_ab_reg[WORD_W+1:WORD_W], 1'b1, slave_ab_reg[WORD_W-1:0]};
    wire [DSP48E1_C_W-1:0] slave_c_int  = {DSP48E1_C_W{1'b0}};


    //
    // Master DSP Input Logic
    //
    always @(posedge clk)
        //
        if (ce) begin
            master_ab_reg <= !phase_ff ? {din_y,      din_y_dly1} : {din_x,    din_x_dly1}; 
            master_c_reg  <= !phase_ff ? {din_z_dly1, din_z_dly2} : {WORD_DNC, WORD_DNC};
        end else begin
            master_ab_reg <= {WORD_DNC, WORD_DNC};
            master_c_reg  <= {WORD_DNC, WORD_DNC};
        end
    
    
    //
    // Slave DSP Input Logic
    //
    always @(posedge clk) begin
        //
        slave_ab_reg      <= {(WORD_W+2){1'bX}};
        slave_ab_next_reg <= {(WORD_W+2){1'bX}};
        //
        if (ce_dly3 && phase_ff_dly3) slave_ab_next_reg <= {master_p_int[2*WORD_W+1:WORD_W]};
        //
        if (ce_dly3 && phase_ff_dly3) slave_ab_reg <= {2'b00, master_p_int[WORD_W-1:0]};
        if (ce_dly4 && phase_ff_dly4) slave_ab_reg <= slave_ab_next_reg; 
        //
    end
    
    
    //
    // OPMODE Logic
    //
    reg [DSP48E1_OPMODE_W-1:0] master_opmode;
    reg [DSP48E1_OPMODE_W-1:0] slave_opmode;
    
    always @(posedge clk) begin
        //
        if (ce) master_opmode <= !phase_ff ? DSP48E1_OPMODE_Z0_YC_XAB : DSP48E1_OPMODE_ZP_Y0_XAB;
        else    master_opmode <= DSP48E1_OPMODE_DNC;
        //
        if (ce_dly4) slave_opmode <= clr_dly4 ? DSP48E1_OPMODE_Z0_Y0_XAB : DSP48E1_OPMODE_ZP17_Y0_XAB;
        else         slave_opmode <= DSP48E1_OPMODE_DNC;
        //
    end
        
    
    //
    // DSP Slice Instances
    //
    `MODEXPNG_DSP_SLICE_ADDSUB dsp_master_inst
    (
        .clk            (clk),
        .ce_abc         (ce_dly1),
        .ce_p           (ce_dly2),
        .ce_ctrl        (ce_dly1),
        .ab             (master_ab_int),
        .c              (master_c_int),
        .p              (master_p_int),
        .op_mode        (master_opmode),
        .alu_mode       (DSP48E1_ALUMODE_Z_PLUS_X_AND_Y_AND_CIN),
        .carry_in_sel   (DSP48E1_CARRYINSEL_CARRYIN),
        .casc_p_in      (),
        .casc_p_out     (),
        .carry_out      ()
    );
    
    `MODEXPNG_DSP_SLICE_ADDSUB dsp_slave_inst
    (
        .clk            (clk),
        .ce_abc         (ce_dly5),
        .ce_p           (ce_dly6),
        .ce_ctrl        (ce_dly5),
        .ab             (slave_ab_int),
        .c              (slave_c_int),
        .p              (slave_p_int),
        .op_mode        (slave_opmode),
        .alu_mode       (DSP48E1_ALUMODE_Z_PLUS_X_AND_Y_AND_CIN),
        .carry_in_sel   (DSP48E1_CARRYINSEL_CARRYIN),
        .casc_p_in      (),
        .casc_p_out     (),
        .carry_out      ()
    );


    //
    // Output Register
    //    
    assign dout  = {slave_p_int[WORD_W-1:0]};
    assign doutw = {slave_p_int[WORD_W+1], dout}; 
    
endmodule