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// ========== Copyright Header Begin ==========================================

// 

// OpenSPARC T1 Processor File: sparc_exu_ecl_divcntl.v

// Copyright (c) 2006 Sun Microsystems, Inc.  All Rights Reserved.

// DO NOT ALTER OR REMOVE COPYRIGHT NOTICES.

// 

// The above named program is free software; you can redistribute it and/or

// modify it under the terms of the GNU General Public

// License version 2 as published by the Free Software Foundation.

// 

// The above named program is distributed in the hope that it will be 

// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

// General Public License for more details.

// 

// You should have received a copy of the GNU General Public

// License along with this work; if not, write to the Free Software

// Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.

// 

// ========== Copyright Header End ============================================

////////////////////////////////////////////////////////////////////////

/*

//  Module Name: sparc_exu_divcntl

//      Description: Control block for div.  Division takes 1 cycle to load

//              the values, 65 cycles to calculate the result, and 1 cycle to

//    calculate the ccs and check for overflow.

//      Controlled by a one hot state machine and a 6 bit counter.

*/

`define IDLE 0

`define RUN 1

`define LAST_CALC 2

`define CHK_OVFL 3

`define FIX_OVFL 4

`define DONE 5

module sparc_exu_ecl_divcntl (/*AUTOARG*/

   // Outputs

   ecl_div_xinmask, ecl_div_keep_d, ecl_div_ld_inputs,

   ecl_div_sel_adder, ecl_div_last_cycle, ecl_div_almostlast_cycle,

   ecl_div_sel_div, divcntl_wb_req_g, divcntl_ccr_cc_w2,

   ecl_div_sel_64b, ecl_div_sel_u32, ecl_div_sel_pos32,

   ecl_div_sel_neg32, ecl_div_upper32_zero, ecl_div_upper33_one,

   ecl_div_upper33_zero, ecl_div_dividend_sign, ecl_div_newq,

   ecl_div_subtract_l, ecl_div_keepx, ecl_div_cin,

   // Inputs

   clk, se, reset, mdqctl_divcntl_input_vld, wb_divcntl_ack_g,

   mdqctl_divcntl_reset_div, div_ecl_gencc_in_msb_l,

   div_ecl_gencc_in_31, div_ecl_upper32_equal, div_ecl_low32_nonzero,

   ecl_div_signed_div, div_ecl_dividend_msb, div_ecl_xin_msb_l,

   div_ecl_x_msb, div_ecl_d_msb, div_ecl_cout64,

   div_ecl_divisorin_31, ecl_div_div64, mdqctl_divcntl_muldone,

   ecl_div_muls, div_ecl_adder_out_31, muls_rs1_31_m_l,

   div_ecl_cout32, rs2_data_31_m, div_ecl_detect_zero_high,

   div_ecl_detect_zero_low, div_ecl_d_62

   ) ;

   input     clk;

   input     se;

   input     reset;

   input     mdqctl_divcntl_input_vld;

   input     wb_divcntl_ack_g;

   input     mdqctl_divcntl_reset_div;

   input     div_ecl_gencc_in_msb_l;

   input     div_ecl_gencc_in_31;

   input     div_ecl_upper32_equal;

   input     div_ecl_low32_nonzero;

   input     ecl_div_signed_div;

   input     div_ecl_dividend_msb;

   input     div_ecl_xin_msb_l;

   input     div_ecl_x_msb;

   input     div_ecl_d_msb;

   input     div_ecl_cout64;

   input     div_ecl_divisorin_31;

   input     ecl_div_div64;

   input     mdqctl_divcntl_muldone;

   input     ecl_div_muls;

   input  div_ecl_adder_out_31;

   input  muls_rs1_31_m_l;

   input  div_ecl_cout32;

   input  rs2_data_31_m;

   input         div_ecl_detect_zero_high;

   input         div_ecl_detect_zero_low;

   input         div_ecl_d_62;

   output    ecl_div_xinmask;

   output    ecl_div_keep_d;

   output    ecl_div_ld_inputs;

   output    ecl_div_sel_adder;

   output    ecl_div_last_cycle;   // last cycle of calculation

   output    ecl_div_almostlast_cycle;//

   output    ecl_div_sel_div;

   output    divcntl_wb_req_g;

   output [7:0] divcntl_ccr_cc_w2;

   output       ecl_div_sel_64b;

   output       ecl_div_sel_u32;

   output       ecl_div_sel_pos32;

   output       ecl_div_sel_neg32;

   output       ecl_div_upper32_zero;

   output       ecl_div_upper33_one;

   output       ecl_div_upper33_zero;

   output       ecl_div_dividend_sign;

   output       ecl_div_newq;

   output       ecl_div_subtract_l;

   output       ecl_div_keepx;

   output        ecl_div_cin;

   wire         firstq;

   wire         q_next;        // next q bit

   wire         adderin1_64;   // msbs for adder

   wire         adderin2_64;

   wire         firstlast_sub; // subtract for first and last cycle

   wire         sub_next;      // next cycle will subtract

   wire         subtract;

   wire         bit64_halfadd; // partial result for qpredict

   wire         partial_qpredict;

   wire [1:0]   q_next_nocout;

   wire [1:0]   sub_next_nocout;

   wire         partial_qpredict_l;

   wire          divisor_sign;

   wire          detect_zero;

   wire          new_zero_rem_with_zero;

   wire          new_zero_rem_no_zero;

   wire          zero_rem_d;

   wire          zero_rem_q;

   wire          last_cin_with_zero;

   wire          last_cin_no_zero;

   wire          last_cin;

   wire          last_cin_next;

   // overflow correction wires

   wire          upper32_equal_d1;

   wire          gencc_in_msb_l_d1;

   wire          gencc_in_31_d1;

   wire          sel_div_d1;

   wire          low32_nonzero_d1;

   // Condition code generation wires

   wire [3:0]   xcc;

   wire [3:0]   icc;

   wire         unsign_ovfl;

   wire         pos_ovfl;

   wire         neg_ovfl;

   wire         muls_c;

   wire         next_muls_c;

   wire         muls_v;

   wire         next_muls_v;

   wire         muls_rs1_data_31_m;

   wire         div_adder_out_31_w;

   wire         rs2_data_31_w;

   wire         muls_rs1_data_31_w;

   wire         ovfl_32;

   wire         div_v;

   wire [5:0]   div_state;

   wire [5:0]   next_state;

   wire         go_idle,

                stay_idle,

                go_run,

                stay_run,

                go_last_calc,

                go_chk_ovfl,

                go_fix_ovfl,

                go_done,

                stay_done;

   wire         reset_cnt;

   wire [5:0]   cntr;

   wire         cntris63;

   /////////////////////////////////

   // G arbitration between MUL/DIV

   /////////////////////////////////

   assign        divcntl_wb_req_g = div_state[`DONE] |

                      (~(div_state[`DONE] | div_state[`CHK_OVFL] | div_state[`FIX_OVFL]) &mdqctl_divcntl_muldone);

   assign        ecl_div_sel_div = ~(~(div_state[`DONE] | div_state[`CHK_OVFL] | div_state[`FIX_OVFL]) &

                                    mdqctl_divcntl_muldone);

   // state flop

   dff_s #(6) divstate_dff(.din(next_state[5:0]), .clk(clk), .q(div_state[5:0]), .se(se), .si(),

                    .so());

   // output logic and state decode

   assign        ecl_div_almostlast_cycle = go_last_calc & ~ecl_div_ld_inputs;

   assign        ecl_div_sel_adder = (div_state[`RUN] | div_state[`LAST_CALC]) & ~ecl_div_ld_inputs;

   assign        ecl_div_last_cycle = div_state[`LAST_CALC];

   assign        ecl_div_ld_inputs = mdqctl_divcntl_input_vld;

   assign        ecl_div_keep_d = ~(ecl_div_sel_adder | ecl_div_ld_inputs);

   assign        reset_cnt = ~div_state[`RUN];

   // next state logic

   assign        stay_idle = div_state[`IDLE] & ~mdqctl_divcntl_input_vld;

   assign        go_idle = div_state[`DONE] & wb_divcntl_ack_g;

   assign        next_state[`IDLE] = go_idle | stay_idle | mdqctl_divcntl_reset_div | reset;

   assign        stay_run = div_state[`RUN] & ~cntris63 & ~ecl_div_muls;

   assign        go_run = (div_state[`IDLE] & mdqctl_divcntl_input_vld);

   assign        next_state[`RUN] = (go_run | stay_run) &

                                      ~mdqctl_divcntl_reset_div & ~reset;

   assign        go_last_calc = div_state[`RUN] & (cntris63);

   assign        next_state[`LAST_CALC] = go_last_calc & ~mdqctl_divcntl_reset_div & ~reset;

   // chk_ovfl and fix_ovfl are place holders to guarantee that the overflow checking

   // takes place on the result.  No special logic occurs in them compared to the done state.

   assign        go_chk_ovfl = div_state[`LAST_CALC];

   assign        next_state[`CHK_OVFL] = go_chk_ovfl & ~mdqctl_divcntl_reset_div & ~reset;

   assign        go_fix_ovfl = div_state[`CHK_OVFL] | (div_state[`RUN] & ecl_div_muls);

   assign        next_state[`FIX_OVFL] = go_fix_ovfl & ~mdqctl_divcntl_reset_div & ~reset;

   assign        go_done = div_state[`FIX_OVFL];

   assign        stay_done = div_state[`DONE] & ~wb_divcntl_ack_g;

   assign        next_state[`DONE] = (go_done | stay_done) & ~mdqctl_divcntl_reset_div & ~reset;

   // counter

   sparc_exu_ecl_cnt6 cnt6(.reset       (reset_cnt),

                           /*AUTOINST*/

                           // Outputs

                           .cntr        (cntr[5:0]),

                           // Inputs

                           .clk         (clk),

                           .se          (se));

   assign        cntris63 = cntr[5] & cntr[4] & cntr[3] & cntr[2] & cntr[1] & cntr[0];

   ///////////////////////////////

   // Random logic for divider

   ///////////////////////////////

   // Generation of sign extension of dividend and divisor

   assign        ecl_div_dividend_sign = ecl_div_signed_div & div_ecl_dividend_msb;

   assign        ecl_div_xinmask = div_ecl_divisorin_31 & ecl_div_signed_div;

   assign        divisor_sign = div_ecl_x_msb & ecl_div_signed_div;

   // Generation of next bit of quotient

   ////////////////////////////////////////////////////////////////

   //   Calculate the next q.  Requires calculating the result

   // of the 65th bit of the adder and xoring it with the sign of

   // the divisor.  The order of these xors is switched for critical

   // path considerations.

   ////////////////////////////////////////////////////////////////

   assign        adderin1_64 = div_ecl_d_msb;

   assign        adderin2_64 = (ecl_div_signed_div & div_ecl_x_msb) ^ subtract;

   assign        bit64_halfadd = adderin1_64 ^ adderin2_64;

   assign        partial_qpredict = bit64_halfadd ^ ~(div_ecl_x_msb & ecl_div_signed_div);

   assign        partial_qpredict_l = ~partial_qpredict;

   //assign        qpredict = partial_qpredict ^ div_ecl_cout64;

   //assign        firstq = ~ecl_div_signed_div | div_ecl_xin_msb_l; 

   assign        firstq = ecl_div_dividend_sign;

   mux2ds #(2) qnext_mux(.dout(q_next_nocout[1:0]),

                            .in0({partial_qpredict, partial_qpredict_l}),

                            .in1({2{firstq}}),

                            .sel0(~ecl_div_ld_inputs),

                            .sel1(ecl_div_ld_inputs));

   dp_mux2es qnext_cout_mux(.dout(q_next),

                            .in0(q_next_nocout[1]),

                            .in1(q_next_nocout[0]),

                            .sel(div_ecl_cout64));

   dff_s q_dff(.din(q_next), .clk(clk), .q(ecl_div_newq), .se(se), .si(),

               .so());

   ////////////////////////////

   // Subtraction logic and subtract flop

   //-------------------------------------

   // To take the subtraction calc out of the critical path,

   // it is done in the previous cycle and part is done with a

   // mux.  The result is put into a flop.

   ////////////////////////////

   assign firstlast_sub = ~ecl_div_almostlast_cycle & ~ecl_div_muls &

          (~ecl_div_signed_div | ~(div_ecl_dividend_msb ^ ~div_ecl_xin_msb_l));

   assign        ecl_div_keepx = ~(ecl_div_ld_inputs |

                                  ecl_div_almostlast_cycle);

   mux2ds #(2) subnext_mux(.dout(sub_next_nocout[1:0]),

                              .in0({2{firstlast_sub}}),

                              .in1({partial_qpredict, partial_qpredict_l}),

                              .sel0(~ecl_div_keepx),

                              .sel1(ecl_div_keepx));

   dp_mux2es subtract_cout_mux(.dout(sub_next),

                            .in0(sub_next_nocout[1]),

                            .in1(sub_next_nocout[0]),

                            .sel(div_ecl_cout64));

   dff_s sub_dff(.din(sub_next), .clk(clk), .q(subtract), .se(se), .si(),

               .so());

   assign        ecl_div_subtract_l = ~subtract;

   /////////////////////////////////////////////

   // Carry in logic

   //--------------------------------------------

   // The carry is usually just subtract.  The

   // quotient correction for signed division

   // sometimes has to adjust it though.

   /////////////////////////////////////////////

   assign        detect_zero = div_ecl_detect_zero_low & div_ecl_detect_zero_high;

   assign ecl_div_cin = (ecl_div_last_cycle)? last_cin: subtract;

   // stores if the partial remainder was ever zero.

/* -----\/----- EXCLUDED -----\/-----

   // changed for timing

    assign        zero_rem_d = ~ecl_div_ld_inputs & (div_ecl_detect_zero | zero_rem_q) &

                                                     (~div_ecl_d_62 | ecl_div_almostlast_cycle);

 -----/\----- EXCLUDED -----/\----- */

   assign new_zero_rem_with_zero = ~ecl_div_ld_inputs & (~div_ecl_d_62 | ecl_div_almostlast_cycle);

   assign new_zero_rem_no_zero = zero_rem_q & new_zero_rem_with_zero;

   assign zero_rem_d = (detect_zero)? new_zero_rem_with_zero: new_zero_rem_no_zero;

   dff_s zero_rem_dff(.din(zero_rem_d), .clk(clk), .q(zero_rem_q),

                    .se(se), .si(), .so());

/* -----\/----- EXCLUDED -----\/-----

   // changed for timing

   assign last_cin_next = ecl_div_signed_div & (divisor_sign & ~div_ecl_d_62 |

                                                ~divisor_sign &div_ecl_d_62&~zero_rem_d |

                                                divisor_sign &div_ecl_d_62&zero_rem_d);

 -----/\----- EXCLUDED -----/\----- */

   assign last_cin_with_zero = ecl_div_signed_div & (divisor_sign & ~div_ecl_d_62 |

                                                ~divisor_sign &div_ecl_d_62&~new_zero_rem_with_zero |

                                                divisor_sign &div_ecl_d_62&new_zero_rem_with_zero);

   assign last_cin_no_zero = ecl_div_signed_div & (divisor_sign & ~div_ecl_d_62 |

                                                ~divisor_sign &div_ecl_d_62&~new_zero_rem_no_zero |

                                                divisor_sign &div_ecl_d_62&new_zero_rem_no_zero);

   assign last_cin_next = (detect_zero)? last_cin_with_zero: last_cin_no_zero;

   dff_s last_cin_dff(.din(last_cin_next), .clk(clk), .q(last_cin),

                    .se(se), .si(), .so());

   ///////////////////////////////

   // Condition code generation

   ///////////////////////////////

   // There is a special case:

   // For 64 bit signed division largest neg/-1 = largest neg

   // However for 32 bit division this will give us positive overflow.

   // This is detected by a sign switch on this case.

   wire   inputs_neg_d;

   wire   inputs_neg_q;

   wire   large_neg_ovfl;

   assign inputs_neg_d = div_ecl_dividend_msb & div_ecl_divisorin_31;

   assign large_neg_ovfl = inputs_neg_q & ~gencc_in_msb_l_d1;

   dffe_s inputs_neg_dff(.din(inputs_neg_d), .clk(clk), .q(inputs_neg_q),

                       .en(ecl_div_ld_inputs), .se(se), .si(), .so());

   dff_s #(5) cc_sig_dff(.din({div_ecl_upper32_equal, div_ecl_gencc_in_msb_l,

                             div_ecl_gencc_in_31, ecl_div_sel_div, div_ecl_low32_nonzero}),

                         .q({upper32_equal_d1, gencc_in_msb_l_d1,

                             gencc_in_31_d1, sel_div_d1, low32_nonzero_d1}),

                         .clk(clk), .se(se), .si(), .so());

   // selects for correcting divide overflow

   assign        ecl_div_sel_64b = ecl_div_div64 | ecl_div_muls;

   assign        ecl_div_sel_u32 = ~ecl_div_sel_64b & ~ecl_div_signed_div;

   assign                        ecl_div_sel_pos32 = (~ecl_div_sel_64b & ecl_div_signed_div &

                                      (gencc_in_msb_l_d1 | large_neg_ovfl));

   assign        ecl_div_sel_neg32 = (~ecl_div_sel_64b & ecl_div_signed_div &

                                      ~gencc_in_msb_l_d1 & ~large_neg_ovfl);

   // results of checking are staged one cycle for timing reasons

   // this is the reason for the chk and fix ovfl states

   assign        ecl_div_upper32_zero = upper32_equal_d1 & gencc_in_msb_l_d1;

   assign        ecl_div_upper33_zero = (upper32_equal_d1 & gencc_in_msb_l_d1 &

                                         ~gencc_in_31_d1);

   assign        ecl_div_upper33_one = (upper32_equal_d1 & ~gencc_in_msb_l_d1 &

                                        gencc_in_31_d1);

   // divide overflow

   assign        unsign_ovfl = ecl_div_sel_u32 & ~ecl_div_upper32_zero & sel_div_d1;

   assign        pos_ovfl = ecl_div_sel_pos32 & ~ecl_div_upper33_zero & sel_div_d1;

   assign        neg_ovfl = ecl_div_sel_neg32 & ~ecl_div_upper33_one & sel_div_d1;

   assign        div_v = pos_ovfl | unsign_ovfl | neg_ovfl;

   // muls carry and overflow

   assign next_muls_c = (div_state[`RUN]) ? div_ecl_cout32: muls_c;

   assign        muls_rs1_data_31_m = ~muls_rs1_31_m_l;

   dff_s #(3) muls_overlow_dff(.din({muls_rs1_data_31_m, rs2_data_31_m, div_ecl_adder_out_31}),

                             .q({muls_rs1_data_31_w, rs2_data_31_w, div_adder_out_31_w}),

                             .clk(clk), .se(se), .si(), .so());

   assign ovfl_32 = ((muls_rs1_data_31_w & rs2_data_31_w & ~div_adder_out_31_w) |

                     (~muls_rs1_data_31_w & ~rs2_data_31_w & div_adder_out_31_w));

   assign next_muls_v = (div_state[`FIX_OVFL]) ? ovfl_32: muls_v;

   dff_s muls_c_dff(.din(next_muls_c), .clk(clk), .q(muls_c),

                  .se(se), .si(), .so());

   dff_s muls_v_dff(.din(next_muls_v), .clk(clk), .q(muls_v),

                  .se(se), .si(), .so());

   // negative

   assign xcc[3] = ~gencc_in_msb_l_d1 & ~unsign_ovfl & ~pos_ovfl;

   assign icc[3] = (gencc_in_31_d1 & ~pos_ovfl) | neg_ovfl | unsign_ovfl;

   // zero

   assign xcc[2] = upper32_equal_d1 & gencc_in_msb_l_d1 & ~low32_nonzero_d1;

   assign icc[2] = ~low32_nonzero_d1 & ~div_v; // nonzero checks before ovfl

   //overflow

   assign xcc[1] = 1'b0;

   assign icc[1] = (ecl_div_muls & sel_div_d1) ? muls_v: div_v;

   // carry

   assign xcc[0] = 1'b0;

   assign icc[0] = ecl_div_muls & sel_div_d1 & muls_c;

   assign divcntl_ccr_cc_w2 = {xcc, icc};

endmodule // sparc_exu_divcntl