Subversion Repositories openrisc_2011-10-31

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

////                                                              ////

////  OR1200's FPU Wrapper                                        ////

////                                                              ////

////  This file is part of the OpenRISC 1200 project              ////

////  http://opencores.org/project,or1k                           ////

////                                                              ////

////  Description                                                 ////

////  Wrapper for floating point unit.                            ////

////  Interface based on MULT/MAC unit.                           ////

////                                                              ////

////  To Do:                                                      ////

////   - lf.rem.s and lf.madd.s instruction support               ////

////   - implement FP SPRs as needed                              ////

////                                                              ////

////  Author(s):                                                  ////

////      - Julius Baxter, julius@opencores.org                   ////

////                                                              ////

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

////                                                              ////

//// Copyright (C) 2009,2010 Authors and OPENCORES.ORG            ////

////                                                              ////

//// This source file may be used and distributed without         ////

//// restriction provided that this copyright statement is not    ////

//// removed from the file and that any derivative work contains  ////

//// the original copyright notice and the associated disclaimer. ////

////                                                              ////

//// This source file is free software; you can redistribute it   ////

//// and/or modify it under the terms of the GNU Lesser General   ////

//// Public License as published by the Free Software Foundation; ////

//// either version 2.1 of the License, or (at your option) any   ////

//// later version.                                               ////

////                                                              ////

//// This source 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 Lesser General Public License for more ////

//// details.                                                     ////

////                                                              ////

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

//// Public License along with this source; if not, download it   ////

//// from http://www.opencores.org/lgpl.shtml                     ////

////                                                              ////

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

// synopsys translate_off

`include "timescale.v"

// synopsys translate_on

`include "or1200_defines.v"

module or1200_fpu(

                  // Clock and reset

                  clk, rst,

                  // FPU interface

                  ex_freeze, a, b, fpu_op, result, done,

                  // Flag controls

                  flagforw, flag_we,

                  // Exception signal

                  sig_fp, except_started,

                  // FPCSR system register

                  fpcsr_we, fpcsr,

                  // SPR interface -- currently unused

                  spr_cs, spr_write, spr_addr, spr_dat_i, spr_dat_o

                  );

   parameter width = `OR1200_OPERAND_WIDTH;

   //

   // I/O

   //

   //

   // Clock and reset

   //

   input                                clk;

   input                                rst;

   //

   // FPU interface

   //

   input                                ex_freeze;

   input [width-1:0]                     a;

   input [width-1:0]                     b;

   input [`OR1200_FPUOP_WIDTH-1:0]       fpu_op;

   output [width-1:0]                    result;

   output                               done;

   //

   // Flag signals

   //

   output                               flagforw;

   output                               flag_we;

   //

   // FPCSR interface

   //  

   input                                fpcsr_we;

   output [`OR1200_FPCSR_WIDTH-1:0]      fpcsr;

   //

   // Exception signal

   //   

   output                               sig_fp;

   input                                except_started;

   //

   // SPR interface

   //

   input                                spr_cs;

   input                                spr_write;

   input [31:0]                  spr_addr;

   input [31:0]                  spr_dat_i;

   output [31:0]                         spr_dat_o;

`ifndef OR1200_FPU_IMPLEMENTED

   // No FPU needed

   assign result = 0;

   assign flagforw  = 0;

   assign flag_we = 0;

   assign sig_fp = 0;

   assign spr_dat_o = 0;

   assign fpcsr = 0;

   assign done = 1;

`else

   //

   // Internals

   //

   wire                                 fpu_op_is_arith, fpu_op_is_conv,

                                        fpu_op_is_comp;

   wire                                 fpu_op_r_is_arith, fpu_op_r_is_conv,

                                        fpu_op_r_is_comp;

   wire                                 fpu_arith_done, fpu_conv_done,

                                        fpu_comp_done;

   wire [width-1:0]                      result_arith, result_conv;

   reg [`OR1200_FPUOP_WIDTH:0]           fpu_op_r;

   reg [`OR1200_FPCSR_WIDTH-1:0]         fpcsr_r;

   wire                                 fpu_op_valid;

   reg                                  fpu_op_valid_re;

   wire                                 fpu_check_op;

   wire                                 inf, inv_inf_op_in,snan, snan_in,qnan,

                                        ine, overflow, underflow, zero, dbz,

                                        dbz_in, mul_z_inf, nan_in;

   wire                                 altb, blta, aeqb, inf_cmp, zero_cmp,

                                        unordered ;

   wire                                 snan_conv, ine_conv, inv_conv,

                                        zero_conv, underflow_conv,

                                        overflow_conv;

   wire                                 inv_comp;

   reg                                  flag;

   assign spr_dat_o = 0;

   assign fpcsr = fpcsr_r;

   assign sig_fp = fpcsr_r[`OR1200_FPCSR_FPEE]

            & (|fpcsr_r[`OR1200_FPCSR_WIDTH-1:`OR1200_FPCSR_OVF]);

   // Top bit indicates FPU instruction

   assign fpu_op_valid = fpu_op[`OR1200_FPUOP_WIDTH-1];

   assign fpu_check_op = !ex_freeze & fpu_op_valid;

   // Generate signals to latch fpu_op from decode instruction, then latch 

   // operands when they appear during execute stage

   assign fpu_op_is_arith = !(|fpu_op[3:2]);

   assign fpu_op_is_conv = fpu_op[2] & !fpu_op[3];

   assign fpu_op_is_comp = fpu_op[3];

   assign fpu_op_r_is_arith = !(|fpu_op_r[3:2]);

   assign fpu_op_r_is_conv = fpu_op_r[2] & !fpu_op_r[3];

   assign fpu_op_r_is_comp = fpu_op_r[3];

   assign done = (fpu_op_r_is_arith & fpu_arith_done) |

                 (fpu_op_r_is_conv & fpu_conv_done)   |

                 (fpu_op_r_is_comp & fpu_comp_done)   ;

   // Register fpu_op (remove FPU op valid bit [7], replace with 0)

   always @(posedge clk)

     if (fpu_check_op)

       fpu_op_r <= {1'b0,fpu_op[`OR1200_FPUOP_WIDTH-2:0]};

   // Indicate new FPU op

   always @(posedge clk or posedge rst)

     if (rst)

       fpu_op_valid_re <= 0;

     else if (fpu_op_valid_re)

       fpu_op_valid_re <= 0;

     else if (fpu_check_op)

       fpu_op_valid_re <= 1;

   //

   // FPCSR system group register implementation

   //   

   always @(posedge clk or posedge rst) begin

      if (rst)

        fpcsr_r <= 0;

      else

        begin

           if (fpcsr_we)

             fpcsr_r <= b[`OR1200_FPCSR_WIDTH-1:0];

           else if (done)

             begin

                fpcsr_r[`OR1200_FPCSR_OVF] <= (overflow & fpu_op_r_is_arith);

                fpcsr_r[`OR1200_FPCSR_UNF] <= (underflow & fpu_op_r_is_arith) |

                                          (underflow_conv  & fpu_op_r_is_conv);

                fpcsr_r[`OR1200_FPCSR_SNF] <= (snan  & fpu_op_r_is_arith)|

                                              (snan_conv & fpu_op_r_is_conv);

                fpcsr_r[`OR1200_FPCSR_QNF] <= (qnan  & fpu_op_r_is_arith);

                fpcsr_r[`OR1200_FPCSR_ZF]  <= (zero  & fpu_op_r_is_arith) |

                                              (zero_cmp & fpu_op_r_is_comp) |

                                              (zero_conv & fpu_op_r_is_conv);

                fpcsr_r[`OR1200_FPCSR_IXF] <= (ine  & fpu_op_r_is_arith) |

                                              (ine_conv & fpu_op_r_is_conv);

                fpcsr_r[`OR1200_FPCSR_IVF] <=

                                ((snan_in | dbz_in | inv_inf_op_in | mul_z_inf) &

                                           fpu_op_r_is_arith) |

                                  ((inv_conv | snan_conv) & fpu_op_r_is_conv) |

                                              (inv_comp & fpu_op_r_is_comp);

                fpcsr_r[`OR1200_FPCSR_INF] <= (inf  & fpu_op_r_is_arith) |

                                              (inf_cmp & fpu_op_r_is_comp);

                fpcsr_r[`OR1200_FPCSR_DZF] <= (dbz & fpu_op_r_is_arith);

             end // if (fpu_arith_done | fpu_conv_done)    

           if (except_started)

             fpcsr_r[`OR1200_FPCSR_FPEE] <= 0;

        end // else: !if(rst)

   end // always @ (posedge clk or posedge rst)

   //

   // Comparison flag generation

   //

   always @*

     begin

        // Get rid of top bit - is FPU op valid bit

        case({1'b0,fpu_op_r[`OR1200_FPUOP_WIDTH-2:0]})

          `OR1200_FPCOP_SFEQ: begin

             flag = aeqb;

          end

          `OR1200_FPCOP_SFNE: begin

             flag = !aeqb;

               end

          `OR1200_FPCOP_SFGT: begin

             flag = blta & !aeqb;

          end

          `OR1200_FPCOP_SFGE: begin

             flag = blta | aeqb;

          end

          `OR1200_FPCOP_SFLT: begin

             flag = altb & !aeqb;

          end

          `OR1200_FPCOP_SFLE: begin

             flag = altb | aeqb;

          end

          default: begin

             flag = 0;

          end

        endcase // case (fpu_op_r)

     end // always@ (posedge clk)

   assign flagforw = flag;

   // Determine here where we do the write, ie how much we pipeline the 

   // comparison

   assign flag_we = fpu_op_r_is_comp & fpu_comp_done;

   // MUX for outputs from arith and conversion modules

   assign result = fpu_op_r_is_conv ? result_conv : result_arith;

   //

   // Instantiate FPU modules

   //

   // FPU 100 VHDL core from OpenCores.org: http://opencores.org/project,fpu100

   // Used only for add,sub,mul,div

   or1200_fpu_arith fpu_arith

     (

      .clk_i(clk),

      .opa_i(a),

      .opb_i(b),

      .fpu_op_i({1'b0,fpu_op_r[1:0]}), // Only bottom 2 bits

      .rmode_i(fpcsr_r[`OR1200_FPCSR_RM]),

      .output_o(result_arith),

      .start_i(fpu_op_valid_re & fpu_op_r_is_arith),

      .ready_o(fpu_arith_done),

      .ine_o(ine),

      .overflow_o(overflow),

      .underflow_o(underflow),

      .div_zero_o(dbz),

      .inf_o(inf),

      .zero_o(zero),

      .qnan_o(qnan),

      .snan_o(snan)

      );

   // Logic for detection of signaling NaN on input

   // signaling NaN: exponent is 8hff, [22] is zero, rest of fract is non-zero

   // quiet NaN: exponent is 8hff, [22] is 1

   reg a_is_snan, b_is_snan;

   reg a_is_qnan, b_is_qnan;

   always @(posedge clk)

     begin

        a_is_snan <= (a[30:23]==8'hff) & !a[22] & (|a[21:0]);

        b_is_snan <= (b[30:23]==8'hff) & !b[22] & (|b[21:0]);

        a_is_qnan <= (a[30:23]==8'hff) & a[22];

        b_is_qnan <= (b[30:23]==8'hff) & b[22];

     end

   // Signal to indicate there was a signaling NaN on input

   assign snan_in = a_is_snan | b_is_snan;

   // Check for, add with opposite signed infinities, or subtract with 

   // same signed infinities.

   reg a_is_inf, b_is_inf, a_b_sign_xor;

   always @(posedge clk)

     begin

        a_is_inf <= (a[30:23]==8'hff) & !(|a[22:0]);

        b_is_inf <= (b[30:23]==8'hff) & !(|a[22:0]);

        a_b_sign_xor <= a[31] ^ b[31];

     end

   assign inv_inf_op_in = (a_is_inf & b_is_inf) &

                          ((a_b_sign_xor &

                            ({1'b0,fpu_op_r[`OR1200_FPUOP_WIDTH-2:0]} ==

                             `OR1200_FPUOP_ADD)) |

                           (!a_b_sign_xor &

                            ({1'b0,fpu_op_r[`OR1200_FPUOP_WIDTH-2:0]} ==

                             `OR1200_FPUOP_SUB))) ;

   // Check if it's 0.0/0.0 to generate invalid signal (ignore sign bit)

   reg a_is_zero, b_is_zero;

   always @(posedge clk)

     begin

        a_is_zero <= !(|a[30:0]);

        b_is_zero <= !(|b[30:0]);

     end

   assign dbz_in = ({1'b0,fpu_op_r[`OR1200_FPUOP_WIDTH-2:0]} ==

                    `OR1200_FPUOP_DIV) & (a_is_zero & b_is_zero);

   assign mul_z_inf = ({1'b0,fpu_op_r[`OR1200_FPUOP_WIDTH-2:0]} ==

                       `OR1200_FPUOP_MUL) &

                      ((a_is_zero & b_is_inf) | (b_is_zero & a_is_inf));

   assign nan_in = (a_is_snan | b_is_snan | a_is_qnan | b_is_qnan);

   // 32-bit integer <-> single precision floating point conversion unit

   or1200_fpu_intfloat_conv fpu_intfloat_conv

     (

       .clk(clk),

       .rmode(fpcsr_r[`OR1200_FPCSR_RM]),

       .fpu_op(fpu_op_r[2:0]),

       .opa(a),

       .out(result_conv),

       .snan(snan_conv),

       .ine(ine_conv),

       .inv(inv_conv),

       .overflow(overflow_conv),

       .underflow(underflow_conv),

       .zero(zero_conv)

       );

   // 5-long shift reg for conversion ready counter

   reg [6:0] fpu_conv_shr;

   always @(posedge clk)

     fpu_conv_shr <= {fpu_conv_shr[5:0],fpu_check_op & fpu_op_is_conv};

   assign fpu_conv_done = fpu_conv_shr[6];

   // Single precision floating point number comparison module

   or1200_fpu_fcmp fpu_fcmp

     (

      .opa(a),

      .opb(b),

      .unordered(unordered),

      // I am convinced the comparison logic is wrong way around in this 

      // module, simplest to swap them on output -- julius       

      .altb(blta),

      .blta(altb),

      .aeqb(aeqb),

      .inf(inf_cmp),

      .zero(zero_cmp));

   reg       fpu_op_valid_re_r;

   always @(posedge clk)

     fpu_op_valid_re_r  <= fpu_op_valid_re;

   assign fpu_comp_done = fpu_op_valid_re_r & fpu_op_r_is_comp;

   // Comparison invalid when sNaN in on an equal comparison, or any NaN 

   // for any other comparison.

   assign inv_comp =  (snan_in & ({1'b0,fpu_op_r[`OR1200_FPUOP_WIDTH-2:0]}

                                  == `OR1200_FPCOP_SFEQ)) |

                      (nan_in & ({1'b0,fpu_op_r[`OR1200_FPUOP_WIDTH-2:0]}

                                 != `OR1200_FPCOP_SFEQ));

`endif // !`ifndef OR1200_FPU_IMPLEMENTED

endmodule // or1200_fpu