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// ============================================================================

//        __

//   \\__/ o\    (C) 2013  Robert Finch, Stratford

//    \  __ /    All rights reserved.

//     \/_//     robfinch<remove>@opencores.org

//       ||

//

// 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 3 of the License, or     

// (at your option) any later version.                                      

//                                                                          

// This source file 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 program.  If not, see <http://www.gnu.org/licenses/>.    

//                                                   

// Datapath calculations for 32 bit mode.                       

// ============================================================================

//

CALC:

        begin

                state <= IFETCH;

                case(ir[7:0])

                //The following handled in the DECODE stage which reduces the CPI at a cost of clock frequency.

                `RR:

                        case(ir[23:20])

//                              `ADD_RR:        res <= a + b;

//                              `SUB_RR:        res <= a - b;   // Also CMP

//                              `AND_RR:        res <= a & b;   // Also BIT

//                              `OR_RR:         res <= a | b;

//                              `EOR_RR:        res <= a ^ b;

//                              `MUL_RR:        prod <= a * b;  // slows the whole core down

                        `ASL_RRR:       res <= shlo;

                        `LSR_RRR:       res <= shro;

                        endcase

                `ADD_ZPX,`ADD_IX,`ADD_IY,`ADD_ABS,`ADD_ABSX,`ADD_RIND:  begin res <= a + b + {31'b0,df&cf};     end

                `SUB_ZPX,`SUB_IX,`SUB_IY,`SUB_ABS,`SUB_ABSX,`SUB_RIND:  begin res <= a - b - {31'b0,df&~cf&|Rt};        end // Also CMP

                `AND_ZPX,`AND_IX,`AND_IY,`AND_ABS,`AND_ABSX,`AND_RIND:  begin res <= a & b; end // Also BIT

                `OR_ZPX,`OR_IX,`OR_IY,`OR_ABS,`OR_ABSX,`OR_RIND:                        begin res <= a | b; end // Also LD

                `EOR_ZPX,`EOR_IX,`EOR_IY,`EOR_ABS,`EOR_ABSX,`EOR_RIND:  begin res <= a ^ b; end

                `LDX_ZPY,`LDX_ABS,`LDX_ABSY:    begin res <= b; end

                `LDY_ZPX,`LDY_ABS,`LDY_ABSX:    begin res <= b; end

                `CPX_ZPX,`CPX_ABS:      begin res <= x - b; end

                `CPY_ZPX,`CPY_ABS:      begin res <= y - b; end

                `ASL_IMM8:      res <= shlo;

                `LSR_IMM8:      res <= shro;

                //The following handled in the DECODE stage which reduces the CPI at a cost of clock frequency.

//                      `ASL_RR:        begin res <= {a,1'b0}; end

//                      `ROL_RR:        begin res <= {a,cf}; end

//                      `LSR_RR:        begin res <= {a[0],1'b0,a[31:1]}; end

//                      `ROR_RR:        begin res <= {a[0],cf,a[31:1]}; end

                `ASL_ZPX,`ASL_ABS,`ASL_ABSX:    begin res <= {b,1'b0}; wdat <= {b,1'b0}; wadr <= radr; wadr2LSB <= radr2LSB; state <= STORE1; end

                `ROL_ZPX,`ROL_ABS,`ROL_ABSX:    begin res <= {b,cf}; wdat <= {b,cf}; wadr <= radr; wadr2LSB <= radr2LSB; state <= STORE1; end

                `LSR_ZPX,`LSR_ABS,`LSR_ABSX:    begin res <= {b[0],1'b0,b[31:1]}; wdat <= {b[0],1'b0,b[31:1]}; wadr <= radr; wadr2LSB <= radr2LSB; state <= STORE1; end

                `ROR_ZPX,`ROR_ABS,`ROR_ABSX:    begin res <= {b[0],cf,b[31:1]}; wdat <= {b[0],cf,b[31:1]}; wadr <= radr; wadr2LSB <= radr2LSB; state <= STORE1; end

                `INC_ZPX,`INC_ABS,`INC_ABSX:    begin res <= b + 1; wdat <= b + 1; wadr <= radr; wadr2LSB <= radr2LSB; state <= STORE1; end

                `DEC_ZPX,`DEC_ABS,`DEC_ABSX:    begin res <= b - 1; wdat <= b - 1; wadr <= radr; wadr2LSB <= radr2LSB; state <= STORE1; end

                `ORB_ZPX,`ORB_ABS,`ORB_ABSX:    begin res <= a | {24'h0,b8}; end

                endcase

        end