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////////////////////////////////////////////////////////////////////////////
////                                                                    ////
//// T6507LP IP Core                                                    ////
////                                                                    ////
//// This file is part of the T6507LP project                           ////
//// http://www.opencores.org/cores/t6507lp/                            ////
////                                                                    ////
//// Description                                                        ////
//// 6507 ALU                                                           ////
////                                                                    ////
//// To Do:                                                             ////
//// - Search for TODO                                                  ////
////                                                                    ////
//// Author(s):                                                         ////
//// - Gabriel Oshiro Zardo, gabrieloshiro@gmail.com                    ////
//// - Samuel Nascimento Pagliarini (creep), snpagliarini@gmail.com     ////
////                                                                    ////
////////////////////////////////////////////////////////////////////////////
////                                                                    ////
//// Copyright (C) 2001 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                           ////
////                                                                    ////
////////////////////////////////////////////////////////////////////////////
 
`include "timescale.v"
 
// TODO: verify code identation
 
module t6507lp_alu( clk, reset_n, alu_enable, alu_result, alu_status, alu_opcode, alu_a, alu_x, alu_y );
 
input wire       clk;
input wire       reset_n;
input wire       alu_enable;
input wire [7:0] alu_opcode;
input wire [7:0] alu_a;
output reg [7:0] alu_result;
output reg [7:0] alu_status;
output reg [7:0] alu_x;
output reg [7:0] alu_y;
 
reg [7:0] A;
reg [7:0] X;
reg [7:0] Y;
 
reg [7:0] STATUS;
reg [7:0] result;
reg [7:0] op1;
reg [7:0] op2;
reg [7:0] bcdl;
reg [7:0] bcdh;
reg [7:0] bcdh2;
reg [7:0] AL;
reg [7:0] AH;
reg C_aux;
reg sign;
 
`include "t6507lp_package.v"
 
always @ (posedge clk or negedge reset_n)
begin
        if (reset_n == 0) begin
                alu_result <= 0;
                alu_status[C] <= 0;
                alu_status[N] <= 0;
                alu_status[V] <= 0;
                alu_status[5] <= 1;
                alu_status[Z] <= 1;
                alu_status[I] <= 0;
                alu_status[B] <= 0;
                alu_status[D] <= 0;
                A <= 0;
                X <= 0;
                Y <= 0;
                alu_x <= 0;
                alu_y <= 0;
        end
        else if ( alu_enable == 1 ) begin
                case (alu_opcode)
                        ADC_IMM, ADC_ZPG, ADC_ZPX, ADC_ABS, ADC_ABX, ADC_ABY, ADC_IDX, ADC_IDY,
                        AND_IMM, AND_ZPG, AND_ZPX, AND_ABS, AND_ABX, AND_ABY, AND_IDX, AND_IDY,
                        ASL_ACC, EOR_IMM, EOR_ZPG, EOR_ZPX, EOR_ABS, EOR_ABX, EOR_ABY, EOR_IDX,
                        EOR_IDY, LSR_ACC, ORA_IMM, ORA_ZPG, ORA_ZPX, ORA_ABS, ORA_ABX, ORA_ABY,
                        ORA_IDX, ORA_IDY, ROL_ACC, ROR_ACC, SBC_IMM, SBC_ZPG, SBC_ZPX, SBC_ABS,
                        SBC_ABX, SBC_ABY, SBC_IDX, SBC_IDY, LDA_IMM, LDA_ZPG, LDA_ZPX, LDA_ABS,
                        LDA_ABX, LDA_ABY, LDA_IDX, LDA_IDY, PLA_IMP, TXA_IMP, TYA_IMP :
                        begin
                                A          <= result;
                                alu_result <= result;
                                alu_status <= STATUS;
                        end
                        LDX_IMM, LDX_ZPG, LDX_ZPY, LDX_ABS, LDX_ABY, TAX_IMP, TSX_IMP, INX_IMP, DEX_IMP :
                        begin
                                X          <= result;
                                alu_x      <= result;
                                alu_status <= STATUS;
                        end
                        TXS_IMP :
                        begin
                                X          <= result;
                                alu_x      <= result;
                        end
                        LDY_IMM, LDY_ZPG, LDY_ZPX, LDY_ABS, LDY_ABX, TAY_IMP, INY_IMP, DEY_IMP :
                        begin
                                Y          <= result;
                                alu_y      <= result;
                                alu_status <= STATUS;
                        end
                        CMP_IMM, CMP_ZPG, CMP_ZPX, CMP_ABS, CMP_ABX, CMP_ABY, CMP_IDX, CMP_IDY,
                        CPX_IMM, CPX_ZPG, CPX_ABS, CPY_IMM, CPY_ZPG, CPY_ABS :
                        begin
                                alu_status <= STATUS;
                        end
                        PHA_IMP, STA_ZPG, STA_ZPX, STA_ABS, STA_ABX, STA_ABY, STA_IDX, STA_IDY : begin
                                alu_result <= result;
                        end
                        STX_ZPG, STX_ZPY, STX_ABS : begin
                                alu_x <= result;
                        end
                        STY_ZPG, STY_ZPX, STY_ABS : begin
                                alu_y <= result;
                        end
                        SEC_IMP :
                        begin
                                alu_status[C] <= 1;
                        end
                        SED_IMP :
                        begin
                                alu_status[D] <= 1;
                        end
                        SEI_IMP :
                        begin
                                alu_status[I] <= 1;
                        end
                        CLC_IMP :
                        begin
                                alu_status[C] <= 0;
                        end
                        CLD_IMP :
                        begin
                                alu_status[D] <= 0;
                        end
                        CLI_IMP :
                        begin
                                alu_status[I] <= 0;
                        end
                        CLV_IMP :
                        begin
                                alu_status[V] <= 0;
                        end
                        BRK_IMP :
                        begin
                                alu_status[B] <= 1;
                        end
                        PLP_IMP, RTI_IMP :
                        begin
                                alu_status[C] <= alu_a[C];
                                alu_status[Z] <= alu_a[Z];
                                alu_status[I] <= alu_a[I];
                                alu_status[D] <= alu_a[D];
                                alu_status[B] <= alu_a[B];
                                alu_status[V] <= alu_a[V];
                                alu_status[N] <= alu_a[N];
                                alu_status[5] <= 1;
                        end
                        BIT_ZPG, BIT_ABS :
                        begin
                                alu_status[Z] <= STATUS[Z];
                                alu_status[V] <= alu_a[6];
                                alu_status[N] <= alu_a[7];
                        end
                        INC_ZPG, INC_ZPX, INC_ABS, INC_ABX, DEC_ZPG, DEC_ZPX, DEC_ABS, DEC_ABX,
                        ASL_ZPG, ASL_ZPX, ASL_ABS, ASL_ABX, LSR_ZPG, LSR_ZPX, LSR_ABS, LSR_ABX,
                        ROL_ZPG, ROL_ZPX, ROL_ABS, ROL_ABX, ROR_ZPG, ROR_ZPX, ROR_ABS, ROR_ABX :
                        begin
                                alu_result <= result;
                                alu_status <= STATUS;
                        end
                        //PHP_IMP : begin
                        //end
                        default : begin
                                //$display("ERROR");
                        end
                endcase
        end
end
 
always @ (*) begin
if (alu_enable == 1) begin
        op1      = A;
        op2      = alu_a;
        result    = alu_result;
        STATUS[N] = alu_status[N];
        STATUS[C] = alu_status[C];
        STATUS[V] = alu_status[V];
        STATUS[B] = alu_status[B];
        STATUS[I] = alu_status[I];
        STATUS[D] = alu_status[D];
        STATUS[Z] = alu_status[Z];
        STATUS[N] = alu_status[N];
        STATUS[5] = 1;
 
        bcdl = 0;
        bcdh = 0;
        bcdh2 = 0;
        AL = 0;
        AH = 0;
        sign = op2[7];
 
        case (alu_opcode)
                // BIT - Bit Test
                BIT_ZPG, BIT_ABS: begin
                        result = A & alu_a;
                end
 
                // BRK - Force Interrupt
                BRK_IMP: begin
                        STATUS[B] = 1'b1;
                end
 
                // CLC - Clear Carry Flag
                CLC_IMP: begin
                        STATUS[C] = 1'b0;
                end
 
                // CLD - Clear Decimal Flag
                CLD_IMP: begin
                        STATUS[D] = 1'b0;
                end
 
                // CLI - Clear Interrupt Disable
                CLI_IMP: begin
                        STATUS[I] = 1'b0;
                end
 
                // CLV - Clear Overflow Flag
                CLV_IMP: begin
                        STATUS[V] = 1'b0;
                end
 
                // NOP - No Operation
                //NOP_IMP: begin
                        // Do nothing :-D
                //end
 
                // PLP - Pull Processor Status Register
                // RTI - Return from Interrupt
                //PLP_IMP, RTI_IMP: begin
                //      STATUS = alu_a;
                //end
 
                PLA_IMP : begin
                        result = alu_a;
                end
 
                // STA - Store Accumulator
                // PHA - Push A
                // TAX - Transfer Accumulator to X
                // TAY - Transfer Accumulator to Y
                TAX_IMP, TAY_IMP, PHA_IMP, STA_ZPG, STA_ZPX, STA_ABS, STA_ABX, STA_ABY, STA_IDX, STA_IDY : begin
                        result = A;
                end
 
                // STX - Store X Register
                // TXA - Transfer X to Accumulator
                // TXS - Transfer X to Stack pointer
                STX_ZPG, STX_ZPY, STX_ABS, TXA_IMP, TXS_IMP : begin
                        result = X;
                end
 
                // STY - Store Y Register
                // TYA - Transfer Y to Accumulator
                STY_ZPG, STY_ZPX, STY_ABS, TYA_IMP : begin
                        result = Y;
                end
 
                // SEC - Set Carry Flag
                SEC_IMP: begin
                        STATUS[C] = 1'b1;
                end
 
                // SED - Set Decimal Flag
                SED_IMP: begin
                        STATUS[D] = 1'b1;
                end
 
                // SEI - Set Interrupt Disable
                SEI_IMP: begin
                        STATUS[I] = 1'b1;
                end
 
                // INC - Increment memory
                INC_ZPG, INC_ZPX, INC_ABS, INC_ABX : begin
                        result = alu_a + 1;
                end
 
                // INX - Increment X Register
                INX_IMP: begin
                        result = X + 1;
                end
 
                // INY - Increment Y Register
                INY_IMP : begin
                        result = Y + 1;
                end
 
                // DEC - Decrement memory
                DEC_ZPG, DEC_ZPX, DEC_ABS, DEC_ABX : begin
                        result = alu_a - 1;
                end
 
                // DEX - Decrement X register
                DEX_IMP: begin
                        result = X - 1;
                end
 
                // DEY - Decrement Y Register
                DEY_IMP: begin
                        result = Y - 1;
                end
 
                // ADC - Add with carry
                // TODO: verify synthesis for % operand
                ADC_IMM, ADC_ZPG, ADC_ZPX, ADC_ABS, ADC_ABX, ADC_ABY, ADC_IDX, ADC_IDY : begin
                        if (alu_status[D] == 1) begin
                                //$display("MODO DECIMAL");
                                AL = A[3:0] + alu_a[3:0] + alu_status[C];
                                AH = A[7:4] + alu_a[7:4];
                                //$display("AL = %d", AL);
                                //$display("AH = %d", AH);
                                if (AL > 9) begin
                                        bcdh = AH + (AL / 10);
                                        bcdl = AL % 10;
                                end
                                else begin
                                        bcdh = AH;
                                        bcdl = AL;
                                end
 
                                // ok
 
                                if (bcdh > 9) begin
                                        STATUS[C] = 1;
                                        bcdh2 = bcdh % 10;
                                end
                                else begin
                                        STATUS[C] = 0;
                                        bcdh2 = bcdh;
                                end
                                //$display("bcdh2 = %d", bcdh2);
                                //$display("bcdl = %d", bcdl);
                                result = {bcdh2[3:0],bcdl[3:0]};
                        end
                        else begin
                                //$display("MODO NORMAL");
                                {STATUS[C],result} = op1 + op2 + alu_status[C];
                        end
 
                        if ((op1[7] == op2[7]) && (op1[7] != result[7]))
                                STATUS[V] = 1;
                        else
                                STATUS[V] = 0;
                end
 
                // AND - Logical AND
                AND_IMM, AND_ZPG, AND_ZPX, AND_ABS, AND_ABX, AND_ABY, AND_IDX, AND_IDY : begin
                        result = A & alu_a;
                end
 
                // CMP - Compare
                CMP_IMM, CMP_ZPG, CMP_ZPX, CMP_ABS, CMP_ABX, CMP_ABY, CMP_IDX, CMP_IDY : begin
                        result = A - alu_a;
                        STATUS[C] = (A >= alu_a) ? 1 : 0;
                end
 
                // EOR - Exclusive OR
                EOR_IMM, EOR_ZPG, EOR_ZPX, EOR_ABS, EOR_ABX, EOR_ABY, EOR_IDX, EOR_IDY : begin
                        result = A ^ alu_a;
                        //$display("op1 ^ op2 = result");
                        //$display("%d  ^ %d  = %d", op1, op2, result);
                end
 
                // LDA - Load Accumulator
                // LDX - Load X Register
                // LDY - Load Y Register
                // TSX - Transfer Stack Pointer to X
                LDA_IMM, LDA_ZPG, LDA_ZPX, LDA_ABS, LDA_ABX, LDA_ABY, LDA_IDX, LDA_IDY,
                LDX_IMM, LDX_ZPG, LDX_ZPY, LDX_ABS, LDX_ABY,
                LDY_IMM, LDY_ZPG, LDY_ZPX, LDY_ABS, LDY_ABX,
                TSX_IMP : begin
                        result = alu_a;
                end
 
                // ORA - Logical OR
                ORA_IMM, ORA_ZPG, ORA_ZPX, ORA_ABS, ORA_ABX, ORA_ABY, ORA_IDX, ORA_IDY : begin
                        result = A | alu_a;
                end
 
                // SBC - Subtract with Carry
                SBC_IMM, SBC_ZPG, SBC_ZPX, SBC_ABS, SBC_ABX, SBC_ABY, SBC_IDX, SBC_IDY : begin
                        if (alu_status[D] == 1) begin
                                bcdl = op1[3:0] - op2[3:0] - (1 - alu_status[C]);
                                bcdh = op1[7:4] - op2[7:4];
                                if (bcdl > 9) begin
                                        bcdh = bcdh + bcdl[5:4];
                                        bcdl = bcdl % 10;
                                end
                                if (bcdh > 9) begin
                                        STATUS[C] = 1;
                                        bcdh = bcdh % 10;
                                end
                                result = {bcdh[3:0],bcdl[3:0]};
                        end
                        else begin
                                op2 = ~alu_a;
                                result = op1 + op2 + alu_status[C];
                                STATUS[C] = ~result[7];
                        end
 
 
                        if ((op1[7] == sign) && (op1[7] != result[7]))
                                STATUS[V] = 1;
                        else
                                STATUS[V] = 0;
 
                end
 
                // ASL - Arithmetic Shift Left
                ASL_ACC : begin
                        //{STATUS[C],result} = A << 1;
                        {STATUS[C],result} = {A,1'b0};
                end
                ASL_ZPG, ASL_ZPX, ASL_ABS, ASL_ABX : begin
                        //{STATUS[C],result} = alu_a << 1;
                        {STATUS[C],result} = {alu_a,1'b0};
                end
 
                // LSR - Logical Shift Right
                LSR_ACC: begin
                        //{result, STATUS[C]} = A >> 1;
                        {result,STATUS[C]} = {1'b0,A};
                end
                LSR_ZPG, LSR_ZPX, LSR_ABS, LSR_ABX : begin
                        //{result, STATUS[C]} = alu_a >> 1;
                        {result,STATUS[C]} = {1'b0,alu_a};
                end
 
                // ROL - Rotate Left
                ROL_ACC : begin
                        {STATUS[C],result} = {A,alu_status[C]};
                end
                ROL_ZPG, ROL_ZPX, ROL_ABS, ROL_ABX : begin
                        {STATUS[C],result} = {alu_a,alu_status[C]};
                end
 
                // ROR - Rotate Right
                ROR_ACC : begin
                        {result,STATUS[C]} = {alu_status[C],A};
                end
                ROR_ZPG, ROR_ZPX, ROR_ABS, ROR_ABX : begin
                        {result, STATUS[C]} = {alu_status[C], alu_a};
                end
 
                // CPX - Compare X Register
                CPX_IMM, CPX_ZPG, CPX_ABS : begin
                        result = X - alu_a;
                        STATUS[C] = (X >= alu_a) ? 1 : 0;
                end
 
                // CPY - Compare Y Register
                CPY_IMM, CPY_ZPG, CPY_ABS : begin
                        result = Y - alu_a;
                        STATUS[C] = (Y >= alu_a) ? 1 : 0;
                end
 
                default: begin // NON-DEFAULT OPCODES FALL HERE
                end
        endcase
        STATUS[Z] = (result == 0) ? 1 : 0;
        STATUS[N] = result[7];
end
end
endmodule
 

Line No.	Rev	Author	Line
1	141	creep	`////////////////////////////////////////////////////////////////////////////`
2	152	gabrielosh	`//// ////`
3			`//// T6507LP IP Core ////`
4			`//// ////`
5			`//// This file is part of the T6507LP project ////`
6			`//// http://www.opencores.org/cores/t6507lp/ ////`
7			`//// ////`
8			`//// Description ////`
9			`//// 6507 ALU ////`
10			`//// ////`
11			`//// To Do: ////`
12			`//// - Search for TODO ////`
13			`//// ////`
14			`//// Author(s): ////`
15			`//// - Gabriel Oshiro Zardo, gabrieloshiro@gmail.com ////`
16			`//// - Samuel Nascimento Pagliarini (creep), snpagliarini@gmail.com ////`
17			`//// ////`
18	141	creep	`////////////////////////////////////////////////////////////////////////////`
19	152	gabrielosh	`//// ////`
20			`//// Copyright (C) 2001 Authors and OPENCORES.ORG ////`
21			`//// ////`
22			`//// This source file may be used and distributed without ////`
23			`//// restriction provided that this copyright statement is not ////`
24			`//// removed from the file and that any derivative work contains ////`
25			`//// the original copyright notice and the associated disclaimer. ////`
26			`//// ////`
27			`//// This source file is free software; you can redistribute it ////`
28			`//// and/or modify it under the terms of the GNU Lesser General ////`
29			`//// Public License as published by the Free Software Foundation; ////`
30			`//// either version 2.1 of the License, or (at your option) any ////`
31			`//// later version. ////`
32			`//// ////`
33			`//// This source is distributed in the hope that it will be ////`
34			`//// useful, but WITHOUT ANY WARRANTY; without even the implied ////`
35			`//// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR ////`
36			`//// PURPOSE. See the GNU Lesser General Public License for more ////`
37			`//// details. ////`
38			`//// ////`
39			`//// You should have received a copy of the GNU Lesser General ////`
40			`//// Public License along with this source; if not, download it ////`
41			`//// from http://www.opencores.org/lgpl.shtml ////`
42			`//// ////`
43	141	creep	`////////////////////////////////////////////////////////////////////////////`
44
45			`include "timescale.v"
46
47			`// TODO: verify code identation`
48
49			`module t6507lp_alu( clk, reset_n, alu_enable, alu_result, alu_status, alu_opcode, alu_a, alu_x, alu_y );`
50
51			`input wire clk;`
52			`input wire reset_n;`
53			`input wire alu_enable;`
54			`input wire [7:0] alu_opcode;`
55			`input wire [7:0] alu_a;`
56			`output reg [7:0] alu_result;`
57			`output reg [7:0] alu_status;`
58			`output reg [7:0] alu_x;`
59			`output reg [7:0] alu_y;`
60
61			`reg [7:0] A;`
62			`reg [7:0] X;`
63			`reg [7:0] Y;`
64
65			`reg [7:0] STATUS;`
66			`reg [7:0] result;`
67	152	gabrielosh	`reg [7:0] op1;`
68			`reg [7:0] op2;`
69	161	gabrielosh	`reg [7:0] bcdl;`
70			`reg [7:0] bcdh;`
71	164	gabrielosh	`reg [7:0] bcdh2;`
72			`reg [7:0] AL;`
73			`reg [7:0] AH;`
74	173	gabrielosh	`reg C_aux;`
75			`reg sign;`
76	141	creep
77			`include "t6507lp_package.v"
78
79			`always @ (posedge clk or negedge reset_n)`
80			`begin`
81			`if (reset_n == 0) begin`
82			`alu_result <= 0;`
83			`alu_status[C] <= 0;`
84			`alu_status[N] <= 0;`
85			`alu_status[V] <= 0;`
86	148	gabrielosh	`alu_status[5] <= 1;`
87	141	creep	`alu_status[Z] <= 1;`
88			`alu_status[I] <= 0;`
89			`alu_status[B] <= 0;`
90			`alu_status[D] <= 0;`
91			`A <= 0;`
92			`X <= 0;`
93			`Y <= 0;`
94			`alu_x <= 0;`
95			`alu_y <= 0;`
96			`end`
97			`else if ( alu_enable == 1 ) begin`
98			`case (alu_opcode)`
99			`ADC_IMM, ADC_ZPG, ADC_ZPX, ADC_ABS, ADC_ABX, ADC_ABY, ADC_IDX, ADC_IDY,`
100			`AND_IMM, AND_ZPG, AND_ZPX, AND_ABS, AND_ABX, AND_ABY, AND_IDX, AND_IDY,`
101			`ASL_ACC, EOR_IMM, EOR_ZPG, EOR_ZPX, EOR_ABS, EOR_ABX, EOR_ABY, EOR_IDX,`
102			`EOR_IDY, LSR_ACC, ORA_IMM, ORA_ZPG, ORA_ZPX, ORA_ABS, ORA_ABX, ORA_ABY,`
103			`ORA_IDX, ORA_IDY, ROL_ACC, ROR_ACC, SBC_IMM, SBC_ZPG, SBC_ZPX, SBC_ABS,`
104			`SBC_ABX, SBC_ABY, SBC_IDX, SBC_IDY, LDA_IMM, LDA_ZPG, LDA_ZPX, LDA_ABS,`
105			`LDA_ABX, LDA_ABY, LDA_IDX, LDA_IDY, PLA_IMP, TXA_IMP, TYA_IMP :`
106			`begin`
107			`A <= result;`
108			`alu_result <= result;`
109			`alu_status <= STATUS;`
110			`end`
111			`LDX_IMM, LDX_ZPG, LDX_ZPY, LDX_ABS, LDX_ABY, TAX_IMP, TSX_IMP, INX_IMP, DEX_IMP :`
112			`begin`
113			`X <= result;`
114			`alu_x <= result;`
115			`alu_status <= STATUS;`
116			`end`
117			`TXS_IMP :`
118			`begin`
119	148	gabrielosh	`X <= result;`
120			`alu_x <= result;`
121	141	creep	`end`
122			`LDY_IMM, LDY_ZPG, LDY_ZPX, LDY_ABS, LDY_ABX, TAY_IMP, INY_IMP, DEY_IMP :`
123			`begin`
124			`Y <= result;`
125			`alu_y <= result;`
126			`alu_status <= STATUS;`
127			`end`
128	148	gabrielosh	`CMP_IMM, CMP_ZPG, CMP_ZPX, CMP_ABS, CMP_ABX, CMP_ABY, CMP_IDX, CMP_IDY,`
129	165	gabrielosh	`CPX_IMM, CPX_ZPG, CPX_ABS, CPY_IMM, CPY_ZPG, CPY_ABS :`
130	141	creep	`begin`
131			`alu_status <= STATUS;`
132			`end`
133	178	gabrielosh	`PHA_IMP, STA_ZPG, STA_ZPX, STA_ABS, STA_ABX, STA_ABY, STA_IDX, STA_IDY : begin`
134	158	gabrielosh	`alu_result <= result;`
135			`end`
136	178	gabrielosh	`STX_ZPG, STX_ZPY, STX_ABS : begin`
137			`alu_x <= result;`
138			`end`
139			`STY_ZPG, STY_ZPX, STY_ABS : begin`
140			`alu_y <= result;`
141			`end`
142	141	creep	`SEC_IMP :`
143			`begin`
144			`alu_status[C] <= 1;`
145			`end`
146			`SED_IMP :`
147			`begin`
148			`alu_status[D] <= 1;`
149			`end`
150			`SEI_IMP :`
151			`begin`
152			`alu_status[I] <= 1;`
153			`end`
154			`CLC_IMP :`
155			`begin`
156			`alu_status[C] <= 0;`
157			`end`
158			`CLD_IMP :`
159			`begin`
160			`alu_status[D] <= 0;`
161			`end`
162			`CLI_IMP :`
163			`begin`
164			`alu_status[I] <= 0;`
165			`end`
166			`CLV_IMP :`
167			`begin`
168			`alu_status[V] <= 0;`
169			`end`
170			`BRK_IMP :`
171			`begin`
172	154	gabrielosh	`alu_status[B] <= 1;`
173	141	creep	`end`
174	171	creep	`PLP_IMP, RTI_IMP :`
175	141	creep	`begin`
176	175	gabrielosh	`alu_status[C] <= alu_a[C];`
177			`alu_status[Z] <= alu_a[Z];`
178			`alu_status[I] <= alu_a[I];`
179			`alu_status[D] <= alu_a[D];`
180			`alu_status[B] <= alu_a[B];`
181			`alu_status[V] <= alu_a[V];`
182			`alu_status[N] <= alu_a[N];`
183	173	gabrielosh	`alu_status[5] <= 1;`
184	141	creep	`end`
185			`BIT_ZPG, BIT_ABS :`
186			`begin`
187			`alu_status[Z] <= STATUS[Z];`
188			`alu_status[V] <= alu_a[6];`
189			`alu_status[N] <= alu_a[7];`
190			`end`
191	148	gabrielosh	`INC_ZPG, INC_ZPX, INC_ABS, INC_ABX, DEC_ZPG, DEC_ZPX, DEC_ABS, DEC_ABX,`
192			`ASL_ZPG, ASL_ZPX, ASL_ABS, ASL_ABX, LSR_ZPG, LSR_ZPX, LSR_ABS, LSR_ABX,`
193			`ROL_ZPG, ROL_ZPX, ROL_ABS, ROL_ABX, ROR_ZPG, ROR_ZPX, ROR_ABS, ROR_ABX :`
194	141	creep	`begin`
195			`alu_result <= result;`
196			`alu_status <= STATUS;`
197			`end`
198	173	gabrielosh	`//PHP_IMP : begin`
199			`//end`
200	141	creep	`default : begin`
201			`//$display("ERROR");`
202			`end`
203			`endcase`
204			`end`
205			`end`
206
207			`always @ (*) begin`
208	175	gabrielosh	`if (alu_enable == 1) begin`
209	152	gabrielosh	`op1 = A;`
210			`op2 = alu_a;`
211	150	gabrielosh	`result = alu_result;`
212			`STATUS[N] = alu_status[N];`
213			`STATUS[C] = alu_status[C];`
214			`STATUS[V] = alu_status[V];`
215			`STATUS[B] = alu_status[B];`
216			`STATUS[I] = alu_status[I];`
217			`STATUS[D] = alu_status[D];`
218			`STATUS[Z] = alu_status[Z];`
219			`STATUS[N] = alu_status[N];`
220	151	gabrielosh	`STATUS[5] = 1;`
221	141	creep
222	171	creep	`bcdl = 0;`
223			`bcdh = 0;`
224			`bcdh2 = 0;`
225			`AL = 0;`
226			`AH = 0;`
227	173	gabrielosh	`sign = op2[7];`
228	171	creep
229	141	creep	`case (alu_opcode)`
230			`// BIT - Bit Test`
231			`BIT_ZPG, BIT_ABS: begin`
232			`result = A & alu_a;`
233			`end`
234
235			`// BRK - Force Interrupt`
236			`BRK_IMP: begin`
237			`STATUS[B] = 1'b1;`
238			`end`
239
240			`// CLC - Clear Carry Flag`
241			`CLC_IMP: begin`
242			`STATUS[C] = 1'b0;`
243			`end`
244
245			`// CLD - Clear Decimal Flag`
246			`CLD_IMP: begin`
247			`STATUS[D] = 1'b0;`
248			`end`
249
250			`// CLI - Clear Interrupt Disable`
251			`CLI_IMP: begin`
252			`STATUS[I] = 1'b0;`
253			`end`
254
255			`// CLV - Clear Overflow Flag`
256			`CLV_IMP: begin`
257			`STATUS[V] = 1'b0;`
258			`end`
259
260			`// NOP - No Operation`
261			`//NOP_IMP: begin`
262			`// Do nothing :-D`
263			`//end`
264
265			`// PLP - Pull Processor Status Register`
266	175	gabrielosh	`// RTI - Return from Interrupt`
267	176	gabrielosh	`//PLP_IMP, RTI_IMP: begin`
268			`// STATUS = alu_a;`
269			`//end`
270	157	gabrielosh
271			`PLA_IMP : begin`
272			`result = alu_a;`
273			`end`
274	141	creep
275			`// STA - Store Accumulator`
276			`// PHA - Push A`
277			`// TAX - Transfer Accumulator to X`
278			`// TAY - Transfer Accumulator to Y`
279			`TAX_IMP, TAY_IMP, PHA_IMP, STA_ZPG, STA_ZPX, STA_ABS, STA_ABX, STA_ABY, STA_IDX, STA_IDY : begin`
280			`result = A;`
281			`end`
282
283			`// STX - Store X Register`
284			`// TXA - Transfer X to Accumulator`
285			`// TXS - Transfer X to Stack pointer`
286			`STX_ZPG, STX_ZPY, STX_ABS, TXA_IMP, TXS_IMP : begin`
287			`result = X;`
288			`end`
289
290			`// STY - Store Y Register`
291			`// TYA - Transfer Y to Accumulator`
292			`STY_ZPG, STY_ZPX, STY_ABS, TYA_IMP : begin`
293			`result = Y;`
294			`end`
295
296			`// SEC - Set Carry Flag`
297			`SEC_IMP: begin`
298			`STATUS[C] = 1'b1;`
299			`end`
300
301			`// SED - Set Decimal Flag`
302			`SED_IMP: begin`
303			`STATUS[D] = 1'b1;`
304			`end`
305
306			`// SEI - Set Interrupt Disable`
307			`SEI_IMP: begin`
308			`STATUS[I] = 1'b1;`
309			`end`
310
311			`// INC - Increment memory`
312			`INC_ZPG, INC_ZPX, INC_ABS, INC_ABX : begin`
313			`result = alu_a + 1;`
314			`end`
315
316			`// INX - Increment X Register`
317			`INX_IMP: begin`
318			`result = X + 1;`
319			`end`
320
321			`// INY - Increment Y Register`
322			`INY_IMP : begin`
323			`result = Y + 1;`
324			`end`
325
326			`// DEC - Decrement memory`
327			`DEC_ZPG, DEC_ZPX, DEC_ABS, DEC_ABX : begin`
328			`result = alu_a - 1;`
329			`end`
330
331			`// DEX - Decrement X register`
332			`DEX_IMP: begin`
333			`result = X - 1;`
334			`end`
335
336			`// DEY - Decrement Y Register`
337			`DEY_IMP: begin`
338			`result = Y - 1;`
339			`end`
340
341			`// ADC - Add with carry`
342	162	gabrielosh	`// TODO: verify synthesis for % operand`
343	141	creep	`ADC_IMM, ADC_ZPG, ADC_ZPX, ADC_ABS, ADC_ABX, ADC_ABY, ADC_IDX, ADC_IDY : begin`
344			`if (alu_status[D] == 1) begin`
345	171	creep	`//$display("MODO DECIMAL");`
346	164	gabrielosh	`AL = A[3:0] + alu_a[3:0] + alu_status[C];`
347			`AH = A[7:4] + alu_a[7:4];`
348	171	creep	`//$display("AL = %d", AL);`
349			`//$display("AH = %d", AH);`
350	164	gabrielosh	`if (AL > 9) begin`
351			`bcdh = AH + (AL / 10);`
352			`bcdl = AL % 10;`
353	141	creep	`end`
354	171	creep	`else begin`
355			`bcdh = AH;`
356			`bcdl = AL;`
357			`end`
358
359			`// ok`
360
361			`if (bcdh > 9) begin`
362	161	gabrielosh	`STATUS[C] = 1;`
363	164	gabrielosh	`bcdh2 = bcdh % 10;`
364	161	gabrielosh	`end`
365	171	creep	`else begin`
366			`STATUS[C] = 0;`
367			`bcdh2 = bcdh;`
368			`end`
369			`//$display("bcdh2 = %d", bcdh2);`
370			`//$display("bcdl = %d", bcdl);`
371	164	gabrielosh	`result = {bcdh2[3:0],bcdl[3:0]};`
372	141	creep	`end`
373	165	gabrielosh	`else begin`
374	171	creep	`//$display("MODO NORMAL");`
375	161	gabrielosh	`{STATUS[C],result} = op1 + op2 + alu_status[C];`
376	165	gabrielosh	`end`
377	162	gabrielosh
378	152	gabrielosh	`if ((op1[7] == op2[7]) && (op1[7] != result[7]))`
379	141	creep	`STATUS[V] = 1;`
380			`else`
381			`STATUS[V] = 0;`
382			`end`
383
384			`// AND - Logical AND`
385			`AND_IMM, AND_ZPG, AND_ZPX, AND_ABS, AND_ABX, AND_ABY, AND_IDX, AND_IDY : begin`
386			`result = A & alu_a;`
387			`end`
388
389			`// CMP - Compare`
390			`CMP_IMM, CMP_ZPG, CMP_ZPX, CMP_ABS, CMP_ABX, CMP_ABY, CMP_IDX, CMP_IDY : begin`
391			`result = A - alu_a;`
392			`STATUS[C] = (A >= alu_a) ? 1 : 0;`
393			`end`
394
395			`// EOR - Exclusive OR`
396			`EOR_IMM, EOR_ZPG, EOR_ZPX, EOR_ABS, EOR_ABX, EOR_ABY, EOR_IDX, EOR_IDY : begin`
397	156	gabrielosh	`result = A ^ alu_a;`
398	158	gabrielosh	`//$display("op1 ^ op2 = result");`
399			`//$display("%d ^ %d = %d", op1, op2, result);`
400	141	creep	`end`
401
402			`// LDA - Load Accumulator`
403			`// LDX - Load X Register`
404			`// LDY - Load Y Register`
405			`// TSX - Transfer Stack Pointer to X`
406			`LDA_IMM, LDA_ZPG, LDA_ZPX, LDA_ABS, LDA_ABX, LDA_ABY, LDA_IDX, LDA_IDY,`
407			`LDX_IMM, LDX_ZPG, LDX_ZPY, LDX_ABS, LDX_ABY,`
408			`LDY_IMM, LDY_ZPG, LDY_ZPX, LDY_ABS, LDY_ABX,`
409			`TSX_IMP : begin`
410			`result = alu_a;`
411			`end`
412
413			`// ORA - Logical OR`
414			`ORA_IMM, ORA_ZPG, ORA_ZPX, ORA_ABS, ORA_ABX, ORA_ABY, ORA_IDX, ORA_IDY : begin`
415			`result = A \| alu_a;`
416			`end`
417
418			`// SBC - Subtract with Carry`
419			`SBC_IMM, SBC_ZPG, SBC_ZPX, SBC_ABS, SBC_ABX, SBC_ABY, SBC_IDX, SBC_IDY : begin`
420	174	gabrielosh	`if (alu_status[D] == 1) begin`
421	178	gabrielosh	`bcdl = op1[3:0] - op2[3:0] - (1 - alu_status[C]);`
422			`bcdh = op1[7:4] - op2[7:4];`
423	162	gabrielosh	`if (bcdl > 9) begin`
424			`bcdh = bcdh + bcdl[5:4];`
425			`bcdl = bcdl % 10;`
426			`end`
427			`if (bcdh > 9) begin`
428			`STATUS[C] = 1;`
429			`bcdh = bcdh % 10;`
430			`end`
431	163	gabrielosh	`result = {bcdh[3:0],bcdl[3:0]};`
432	162	gabrielosh	`end`
433	173	gabrielosh	`else begin`
434	178	gabrielosh	`op2 = ~alu_a;`
435			`result = op1 + op2 + alu_status[C];`
436	174	gabrielosh	`STATUS[C] = ~result[7];`
437	173	gabrielosh	`end`
438
439	162	gabrielosh
440	173	gabrielosh	`if ((op1[7] == sign) && (op1[7] != result[7]))`
441	162	gabrielosh	`STATUS[V] = 1;`
442			`else`
443			`STATUS[V] = 0;`
444
445	141	creep	`end`
446
447			`// ASL - Arithmetic Shift Left`
448			`ASL_ACC : begin`
449	145	gabrielosh	`//{STATUS[C],result} = A << 1;`
450			`{STATUS[C],result} = {A,1'b0};`
451	141	creep	`end`
452			`ASL_ZPG, ASL_ZPX, ASL_ABS, ASL_ABX : begin`
453	145	gabrielosh	`//{STATUS[C],result} = alu_a << 1;`
454			`{STATUS[C],result} = {alu_a,1'b0};`
455	141	creep	`end`
456
457			`// LSR - Logical Shift Right`
458			`LSR_ACC: begin`
459	145	gabrielosh	`//{result, STATUS[C]} = A >> 1;`
460			`{result,STATUS[C]} = {1'b0,A};`
461	141	creep	`end`
462			`LSR_ZPG, LSR_ZPX, LSR_ABS, LSR_ABX : begin`
463	145	gabrielosh	`//{result, STATUS[C]} = alu_a >> 1;`
464			`{result,STATUS[C]} = {1'b0,alu_a};`
465	141	creep	`end`
466
467			`// ROL - Rotate Left`
468			`ROL_ACC : begin`
469	152	gabrielosh	`{STATUS[C],result} = {A,alu_status[C]};`
470	141	creep	`end`
471			`ROL_ZPG, ROL_ZPX, ROL_ABS, ROL_ABX : begin`
472			`{STATUS[C],result} = {alu_a,alu_status[C]};`
473			`end`
474
475	152	gabrielosh	`// ROR - Rotate Right`
476	141	creep	`ROR_ACC : begin`
477			`{result,STATUS[C]} = {alu_status[C],A};`
478			`end`
479			`ROR_ZPG, ROR_ZPX, ROR_ABS, ROR_ABX : begin`
480			`{result, STATUS[C]} = {alu_status[C], alu_a};`
481			`end`
482
483			`// CPX - Compare X Register`
484			`CPX_IMM, CPX_ZPG, CPX_ABS : begin`
485			`result = X - alu_a;`
486			`STATUS[C] = (X >= alu_a) ? 1 : 0;`
487			`end`
488
489			`// CPY - Compare Y Register`
490			`CPY_IMM, CPY_ZPG, CPY_ABS : begin`
491			`result = Y - alu_a;`
492			`STATUS[C] = (Y >= alu_a) ? 1 : 0;`
493			`end`
494
495			`default: begin // NON-DEFAULT OPCODES FALL HERE`
496	142	gabrielosh	`end`
497	141	creep	`endcase`
498	142	gabrielosh	`STATUS[Z] = (result == 0) ? 1 : 0;`
499			`STATUS[N] = result[7];`
500	141	creep	`end`

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