| Line 217... |
Line 217... |
if (alu_enable == 1'b1) begin
|
if (alu_enable == 1'b1) begin
|
case (alu_opcode)
|
case (alu_opcode)
|
// BIT - Bit Test
|
// BIT - Bit Test
|
BIT_ZPG, BIT_ABS: begin
|
BIT_ZPG, BIT_ABS: begin
|
result[7:0] = A & alu_a;
|
result[7:0] = A & alu_a;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// PLA - Pull Accumulator
|
// PLA - Pull Accumulator
|
PLA_IMP : begin
|
PLA_IMP : begin
|
result[7:0] = alu_a;
|
result[7:0] = alu_a;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// TAX - Transfer Accumulator to X
|
// TAX - Transfer Accumulator to X
|
// TAY - Transfer Accumulator to Y
|
// TAY - Transfer Accumulator to Y
|
// PHA - Push Accumulator
|
// PHA - Push Accumulator
|
// STA - Store Accumulator
|
// STA - Store Accumulator
|
TAX_IMP, TAY_IMP, PHA_IMP, STA_ZPG, STA_ZPX, STA_ABS, STA_ABX,
|
TAX_IMP, TAY_IMP, PHA_IMP, STA_ZPG, STA_ZPX, STA_ABS, STA_ABX,
|
STA_ABY, STA_IDX, STA_IDY : begin
|
STA_ABY, STA_IDX, STA_IDY : begin
|
result[7:0] = A;
|
result[7:0] = A;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// STX - Store X Register
|
// STX - Store X Register
|
// TXA - Transfer X to Accumulator
|
// TXA - Transfer X to Accumulator
|
// TXS - Transfer X to Stack pointer
|
// TXS - Transfer X to Stack pointer
|
STX_ZPG, STX_ZPY, STX_ABS, TXA_IMP, TXS_IMP : begin
|
STX_ZPG, STX_ZPY, STX_ABS, TXA_IMP, TXS_IMP : begin
|
result[7:0] = alu_x;
|
result[7:0] = alu_x;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// STY - Store Y Register
|
// STY - Store Y Register
|
// TYA - Transfer Y to Accumulator
|
// TYA - Transfer Y to Accumulator
|
STY_ZPG, STY_ZPX, STY_ABS, TYA_IMP : begin
|
STY_ZPG, STY_ZPX, STY_ABS, TYA_IMP : begin
|
result[7:0] = alu_y;
|
result[7:0] = alu_y;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// INC - Increment memory
|
// INC - Increment memory
|
INC_ZPG, INC_ZPX, INC_ABS, INC_ABX : begin
|
INC_ZPG, INC_ZPX, INC_ABS, INC_ABX : begin
|
result[7:0] = alu_a + 8'd1;
|
result[7:0] = alu_a + 8'd1;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// INX - Increment X Register
|
// INX - Increment X Register
|
INX_IMP: begin
|
INX_IMP: begin
|
result[7:0] = alu_x + 8'd1;
|
result[7:0] = alu_x + 8'd1;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// INY - Increment Y Register
|
// INY - Increment Y Register
|
INY_IMP : begin
|
INY_IMP : begin
|
result[7:0] = alu_y + 8'd1;
|
result[7:0] = alu_y + 8'd1;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// DEC - Decrement memory
|
// DEC - Decrement memory
|
DEC_ZPG, DEC_ZPX, DEC_ABS, DEC_ABX : begin
|
DEC_ZPG, DEC_ZPX, DEC_ABS, DEC_ABX : begin
|
result[7:0] = alu_a - 8'd1;
|
result[7:0] = alu_a - 8'd1;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// DEX - Decrement X register
|
// DEX - Decrement X register
|
DEX_IMP: begin
|
DEX_IMP: begin
|
result[7:0] = alu_x - 8'd1;
|
result[7:0] = alu_x - 8'd1;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// DEY - Decrement Y Register
|
// DEY - Decrement Y Register
|
DEY_IMP: begin
|
DEY_IMP: begin
|
result[7:0] = alu_y - 8'd1;
|
result[7:0] = alu_y - 8'd1;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// ADC - Add with carry
|
// ADC - Add with carry
|
ADC_IMM, ADC_ZPG, ADC_ZPX, ADC_ABS,
|
ADC_IMM, ADC_ZPG, ADC_ZPX, ADC_ABS,
|
ADC_ABX, ADC_ABY, ADC_IDX, ADC_IDY : begin
|
ADC_ABX, ADC_ABY, ADC_IDX, ADC_IDY : begin
|
if (!alu_status[D]) begin
|
if (!alu_status[D]) begin
|
result = op1 + op2 + {7'd0, alu_status[C]}; // this looks so ugly but the operands are all 8 bits now
|
result = op1 + op2 + {7'd0, alu_status[C]}; // this looks so ugly but the operands are all 8 bits now
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[V] = ((op1[7] == op2[7]) && (op1[7] != result[7])) ? 1'b1 : 1'b0;
|
STATUS[V] = ((op1[7] == op2[7]) && (op1[7] != result[7])) ? 1'b1 : 1'b0;
|
STATUS[C] = result[8];
|
STATUS[C] = result[8];
|
end
|
end
|
else begin
|
else begin
|
AL = op1[3:0] + op2[3:0] + {7'd0, alu_status[C]};
|
AL = op1[3:0] + op2[3:0] + {7'd0, alu_status[C]};
|
| Line 337... |
Line 337... |
|
|
// AND - Logical AND
|
// AND - Logical AND
|
AND_IMM, AND_ZPG, AND_ZPX, AND_ABS, AND_ABX, AND_ABY, AND_IDX,
|
AND_IMM, AND_ZPG, AND_ZPX, AND_ABS, AND_ABX, AND_ABY, AND_IDX,
|
AND_IDY : begin
|
AND_IDY : begin
|
result[7:0] = A & alu_a;
|
result[7:0] = A & alu_a;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// CMP - Compare
|
// CMP - Compare
|
CMP_IMM, CMP_ZPG, CMP_ZPX, CMP_ABS, CMP_ABX, CMP_ABY, CMP_IDX,
|
CMP_IMM, CMP_ZPG, CMP_ZPX, CMP_ABS, CMP_ABX, CMP_ABY, CMP_IDX,
|
CMP_IDY : begin
|
CMP_IDY : begin
|
result[7:0] = A - alu_a;
|
result[7:0] = A - alu_a;
|
STATUS[C] = (A >= alu_a) ? 1'b1 : 1'b0;
|
STATUS[C] = (A >= alu_a) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// EOR - Exclusive OR
|
// EOR - Exclusive OR
|
EOR_IMM, EOR_ZPG, EOR_ZPX, EOR_ABS, EOR_ABX, EOR_ABY,
|
EOR_IMM, EOR_ZPG, EOR_ZPX, EOR_ABS, EOR_ABX, EOR_ABY,
|
EOR_IDX, EOR_IDY : begin
|
EOR_IDX, EOR_IDY : begin
|
result[7:0] = A ^ alu_a;
|
result[7:0] = A ^ alu_a;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// LDA - Load Accumulator
|
// LDA - Load Accumulator
|
// LDX - Load X Register
|
// LDX - Load X Register
|
| Line 366... |
Line 366... |
// TSX - Transfer Stack Pointer to X
|
// TSX - Transfer Stack Pointer to X
|
LDA_IMM, LDA_ZPG, LDA_ZPX, LDA_ABS, LDA_ABX, LDA_ABY, LDA_IDX,
|
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,
|
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
|
LDY_ZPG, LDY_ZPX, LDY_ABS, LDY_ABX, TSX_IMP : begin
|
result[7:0] = alu_a;
|
result[7:0] = alu_a;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// ORA - Logical OR
|
// ORA - Logical OR
|
ORA_IMM, ORA_ZPG, ORA_ZPX, ORA_ABS, ORA_ABX, ORA_ABY, ORA_IDX,
|
ORA_IMM, ORA_ZPG, ORA_ZPX, ORA_ABS, ORA_ABX, ORA_ABY, ORA_IDX,
|
ORA_IDY : begin
|
ORA_IDY : begin
|
result[7:0] = A | alu_a;
|
result[7:0] = A | alu_a;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// SBC - Subtract with Carry
|
// SBC - Subtract with Carry
|
SBC_IMM, SBC_ZPG, SBC_ZPX, SBC_ABS, SBC_ABX, SBC_ABY, SBC_IDX,
|
SBC_IMM, SBC_ZPG, SBC_ZPX, SBC_ABS, SBC_ABX, SBC_ABY, SBC_IDX,
|
SBC_IDY : begin
|
SBC_IDY : begin
|
result = op1 - op2 - (1'b1 - alu_status[C]);
|
result = op1 - op2 - (1'b1 - alu_status[C]);
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
STATUS[V] = ((op1[7] ^ op2[7]) && (op1[7] ^ result[7])) ? 1'b1 : 1'b0;
|
STATUS[V] = ((op1[7] ^ op2[7]) && (op1[7] ^ result[7])) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[C] = ~(result[8] || result[9]);
|
STATUS[C] = ~(result[8] || result[9]);
|
if (alu_status[D]) begin
|
if (alu_status[D]) begin
|
AL = op1[3:0] - op2[3:0] - (1'b1 - alu_status[C]);
|
AL = op1[3:0] - op2[3:0] - (1'b1 - alu_status[C]);
|
AH = op1[7:4] - op2[7:4];
|
AH = op1[7:4] - op2[7:4];
|
if (AL[4]) begin
|
if (AL[4]) begin
|
| Line 410... |
Line 410... |
end
|
end
|
|
|
// ASL - Arithmetic Shift Left
|
// ASL - Arithmetic Shift Left
|
ASL_ACC : begin
|
ASL_ACC : begin
|
{STATUS[C],result[7:0]} = {A, 1'b0};
|
{STATUS[C],result[7:0]} = {A, 1'b0};
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
ASL_ZPG, ASL_ZPX, ASL_ABS, ASL_ABX : begin
|
ASL_ZPG, ASL_ZPX, ASL_ABS, ASL_ABX : begin
|
{STATUS[C],result[7:0]} = {alu_a, 1'b0};
|
{STATUS[C],result[7:0]} = {alu_a, 1'b0};
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// LSR - Logical Shift Right
|
// LSR - Logical Shift Right
|
LSR_ACC: begin
|
LSR_ACC: begin
|
{result[7:0],STATUS[C]} = {1'b0,A};
|
{result[7:0],STATUS[C]} = {1'b0,A};
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
LSR_ZPG, LSR_ZPX, LSR_ABS, LSR_ABX : begin
|
LSR_ZPG, LSR_ZPX, LSR_ABS, LSR_ABX : begin
|
{result[7:0],STATUS[C]} = {1'b0,alu_a};
|
{result[7:0],STATUS[C]} = {1'b0,alu_a};
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// ROL - Rotate Left
|
// ROL - Rotate Left
|
ROL_ACC : begin
|
ROL_ACC : begin
|
{STATUS[C],result[7:0]} = {A,alu_status[C]};
|
{STATUS[C],result[7:0]} = {A,alu_status[C]};
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
ROL_ZPG, ROL_ZPX, ROL_ABS, ROL_ABX : begin
|
ROL_ZPG, ROL_ZPX, ROL_ABS, ROL_ABX : begin
|
{STATUS[C],result[7:0]} = {alu_a,alu_status[C]};
|
{STATUS[C],result[7:0]} = {alu_a,alu_status[C]};
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// ROR - Rotate Right
|
// ROR - Rotate Right
|
ROR_ACC : begin
|
ROR_ACC : begin
|
{result[7:0],STATUS[C]} = {alu_status[C],A};
|
{result[7:0],STATUS[C]} = {alu_status[C],A};
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
ROR_ZPG, ROR_ZPX, ROR_ABS, ROR_ABX : begin
|
ROR_ZPG, ROR_ZPX, ROR_ABS, ROR_ABX : begin
|
{result[7:0], STATUS[C]} = {alu_status[C], alu_a};
|
{result[7:0], STATUS[C]} = {alu_status[C], alu_a};
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// CPX - Compare X Register
|
// CPX - Compare X Register
|
CPX_IMM, CPX_ZPG, CPX_ABS : begin
|
CPX_IMM, CPX_ZPG, CPX_ABS : begin
|
result[7:0] = alu_x - alu_a;
|
result[7:0] = alu_x - alu_a;
|
STATUS[C] = (alu_x >= alu_a) ? 1'b1 : 1'b0;
|
STATUS[C] = (alu_x >= alu_a) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
// CPY - Compare Y Register
|
// CPY - Compare Y Register
|
CPY_IMM, CPY_ZPG, CPY_ABS : begin
|
CPY_IMM, CPY_ZPG, CPY_ABS : begin
|
result[7:0] = alu_y - alu_a;
|
result[7:0] = alu_y - alu_a;
|
STATUS[C] = (alu_y >= alu_a) ? 1'b1 : 1'b0;
|
STATUS[C] = (alu_y >= alu_a) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result == 0) ? 1'b1 : 1'b0;
|
STATUS[Z] = (result[7:0] == 0) ? 1'b1 : 1'b0;
|
STATUS[N] = result[7];
|
STATUS[N] = result[7];
|
end
|
end
|
|
|
default: begin
|
default: begin
|
result = 10'h3FF;
|
result = 10'h3FF;
|
