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cpu6502.pas
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cpu6502.pas
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{ SYS6502 - A MOS Technology MCS6502 emulator
Copyright (C) 2020-2021 Bernd Böckmann
Distributed under MIT license. Please see LICENSE file.
}
unit cpu6502;
{$MODE objfpc}{$H+}{$J-}
{$OVERFLOWCHECKS off} // some code depends on value wrap around
interface
type
PCpu6502 = ^TCpu6502;
TLoadFunc = function(const addr: word) : byte;
TStoreProc = procedure(const addr: word; const m: byte);
TBuiltinProc = procedure(cpu: PCpu6502);
TCpu6502 = object
{ cpu registers }
{ }
PC: word; //< 16-bit program counter PC
A: byte; //< 8-bit accumulator register A
X: byte; //< 8-bit register X
Y: byte; //< 8-bit register Y
S: byte; //< 8-bit stack register
FlagC: boolean; //< carry flag
FlagZ: boolean; //< zero flag
FlagI: boolean; //< interrupt disable flag
FlagD: boolean; //< decimal flag
FlagV: boolean; //< overflow flag
FlagN: boolean; //< negative (sign) flag
{ function pointers to external memory interface }
{ }
LoadByte: TLoadFunc; //< load byte from external memory
StoreByte: TStoreProc; //< store byte to external memory
{ opcode function dispatch table }
OpTbl: array[0..$FF] of procedure of object;
{ function call table - determines what happens if CPU executes mem[PC] }
{ if FuncTbl[PC] is nil simulator continues executing 6502 instructions }
{ if FuncTbl[PC] <> nil then the given function is called }
FuncTbl: array[0..$FFFF] of TBuiltinProc;
constructor Init(const load: TLoadFunc; const store: TStoreProc);
procedure ResetCPU;
procedure InstallBuiltinProc(const addr: word; func: TBuiltinProc);
{ fetch and execute next instruction }
procedure ExecuteNext;
{ fetch and execute next instruction end dexplay cpu status }
procedure ExecuteTo(pcBreak: word);
procedure ExecuteToWithDump(pcBreak: word);
{ flag functions }
{ }
function FlagsToByte : byte;
procedure ByteToFlags(const b: byte);
{ fetch next byte from PC address and increment PC by 1 }
function LoadByteIncPC : byte;
{ fetch next word from PC address and increment PC by 2 }
function LoadWord(const addr: word) : word;
function LoadWordIncPC : word;
{ add a signed byte to current PC }
procedure PCAddByteSigned(const addr: byte);
{ addressing functions }
{ }
function LoadImm : byte;
function LoadZp : byte;
function LoadZpWithAddr(out addr: word) : byte;
procedure StoreZp(m: byte);
function LoadZpX : byte;
function LoadZpXWithAddr(out addr: word) : byte;
procedure StoreZpX(const m: byte);
function LoadZpY : byte;
procedure StoreZpY(const m: byte);
function LoadAbs : byte;
function LoadAbsWithAddr(out addr: word) : byte;
procedure StoreAbs(const m: byte);
function LoadAbsX : byte;
function LoadAbsXWithAddr(out addr: word) : byte;
procedure StoreAbsX(const m: byte);
function LoadAbsY : byte;
procedure StoreAbsY(const m: byte);
function LoadIndX : byte;
procedure StoreIndX(const m: byte);
function LoadIndY : byte;
procedure StoreIndY(const m: byte);
{ ALU routines }
{ }
procedure AluADC(const m: byte);
procedure AluSBC(const m: byte);
procedure AluAND(const m: byte);
procedure AluORA(const m: byte);
procedure AluEOR(const m: byte);
procedure AluCMP(const m: byte);
procedure AluCPX(const m: byte);
procedure AluCPY(const m: byte);
function AluINC(const m: byte) : byte;
function AluDEC(const m: byte) : byte;
function AluASL(const m: byte) : byte;
function AluLSR(const m: byte) : byte;
function AluROL(const m: byte) : byte;
function AluROR(const m: byte) : byte;
procedure AluUpdateFlags(const op1: byte; const op2: byte; const res: word);
procedure AluUpdateNZ(const op: byte);
procedure AluUpdateNZC(const op: byte);
{ stack routines }
{ }
procedure PushStack(v: byte);
function PullStack : byte;
procedure InitFuncTbl;
{ opcode execution routines }
{ }
procedure InitOpTbl;
procedure OpBRK; //< opcode $00 - break
procedure OpORAindX;//< opcode $01 - bitwise or A with (ind,X)
procedure OpORAzp; //< opcode $05 - bitwise or A with zp
procedure OpASLzp; //< opcode $06 - arithmetic shift left zp
procedure OpPHP; //< opcode $08 - push flags
procedure OpORAimm; //< opcode $09 - bitwise or A with imm
procedure OpASL; //< opcode $0A - arithmetic shift left accumulator
procedure OpORAabs; //< opcode $0D - bitwise or A with abs
procedure OpASLabs; //< opcode $0E - arithmetic shift left abs
procedure OpBPL; //< opcode $10 - branch on PLus
procedure OpORAindY;//< opcode $11 - bitwise or A with (ind),Y
procedure OpORAzpX; //< opcode $15 - bitwise or A with zp,X
procedure OpASLzpX; //< opcode $16 - arithmetic shift left zp,X
procedure OpCLC; //< opcode $18 - clear carry
procedure OpORAabsY;//< opcode $19 - bitwise or A with abs,Y
procedure OpORAabsX;//< opcode $1D - bitwise or A with abs,X
procedure OpASLabsX;//< opcode $1E - arithmetic shift left abs,X
procedure OpJSR; //< opcode $20 - jump service routine
procedure OpANDindX;//< opcode $21 - and A with (ind,X)
procedure OpBITzp; //< opcode $24 - test zp bits ans set flags
procedure OpANDzp; //< opcode $25 - and A with zp
procedure OpROLzp; //< opcode $26 - rotate right zp
procedure OpPLP; //< opcode $28 - pull flags
procedure OpANDimm; //< opcode $29 - and A with imm
procedure OpROL; //< opcode $2A - rotate right A
procedure OpBITabs; //< opcode $2C - test abs bits ans set flags
procedure OpANDabs; //< opcode $2D - and A with abs
procedure OpROLabs; //< opcode $2E - rotate right abs
procedure OpBMI; //< opcode $30 - branch on MInus
procedure OpANDindY;//< opcode $31 - and A with (ind),Y
procedure OpANDzpX; //< opcode $35 - and A with zp,X
procedure OpROLzpX; //< opcode $36 - rotate right zp,X
procedure OpSEC; //< opcode $38 - set carry flag
procedure OpANDabsY;//< opcode $39 - and A with abs,Y
procedure OpANDabsX;//< opcode $3D - and A with abs,X
procedure OpROLabsX;//< opcode $3E - rotate right abs,X
procedure OpRTI; //< opcode $40 - return from interrupt
procedure OpEORindX;//< opcode $41 - eor A with (ind,X)
procedure OpEORzp; //< opcode $45 - eor A with zp
procedure OpLSRzp; //< opcode $46 - logical shift right zp
procedure OpPHA; //< opcode $48 - push A
procedure OpEORimm; //< opcode $49 - eor A with imm
procedure OpLSR; //< opcode $4A - logical shift right A
procedure OpJMPabs; //< opcode $4C - jump absolute
procedure OpEORabs; //< opcode $4D - eor A with abs
procedure OpLSRabs; //< opcode $4E - logical shift right abs
procedure OpBVC; //< opcode $50 - branch if overflow clear
procedure OpEORindY;//< opcode $51 - eor A with (ind),Y
procedure OpEORzpX; //< opcode $55 - eor A with zp,X
procedure OpLSRzpX; //< opcode $56 - logical shift right zp,X
procedure OpCLI; //< opcode $58 - clear interrupt enable flag
procedure OpEORabsY;//< opcode $59 - eor A with abs,Y
procedure OpEORabsX;//< opcode $5D - eor A with abs,X
procedure OpLSRabsX;//< opcode $5E - logical shift right abs,X
procedure OpRTS; //< opcode $60 - return from subroutine
procedure OpADCindX;//< opcode $61 - add (ind,X) to accumulator with carry
procedure OpADCzp; //< opcode $65 - add zp to accumulator with carry
procedure OpRORzp; //< opcode $66 - rotate right zp
procedure OpPLA; //< opcode $68 - pull A
procedure OpADCimm; //< opcode $69 - add imm to accumulator with carry
procedure OpROR; //< opcode $6A - rotate right A
procedure OpJMPind; //< opcode $6C - jump indirect
procedure OpADCabs; //< opcode $6D - add abs to accumulator with carry
procedure OpRORabs; //< opcode $6E - rotate right abs
procedure OpBVS; //< opcode $70 - branch if overflow set
procedure OpADCindY;//< opcode $71 - add (ind),Y to accumulator with carry
procedure OpADCzpX; //< opcode $75 - add zp,X to accumulator with carry
procedure OpRORzpX; //< opcode $76 - rotate right zp,X
procedure OpSEI; //< opcode $78 - set interrupt enable flag
procedure OpADCabsY;//< opcode $79 - add abs,Y to accumulator with carry
procedure OpADCabsX;//< opcode $7D - add abs,X to accumulator with carry
procedure OpRORabsX;//< opcode $7E - rotate right abs
procedure OpSTAindX;//< opcode $81 - store A at (ind,X)
procedure OpSTYzp; //< opcode $84 - store Y at zp
procedure OpSTAzp; //< opcode $85 - store accumulator at zp
procedure OpSTXzp; //< opcode $86 - store X at zp
procedure OpDEY; //< opcode $88 - decrement y
procedure OpTXA; //< opcode $8A - transfer X to A
procedure OpSTYabs; //< opcode $8C - store Y at abs
procedure OpSTAabs; //< opcode $8D - store A at abs
procedure OpSTXabs; //< opcode $8E - store X at abs
procedure OpBCC; //< opcode $90 - branch if carry clear
procedure OpSTAindY;//< opcode $91 - store A at (ind),Y
procedure OpSTYzpX; //< opcode $94 - store Y at zp,X
procedure OpSTAzpX; //< opcode $95 - store A at zp,X
procedure OpSTXzpY; //< opcode $96 - store X at zp,Y
procedure OpTYA; //< opcode $98 - transfer Y to A
procedure OpSTAabsY;//< opcode $99 - store A at abs,Y
procedure OpTXS; //< opcode $9A - store X in S
procedure OpSTAabsX;//< opcode $9D - store A at abs,X
procedure OpLDYimm; //< opcode $A0 - load Y with imm
procedure OpLDAindX;//< opcode $A1 - load A with (ind,X)
procedure OpLDXimm; //< opcode $A2 - load X with imm
procedure OpLDYzp; //< opcode $A4 - load Y with zp
procedure OpLDAzp; //< opcode $A5 - load A with zp
procedure OpLDXzp; //< opcode $A6 - load X with zp
procedure OpTAY; //< opcode $A8 - transfer A to Y
procedure OpLDAimm; //< opcode $A9 - load accumulator with immediate
procedure OpTAX; //< opcode $AA - transfer A to X
procedure OpLDYabs; //< opcode $AC - load Y with abs
procedure OpLDAabs; //< opcode $AD - load A with abs
procedure OpLDXabs; //< opcode $AE - load X with abs
procedure OpBCS; //< opcode $B0 - branch if carry set
procedure OpLDAindY;//< opcode $B1 - load A with (ind),Y
procedure OpLDYzpX; //< opcode $B4 - load Y with zp,X
procedure OpLDAzpX; //< opcode $B5 - load A with zp,X
procedure OpLDXzpY; //< opcode $B6 - load X with zp,Y
procedure OpCLV; //< opcode $B8 - clear overflow flag
procedure OpLDAabsY;//< opcode $B9 - load A with abs,Y
procedure OpTSX; //< opcode $BA - store S in X
procedure OpLDYabsX;//< opcode $BC - load Y with abs,X
procedure OpLDAabsX;//< opcode $BD - load A with abs,X
procedure OpLDXabsY;//< opcode $BE - load X with abs,Y
procedure OpCPYimm; //< opcode $C0 - compare Y with imm
procedure OpCMPindX;//< opcode $C1 - compare A with (ind,X)
procedure OpCPYzp; //< opcode $C4 - compare Y with zp
procedure OpCMPzp; //< opcode $C5 - compare A with zp
procedure OpDECzp; //< opcode $C6 - decrement zp
procedure OpINY; //< opcode $C8 - increment Y
procedure OpCMPimm; //< opcode $C9 - compare accumulator with immediate
procedure OpDEX; //< opcode $CA - decrement X
procedure OpCPYabs; //< opcode $CC - compare Y with abs
procedure OpCMPabs; //< opcode $CD - compare A with abs
procedure OpDECabs; //< opcode $CE - decrement abs
procedure OpBNE; //< opcode $D0 - branch if not equal
procedure OpCMPindY;//< opcode $D1 - compare A with (ind),Y
procedure OpCMPzpX; //< opcode $D5 - compare A with zp,X
procedure OpDECzpX; //< opcode $D6 - decrement zp,X
procedure OpCLD; //< opcode $D8 - clear decimal flag
procedure OpCMPabsY;//< opcode $D9 - compare A with abs,Y
procedure OpCMPabsX;//< opcode $DD - compare A with abs,X
procedure OpDECabsX;//< opcode $DE - decrement abs,X
procedure OpCPXimm; //< opcode $E0 - compare X with imm
procedure OpSBCindX;//< opcode $E1 - subtract (ind,X) from A with carry
procedure OpCPXzp; //< opcode $E4 - compare X with zp
procedure OpSBCzp; //< opcode $E5 - subtract zp from A with carry
procedure OpINCzp; //< opcode $E6 - increment zp
procedure OpINX; //< opcode $E8 - increment X
procedure OpSBCimm; //< opcode $E9 - subtract imm from A with carry
procedure OpNOP; //< opcode $EA - no operation
procedure OpCPXabs; //< opcode $EC - compare X with abs
procedure OpSBCabs; //< opcode $ED - subtract abs from A with carry
procedure OpINCabs; //< opcode $EE - increment abs
procedure OpBEQ; //< opcode $F0 - branch if equal
procedure OpSBCindY;//< opcode $F1 - subtract (ind),Y from A with carry
procedure OpSBCzpX; //< opcode $F5 - subtract zp,X from A with carry
procedure OpINCzpX; //< opcode $F6 - increment zp,X
procedure OpSED; //< opcode $F8 - set decimal flag
procedure OpSBCabsY;//< opcode $F9 - subtract abs,Y from A with carry
procedure OpSBCabsX;//< opcode $FD - subtract abs,X from A with carry
procedure OpINCabsX;//< opcode $FE - increment abs,X
{ debugging routines }
{ }
procedure DumpRegs; //< dump all registers
end;
implementation
uses
sysutils;
const
BIT_0 = $001; BIT_1 = $002; BIT_2 = $004; BIT_3 = $008;
BIT_4 = $010; BIT_5 = $020; BIT_6 = $040; BIT_7 = $080;
BIT_8 = $100;
function BtoD(const b: boolean; const v: byte) : byte;
begin
if b then BtoD := v else BtoD := 0;
end;
function DtoB(const v: byte) : boolean;
begin
DToB := v <> 0;
end;
constructor TCpu6502.Init(const load: TLoadFunc; const store: TStoreProc);
begin
LoadByte := load;
StoreByte := store;
InitOpTbl;
InitFuncTbl;
ResetCPU;
end;
procedure TCpu6502.ResetCPU;
begin
PC := LoadWord($FFFC);
S := $FD;
FlagI := true;
end;
procedure TCpu6502.InstallBuiltinProc(const addr: word; func: TBuiltinProc);
begin
FuncTbl[addr] := func;
end;
{--- high level execution routines ------------------------------------------}
procedure TCpu6502.ExecuteNext;
var
opcode: byte;
begin
if FuncTbl[PC] = nil then begin
opcode := LoadByteIncPC;
OpTbl[opcode]();
end else
FuncTbl[PC](@self);
end;
procedure TCpu6502.ExecuteTo(pcBreak: word);
begin
while PC <> pcBreak do begin
ExecuteNext;
end;
end;
procedure TCpu6502.ExecuteToWithDump(pcBreak: word);
begin
while PC <> pcBreak do begin
ExecuteNext;
DumpRegs;
end;
end;
{--- Flag functions -----------------------------------------------------------}
function TCpu6502.FlagsToByte : byte;
begin
FlagsToByte := BtoD(FlagC, $01) or BtoD(FlagZ, $02) or BtoD(FlagI, $04) or
BtoD(FlagD, $08) or BtoD(FlagV, $40) or BtoD(FlagN, $80);
end;
procedure TCpu6502.ByteToFlags(const b: byte);
begin
FlagC := DtoB(b and $01);
FlagZ := DtoB(b and $02);
FlagI := DtoB(b and $04);
FlagD := DtoB(b and $08);
FlagV := DtoB(b and $40);
FlagN := DtoB(b and $80);
end;
{--- PC and memory access functions -------------------------------------------}
{ load byte from PC abs, PC <- PC + 1 }
function TCpu6502.LoadByteIncPC : byte;
begin
LoadByteIncPC := LoadByte(PC);
inc(PC);
end;
function TCpu6502.LoadWord(const addr : word) : word;
var l, h: word;
begin
l := LoadByte(addr);
h := LoadByte(addr+1) shl 8;
LoadWord := l or h;
end;
{ load word from PC abs, PC <- PC + 2 }
function TCpu6502.LoadWordIncPC : word;
begin
LoadWordIncPC := LoadWord(PC);
PC := PC + 2;
end;
{ addressing modes implementation }
function TCpu6502.LoadImm : byte;
begin
LoadImm := LoadByteIncPC;
end;
function TCpu6502.LoadZp : byte;
var
addr: word;
begin
addr := LoadByteIncPC;
LoadZP := LoadByte(addr);
end;
function TCpu6502.LoadZpWithAddr(out addr: word) : byte;
begin
addr := LoadByteIncPC;
LoadZPWithAddr := LoadByte(addr);
end;
procedure TCpu6502.StoreZp(m: byte);
var
addr: word;
begin
addr := LoadByteIncPC;
StoreByte(addr, m);
end;
function TCpu6502.LoadZpX : byte;
var
addr: word;
begin
addr := (LoadByteIncPC + X) and $FF;
LoadZpX := LoadByte(addr);
end;
function TCpu6502.LoadZpXWithAddr(out addr: word) : byte;
begin
addr := (LoadByteIncPC + X) and $FF;
LoadZpXWithAddr := LoadByte(addr);
end;
procedure TCpu6502.StoreZpX(const m: byte);
var
addr: word;
begin
addr := (LoadByteIncPC + X) and $FF;
StoreByte(addr, m);
end;
function TCpu6502.LoadZpY : byte;
var
addr: word;
begin
addr := (LoadByteIncPC + Y) and $FF;
LoadZpY := LoadByte(addr);
end;
procedure TCpu6502.StoreZpY(const m: byte);
var
addr: word;
begin
addr := (LoadByteIncPC + Y) and $FF;
StoreByte(addr, m);
end;
function TCpu6502.LoadAbs : byte;
var
addr: word;
begin
addr := LoadWordIncPC;
LoadAbs := LoadByte(addr);
end;
function TCpu6502.LoadAbsWithAddr(out addr: word) : byte;
begin
addr := LoadWordIncPC;
LoadAbsWithAddr := LoadByte(addr);
end;
procedure TCpu6502.StoreAbs(const m : byte);
var
addr: word;
begin
addr := LoadWordIncPC;
StoreByte(addr, m);
end;
function TCpu6502.LoadAbsX : byte;
var
addr: word;
begin
addr := LoadWordIncPC + X;
LoadAbsX := LoadByte(addr);
end;
function TCpu6502.LoadAbsXWithAddr(out addr: word) : byte;
begin
addr := LoadWordIncPC + X;
LoadAbsXWithAddr := LoadByte(addr);
end;
procedure TCpu6502.StoreAbsX(const m : byte);
var
addr: word;
begin
addr := LoadWordIncPC + X;
StoreByte(addr, m);
end;
function TCpu6502.LoadAbsY : byte;
var
addr: word;
begin
addr := LoadWordIncPC + Y;
LoadAbsY := LoadByte(addr);
end;
procedure TCpu6502.StoreAbsY(const m : byte);
var
addr: word;
begin
addr := LoadWordIncPC + Y;
StoreByte(addr, m);
end;
function TCpu6502.LoadIndX : byte;
var
zp: byte;
addr: word;
begin
zp := (LoadByteIncPC + X) and $ff;
addr := LoadByte(zp) or LoadByte((zp + 1) and $ff) shl 8;
LoadIndX := LoadByte(addr);
end;
procedure TCpu6502.StoreIndX(const m: byte);
var
zp: byte;
addr: word;
begin
zp := (LoadByteIncPC + X) and $ff;
addr := LoadByte(zp) or LoadByte((zp + 1) and $ff) shl 8;
StoreByte(addr, m);
end;
function TCpu6502.LoadIndY : byte;
var
zp: byte;
addr: word;
begin
zp := LoadByteIncPC;
addr := LoadByte(zp) or LoadByte((zp + 1) and $ff) shl 8;
LoadIndY := LoadByte(addr + Y);
end;
procedure TCpu6502.StoreIndY(const m: byte);
var
zp: byte;
addr: word;
begin
zp := LoadByteIncPC;
addr := LoadByte(zp) or LoadByte((zp + 1) and $ff) shl 8;
StoreByte(addr + Y, m);
end;
{ add signed byte to PC }
procedure TCpu6502.PCAddByteSigned(const addr: byte);
var
tmp: byte;
begin
if (addr and BIT_7) <> 0 then begin
{ negative relative value }
tmp := (addr xor $FF) + 1;
PC := PC - tmp;
end else begin
PC := PC + addr;
end;
end;
{--- stack functions ---------------------------------------------------------}
procedure TCpu6502.PushStack(v: byte);
begin
StoreByte($100 + S, v);
dec(S);
end;
function TCpu6502.PullStack : byte;
begin
inc(S);
PullStack := LoadByte($100 + S);
end;
{--- ALU functions -----------------------------------------------------------}
procedure TCpu6502.AluADC(const m: byte);
var
oldA: byte;
tmp: word;
begin
oldA := A;
tmp := A + m;
if FlagC then inc(tmp);
A := byte(tmp);
AluUpdateFlags(oldA, m, tmp);
end;
procedure TCpu6502.AluSBC(const m: byte);
begin
AluADC(m xor $ff);
end;
procedure TCpu6502.AluAND(const m: byte);
begin
A := A and m;
AluUpdateNZ(A);
end;
procedure TCpu6502.AluORA(const m: byte);
begin
A := A and m;
AluUpdateNZ(A);
end;
procedure TCpu6502.AluEOR(const m: byte);
begin
A := A xor m;
AluUpdateNZ(A);
end;
procedure TCpu6502.AluCMP(const m: byte);
var
tmp: byte;
begin
tmp := A - m;
AluUpdateNZC(tmp);
end;
procedure TCpu6502.AluCPX(const m: byte);
var
tmp: byte;
begin
tmp := X - m;
AluUpdateNZC(tmp);
end;
procedure TCpu6502.AluCPY(const m: byte);
var
tmp: byte;
begin
tmp := Y - m;
AluUpdateNZC(tmp);
end;
function TCpu6502.AluINC(const m: byte) : byte;
begin
AluINC := m + 1;
AluUpdateNZ(AluINC);
end;
function TCpu6502.AluDEC(const m: byte) : byte;
begin
AluDEC := m - 1;
AluUpdateNZ(AluDEC);
end;
function TCpu6502.AluASL(const m: byte) : byte;
begin
FlagC := (m and $80) <> 0;
AluASL := m shl 1;
AluUpdateNZ(AluASL);
end;
function TCpu6502.AluLSR(const m: byte) : byte;
begin
FlagC := (m and $1) <> 0;
AluLSR := m shr 1;
AluUpdateNZ(AluLSR);
end;
function TCpu6502.AluROL(const m: byte) : byte;
var
tmpC: boolean;
begin
tmpC := FlagC;
FlagC := (m and BIT_7) <> 0;
AluROL := (m shl 1);
if tmpC then AluROL := AluROL or BIT_0;
AluUpdateNZ(AluROL);
end;
function TCpu6502.AluROR(const m: byte) : byte;
var
tmpC: boolean;
begin
tmpC := FlagC;
FlagC := (m and BIT_0) <> 0;
AluROR := (m shr 1);
if tmpC then AluROR := AluROR or BIT_7;
AluUpdateNZ(AluROR);
end;
procedure TCpu6502.AluUpdateFlags(const op1: byte; const op2: byte; const res: word);
begin
FlagC := ((res and BIT_8) <> 0);
FlagZ := ((res and $ff) = 0);
FlagN := ((res and BIT_7) <> 0);
FlagV := (((op1 and BIT_7) = (op2 and BIT_7))) and ((op1 and BIT_7) <> (res and BIT_7));
end;
procedure TCpu6502.AluUpdateNZ(const op: byte);
begin
FlagZ := ((op and $ff) = 0);
FlagN := ((op and BIT_7) <> 0);
end;
procedure TCpu6502.AluUpdateNZC(const op: byte);
begin
FlagC := ((op and BIT_8) <> 0);
FlagZ := ((op and $ff) = 0);
FlagN := ((op and BIT_7) <> 0);
end;
{--- opcode implementation ---------------------------------------------------}
procedure TCpu6502.OpBRK; { opcode $00 }
begin
PC := PC + 1;
PushStack(PC shr 8);
PushStack(PC and $FF);
PushStack(FlagsToByte or BIT_4 or BIT_5);
PC := LoadWord($FFFE);
end;
procedure TCpu6502.OpORAindX; { opcode $01 }
begin
AluORA(LoadIndX);
end;
procedure TCpu6502.OpORAzp; { opcode $05 }
begin
AluORA(LoadZp);
end;
procedure TCpu6502.OpASLzp; {opcode $06 }
var
addr: word;
tmp: byte;
begin
tmp := LoadZpWithAddr(addr);
tmp := AluASL(tmp);
StoreByte(addr, tmp);
end;
procedure TCpu6502.OpPHP; { opcode $08 }
begin
PushStack(FlagsToByte or BIT_4 or BIT_5);
end;
procedure TCpu6502.OpORAimm; { opcode $09 }
begin
AluORA(LoadImm);
end;
procedure TCpu6502.OpASL; { opcode $0A }
begin
A := AluASL(A);
end;
procedure TCpu6502.OpORAabs; { opcode $0D }
begin
AluORA(LoadAbs);
end;
procedure TCpu6502.OpASLabs; {opcode $0E }
var
addr: word;
tmp: byte;
begin
tmp := LoadAbsWithAddr(addr);
tmp := AluASL(tmp);
StoreByte(addr, tmp);
end;
procedure TCpu6502.OpBPL; { opcode $10 - branch on PLus }
var
rel: byte;
begin
rel := LoadByteIncPC;
if not FlagN then PCAddByteSigned(rel);
end;
procedure TCpu6502.OpORAindY; { opcode $11 }
begin
AluORA(LoadIndY);
end;
procedure TCpu6502.OpORAzpX; { opcode $15 }
begin
AluORA(LoadZpX);
end;
procedure TCpu6502.OpASLzpX; {opcode $16 }
var
addr: word;
tmp: byte;
begin
tmp := LoadZpXWithAddr(addr);
tmp := AluASL(tmp);
StoreByte(addr, tmp);
end;
procedure TCpu6502.OpCLC; { opcode $18 - clear carry flag }
begin
FlagC := false;
end;
procedure TCpu6502.OpORAabsY; { opcode $19 }
begin
AluORA(LoadAbsY);
end;
procedure TCpu6502.OpORAabsX; { opcode $1D }
begin
AluORA(LoadAbsX);
end;
procedure TCpu6502.OpASLabsX; {opcode $1E }
var
addr: word;
tmp: byte;
begin
tmp := LoadAbsXWithAddr(addr);
tmp := AluASL(tmp);
StoreByte(addr, tmp);
end;
procedure TCpu6502.OpJSR; { opcode $20 }
var
addr: word;
begin
addr := LoadWord(PC);
PC := PC + 1;
PushStack(PC shr 8);
PushStack(PC and $FF);
PC := addr;
end;
procedure TCpu6502.OpANDindX; { opcode $21 }
begin
AluAND(LoadIndX);
end;
procedure TCpu6502.OpBITzp; { opcode $24 }
var
m: byte;
begin
m := LoadZp;
FlagZ := m = 0;
FlagV := (m and BIT_6) <> 0;
FlagN := (m and BIT_7) <> 0;
end;
procedure TCpu6502.OpANDzp; { opcode $25 }
begin
AluAND(LoadZp);
end;
procedure TCpu6502.OpROLzp; {opcode $26 }
var
addr: word;
tmp: byte;
begin
tmp := LoadZpWithAddr(addr);
tmp := AluROL(tmp);
StoreByte(addr, tmp);
end;
procedure TCpu6502.OpPLP; { opcode $28 }
begin
ByteToFlags(PullStack);
end;
procedure TCpu6502.OpANDimm; { opcode $29 }
begin
AluAND(LoadImm);
end;
procedure TCpu6502.OpROL; { opcode $2A }
begin
A := AluROL(A);
end;
procedure TCpu6502.OpBITabs; { opcode $2C }
var
m: byte;
begin
m := LoadAbs;
FlagZ := m = 0;
FlagV := (m and BIT_6) <> 0;
FlagN := (m and BIT_7) <> 0;
end;
procedure TCpu6502.OpANDabs; { opcode $2D }
begin
AluAND(LoadAbs);
end;
procedure TCpu6502.OpROLabs; {opcode $2E }
var
addr: word;
tmp: byte;
begin
tmp := LoadAbsWithAddr(addr);
tmp := AluROL(tmp);
StoreByte(addr, tmp);
end;
procedure TCpu6502.OpBMI; { opcode $30 - branch on MInus }
var
rel: byte;
begin
rel := LoadByteIncPC;
if FlagN then PCAddByteSigned(rel);
end;
procedure TCpu6502.OpANDindY; { opcode $31 }
begin
AluAND(LoadIndY);
end;
procedure TCpu6502.OpANDzpX; { opcode $35 }
begin
AluAND(LoadZpX);
end;
procedure TCpu6502.OpROLzpX; {opcode $36 }
var
addr: word;
tmp: byte;
begin
tmp := LoadZpXWithAddr(addr);
tmp := AluROL(tmp);
StoreByte(addr, tmp);
end;
procedure TCpu6502.OpSEC; { opcode $38 - set carry flag }
begin
FlagC := true;
end;
procedure TCpu6502.OpANDabsY; { opcode $39 }
begin
AluAND(LoadAbsY);
end;
procedure TCpu6502.OpANDabsX; { opcode $3D }
begin
AluAND(LoadAbsX);
end;
procedure TCpu6502.OpROLabsX; {opcode $3E }
var
addr: word;
tmp: byte;
begin
tmp := LoadAbsXWithAddr(addr);
tmp := AluROL(tmp);
StoreByte(addr, tmp);
end;
procedure TCpu6502.OpRTI; { opcode $40 }
begin
ByteToFlags(PullStack);
PC := PullStack;
PC := PC or (PullStack shl 8);
end;
procedure TCpu6502.OpEORindX; { opcode $41 }
begin
AluEOR(LoadIndX);
end;
procedure TCpu6502.OpEORzp; { opcode $45 }
begin
AluEOR(LoadZp);