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/* Fake6502 CPU emulator core v1.1 *******************
* (c)2011 Mike Chambers (miker00lz@gmail.com) *
*****************************************************
* v1.1 - Small bugfix in BIT opcode, but it was the *
* difference between a few games in my NES *
* emulator working and being broken! *
* I went through the rest carefully again *
* after fixing it just to make sure I didn't *
* have any other typos! (Dec. 17, 2011) *
* *
* v1.0 - First release (Nov. 24, 2011) *
*****************************************************
* LICENSE: This source code is released into the *
* public domain, but if you use it please do give *
* credit. I put a lot of effort into writing this! *
* *
*****************************************************
* Fake6502 is a MOS Technology 6502 CPU emulation *
* engine in C. It was written as part of a Nintendo *
* Entertainment System emulator I've been writing. *
* *
* It has been pretty well-tested in the NES emu, *
* and the clock-cycle timing in particular has been *
* VERY thoroughly checked out. It matches with the *
* real 6502 processor 100%. *
* *
* A couple important things to know about are two *
* defines in the code. One is "UNDOCUMENTED" which, *
* when defined, allows Fake6502 to compile with *
* full support for the more predictable *
* undocumented instructions of the 6502. If it is *
* undefined, undocumented opcodes just act as NOPs. *
* *
* The other define is "NES_CPU", which causes the *
* code to compile without support for binary-coded *
* decimal (BCD) support for the ADC and SBC *
* opcodes. The Ricoh 2A03 CPU in the NES does not *
* support BCD, but is otherwise identical to the *
* standard MOS 6502. (Note that this define is *
* enabled in this file if you haven't changed it *
* yourself. If you're not emulating a NES, you *
* should comment it out.) *
* *
* If you do discover an error in timing accuracy, *
* or operation in general please e-mail me at the *
* address above so that I can fix it. Thank you! *
* *
*****************************************************
* Usage: *
* *
* Fake6502 requires you to provide two external *
* functions: *
* *
* uint8_t read6502(uint16_t address) *
* void write6502(uint16_t address, uint8_t value) *
* *
* You may optionally pass Fake6502 the pointer to a *
* function which you want to be called after every *
* emulated instruction. This function should be a *
* void with no parameters expected to be passed to *
* it. *
* *
* This can be very useful. For example, in a NES *
* emulator, you check the number of clock ticks *
* that have passed so you can know when to handle *
* APU events. *
* *
* To pass Fake6502 this pointer, use the *
* hookexternal(void *funcptr) function provided. *
* *
* To disable the hook later, pass NULL to it. *
*****************************************************
* Useful functions in this emulator: *
* *
* void reset6502() *
* - Call this once before you begin execution. *
* *
* void exec6502(uint32_t tickcount) *
* - Execute 6502 code up to the next specified *
* count of clock ticks. *
* *
* void step6502() *
* - Execute a single instrution. *
* *
* void irq6502() *
* - Trigger a hardware IRQ in the 6502 core. *
* *
* void nmi6502() *
* - Trigger an NMI in the 6502 core. *
* *
* void hookexternal(void *funcptr) *
* - Pass a pointer to a void function taking no *
* parameters. This will cause Fake6502 to call *
* that function once after each emulated *
* instruction. *
* *
*****************************************************
* Useful variables in this emulator: *
* *
* uint32_t clockticks6502 *
* - A running total of the emulated cycle count. *
* *
* uint32_t instructions *
* - A running total of the total emulated *
* instruction count. This is not related to *
* clock cycle timing. *
* *
*****************************************************/
#include <stdio.h>
#include <stdint.h>
//6502 defines
//#define UNDOCUMENTED //when this is defined, undocumented opcodes are handled.
//otherwise, they're simply treated as NOPs.
//#define NES_CPU //when this is defined, the binary-coded decimal (BCD)
//status flag is not honored by ADC and SBC. the 2A03
//CPU in the Nintendo Entertainment System does not
//support BCD operation.
#define FLAG_CARRY 0x01
#define FLAG_ZERO 0x02
#define FLAG_INTERRUPT 0x04
#define FLAG_DECIMAL 0x08
#define FLAG_BREAK 0x10
#define FLAG_CONSTANT 0x20
#define FLAG_OVERFLOW 0x40
#define FLAG_SIGN 0x80
#define BASE_STACK 0x100
#define saveaccum(n) a = (uint8_t)((n) & 0x00FF)
//flag modifier macros
#define setcarry() status |= FLAG_CARRY
#define clearcarry() status &= (~FLAG_CARRY)
#define setzero() status |= FLAG_ZERO
#define clearzero() status &= (~FLAG_ZERO)
#define setinterrupt() status |= FLAG_INTERRUPT
#define clearinterrupt() status &= (~FLAG_INTERRUPT)
#define setdecimal() status |= FLAG_DECIMAL
#define cleardecimal() status &= (~FLAG_DECIMAL)
#define setoverflow() status |= FLAG_OVERFLOW
#define clearoverflow() status &= (~FLAG_OVERFLOW)
#define setsign() status |= FLAG_SIGN
#define clearsign() status &= (~FLAG_SIGN)
//flag calculation macros
#define zerocalc(n) {\
if ((n) & 0x00FF) clearzero();\
else setzero();\
}
#define signcalc(n) {\
if ((n) & 0x0080) setsign();\
else clearsign();\
}
#define carrycalc(n) {\
if ((n) & 0xFF00) setcarry();\
else clearcarry();\
}
#define overflowcalc(n, m, o) { /* n = result, m = accumulator, o = memory */ \
if (((n) ^ (uint16_t)(m)) & ((n) ^ (o)) & 0x0080) setoverflow();\
else clearoverflow();\
}
//6502 CPU registers
uint16_t pc;
uint8_t sp, a, x, y, status;
//helper variables
uint32_t instructions = 0; //keep track of total instructions executed
uint32_t clockticks6502 = 0, clockgoal6502 = 0;
uint16_t oldpc, ea, reladdr, value, result;
uint8_t opcode, oldstatus;
//externally supplied functions
extern uint8_t read6502(uint16_t address);
extern void write6502(uint16_t address, uint8_t value);
//a few general functions used by various other functions
void push16(uint16_t pushval) {
write6502(BASE_STACK + sp, (pushval >> 8) & 0xFF);
write6502(BASE_STACK + ((sp - 1) & 0xFF), pushval & 0xFF);
sp -= 2;
}
void push8(uint8_t pushval) {
write6502(BASE_STACK + sp--, pushval);
}
uint16_t pull16() {
uint16_t temp16;
temp16 = read6502(BASE_STACK + ((sp + 1) & 0xFF)) | ((uint16_t)read6502(BASE_STACK + ((sp + 2) & 0xFF)) << 8);
sp += 2;
return(temp16);
}
uint8_t pull8() {
return (read6502(BASE_STACK + ++sp));
}
void reset6502() {
pc = (uint16_t)read6502(0xFFFC) | ((uint16_t)read6502(0xFFFD) << 8);
a = 0;
x = 0;
y = 0;
sp = 0xFD;
status |= FLAG_CONSTANT;
}
static void (*addrtable[256])();
static void (*optable[256])();
uint8_t penaltyop, penaltyaddr;
//addressing mode functions, calculates effective addresses
static void imp() { //implied
}
static void acc() { //accumulator
}
static void imm() { //immediate
ea = pc++;
}
static void zp() { //zero-page
ea = (uint16_t)read6502((uint16_t)pc++);
}
static void zpx() { //zero-page,X
ea = ((uint16_t)read6502((uint16_t)pc++) + (uint16_t)x) & 0xFF; //zero-page wraparound
}
static void zpy() { //zero-page,Y
ea = ((uint16_t)read6502((uint16_t)pc++) + (uint16_t)y) & 0xFF; //zero-page wraparound
}
static void rel() { //relative for branch ops (8-bit immediate value, sign-extended)
reladdr = (uint16_t)read6502(pc++);
if (reladdr & 0x80) reladdr |= 0xFF00;
}
static void abso() { //absolute
ea = (uint16_t)read6502(pc) | ((uint16_t)read6502(pc+1) << 8);
pc += 2;
}
static void absx() { //absolute,X
uint16_t startpage;
ea = ((uint16_t)read6502(pc) | ((uint16_t)read6502(pc+1) << 8));
startpage = ea & 0xFF00;
ea += (uint16_t)x;
if (startpage != (ea & 0xFF00)) { //one cycle penlty for page-crossing on some opcodes
penaltyaddr = 1;
}
pc += 2;
}
static void absy() { //absolute,Y
uint16_t startpage;
ea = ((uint16_t)read6502(pc) | ((uint16_t)read6502(pc+1) << 8));
startpage = ea & 0xFF00;
ea += (uint16_t)y;
if (startpage != (ea & 0xFF00)) { //one cycle penlty for page-crossing on some opcodes
penaltyaddr = 1;
}
pc += 2;
}
static void ind() { //indirect
uint16_t eahelp, eahelp2;
eahelp = (uint16_t)read6502(pc) | (uint16_t)((uint16_t)read6502(pc+1) << 8);
eahelp2 = (eahelp & 0xFF00) | ((eahelp + 1) & 0x00FF); //replicate 6502 page-boundary wraparound bug
ea = (uint16_t)read6502(eahelp) | ((uint16_t)read6502(eahelp2) << 8);
pc += 2;
}
static void indx() { // (indirect,X)
uint16_t eahelp;
eahelp = (uint16_t)(((uint16_t)read6502(pc++) + (uint16_t)x) & 0xFF); //zero-page wraparound for table pointer
ea = (uint16_t)read6502(eahelp & 0x00FF) | ((uint16_t)read6502((eahelp+1) & 0x00FF) << 8);
}
static void indy() { // (indirect),Y
uint16_t eahelp, eahelp2, startpage;
eahelp = (uint16_t)read6502(pc++);
eahelp2 = (eahelp & 0xFF00) | ((eahelp + 1) & 0x00FF); //zero-page wraparound
ea = (uint16_t)read6502(eahelp) | ((uint16_t)read6502(eahelp2) << 8);
startpage = ea & 0xFF00;
ea += (uint16_t)y;
if (startpage != (ea & 0xFF00)) { //one cycle penlty for page-crossing on some opcodes
penaltyaddr = 1;
}
}
static uint16_t getvalue() {
if (addrtable[opcode] == acc) return((uint16_t)a);
else return((uint16_t)read6502(ea));
}
static uint16_t getvalue16() {
return((uint16_t)read6502(ea) | ((uint16_t)read6502(ea+1) << 8));
}
static void putvalue(uint16_t saveval) {
if (addrtable[opcode] == acc) a = (uint8_t)(saveval & 0x00FF);
else write6502(ea, (saveval & 0x00FF));
}
//instruction handler functions
static void adc() {
penaltyop = 1;
value = getvalue();
result = (uint16_t)a + value + (uint16_t)(status & FLAG_CARRY);
carrycalc(result);
zerocalc(result);
overflowcalc(result, a, value);
signcalc(result);
#ifndef NES_CPU
if (status & FLAG_DECIMAL) {
clearcarry();
if ((a & 0x0F) > 0x09) {
a += 0x06;
}
if ((a & 0xF0) > 0x90) {
a += 0x60;
setcarry();
}
clockticks6502++;
}
#endif
saveaccum(result);
}
static void and() {
penaltyop = 1;
value = getvalue();
result = (uint16_t)a & value;
zerocalc(result);
signcalc(result);
saveaccum(result);
}
static void asl() {
value = getvalue();
result = value << 1;
carrycalc(result);
zerocalc(result);
signcalc(result);
putvalue(result);
}
static void bcc() {
if ((status & FLAG_CARRY) == 0) {
oldpc = pc;
pc += reladdr;
if ((oldpc & 0xFF00) != (pc & 0xFF00)) clockticks6502 += 2; //check if jump crossed a page boundary
else clockticks6502++;
}
}
static void bcs() {
if ((status & FLAG_CARRY) == FLAG_CARRY) {
oldpc = pc;
pc += reladdr;
if ((oldpc & 0xFF00) != (pc & 0xFF00)) clockticks6502 += 2; //check if jump crossed a page boundary
else clockticks6502++;
}
}
static void beq() {
if ((status & FLAG_ZERO) == FLAG_ZERO) {
oldpc = pc;
pc += reladdr;
if ((oldpc & 0xFF00) != (pc & 0xFF00)) clockticks6502 += 2; //check if jump crossed a page boundary
else clockticks6502++;
}
}
static void bit() {
value = getvalue();
result = (uint16_t)a & value;
zerocalc(result);
status = (status & 0x3F) | (uint8_t)(value & 0xC0);
}
static void bmi() {
if ((status & FLAG_SIGN) == FLAG_SIGN) {
oldpc = pc;
pc += reladdr;
if ((oldpc & 0xFF00) != (pc & 0xFF00)) clockticks6502 += 2; //check if jump crossed a page boundary
else clockticks6502++;
}
}
static void bne() {
if ((status & FLAG_ZERO) == 0) {
oldpc = pc;
pc += reladdr;
if ((oldpc & 0xFF00) != (pc & 0xFF00)) clockticks6502 += 2; //check if jump crossed a page boundary
else clockticks6502++;
}
}
static void bpl() {
if ((status & FLAG_SIGN) == 0) {
oldpc = pc;
pc += reladdr;
if ((oldpc & 0xFF00) != (pc & 0xFF00)) clockticks6502 += 2; //check if jump crossed a page boundary
else clockticks6502++;
}
}
static void brk6502() {
pc++;
push16(pc); //push next instruction address onto stack
push8(status | FLAG_BREAK); //push CPU status to stack
setinterrupt(); //set interrupt flag
pc = (uint16_t)read6502(0xFFFE) | ((uint16_t)read6502(0xFFFF) << 8);
}
static void bvc() {
if ((status & FLAG_OVERFLOW) == 0) {
oldpc = pc;
pc += reladdr;
if ((oldpc & 0xFF00) != (pc & 0xFF00)) clockticks6502 += 2; //check if jump crossed a page boundary
else clockticks6502++;
}
}
static void bvs() {
if ((status & FLAG_OVERFLOW) == FLAG_OVERFLOW) {
oldpc = pc;
pc += reladdr;
if ((oldpc & 0xFF00) != (pc & 0xFF00)) clockticks6502 += 2; //check if jump crossed a page boundary
else clockticks6502++;
}
}
static void clc() {
clearcarry();
}
static void cld() {
cleardecimal();
}
static void cli() {
clearinterrupt();
}
static void clv() {
clearoverflow();
}
static void cmp() {
penaltyop = 1;
value = getvalue();
result = (uint16_t)a - value;
if (a >= (uint8_t)(value & 0x00FF)) setcarry();
else clearcarry();
if (a == (uint8_t)(value & 0x00FF)) setzero();
else clearzero();
signcalc(result);
}
static void cpx() {
value = getvalue();
result = (uint16_t)x - value;
if (x >= (uint8_t)(value & 0x00FF)) setcarry();
else clearcarry();
if (x == (uint8_t)(value & 0x00FF)) setzero();
else clearzero();
signcalc(result);
}
static void cpy() {
value = getvalue();
result = (uint16_t)y - value;
if (y >= (uint8_t)(value & 0x00FF)) setcarry();
else clearcarry();
if (y == (uint8_t)(value & 0x00FF)) setzero();
else clearzero();
signcalc(result);
}
static void dec() {
value = getvalue();
result = value - 1;
zerocalc(result);
signcalc(result);
putvalue(result);
}
static void dex() {
x--;
zerocalc(x);
signcalc(x);
}
static void dey() {
y--;
zerocalc(y);
signcalc(y);
}
static void eor() {
penaltyop = 1;
value = getvalue();
result = (uint16_t)a ^ value;
zerocalc(result);
signcalc(result);
saveaccum(result);
}
static void inc() {
value = getvalue();
result = value + 1;
zerocalc(result);
signcalc(result);
putvalue(result);
}
static void inx() {
x++;
zerocalc(x);
signcalc(x);
}
static void iny() {
y++;
zerocalc(y);
signcalc(y);
}
static void jmp() {
pc = ea;
}
static void jsr() {
push16(pc - 1);
pc = ea;
}
static void lda() {
penaltyop = 1;
value = getvalue();
a = (uint8_t)(value & 0x00FF);
zerocalc(a);
signcalc(a);
}
static void ldx() {
penaltyop = 1;
value = getvalue();
x = (uint8_t)(value & 0x00FF);
zerocalc(x);
signcalc(x);
}
static void ldy() {
penaltyop = 1;
value = getvalue();
y = (uint8_t)(value & 0x00FF);
zerocalc(y);
signcalc(y);
}
static void lsr() {
value = getvalue();
result = value >> 1;
if (value & 1) setcarry();
else clearcarry();
zerocalc(result);
signcalc(result);
putvalue(result);
}
static void nop() {
switch (opcode) {
case 0x1C:
case 0x3C:
case 0x5C:
case 0x7C:
case 0xDC:
case 0xFC:
penaltyop = 1;
break;
}
}
static void ora() {
penaltyop = 1;
value = getvalue();
result = (uint16_t)a | value;
zerocalc(result);
signcalc(result);
saveaccum(result);
}
static void pha() {
push8(a);
}
static void php() {
push8(status | FLAG_BREAK);
}
static void pla() {
a = pull8();
zerocalc(a);
signcalc(a);
}
static void plp() {
status = pull8() | FLAG_CONSTANT;
}
static void rol() {
value = getvalue();
result = (value << 1) | (status & FLAG_CARRY);
carrycalc(result);
zerocalc(result);
signcalc(result);
putvalue(result);
}
static void ror() {
value = getvalue();
result = (value >> 1) | ((status & FLAG_CARRY) << 7);
if (value & 1) setcarry();
else clearcarry();
zerocalc(result);
signcalc(result);
putvalue(result);
}
static void rti() {
status = pull8();
value = pull16();
pc = value;
}
static void rts() {
value = pull16();
pc = value + 1;
}
static void sbc() {
penaltyop = 1;
value = getvalue() ^ 0x00FF;
result = (uint16_t)a + value + (uint16_t)(status & FLAG_CARRY);
carrycalc(result);
zerocalc(result);
overflowcalc(result, a, value);
signcalc(result);
#ifndef NES_CPU
if (status & FLAG_DECIMAL) {
clearcarry();
a -= 0x66;
if ((a & 0x0F) > 0x09) {
a += 0x06;
}
if ((a & 0xF0) > 0x90) {
a += 0x60;
setcarry();
}
clockticks6502++;
}
#endif
saveaccum(result);
}
static void sec() {
setcarry();
}
static void sed() {
setdecimal();
}
static void sei() {
setinterrupt();
}
static void sta() {
putvalue(a);
}
static void stx() {
putvalue(x);
}
static void sty() {
putvalue(y);
}
static void tax() {
x = a;
zerocalc(x);
signcalc(x);
}
static void tay() {
y = a;
zerocalc(y);
signcalc(y);
}
static void tsx() {
x = sp;
zerocalc(x);
signcalc(x);
}
static void txa() {
a = x;
zerocalc(a);
signcalc(a);
}
static void txs() {
sp = x;
}
static void tya() {
a = y;
zerocalc(a);
signcalc(a);
}
//undocumented instructions
#ifdef UNDOCUMENTED
static void lax() {
lda();
ldx();
}
static void sax() {
sta();
stx();
putvalue(a & x);
if (penaltyop && penaltyaddr) clockticks6502--;
}
static void dcp() {
dec();
cmp();
if (penaltyop && penaltyaddr) clockticks6502--;
}
static void isb() {
inc();
sbc();
if (penaltyop && penaltyaddr) clockticks6502--;
}
static void slo() {
asl();
ora();
if (penaltyop && penaltyaddr) clockticks6502--;
}
static void rla() {
rol();
and();
if (penaltyop && penaltyaddr) clockticks6502--;
}
static void sre() {
lsr();
eor();
if (penaltyop && penaltyaddr) clockticks6502--;
}
static void rra() {
ror();
adc();
if (penaltyop && penaltyaddr) clockticks6502--;
}
#else
#define lax nop
#define sax nop
#define dcp nop
#define isb nop
#define slo nop
#define rla nop
#define sre nop
#define rra nop
#endif
static void (*addrtable[256])() = {
/* | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F | */
/* 0 */ imp, indx, imp, indx, zp, zp, zp, zp, imp, imm, acc, imm, abso, abso, abso, abso, /* 0 */
/* 1 */ rel, indy, imp, indy, zpx, zpx, zpx, zpx, imp, absy, imp, absy, absx, absx, absx, absx, /* 1 */
/* 2 */ abso, indx, imp, indx, zp, zp, zp, zp, imp, imm, acc, imm, abso, abso, abso, abso, /* 2 */
/* 3 */ rel, indy, imp, indy, zpx, zpx, zpx, zpx, imp, absy, imp, absy, absx, absx, absx, absx, /* 3 */
/* 4 */ imp, indx, imp, indx, zp, zp, zp, zp, imp, imm, acc, imm, abso, abso, abso, abso, /* 4 */
/* 5 */ rel, indy, imp, indy, zpx, zpx, zpx, zpx, imp, absy, imp, absy, absx, absx, absx, absx, /* 5 */
/* 6 */ imp, indx, imp, indx, zp, zp, zp, zp, imp, imm, acc, imm, ind, abso, abso, abso, /* 6 */
/* 7 */ rel, indy, imp, indy, zpx, zpx, zpx, zpx, imp, absy, imp, absy, absx, absx, absx, absx, /* 7 */
/* 8 */ imm, indx, imm, indx, zp, zp, zp, zp, imp, imm, imp, imm, abso, abso, abso, abso, /* 8 */
/* 9 */ rel, indy, imp, indy, zpx, zpx, zpy, zpy, imp, absy, imp, absy, absx, absx, absy, absy, /* 9 */
/* A */ imm, indx, imm, indx, zp, zp, zp, zp, imp, imm, imp, imm, abso, abso, abso, abso, /* A */
/* B */ rel, indy, imp, indy, zpx, zpx, zpy, zpy, imp, absy, imp, absy, absx, absx, absy, absy, /* B */
/* C */ imm, indx, imm, indx, zp, zp, zp, zp, imp, imm, imp, imm, abso, abso, abso, abso, /* C */
/* D */ rel, indy, imp, indy, zpx, zpx, zpx, zpx, imp, absy, imp, absy, absx, absx, absx, absx, /* D */
/* E */ imm, indx, imm, indx, zp, zp, zp, zp, imp, imm, imp, imm, abso, abso, abso, abso, /* E */
/* F */ rel, indy, imp, indy, zpx, zpx, zpx, zpx, imp, absy, imp, absy, absx, absx, absx, absx /* F */
};
static void (*optable[256])() = {
/* | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F | */
/* 0 */ brk6502, ora, nop, slo, nop, ora, asl, slo, php, ora, asl, nop, nop, ora, asl, slo, /* 0 */
/* 1 */ bpl, ora, nop, slo, nop, ora, asl, slo, clc, ora, nop, slo, nop, ora, asl, slo, /* 1 */
/* 2 */ jsr, and, nop, rla, bit, and, rol, rla, plp, and, rol, nop, bit, and, rol, rla, /* 2 */
/* 3 */ bmi, and, nop, rla, nop, and, rol, rla, sec, and, nop, rla, nop, and, rol, rla, /* 3 */
/* 4 */ rti, eor, nop, sre, nop, eor, lsr, sre, pha, eor, lsr, nop, jmp, eor, lsr, sre, /* 4 */
/* 5 */ bvc, eor, nop, sre, nop, eor, lsr, sre, cli, eor, nop, sre, nop, eor, lsr, sre, /* 5 */
/* 6 */ rts, adc, nop, rra, nop, adc, ror, rra, pla, adc, ror, nop, jmp, adc, ror, rra, /* 6 */
/* 7 */ bvs, adc, nop, rra, nop, adc, ror, rra, sei, adc, nop, rra, nop, adc, ror, rra, /* 7 */
/* 8 */ nop, sta, nop, sax, sty, sta, stx, sax, dey, nop, txa, nop, sty, sta, stx, sax, /* 8 */
/* 9 */ bcc, sta, nop, nop, sty, sta, stx, sax, tya, sta, txs, nop, nop, sta, nop, nop, /* 9 */
/* A */ ldy, lda, ldx, lax, ldy, lda, ldx, lax, tay, lda, tax, nop, ldy, lda, ldx, lax, /* A */
/* B */ bcs, lda, nop, lax, ldy, lda, ldx, lax, clv, lda, tsx, lax, ldy, lda, ldx, lax, /* B */
/* C */ cpy, cmp, nop, dcp, cpy, cmp, dec, dcp, iny, cmp, dex, nop, cpy, cmp, dec, dcp, /* C */
/* D */ bne, cmp, nop, dcp, nop, cmp, dec, dcp, cld, cmp, nop, dcp, nop, cmp, dec, dcp, /* D */
/* E */ cpx, sbc, nop, isb, cpx, sbc, inc, isb, inx, sbc, nop, sbc, cpx, sbc, inc, isb, /* E */
/* F */ beq, sbc, nop, isb, nop, sbc, inc, isb, sed, sbc, nop, isb, nop, sbc, inc, isb /* F */
};
static const uint32_t ticktable[256] = {
/* | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F | */
/* 0 */ 7, 6, 2, 8, 3, 3, 5, 5, 3, 2, 2, 2, 4, 4, 6, 6, /* 0 */
/* 1 */ 2, 5, 2, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7, /* 1 */
/* 2 */ 6, 6, 2, 8, 3, 3, 5, 5, 4, 2, 2, 2, 4, 4, 6, 6, /* 2 */
/* 3 */ 2, 5, 2, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7, /* 3 */
/* 4 */ 6, 6, 2, 8, 3, 3, 5, 5, 3, 2, 2, 2, 3, 4, 6, 6, /* 4 */
/* 5 */ 2, 5, 2, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7, /* 5 */
/* 6 */ 6, 6, 2, 8, 3, 3, 5, 5, 4, 2, 2, 2, 5, 4, 6, 6, /* 6 */
/* 7 */ 2, 5, 2, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7, /* 7 */
/* 8 */ 2, 6, 2, 6, 3, 3, 3, 3, 2, 2, 2, 2, 4, 4, 4, 4, /* 8 */
/* 9 */ 2, 6, 2, 6, 4, 4, 4, 4, 2, 5, 2, 5, 5, 5, 5, 5, /* 9 */
/* A */ 2, 6, 2, 6, 3, 3, 3, 3, 2, 2, 2, 2, 4, 4, 4, 4, /* A */
/* B */ 2, 5, 2, 5, 4, 4, 4, 4, 2, 4, 2, 4, 4, 4, 4, 4, /* B */
/* C */ 2, 6, 2, 8, 3, 3, 5, 5, 2, 2, 2, 2, 4, 4, 6, 6, /* C */
/* D */ 2, 5, 2, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7, /* D */
/* E */ 2, 6, 2, 8, 3, 3, 5, 5, 2, 2, 2, 2, 4, 4, 6, 6, /* E */
/* F */ 2, 5, 2, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7 /* F */
};
void nmi6502() {
push16(pc);
push8(status);
status |= FLAG_INTERRUPT;
pc = (uint16_t)read6502(0xFFFA) | ((uint16_t)read6502(0xFFFB) << 8);
}
void irq6502() {
push16(pc);
push8(status);
status |= FLAG_INTERRUPT;
pc = (uint16_t)read6502(0xFFFE) | ((uint16_t)read6502(0xFFFF) << 8);
}
uint8_t callexternal = 0;
void (*loopexternal)();
/*
void exec6502(uint32_t tickcount) {
clockgoal6502 += tickcount;
while (clockticks6502 < clockgoal6502) {
opcode = read6502(pc++);
status |= FLAG_CONSTANT;
penaltyop = 0;
penaltyaddr = 0;
(*addrtable[opcode])();
(*optable[opcode])();
clockticks6502 += ticktable[opcode];
if (penaltyop && penaltyaddr) clockticks6502++;
instructions++;
if (callexternal) (*loopexternal)();
}
}
*/
void exec6502(unsigned int org) {
clockticks6502 = 0;
pc = org;
while ((opcode = read6502(pc++)) != 0x00) { // end on BRK
status |= FLAG_CONSTANT;
penaltyop = 0;
penaltyaddr = 0;
(*addrtable[opcode])();
(*optable[opcode])();
clockticks6502 += ticktable[opcode];
if (penaltyop && penaltyaddr) clockticks6502++;
instructions++;
if (callexternal) (*loopexternal)();
}
}
void step6502() {
opcode = read6502(pc++);
status |= FLAG_CONSTANT;
penaltyop = 0;
penaltyaddr = 0;
(*addrtable[opcode])();
(*optable[opcode])();
clockticks6502 += ticktable[opcode];
if (penaltyop && penaltyaddr) clockticks6502++;
clockgoal6502 = clockticks6502;
instructions++;
if (callexternal) (*loopexternal)();
}
void hookexternal(void *funcptr) {
if (funcptr != (void *)NULL) {
loopexternal = funcptr;
callexternal = 1;
} else callexternal = 0;
}