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A1Emu/cpu.c

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/*
* 6502 Emulator
*
* Spring Break programming project
*
* 3/5/2019
* by Ben Jones
*/
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <sys/time.h>
#include "cpu.h"
#ifdef _WIN32
#include <curses.h>
#else
#include <ncurses.h>
#endif
unsigned char CROSSED_PAGE;
unsigned char different_page(uint16_t address1, uint16_t address2){
return (address1&0xFF00) != (address2&0xFF00);
}
uint8_t get_absolute(CPU_6502 *cpu, uint8_t index, uint8_t (*read)(uint16_t)){
uint16_t address1;
uint16_t address2;
address1 = ((uint16_t) read(cpu->PC_reg + 1)) | (((uint16_t) read(cpu->PC_reg + 2))<<8);
address2 = address1 + index;
CROSSED_PAGE = different_page(address1, address2);
return read(address2);
}
uint8_t get_indirect_X(CPU_6502 *cpu, uint8_t index, uint8_t (*read)(uint16_t)){
return read(((uint16_t) read(cpu->X_reg + index)) | (((uint16_t) read(cpu->X_reg + index + 1))<<8));
}
uint8_t get_indirect_Y(CPU_6502 *cpu, uint8_t index, uint8_t (*read)(uint16_t)){
uint16_t address1;
uint16_t address2;
address1 = ((uint16_t) read(index)) | (((uint16_t) read(index + 1))<<8);
address2 = address1 + cpu->Y_reg;
CROSSED_PAGE = different_page(address1, address2);
return read(address2);
}
void set_absolute(CPU_6502 *cpu, uint8_t index, uint8_t (*read)(uint16_t), void (*write)(uint16_t, uint8_t), uint8_t value){
uint16_t address1;
uint16_t address2;
address1 = ((uint16_t) read(cpu->PC_reg + 1)) | (((uint16_t) read(cpu->PC_reg + 2))<<8);
address2 = address1 + index;
CROSSED_PAGE = different_page(address1, address2);
write(address2, value);
}
void set_indirect_X(CPU_6502 *cpu, uint8_t index, uint8_t (*read)(uint16_t), void (*write)(uint16_t, uint8_t), uint8_t value){
write(((uint16_t) read(cpu->X_reg + index)) | (((uint16_t) read(cpu->X_reg + index + 1))<<8), value);
}
void set_indirect_Y(CPU_6502 *cpu, uint8_t index, uint8_t (*read)(uint16_t), void (*write)(uint16_t, uint8_t), uint8_t value){
uint16_t address1;
uint16_t address2;
address1 = ((uint16_t) read(index)) | (((uint16_t) read(index + 1))<<8);
address2 = address1 + cpu->Y_reg;
CROSSED_PAGE = different_page(address1, address2);
write(address2, value);
}
void push(CPU_6502 *cpu, void (*write)(uint16_t, uint8_t), uint8_t value){
write(0x100 | cpu->SP_reg, value);
cpu->SP_reg -= 1;
}
uint8_t pop(CPU_6502 *cpu, uint8_t (*read)(uint16_t)){
cpu->SP_reg += 1;
return read(0x100 | cpu->SP_reg);
}
//Execute a single 6502 instruction, updating the state of the CPU
void execute_6502(CPU_6502 *cpu, uint8_t (*read)(uint16_t), void (*write)(uint16_t, uint8_t)){
//Various intermediate values for calculation
uint8_t value1;
uint8_t value2;
uint8_t value3;
uint16_t value_absolute;
uint8_t prev;
//The first byte at PC uniquely determines the operation
uint8_t opcode;
uint16_t address1;
opcode = read(cpu->PC_reg);
//ADC
if(opcode == 0x69 || opcode == 0x65 || opcode == 0x75 || opcode == 0x6D || opcode == 0x7D || opcode == 0x79 || opcode == 0x61 || opcode == 0x71){
if(opcode == 0x69){//Immediate
value1 = read(cpu->PC_reg + 1);
cpu->PC_reg += 2;
cpu->cycles += 2;
} else if(opcode == 0x65){//Zero page
value1 = read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0x75){//Zero page X
value1 = read((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0x6D){//Absolute
value1 = get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
} else if(opcode == 0x7D){//Absolute X
value1 = get_absolute(cpu, cpu->X_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0x79){//Absolute Y
value1 = get_absolute(cpu, cpu->Y_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0x61){//Indirect X
value1 = get_indirect_X(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0x71){//Indirect Y
value1 = get_indirect_Y(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
if(CROSSED_PAGE){
cpu->cycles += 6;
} else {
cpu->cycles += 5;
}
}
prev = cpu->A_reg;
//If the carry flag is set, add 1 more to result
if(cpu->P_reg&(1<<CARRY)){
value1++;
}
cpu->A_reg += value1;
//If the decimal flag is set, correct the output
if(cpu->P_reg&(1<<DECIMAL)){
//Using double-dabble ish trick here
if((cpu->A_reg&0xF) > 9){
cpu->A_reg += 0x6;
}
}
//Set the carry bit accordingly
if(cpu->A_reg < prev){
cpu->P_reg |= (1<<CARRY);
} else {
cpu->P_reg &= ~(1<<CARRY);
}
//Set overflow flag
if(((value1&0x80) && (prev&0x80) && !(cpu->A_reg&0x80)) || (!(value1&0x80) && !(prev&0x80) && (cpu->A_reg&0x80))){
cpu->P_reg |= (1<<OVERFLOW);
} else {
cpu->P_reg &= ~(1<<OVERFLOW);
}
//Set negative flag
if(cpu->A_reg&0x80){
cpu->P_reg |= (1<<NEGATIVE);
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//Set zero flag
if(!cpu->A_reg){
cpu->P_reg |= (1<<ZERO);
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//AND
} else if(opcode == 0x29 || opcode == 0x25 || opcode == 0x35 || opcode == 0x2D || opcode == 0x3D || opcode == 0x39 || opcode == 0x21 || opcode == 0x31){
if(opcode == 0x29){//Immediate
value1 = read(cpu->PC_reg + 1);
cpu->PC_reg += 2;
cpu->cycles += 2;
} else if(opcode == 0x25){//Zero page
value1 = read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0x35){//Zero page X
value1 = read((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0x2D){//Absolute
value1 = get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
} else if(opcode == 0x3D){//Absolute X
value1 = get_absolute(cpu, cpu->X_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0x39){//Absolute Y
value1 = get_absolute(cpu, cpu->Y_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0x21){//Indirect X
value1 = get_indirect_X(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0x31){//Indirect Y
value1 = get_indirect_Y(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
if(CROSSED_PAGE){
cpu->cycles += 6;
} else {
cpu->cycles += 5;
}
}
//Perform the AND
cpu->A_reg &= value1;
//Set the zero flag
if(!cpu->A_reg){
cpu->P_reg |= (1<<ZERO);
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->A_reg&0x80){
cpu->P_reg |= (1<<NEGATIVE);
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//ASL
} else if(opcode == 0x0A || opcode == 0x06 || opcode == 0x16 || opcode == 0x0E || opcode == 0x1E){
if(opcode == 0x0A){//Accumulator
value1 = cpu->A_reg;
cpu->cycles += 2;
} else if(opcode == 0x06){//Zero page
value1 = read(read(cpu->PC_reg + 1));
cpu->cycles += 5;
} else if(opcode == 0x16){//Zero page X
value1 = read((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF);
cpu->cycles += 6;
} else if(opcode == 0x0E){//Absolute
value1 = get_absolute(cpu, 0, read);
cpu->cycles += 6;
} else if(opcode == 0x1E){//Absolute X
value1 = get_absolute(cpu, cpu->X_reg, read);
cpu->cycles += 7;
}
//Set the carry flag
if(value1&0x80){
cpu->P_reg |= (1<<CARRY);
} else {
cpu->P_reg &= ~(1<<CARRY);
}
//Perform the shift
value1 <<= 1;
if(opcode == 0x0A){//Accumulator
cpu->A_reg = value1;
cpu->PC_reg += 1;
} else if(opcode == 0x06){//Zero page
write(read(cpu->PC_reg + 1), value1);
cpu->PC_reg += 2;
} else if(opcode == 0x16){//Zero page X
write((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF, value1);
cpu->PC_reg += 2;
} else if(opcode == 0x0E){//Absolute
set_absolute(cpu, 0, read, write, value1);
cpu->PC_reg += 3;
} else if(opcode == 0x1E){//Absolute X
set_absolute(cpu, cpu->X_reg, read, write, value1);
cpu->PC_reg += 3;
}
//Set the zero flag
if(!value1){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(value1&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//BCC
} else if(opcode == 0x90){//Branch carry clear
cpu->cycles += 2;
if(!(cpu->P_reg&(1<<CARRY))){//If the carry is clear
cpu->cycles++;
value1 = read(cpu->PC_reg + 1);
if(value1&0x80){//If it is a negative jump
address1 = cpu->PC_reg - (((uint16_t) ((~value1) - 1))&0xFF);
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
} else {//If it is a positive jump
address1 = cpu->PC_reg + value1 + 2;
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
}
} else {
cpu->PC_reg += 2;
}
//BCS
} else if(opcode == 0xB0){//Branch carry set
cpu->cycles += 2;
if(cpu->P_reg&(1<<CARRY)){//If the carry is set
cpu->cycles++;
value1 = read(cpu->PC_reg + 1);
if(value1&0x80){//If it is a negative jump
address1 = cpu->PC_reg - (((uint16_t) ((~value1) - 1))&0xFF);
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
} else {//If it is a positive jump
address1 = cpu->PC_reg + value1 + 2;
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
}
} else {
cpu->PC_reg += 2;
}
//BEQ
} else if(opcode == 0xF0){//Branch equals
cpu->cycles += 2;
if(cpu->P_reg&(1<<ZERO)){//If the zero flag is set
cpu->cycles++;
value1 = read(cpu->PC_reg + 1);
if(value1&0x80){//If it is a negative jump
address1 = cpu->PC_reg - (((uint16_t) ((~value1) - 1))&0xFF);
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
} else {//If it is a postive jump
address1 = cpu->PC_reg + value1 + 2;
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
}
} else {
cpu->PC_reg += 2;
}
//BIT
} else if(opcode == 0x24 || opcode == 0x2C){
if(opcode == 0x24){//Zero page
value1 = read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0x2C){//Absolute
value1 = get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
}
//Set the zero flag
if(!(value1&cpu->A_reg)){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(value1&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//Set the overflow flag
if(value1&0x40){
cpu->P_reg |= 1<<OVERFLOW;
} else {
cpu->P_reg &= ~(1<<OVERFLOW);
}
//BMI
} else if(opcode == 0x30){//Branch minus
cpu->cycles += 2;
if(cpu->P_reg&(1<<NEGATIVE)){//Test the negative flag
cpu->cycles++;
value1 = read(cpu->PC_reg + 1);
if(value1&0x80){//If it is a negative jump
address1 = cpu->PC_reg - (((uint16_t) ((~value1) - 1))&0xFF);
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
} else {//If it is a positive jump
address1 = cpu->PC_reg + value1 + 2;
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
}
} else {
cpu->PC_reg += 2;
}
//BNE
} else if(opcode == 0xD0){//Branch not equal
cpu->cycles += 2;
if(!(cpu->P_reg&(1<<ZERO))){
cpu->cycles++;
value1 = read(cpu->PC_reg + 1);
if(value1&0x80){//If it is a negative jump
address1 = cpu->PC_reg - (((uint16_t) ((~value1) - 1))&0xFF);
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
} else {//If it is a positive jump
address1 = cpu->PC_reg + value1 + 2;
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
}
} else {
cpu->PC_reg += 2;
}
//BPL
} else if(opcode == 0x10){//Branch positive
cpu->cycles += 2;
if(!(cpu->P_reg&(1<<NEGATIVE))){
cpu->cycles++;
value1 = read(cpu->PC_reg + 1);
if(value1&0x80){//If it is a negative jump
address1 = cpu->PC_reg - (((uint16_t) ((~value1) - 1))&0xFF);
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
} else {//If it is a positive jump
address1 = cpu->PC_reg + value1 + 2;
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
}
} else {
cpu->PC_reg += 2;
}
//BRK
} else if(opcode == 0x00){//Break (forced interrupt)
//Set the break flag
cpu->P_reg |= 1<<BREAK;
cpu->PC_reg += 2;
push(cpu, write, (cpu->PC_reg&0xFF00)>>8);
push(cpu, write, cpu->PC_reg&0xFF);
push(cpu, write, cpu->P_reg);
cpu->P_reg |= 1<<INTERRUPT;
cpu->PC_reg = (((uint16_t) read(0xFFFF))<<8) | read(0xFFFE);
cpu->cycles += 7;
//BVC
} else if(opcode == 0x50){//Branch overflow clear
cpu->cycles += 2;
if(!(cpu->P_reg&(1<<OVERFLOW))){
cpu->cycles++;
value1 = read(cpu->PC_reg + 1);
if(value1&0x80){//If it is a negative jump
address1 = cpu->PC_reg - (((uint16_t) ((~value1) - 1))&0xFF);
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
} else {//If it is a positive jump
address1 = cpu->PC_reg + value1 + 2;
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
}
} else {
cpu->PC_reg += 2;
}
//BVS
} else if(opcode == 0x70){//Branch overflow set
cpu->cycles += 2;
if(cpu->P_reg&(1<<OVERFLOW)){
cpu->cycles++;
value1 = read(cpu->PC_reg + 1);
if(value1&0x80){//If it is a negative jump
address1 = cpu->PC_reg - (((uint16_t) ((~value1) - 1))&0xFF);
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
} else {//If it is a positive jump
address1 = cpu->PC_reg + value1 + 2;
if(different_page(cpu->PC_reg, address1)){
cpu->cycles++;
}
cpu->PC_reg = address1;
}
} else {
cpu->PC_reg += 2;
}
//CLC
} else if(opcode == 0x18){//Clear carry flag
cpu->P_reg &= ~(1<<CARRY);
cpu->PC_reg += 1;
cpu->cycles += 2;
//CLD
} else if(opcode == 0xD8){//Clear decimal flag
cpu->P_reg &= ~(1<<DECIMAL);
cpu->PC_reg += 1;
cpu->cycles += 2;
//CLI
} else if(opcode == 0x58){//Clear interrupt flag
cpu->P_reg &= ~(1<<INTERRUPT);
cpu->PC_reg += 1;
cpu->cycles += 2;
//CLV
} else if(opcode == 0xB8){//Clear overflow flag
cpu->P_reg &= ~(1<<OVERFLOW);
cpu->PC_reg += 1;
cpu->cycles += 2;
//CMP
} else if(opcode == 0xC9 || opcode == 0xC5 || opcode == 0xD5 || opcode == 0xCD || opcode == 0xDD || opcode == 0xD9 || opcode == 0xC1 || opcode == 0xD1){
if(opcode == 0xC9){//Immediate
value1 = read(cpu->PC_reg + 1);
cpu->PC_reg += 2;
cpu->cycles += 2;
} else if(opcode == 0xC5){//Zero page
value1 = read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0xD5){//Zero page X
value1 = read((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0xCD){//Absolute
value1 = get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
} else if(opcode == 0xDD){//Absolute X
value1 = get_absolute(cpu, cpu->X_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0xD9){//Absolute Y
value1 = get_absolute(cpu, cpu->Y_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0xC1){//Indirect X
value1 = get_indirect_X(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0xD1){//Indirect Y
value1 = get_indirect_Y(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
if(CROSSED_PAGE){
cpu->cycles += 6;
} else {
cpu->cycles += 5;
}
}
value2 = cpu->A_reg - value1;
//Set the zero flag
if(!value2){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(value2&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//Set the carry flag
if(cpu->A_reg >= value1){
cpu->P_reg |= 1<<CARRY;
} else {
cpu->P_reg &= ~(1<<CARRY);
}
//CPX
} else if(opcode == 0xE0 || opcode == 0xE4 || opcode == 0xEC){
if(opcode == 0xE0){//Immediate
value1 = read(cpu->PC_reg + 1);
cpu->PC_reg += 2;
cpu->cycles += 2;
} else if(opcode == 0xE4){//Zero Page
value1 = read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0xEC){//Absolute
value1 = get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
}
value2 = cpu->X_reg - value1;
//Set the zero flag
if(!value2){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(value2&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//Set the carry flag
if(cpu->X_reg >= value1){
cpu->P_reg |= 1<<CARRY;
} else {
cpu->P_reg &= ~(1<<CARRY);
}
//CPY
} else if(opcode == 0xC0 || opcode == 0xC4 || opcode == 0xCC){
if(opcode == 0xC0){//Immediate
value1 = read(cpu->PC_reg + 1);
cpu->PC_reg += 2;
cpu->cycles += 2;
} else if(opcode == 0xC4){//Zero Page
value1 = read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0xCC){//Absolute
value1 = get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
}
value2 = cpu->Y_reg - value1;
//Set the zero flag
if(!value2){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(value2&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//Set the carry flag
if(cpu->Y_reg >= value1){
cpu->P_reg |= 1<<CARRY;
} else {
cpu->P_reg &= ~(1<<CARRY);
}
//DEC
} else if(opcode == 0xC6 || opcode == 0xD6 || opcode == 0xCE || opcode == 0xDE){
if(opcode == 0xC6){//Zero page
value2 = read(cpu->PC_reg + 1);
value1 = read(value2);
value1--;
write(value2, value1);
cpu->PC_reg += 2;
cpu->cycles += 5;
} else if(opcode == 0xD6){//Zero page X
value2 = read(cpu->PC_reg + 1);
value1 = read((value2 + cpu->X_reg)&0xFF);
value1--;
write((value2 + cpu->X_reg)&0xFF, value1);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0xCE){//Absolute
value1 = get_absolute(cpu, 0, read) - 1;
set_absolute(cpu, 0, read, write, value1);
cpu->PC_reg += 3;
cpu->cycles += 6;
} else if(opcode == 0xDE){//Absolute X
value1 = get_absolute(cpu, cpu->X_reg, read) - 1;
set_absolute(cpu, cpu->X_reg, read, write, value1);
cpu->PC_reg += 3;
cpu->cycles += 7;
}
//Set the zero flag
if(!value1){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(value1&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//DEX
} else if(opcode == 0xCA){
cpu->X_reg--;
cpu->PC_reg += 1;
cpu->cycles += 2;
//Set the zero flag
if(!cpu->X_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->X_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//DEY
} else if(opcode == 0x88){
cpu->Y_reg--;
cpu->PC_reg += 1;
cpu->cycles += 2;
//Set the zero flag
if(!cpu->Y_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->Y_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//EOR
} else if(opcode == 0x49 || opcode == 0x45 || opcode == 0x55 || opcode == 0x4D || opcode == 0x5D || opcode == 0x59 || opcode == 0x41 || opcode == 0x51){
if(opcode == 0x49){//Immediate
value1 = read(cpu->PC_reg + 1);
cpu->PC_reg += 2;
cpu->cycles += 2;
} else if(opcode == 0x45){//Zero page
value1 = read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0x55){//Zero page X
value1 = read((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0x4D){//Absolute
value1 = get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
} else if(opcode == 0x5D){//Absolute X
value1 = get_absolute(cpu, cpu->X_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0x59){//Absolute Y
value1 = get_absolute(cpu, cpu->Y_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0x41){//Indirect X
value1 = get_indirect_X(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0x51){//Indirect Y
value1 = get_indirect_Y(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
if(CROSSED_PAGE){
cpu->cycles += 6;
} else {
cpu->cycles += 5;
}
}
cpu->A_reg ^= value1;
//Set the zero flag
if(!cpu->A_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->A_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//INC
} else if(opcode == 0xE6 || opcode == 0xF6 || opcode == 0xEE || opcode == 0xFE){
if(opcode == 0xE6){//Zero page
value2 = read(cpu->PC_reg + 1);
value1 = read(value2);
value1++;
write(value2, value1);
cpu->PC_reg += 2;
cpu->cycles += 5;
} else if(opcode == 0xF6){//Zero page X
value2 = read(cpu->PC_reg + 1);
value1 = read((value2 + cpu->X_reg)&0xFF);
value1++;
write((value2 + cpu->X_reg)&0xFF, value1);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0xEE){//Absolute
value1 = get_absolute(cpu, 0, read) + 1;
set_absolute(cpu, 0, read, write, value1);
cpu->PC_reg += 3;
cpu->cycles += 6;
} else if(opcode == 0xFE){//Absolute X
value1 = get_absolute(cpu, cpu->X_reg, read) + 1;
set_absolute(cpu, cpu->X_reg, read, write, value1);
cpu->PC_reg += 3;
cpu->cycles += 7;
}
//Set the zero flag
if(!value1){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(value1&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//INX
} else if(opcode == 0xE8){
cpu->X_reg++;
cpu->PC_reg += 1;
cpu->cycles += 2;
//Set the zero flag
if(!cpu->X_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->X_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//INY
} else if(opcode == 0xC8){
cpu->Y_reg++;
cpu->PC_reg += 1;
cpu->cycles += 2;
//Set the zero flag
if(!cpu->Y_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->Y_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//JMP
} else if(opcode == 0x4C || opcode == 0x6C){
if(opcode == 0x4C){//Absolute
cpu->PC_reg = ((uint16_t) read(cpu->PC_reg + 1)) | (((uint16_t) read(cpu->PC_reg + 2))<<8);
cpu->cycles += 3;
} else if(opcode == 0x6C){//Indirect
value_absolute = ((uint16_t) read(cpu->PC_reg + 1)) | (((uint16_t) read(cpu->PC_reg + 2))<<8);
value1 = read(value_absolute);
value2 = read((value_absolute&0xFF00) | ((value_absolute + 1)&0xFF));
cpu->PC_reg = (((uint16_t) value2)<<8) | value1;
cpu->cycles += 5;
}
//JSR
} else if(opcode == 0x20){
push(cpu, write, (cpu->PC_reg + 2)&0xFF);
push(cpu, write, (cpu->PC_reg + 2)>>8);
cpu->PC_reg = ((uint16_t) read(cpu->PC_reg + 1)) | (((uint16_t) read(cpu->PC_reg + 2))<<8);
cpu->cycles += 6;
//LDA
} else if(opcode == 0xA9 || opcode == 0xA5 || opcode == 0xB5 || opcode == 0xAD || opcode == 0xBD || opcode == 0xB9 || opcode == 0xA1 || opcode == 0xB1){
if(opcode == 0xA9){//Immediate
cpu->A_reg = read(cpu->PC_reg + 1);
cpu->PC_reg += 2;
cpu->cycles += 2;
} else if(opcode == 0xA5){//Zero page
cpu->A_reg = read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0xB5){//Zero page X
cpu->A_reg = read((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0xAD){//Absolute
cpu->A_reg = get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
} else if(opcode == 0xBD){//Absolute X
cpu->A_reg = get_absolute(cpu, cpu->X_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0xB9){//Absolute Y
cpu->A_reg = get_absolute(cpu, cpu->Y_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0xA1){//Indirect X
cpu->A_reg = get_indirect_X(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0xB1){//Indirect Y
cpu->A_reg = get_indirect_Y(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
if(CROSSED_PAGE){
cpu->cycles += 6;
} else {
cpu->cycles += 5;
}
}
//Set the zero flag
if(!cpu->A_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->A_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//LDX
} else if(opcode == 0xA2 || opcode == 0xA6 || opcode == 0xB6 || opcode == 0xAE || opcode == 0xBE){
if(opcode == 0xA2){//Immediate
cpu->X_reg = read(cpu->PC_reg + 1);
cpu->PC_reg += 2;
cpu->cycles += 2;
} else if(opcode == 0xA6){//Zero page
cpu->X_reg = read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0xB6){//Zero page Y
cpu->X_reg = read((read(cpu->PC_reg + 1) + cpu->Y_reg)&0xFF);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0xAE){//Absolute
cpu->X_reg = get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
} else if(opcode == 0xBE){//Absolute Y
cpu->X_reg = get_absolute(cpu, cpu->Y_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
}
//Set the zero flag
if(!cpu->X_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->X_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//LDY
} else if(opcode == 0xA0 || opcode == 0xA4 || opcode == 0xB4 || opcode == 0xAC || opcode == 0xBC){
if(opcode == 0xA0){//Immediate
cpu->Y_reg = read(cpu->PC_reg + 1);
cpu->PC_reg += 2;
cpu->cycles += 2;
} else if(opcode == 0xA4){//Zero page
cpu->Y_reg = read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0xB4){//Zero page X
cpu->Y_reg = read((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0xAC){//Absolute
cpu->Y_reg = get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
} else if(opcode == 0xBC){//Absolute X
cpu->Y_reg = get_absolute(cpu, cpu->X_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
}
//Set the zero flag
if(!cpu->Y_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->Y_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//LSR
} else if(opcode == 0x4A || opcode == 0x46 || opcode == 0x56 || opcode == 0x4E || opcode == 0x5E){
if(opcode == 0x4A){//Accumulator
value1 = cpu->A_reg;
cpu->A_reg >>= 1;
cpu->PC_reg++;
cpu->cycles += 2;
} else if(opcode == 0x46){//Zero page
value2 = read(cpu->PC_reg + 1);
value1 = read(value2);
write(value2, value1>>1);
cpu->PC_reg += 2;
cpu->cycles += 5;
} else if(opcode == 0x56){//Zero page X
value2 = read(cpu->PC_reg + 1);
value1 = read((value2 + cpu->X_reg)&0xFF);
write((value2 + cpu->X_reg)&0xFF, value1>>1);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0x4E){//Absolute
value1 = get_absolute(cpu, 0, read);
set_absolute(cpu, 0, read, write, value1>>1);
cpu->PC_reg += 3;
cpu->cycles += 6;
} else if(opcode == 0x5E){//Absolute X
value1 = get_absolute(cpu, cpu->X_reg, read);
set_absolute(cpu, cpu->X_reg, read, write, value1>>1);
cpu->PC_reg += 3;
cpu->cycles += 7;
}
//Set the carry flag
if(value1&0x1){
cpu->P_reg |= 1<<CARRY;
} else {
cpu->P_reg &= ~(1<<CARRY);
}
//Set the zero flag
if(!(value1>>1)){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//The negative flag is always set to zero
cpu->P_reg &= ~(1<<NEGATIVE);
//ORA
} else if(opcode == 0x09 || opcode == 0x05 || opcode == 0x15 || opcode == 0x0D || opcode == 0x1D || opcode == 0x19 || opcode == 0x01 || opcode == 0x11){
if(opcode == 0x09){//Immediate
cpu->A_reg |= read(cpu->PC_reg + 1);
cpu->PC_reg += 2;
cpu->cycles += 2;
} else if(opcode == 0x05){//Zero page
cpu->A_reg |= read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0x15){//Zero page X
cpu->A_reg |= read((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0x0D){//Absolute
cpu->A_reg |= get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
} else if(opcode == 0x1D){//Absolute X
cpu->A_reg |= get_absolute(cpu, cpu->X_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0x19){//Absolute Y
cpu->A_reg |= get_absolute(cpu, cpu->Y_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0x01){//Indirect X
cpu->A_reg |= get_indirect_X(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0x11){//Indirect Y
cpu->A_reg |= get_indirect_Y(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
if(CROSSED_PAGE){
cpu->cycles += 6;
} else {
cpu->cycles += 5;
}
}
//Set zero flag
if(!cpu->A_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set negative flag
if(cpu->A_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//PHA
} else if(opcode == 0x48){
push(cpu, write, cpu->A_reg);
cpu->PC_reg += 1;
cpu->cycles += 3;
//PHP (sucks)
} else if(opcode == 0x08){
push(cpu, write, cpu->P_reg);
cpu->PC_reg += 1;
cpu->cycles += 3;
//PLA
} else if(opcode == 0x68){
cpu->A_reg = pop(cpu, read);
cpu->PC_reg += 1;
cpu->cycles += 4;
//Set the zero flag
if(!cpu->A_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->A_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//PLP
} else if(opcode == 0x28){
cpu->P_reg = pop(cpu, read);
cpu->PC_reg += 1;
cpu->cycles += 4;
//ROL
} else if(opcode == 0x2A || opcode == 0x26 || opcode == 0x36 || opcode == 0x2E || opcode == 0x3E){
//Determine whether to append a 1 or 0 for bit 0
if(cpu->P_reg&(1<<CARRY)){
value2 = 1;
} else {
value2 = 0;
}
if(opcode == 0x2A){//Accumulator
value1 = cpu->A_reg;
cpu->A_reg = (value1<<1) | value2;
cpu->PC_reg += 1;
cpu->cycles += 2;
} else if(opcode == 0x26){//Zero page
value3 = read(cpu->PC_reg + 1);
value1 = read(value3);
write(value3, (value1<<1) | value2);
cpu->PC_reg += 2;
cpu->cycles += 5;
} else if(opcode == 0x36){//Zero page X
value3 = read(cpu->PC_reg + 1);
value1 = read((value3 + cpu->X_reg)&0xFF);
write((value3 + cpu->X_reg)&0xFF, (value1<<1) | value2);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0x2E){//Absolute
value1 = get_absolute(cpu, 0, read);
set_absolute(cpu, 0, read, write, (value1<<1) | value2);
cpu->PC_reg += 3;
cpu->cycles += 6;
} else if(opcode == 0x3E){//Absolute X
value1 = get_absolute(cpu, cpu->X_reg, read);
set_absolute(cpu, cpu->X_reg, read, write, (value1<<1) | value2);
cpu->PC_reg += 3;
cpu->cycles += 7;
}
value2 = (value1<<1) | value2;
//value1 stores the value before
//value2 stores the value after
//Set the carry flag
if(value1&0x80){
cpu->P_reg |= 1<<CARRY;
} else {
cpu->P_reg &= ~(1<<CARRY);
}
//Set the zero flag
if(!value2){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(value2&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//ROR
} else if(opcode == 0x6A || opcode == 0x66 || opcode == 0x76 || opcode == 0x6E || opcode == 0x7E){
//Determine whether to append a 1 or 0 for bit 7
if(cpu->P_reg&(1<<CARRY)){
value2 = 0x80;
} else {
value2 = 0;
}
if(opcode == 0x6A){//Accumulator
value1 = cpu->A_reg;
cpu->A_reg = (value1>>1) | value2;
cpu->PC_reg += 1;
cpu->cycles += 2;
} else if(opcode == 0x66){//Zero page
value3 = read(cpu->PC_reg + 1);
value1 = read(value3);
write(value3, (value1>>1) | value2);
cpu->PC_reg += 2;
cpu->cycles += 5;
} else if(opcode == 0x76){//Zero page X
value3 = read(cpu->PC_reg + 1);
value1 = read((value3 + cpu->X_reg)&0xFF);
write((value3 + cpu->X_reg)&0xFF, (value1>>1) | value2);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0x6E){//Absolute
value1 = get_absolute(cpu, 0, read);
set_absolute(cpu, 0, read, write, (value1>>1) | value2);
cpu->PC_reg += 3;
cpu->cycles += 6;
} else if(opcode == 0x7E){//Absolute X
value1 = get_absolute(cpu, cpu->X_reg, read);
set_absolute(cpu, cpu->X_reg, read, write, (value1>>1) | value2);
cpu->PC_reg += 3;
cpu->cycles += 7;
}
value2 = (value1>>1) | value2;
//value1 stores the value before
//value2 stores the value after
//Set the carry flag
if(value1&1){
cpu->P_reg |= 1<<CARRY;
} else {
cpu->P_reg &= ~(1<<CARRY);
}
//Set the zero flag
if(!value2){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(value2&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//RTI
} else if(opcode == 0x40){
cpu->P_reg = pop(cpu, read);
value1 = pop(cpu, read);
value2 = pop(cpu, read);
cpu->PC_reg = (((uint16_t) value1)<<8) | value2;
cpu->cycles += 6;
//RTS
} else if(opcode == 0x60){
value1 = pop(cpu, read);
value2 = pop(cpu, read);
cpu->PC_reg = (((uint16_t) value1)<<8) | value2;
cpu->PC_reg++;
cpu->cycles += 6;
//SBC
} else if(opcode == 0xE9 || opcode == 0xE5 || opcode == 0xF5 || opcode == 0xED || opcode == 0xFD || opcode == 0xF9 || opcode == 0xE1 || opcode == 0xF1){
if(opcode == 0xE9){//Immediate
value1 = read(cpu->PC_reg + 1);
cpu->PC_reg += 2;
cpu->cycles += 2;
} else if(opcode == 0xE5){//Zero page
value1 = read(read(cpu->PC_reg + 1));
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0xF5){//Zero page X
value1 = read((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0xED){//Absolute
value1 = get_absolute(cpu, 0, read);
cpu->PC_reg += 3;
cpu->cycles += 4;
} else if(opcode == 0xFD){//Absolute X
value1 = get_absolute(cpu, cpu->X_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0xF9){//Absolute Y
value1 = get_absolute(cpu, cpu->Y_reg, read);
cpu->PC_reg += 3;
if(CROSSED_PAGE){
cpu->cycles += 5;
} else {
cpu->cycles += 4;
}
} else if(opcode == 0xE1){//Indirect X
value1 = get_indirect_X(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0xF1){//Indirect Y
value1 = get_indirect_Y(cpu, read(cpu->PC_reg + 1), read);
cpu->PC_reg += 2;
if(CROSSED_PAGE){
cpu->cycles += 6;
} else {
cpu->cycles += 5;
}
}
value2 = cpu->A_reg;
value3 = (~value1);//One's complement
if(cpu->P_reg&(1<<CARRY)){
value3++;
cpu->A_reg += value3;
} else {
cpu->A_reg += value3;
}
//If the CPU is in decimal state, correct output
if((cpu->P_reg&(1<<DECIMAL)) && (cpu->A_reg&0xF) > 9){
cpu->A_reg -= 6;
}
//Set the overflow flag
if(((value2&0x80) && (value3&0x80) && !(cpu->A_reg&0x80)) || (!(value2&0x80) && !(value3&0x80) && (cpu->A_reg&0x80))){
cpu->P_reg |= 1<<OVERFLOW;
} else {
cpu->P_reg &= ~(1<<OVERFLOW);
}
//Set the carry flag
if(cpu->A_reg <= value2){
cpu->P_reg |= 1<<CARRY;
} else {
cpu->P_reg &= ~(1<<CARRY);
}
//Set the zero flag
if(!cpu->A_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->A_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//SEC
} else if(opcode == 0x38){
cpu->P_reg |= 1<<CARRY;
cpu->PC_reg += 1;
cpu->cycles += 2;
//SED
} else if(opcode == 0xF8){
cpu->P_reg |= 1<<DECIMAL;
cpu->PC_reg += 1;
cpu->cycles += 2;
//SEI
} else if(opcode == 0x78){
cpu->P_reg |= 1<<INTERRUPT;
cpu->PC_reg += 1;
cpu->cycles += 2;
//STA
} else if(opcode == 0x85 || opcode == 0x95 || opcode == 0x8D || opcode == 0x9D || opcode == 0x99 || opcode == 0x81 || opcode == 0x91){
if(opcode == 0x85){//Zero page
write(read(cpu->PC_reg + 1), cpu->A_reg);
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0x95){//Zero page X
write((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF, cpu->A_reg);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0x8D){//Absolute
set_absolute(cpu, 0, read, write, cpu->A_reg);
cpu->PC_reg += 3;
cpu->cycles += 4;
} else if(opcode == 0x9D){//Absolute X
set_absolute(cpu, cpu->X_reg, read, write, cpu->A_reg);
cpu->PC_reg += 3;
cpu->cycles += 5;
} else if(opcode == 0x99){//Absolute Y
set_absolute(cpu, cpu->Y_reg, read, write, cpu->A_reg);
cpu->PC_reg += 3;
cpu->cycles += 5;
} else if(opcode == 0x81){//Indirect X
set_indirect_X(cpu, read(cpu->PC_reg + 1), read, write, cpu->A_reg);
cpu->PC_reg += 2;
cpu->cycles += 6;
} else if(opcode == 0x91){//Indirect Y
set_indirect_Y(cpu, read(cpu->PC_reg + 1), read, write, cpu->A_reg);
cpu->PC_reg += 2;
cpu->cycles += 6;
}
//STX
} else if(opcode == 0x86 || opcode == 0x96 || opcode == 0x8E){
if(opcode == 0x86){//Zero page
write(read(cpu->PC_reg + 1), cpu->X_reg);
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0x96){//Zero page Y
write((read(cpu->PC_reg + 1) + cpu->Y_reg)&0xFF, cpu->X_reg);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0x8E){//Absolute
set_absolute(cpu, 0, read, write, cpu->X_reg);
cpu->PC_reg += 3;
cpu->cycles += 4;
}
//STY
} else if(opcode == 0x84 || opcode == 0x94 || opcode == 0x8C){
if(opcode == 0x84){//Zero page
write(read(cpu->PC_reg + 1), cpu->Y_reg);
cpu->PC_reg += 2;
cpu->cycles += 3;
} else if(opcode == 0x94){//Zero page X
write((read(cpu->PC_reg + 1) + cpu->X_reg)&0xFF, cpu->Y_reg);
cpu->PC_reg += 2;
cpu->cycles += 4;
} else if(opcode == 0x8C){//Absolute
set_absolute(cpu, 0, read, write, cpu->Y_reg);
cpu->PC_reg += 3;
cpu->cycles += 4;
}
//TAX
} else if(opcode == 0xAA){
cpu->X_reg = cpu->A_reg;
cpu->PC_reg += 1;
cpu->cycles += 2;
//Set the zero flag
if(!cpu->X_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->X_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//TAY
} else if(opcode == 0xA8){
cpu->Y_reg = cpu->A_reg;
cpu->PC_reg += 1;
cpu->cycles += 2;
//Set the zero flag
if(!cpu->Y_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->Y_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//TSX
} else if(opcode == 0xBA){
cpu->X_reg = cpu->SP_reg;
cpu->PC_reg += 1;
cpu->cycles += 2;
//Set the zero flag
if(!cpu->X_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->X_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//TXA
} else if(opcode == 0x8A){
cpu->A_reg = cpu->X_reg;
cpu->PC_reg += 1;
cpu->cycles += 2;
//Set the zero flag
if(!cpu->A_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->A_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//TXS
} else if(opcode == 0x9A){
cpu->SP_reg = cpu->X_reg;
cpu->PC_reg += 1;
cpu->cycles += 2;
//TYA
} else if(opcode == 0x98){
cpu->A_reg = cpu->Y_reg;
cpu->PC_reg += 1;
cpu->cycles += 2;
//Set the zero flag
if(!cpu->A_reg){
cpu->P_reg |= 1<<ZERO;
} else {
cpu->P_reg &= ~(1<<ZERO);
}
//Set the negative flag
if(cpu->A_reg&0x80){
cpu->P_reg |= 1<<NEGATIVE;
} else {
cpu->P_reg &= ~(1<<NEGATIVE);
}
//NOP
} else if(opcode == 0xEA){
cpu->PC_reg += 1;
cpu->cycles += 2;
//Unknown operation
} else {
printw("Error: Unknown operation 0x%x\n", (int) opcode);
exit(1);
}
}
void reset_6502(CPU_6502 *cpu, uint8_t (*read)(uint16_t)){
cpu->SP_reg -= 3;//This actually happens on the chip
cpu->PC_reg = ((uint16_t) read(0xFFFD))<<8 | read(0xFFFC);
}
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