/*
____ _ _ _ ______ _____
| _ \ | | \ | | ____|/ ____|
| |_) | __ _ __| | \| | |__ | (___
| _ < / _` |/ _` | . ` | __| \___ \
| |_) | (_| | (_| | |\ | |____ ____) |
|____/ \__,_|\__,_|_| \_|______|_____/
EMULATOR
*/
#include <bits/stdc++.h>
#include <SDL2/SDL.h>
#define NTH_BIT(x, n) (((x) >> (n)) & 1)
typedef uint8_t u8; typedef int8_t s8;
typedef uint16_t u16; typedef int16_t s16;
typedef uint32_t u32; typedef int32_t s32;
typedef uint64_t u64; typedef int64_t s64;
typedef long cpu_time_t; // CPU clock cycle count
typedef unsigned cpu_addr_t; // 16-bit memory address
// Initial declarations
namespace APU {
template <bool write> u8 access(int elapsed, u16 addr, u8 v = 0);
}
namespace CPU {
enum IntType { NMI, RESET, IRQ, BRK }; // Interrupt type
typedef u16 (*Mode)(void); // Addressing mode
enum Flag { C, Z, I, D, V, N }; // Processor flags
class Flags { bool f[6]; public:
bool& operator[] (const int i) { return f[i]; }
u8 get() { return f[C] | f[Z] << 1 | f[I] << 2 | f[D] << 3 | 1 << 5 | f[V] << 6 | f[N] << 7; }
void set(u8 p) { f[C] = NTH_BIT(p, 0), f[Z] = NTH_BIT(p, 1), f[I] = NTH_BIT(p, 2), f[D] = NTH_BIT(p, 3), f[V] = NTH_BIT(p, 6), f[N] = NTH_BIT(p, 7); }
};
int dmc_read(void*, cpu_addr_t addr);
void set_nmi(bool v = true), set_irq(bool v = true), power(), run_frame();
}
namespace PPU {
enum Scanline { VISIBLE, POST, NMI, PRE };
enum Mirroring { VERTICAL, HORIZONTAL };
struct Sprite { // Sprite buffer
// Index in OAM, X position, Y position, Tile index, Attributes, Tile data (low), Tile data (high)
u8 id, x, y, tile, attr, dataL, dataH;
};
union Ctrl { // PPUCTRL ($2000) register
struct {
// Nametable, Address increment, Sprite pattern table, BG pattern table, Sprite size, PPU master/slave, Enable NMI
unsigned nt : 2, incr : 1, sprTbl : 1, bgTbl : 1, sprSz : 1, slave : 1, nmi : 1;
};
u8 r;
};
union Mask { // PPUMASK ($2001) register
struct {
// Grayscale; Show background in leftmost 8 pixels, sprite in leftmost 8 pixels, background, sprites; Intensify reds, greens, blues
unsigned gray : 1, bgLeft : 1, sprLeft : 1, bg : 1, spr : 1, red : 1, green : 1, blue : 1;
};
u8 r;
};
union Status { // PPUSTATUS ($2002) register
struct {
// Not significant, Sprite overflow, Sprite 0 Hit, In VBlank
unsigned bus : 5, sprOvf : 1, sprHit : 1, vBlank : 1;
};
u8 r;
};
union Addr { // Loopy's VRAM address
struct {
// Coarse X, Coarse Y, Nametable, Fine Y
unsigned cX : 5, cY : 5, nt : 2, fY : 3;
};
struct { unsigned l : 8, h : 7; };
unsigned addr : 14, r : 15;
};
template <bool write> u8 access(u16 index, u8 v = 0);
void set_mirroring(Mirroring mode), step(), reset();
}
namespace Cartridge {
template <bool wr> u8 access(u16 addr, u8 v = 0); template <bool wr> u8 chr_access(u16 addr, u8 v = 0);
void signal_scanline(), load(const char *fileName);
}
namespace Joypad {
u8 read_state(int n); void write_strobe(bool v);
}
namespace GUI {
const unsigned WIDTH = 256, HEIGHT = 240; // Screen size
int query_button();
void init(), run();
void new_frame(u32* pixels);
u8 get_joypad_state(int n);
SDL_Scancode query_key();
}
// Mappers
class Mapper {
u8* rom; bool chrRam = false;
protected:
u8 *prg, *chr, *prgRam;
u32 prgSize, chrSize, prgRamSize, prgMap[4], chrMap[8];
template <int pageKBs> void map_prg(int slot, int bank);
template <int pageKBs> void map_chr(int slot, int bank);
public:
Mapper(u8* rom);
~Mapper();
u8 read(u16 addr), chr_read(u16 addr);
virtual u8 write(u16 addr, u8 v) { return v; }
virtual u8 chr_write(u16 addr, u8 v) { return v; }
virtual void signal_scanline() {}
};
Mapper::Mapper(u8* rom) : rom(rom) {
// Read infos from header
prgSize = rom[4] * 0x4000, chrSize = rom[5] * 0x2000;
prgRamSize = rom[8] ? rom[8] * 0x2000 : 0x2000;
set_mirroring((rom[6] & 1) ? PPU::VERTICAL : PPU::HORIZONTAL);
this->prg = rom + 16, this->prgRam = new u8[prgRamSize];
if (chrSize) this->chr = rom + 16 + prgSize; // CHR ROM
else { chrRam = true, chrSize = 0x2000, this->chr = new u8[chrSize]; } // CHR RAM
}
Mapper::~Mapper() { delete rom; delete prgRam; if (chrRam) delete chr; }
// Access to memory
u8 Mapper::read(u16 addr) { return addr >= 0x8000 ? prg[prgMap[(addr - 0x8000) / 0x2000] + ((addr - 0x8000) % 0x2000)] : prgRam[addr - 0x6000]; }
u8 Mapper::chr_read(u16 addr) { return chr[chrMap[addr / 0x400] + (addr % 0x400)]; }
// PRG mapping functions
template <int pageKBs> void Mapper::map_prg(int slot, int bank) {
if (bank < 0) bank = (prgSize / (0x400*pageKBs)) + bank;
for (int i = 0; i < (pageKBs/8); i++) prgMap[(pageKBs/8) * slot + i] = (pageKBs*0x400*bank + 0x2000*i) % prgSize;
}
template void Mapper::map_prg<32>(int, int);
template void Mapper::map_prg<16>(int, int);
template void Mapper::map_prg<8> (int, int);
// CHR mapping functions
template <int pageKBs> void Mapper::map_chr(int slot, int bank) {
for (int i = 0; i < pageKBs; i++) chrMap[pageKBs*slot + i] = (pageKBs*0x400*bank + 0x400*i) % chrSize;
}
template void Mapper::map_chr<8>(int, int);
template void Mapper::map_chr<4>(int, int);
template void Mapper::map_chr<2>(int, int);
template void Mapper::map_chr<1>(int, int);
class Mapper0 : public Mapper {
public: Mapper0(u8* rom) : Mapper(rom) { map_prg<32>(0, 0); map_chr<8> (0, 0); }
};
class Mapper1 : public Mapper {
int writeN; u8 tmpReg, regs[4];
// Apply the registers state
void apply() {
if (regs[0] & 0b1000) { // 16KB PRG
// 0x8000 swappable, 0xC000 fixed to bank 0x0F
if (regs[0] & 0b100) { map_prg<16>(0, regs[3] & 0xF); map_prg<16>(1, 0xF); }
// 0x8000 fixed to bank 0x00, 0xC000 swappable
else { map_prg<16>(0, 0); map_prg<16>(1, regs[3] & 0xF); }
}
else map_prg<32>(0, (regs[3] & 0xF) >> 1); // 32KB PRG
if (regs[0] & 0b10000) { map_chr<4>(0, regs[1]); map_chr<4>(1, regs[2]); } // 4KB CHR
else map_chr<8>(0, regs[1] >> 1); // 8KB CHR
switch (regs[0] & 0b11) { // Set mirroring
case 2: set_mirroring(PPU::VERTICAL); break;
case 3: set_mirroring(PPU::HORIZONTAL); break;
}
}
public:
Mapper1(u8* rom) : Mapper(rom) {
regs[0] = 0x0C;
writeN = tmpReg = regs[1] = regs[2] = regs[3] = 0;
apply();
}
u8 write(u16 addr, u8 v) {
if (addr < 0x8000) prgRam[addr - 0x6000] = v; // PRG RAM write
else if (addr & 0x8000) { // Mapper register write
if (v & 0x80) { writeN = tmpReg = 0; regs[0] |= 0x0C; apply(); } // Reset
else {
tmpReg = ((v & 1) << 4) | (tmpReg >> 1); // Write a bit into the temporary register
if (++writeN == 5) { regs[(addr >> 13) & 0b11] = tmpReg; writeN = tmpReg = 0; apply(); } // Finished writing all the bits
}
}
return v;
}
u8 chr_write(u16 addr, u8 v) { return chr[addr] = v; }
};
class Mapper2 : public Mapper {
u8 regs[1]; bool vertical_mirroring;
// Apply the registers state
void apply() {
// 16 kb PRG ROM Banks: 0x8000 - 0xBFFF swappable, 0xC000 - 0xFFFF fixed
map_prg<16>(0, regs[0] & 0xF); map_prg<16>(1, 0xF);
map_chr<8>(0, 0); // 8k of CHR
set_mirroring(vertical_mirroring?PPU::VERTICAL:PPU::HORIZONTAL); // mirroring is based on the header (soldered)
}
public:
Mapper2(u8* rom) : Mapper(rom) {
regs[0] = 0;
vertical_mirroring = rom[6] & 0x01;
apply();
}
u8 write(u16 addr, u8 v) {
if (addr & 0x8000) { regs[0] = v; apply(); } // bank switching
return v;
}
u8 chr_write(u16 addr, u8 v) { return chr[addr] = v; }
};
class Mapper3 : public Mapper {
u8 regs[1]; bool vertical_mirroring, PRG_size_16k;
// Apply the registers state
void apply() {
if (PRG_size_16k) { map_prg<16>(0,0); map_prg<16>(1,0); } // mirror the bottom on the top: 0x8000 - 0xBFFF == 0xC000 - 0xFFFF
else { map_prg<16>(0,0); map_prg<16>(1,1); } // no mirroring
map_chr<8>(0, regs[0] & 0b11); // 8k bankswitched CHR
set_mirroring(vertical_mirroring?PPU::VERTICAL:PPU::HORIZONTAL); // mirroring is based on the header (soldered)
}
public:
Mapper3(u8* rom) : Mapper(rom) {
PRG_size_16k = rom[4] == 1;
vertical_mirroring = rom[6] & 0x01;
regs[0] = 0;
apply();
}
u8 write(u16 addr, u8 v) {
if (addr & 0x8000) { regs[0] = v; apply(); } // chr bank switching
return v;
}
u8 chr_write(u16 addr, u8 v) { return chr[addr] = v; }
};
class Mapper4 : public Mapper {
u8 reg8000, regs[8], irqPeriod, irqCounter; bool horizMirroring, irqEnabled;
// Apply the registers state
void apply() {
map_prg<8>(1, regs[7]);
if (!(reg8000 & (1 << 6))) { map_prg<8>(0, regs[6]); map_prg<8>(2, -2); } // PRG Mode 0
else { map_prg<8>(0, -2); map_prg<8>(2, regs[6]); } // PRG Mode 1
if (!(reg8000 & (1 << 7))) { // CHR Mode 0
map_chr<2>(0, regs[0] >> 1); map_chr<2>(1, regs[1] >> 1);
for (int i = 0; i < 4; i++) map_chr<1>(4 + i, regs[2 + i]);
}
else { // CHR Mode 1
for (int i = 0; i < 4; i++) map_chr<1>(i, regs[2 + i]);
map_chr<2>(2, regs[0] >> 1); map_chr<2>(3, regs[1] >> 1);
}
set_mirroring(horizMirroring ? PPU::HORIZONTAL : PPU::VERTICAL);
}
public:
Mapper4(u8* rom) : Mapper(rom) {
for (int i = 0; i < 8; i++) regs[i] = 0;
horizMirroring = true; irqEnabled = false; irqPeriod = irqCounter = 0;
map_prg<8>(3, -1);
apply();
}
u8 write(u16 addr, u8 v) {
if (addr < 0x8000) prgRam[addr - 0x6000] = v;
else if (addr & 0x8000) {
switch (addr & 0xE001) {
case 0x8000: reg8000 = v; break;
case 0x8001: regs[reg8000 & 0b111] = v; break;
case 0xA000: horizMirroring = v & 1; break;
case 0xC000: irqPeriod = v; break;
case 0xC001: irqCounter = 0; break;
case 0xE000: CPU::set_irq(irqEnabled = false); break;
case 0xE001: irqEnabled = true; break;
}
apply();
}
return v;
}
u8 chr_write(u16 addr, u8 v) { return chr[addr] = v; }
void signal_scanline() {
irqCounter == 0 ? irqCounter = irqPeriod : --irqCounter;
if (irqEnabled and irqCounter == 0) CPU::set_irq();
}
};
// Actual code
namespace APU {
const int OUT_SIZE = 4096;
template <bool write> u8 access(int elapsed, u16 addr, u8 v) { return v; }
template u8 access<0>(int, u16, u8); template u8 access<1>(int, u16, u8);
}
namespace CPU {
u8 A, X, Y, S, ram[0x800]; u16 PC; Flags P; bool nmi, irq; // CPU state
// Remaining clocks to end frame
const int TOTAL_CYCLES = 29781; int remainingCycles;
inline int elapsed() { return TOTAL_CYCLES - remainingCycles; }
// Cycle emulation
#define T tick()
inline void tick() { PPU::step(); PPU::step(); PPU::step(); remainingCycles--; }
// Flags updating
inline void upd_cv(u8 x, u8 y, s16 r) { P[C] = (r>0xFF); P[V] = ~(x^y) & (x^r) & 0x80; }
inline void upd_nz(u8 x) { P[N] = x & 0x80; P[Z] = (x == 0); }
inline bool cross(u16 a, u8 i) { return ((a+i) & 0xFF00) != ((a & 0xFF00)); } // Does adding I to A cross a page?
// Memory access
void dma_oam(u8 bank);
template<bool wr> inline u8 access(u16 addr, u8 v = 0) {
u8* r;
switch (addr) {
case 0x0000 ... 0x1FFF: r = &ram[addr % 0x800]; if (wr) *r = v; return *r; // RAM
case 0x2000 ... 0x3FFF: return PPU::access<wr>(addr % 8, v); // PPU
case 0x4000 ... 0x4013: // APU
case 0x4015: return APU::access<wr>(elapsed(), addr, v);
case 0x4017: if (wr) return APU::access<wr>(elapsed(), addr, v);
else return Joypad::read_state(1); // Joypad 1
case 0x4014: if (wr) dma_oam(v); break; // OAM DMA
case 0x4016: if (wr) { Joypad::write_strobe(v & 1); break; } // Joypad strobe
else return Joypad::read_state(0); // Joypad 0
case 0x4018 ... 0xFFFF: return Cartridge::access<wr>(addr, v); // Cartridge
}
return 0;
}
inline u8 wr(u16 a, u8 v) { T; return access<1>(a, v); }
inline u8 rd(u16 a) { T; return access<0>(a); }
inline u16 rd16_d(u16 a, u16 b) { return rd(a) | (rd(b) << 8); } // Read from A and B and merge
inline u16 rd16(u16 a) { return rd16_d(a, a+1); }
inline u8 push(u8 v) { return wr(0x100 + (S--), v); }
inline u8 pop() { return rd(0x100 + (++S)); }
void dma_oam(u8 bank) { for (int i = 0; i < 256; i++) wr(0x2014, rd(bank*0x100 + i)); }
// Addressing modes
inline u16 imm() { return PC++; }
inline u16 imm16() { PC += 2; return PC - 2; }
inline u16 abs() { return rd16(imm16()); }
inline u16 _abx() { T; return abs() + X; } // Exception
inline u16 abx() { u16 a = abs(); if (cross(a, X)) T; return a + X; }
inline u16 aby() { u16 a = abs(); if (cross(a, Y)) T; return a + Y; }
inline u16 zp() { return rd(imm()); }
inline u16 zpx() { T; return (zp() + X) % 0x100; }
inline u16 zpy() { T; return (zp() + Y) % 0x100; }
inline u16 izx() { u8 i = zpx(); return rd16_d(i, (i+1) % 0x100); }
inline u16 _izy() { u8 i = zp(); return rd16_d(i, (i+1) % 0x100) + Y; } // Exception
inline u16 izy() { u16 a = _izy(); if (cross(a-Y, Y)) T; return a; }
// STx
template<u8& r, Mode m> void st() { wr( m() , r); }
template<> void st<A,izy>() { T; wr(_izy() , A); } // Exceptions
template<> void st<A,abx>() { T; wr( abs() + X, A); } // ...
template<> void st<A,aby>() { T; wr( abs() + Y, A); } // ...
#define G u16 a = m(); u8 p = rd(a) // Fetch parameter
template<u8& r, Mode m> void ld() { G; upd_nz(r = p); } // LDx
template<u8& r, Mode m> void cmp() { G; upd_nz(r - p); P[C] = (r >= p); } // CMP, CPx
// Arithmetic and bitwise
template<Mode m> void ADC() { G ; s16 r = A + p + P[C]; upd_cv(A, p, r); upd_nz(A = r); }
template<Mode m> void SBC() { G ^ 0xFF; s16 r = A + p + P[C]; upd_cv(A, p, r); upd_nz(A = r); }
template<Mode m> void BIT() { G; P[Z] = !(A & p); P[N] = p & 0x80; P[V] = p & 0x40; }
template<Mode m> void AND() { G; upd_nz(A &= p); }
template<Mode m> void EOR() { G; upd_nz(A ^= p); }
template<Mode m> void ORA() { G; upd_nz(A |= p); }
// Read-Modify-Write
template<Mode m> void ASL() { G; P[C] = p & 0x80; T; upd_nz(wr(a, p << 1)); }
template<Mode m> void LSR() { G; P[C] = p & 0x01; T; upd_nz(wr(a, p >> 1)); }
template<Mode m> void ROL() { G; u8 c = P[C] ; P[C] = p & 0x80; T; upd_nz(wr(a, (p << 1) | c) ); }
template<Mode m> void ROR() { G; u8 c = P[C] << 7; P[C] = p & 0x01; T; upd_nz(wr(a, c | (p >> 1)) ); }
template<Mode m> void DEC() { G; T; upd_nz(wr(a, --p)); }
template<Mode m> void INC() { G; T; upd_nz(wr(a, ++p)); }
#undef G
// DEx, INx
template<u8& r> void dec() { upd_nz(--r); T; }
template<u8& r> void inc() { upd_nz(++r); T; }
// Bit shifting on the accumulator
void ASL_A() { P[C] = A & 0x80; upd_nz(A <<= 1); T; }
void LSR_A() { P[C] = A & 0x01; upd_nz(A >>= 1); T; }
void ROL_A() { u8 c = P[C] ; P[C] = A & 0x80; upd_nz(A = ((A << 1) | c) ); T; }
void ROR_A() { u8 c = P[C] << 7; P[C] = A & 0x01; upd_nz(A = (c | (A >> 1)) ); T; }
// Txx (move values between registers)
template<u8& s, u8& d> void tr() { upd_nz(d = s); T; }
template<> void tr<X,S>() { S = X; T; } // TSX, exception
// Stack operations
void PLP() { T; T; P.set(pop()); }
void PHP() { T; push(P.get() | (1 << 4)); } // B flag set.
void PLA() { T; T; A = pop(); upd_nz(A); }
void PHA() { T; push(A); }
// Flow control (branches, jumps)
template<Flag f, bool v> void br() {
s8 j = rd(imm());
if (P[f] == v) {
if (cross(PC, j)) T;
T; PC += j;
}
}
void JMP_IND() { u16 i = rd16(imm16()); PC = rd16_d(i, (i&0xFF00) | ((i+1) % 0x100)); }
void JMP() { PC = rd16(imm16()); }
void JSR() { u16 t = PC+1; T; push(t >> 8); push(t); PC = rd16(imm16()); }
// Return instructions
void RTS() { T; T; PC = (pop() | (pop() << 8)) + 1; T; }
void RTI() { PLP(); PC = pop() | (pop() << 8); }
template<Flag f, bool v> void flag() { P[f] = v; T; } // Clear and set flags.
template<IntType t> void INT() {
T; if (t != BRK) T; // BRK already performed the fetch
if (t != RESET) { // Writes on stack are inhibited on RESET
push(PC >> 8); push(PC & 0xFF);
push(P.get() | ((t == BRK) << 4)); // Set B if BRK
}
else { S -= 3; T; T; T; }
P[I] = true; // NMI Reset IRQ BRK
constexpr u16 vect[] = { 0xFFFA, 0xFFFC, 0xFFFE, 0xFFFE };
PC = rd16(vect[t]);
if (t == NMI) nmi = false;
}
void NOP() { T; }
// Execute a CPU instruction
void exec() {
switch (rd(PC++)) { // Fetch the opcode and select the right function to emulate the instruction:
case 0x00: return INT<BRK>() ; case 0x01: return ORA<izx>() ; case 0x05: return ORA<zp>() ; case 0x06: return ASL<zp>() ;
case 0x08: return PHP() ; case 0x09: return ORA<imm>() ; case 0x0A: return ASL_A() ; case 0x0D: return ORA<abs>() ;
case 0x0E: return ASL<abs>() ; case 0x10: return br<N,0>() ; case 0x11: return ORA<izy>() ; case 0x15: return ORA<zpx>() ;
case 0x16: return ASL<zpx>() ; case 0x18: return flag<C,0>() ; case 0x19: return ORA<aby>() ; case 0x1D: return ORA<abx>() ;
case 0x1E: return ASL<_abx>() ; case 0x20: return JSR() ; case 0x21: return AND<izx>() ; case 0x24: return BIT<zp>() ;
case 0x25: return AND<zp>() ; case 0x26: return ROL<zp>() ; case 0x28: return PLP() ; case 0x29: return AND<imm>() ;
case 0x2A: return ROL_A() ; case 0x2C: return BIT<abs>() ; case 0x2D: return AND<abs>() ; case 0x2E: return ROL<abs>() ;
case 0x30: return br<N,1>() ; case 0x31: return AND<izy>() ; case 0x35: return AND<zpx>() ; case 0x36: return ROL<zpx>() ;
case 0x38: return flag<C,1>() ; case 0x39: return AND<aby>() ; case 0x3D: return AND<abx>() ; case 0x3E: return ROL<_abx>() ;
case 0x40: return RTI() ; case 0x41: return EOR<izx>() ; case 0x45: return EOR<zp>() ; case 0x46: return LSR<zp>() ;
case 0x48: return PHA() ; case 0x49: return EOR<imm>() ; case 0x4A: return LSR_A() ; case 0x4C: return JMP() ;
case 0x4D: return EOR<abs>() ; case 0x4E: return LSR<abs>() ; case 0x50: return br<V,0>() ; case 0x51: return EOR<izy>() ;
case 0x55: return EOR<zpx>() ; case 0x56: return LSR<zpx>() ; case 0x58: return flag<I,0>() ; case 0x59: return EOR<aby>() ;
case 0x5D: return EOR<abx>() ; case 0x5E: return LSR<_abx>() ; case 0x60: return RTS() ; case 0x61: return ADC<izx>() ;
case 0x65: return ADC<zp>() ; case 0x66: return ROR<zp>() ; case 0x68: return PLA() ; case 0x69: return ADC<imm>() ;
case 0x6A: return ROR_A() ; case 0x6C: return JMP_IND() ; case 0x6D: return ADC<abs>() ; case 0x6E: return ROR<abs>() ;
case 0x70: return br<V,1>() ; case 0x71: return ADC<izy>() ; case 0x75: return ADC<zpx>() ; case 0x76: return ROR<zpx>() ;
case 0x78: return flag<I,1>() ; case 0x79: return ADC<aby>() ; case 0x7D: return ADC<abx>() ; case 0x7E: return ROR<_abx>() ;
case 0x81: return st<A,izx>() ; case 0x84: return st<Y,zp>() ; case 0x85: return st<A,zp>() ; case 0x86: return st<X,zp>() ;
case 0x88: return dec<Y>() ; case 0x8A: return tr<X,A>() ; case 0x8C: return st<Y,abs>() ; case 0x8D: return st<A,abs>() ;
case 0x8E: return st<X,abs>() ; case 0x90: return br<C,0>() ; case 0x91: return st<A,izy>() ; case 0x94: return st<Y,zpx>() ;
case 0x95: return st<A,zpx>() ; case 0x96: return st<X,zpy>() ; case 0x98: return tr<Y,A>() ; case 0x99: return st<A,aby>() ;
case 0x9A: return tr<X,S>() ; case 0x9D: return st<A,abx>() ; case 0xA0: return ld<Y,imm>() ; case 0xA1: return ld<A,izx>() ;
case 0xA2: return ld<X,imm>() ; case 0xA4: return ld<Y,zp>() ; case 0xA5: return ld<A,zp>() ; case 0xA6: return ld<X,zp>() ;
case 0xA8: return tr<A,Y>() ; case 0xA9: return ld<A,imm>() ; case 0xAA: return tr<A,X>() ; case 0xAC: return ld<Y,abs>() ;
case 0xAD: return ld<A,abs>() ; case 0xAE: return ld<X,abs>() ; case 0xB0: return br<C,1>() ; case 0xB1: return ld<A,izy>() ;
case 0xB4: return ld<Y,zpx>() ; case 0xB5: return ld<A,zpx>() ; case 0xB6: return ld<X,zpy>() ; case 0xB8: return flag<V,0>() ;
case 0xB9: return ld<A,aby>() ; case 0xBA: return tr<S,X>() ; case 0xBC: return ld<Y,abx>() ; case 0xBD: return ld<A,abx>() ;
case 0xBE: return ld<X,aby>() ; case 0xC0: return cmp<Y,imm>(); case 0xC1: return cmp<A,izx>(); case 0xC4: return cmp<Y,zp>() ;
case 0xC5: return cmp<A,zp>() ; case 0xC6: return DEC<zp>() ; case 0xC8: return inc<Y>() ; case 0xC9: return cmp<A,imm>();
case 0xCA: return dec<X>() ; case 0xCC: return cmp<Y,abs>(); case 0xCD: return cmp<A,abs>(); case 0xCE: return DEC<abs>() ;
case 0xD0: return br<Z,0>() ; case 0xD1: return cmp<A,izy>(); case 0xD5: return cmp<A,zpx>(); case 0xD6: return DEC<zpx>() ;
case 0xD8: return flag<D,0>() ; case 0xD9: return cmp<A,aby>(); case 0xDD: return cmp<A,abx>(); case 0xDE: return DEC<_abx>() ;
case 0xE0: return cmp<X,imm>(); case 0xE1: return SBC<izx>() ; case 0xE4: return cmp<X,zp>() ; case 0xE5: return SBC<zp>() ;
case 0xE6: return INC<zp>() ; case 0xE8: return inc<X>() ; case 0xE9: return SBC<imm>() ; case 0xEA: return NOP() ;
case 0xEC: return cmp<X,abs>(); case 0xED: return SBC<abs>() ; case 0xEE: return INC<abs>() ; case 0xF0: return br<Z,1>() ;
case 0xF1: return SBC<izy>() ; case 0xF5: return SBC<zpx>() ; case 0xF6: return INC<zpx>() ; case 0xF8: return flag<D,1>() ;
case 0xF9: return SBC<aby>() ; case 0xFD: return SBC<abx>() ; case 0xFE: return INC<_abx>() ; default:
std::cout << "Invalid Opcode! PC: " << PC << " Opcode: 0x" << std::hex << (int)(rd(PC - 1)) << "\n";
return NOP();
}
}
void set_nmi(bool v) { nmi = v; }
void set_irq(bool v) { irq = v; }
int dmc_read(void*, cpu_addr_t addr) { return access<0>(addr); }
// Turn on the CPU
void power() {
remainingCycles = 0;
P.set(0x04);
A = X = Y = S = 0x00;
memset(ram, 0xFF, sizeof(ram));
nmi = irq = false;
INT<RESET>();
}
// Run the CPU for roughly a frame
void run_frame() {
remainingCycles += TOTAL_CYCLES;
while (remainingCycles > 0) {
if (nmi) INT<NMI>();
else if (irq and !P[I]) INT<IRQ>();
exec();
}
}
}
namespace PPU {
u32 nesRgb[] = { 0x7C7C7C, 0x0000FC, 0x0000BC, 0x4428BC, 0x940084, 0xA80020, 0xA81000, 0x881400,
0x503000, 0x007800, 0x006800, 0x005800, 0x004058, 0x000000, 0x000000, 0x000000,
0xBCBCBC, 0x0078F8, 0x0058F8, 0x6844FC, 0xD800CC, 0xE40058, 0xF83800, 0xE45C10,
0xAC7C00, 0x00B800, 0x00A800, 0x00A844, 0x008888, 0x000000, 0x000000, 0x000000,
0xF8F8F8, 0x3CBCFC, 0x6888FC, 0x9878F8, 0xF878F8, 0xF85898, 0xF87858, 0xFCA044,
0xF8B800, 0xB8F818, 0x58D854, 0x58F898, 0x00E8D8, 0x787878, 0x000000, 0x000000,
0xFCFCFC, 0xA4E4FC, 0xB8B8F8, 0xD8B8F8, 0xF8B8F8, 0xF8A4C0, 0xF0D0B0, 0xFCE0A8,
0xF8D878, 0xD8F878, 0xB8F8B8, 0xB8F8D8, 0x00FCFC, 0xF8D8F8, 0x000000, 0x000000 };
Mirroring mirroring; // Mirroring mode
u8 ciRam[0x800], cgRam[0x20], oamMem[0x100]; // VRAM for nametables, palettes, sprite properties
Sprite oam[8], secOam[8]; // Sprite buffers
u32 pixels[256 * 240]; // Video buffer
Addr vAddr, tAddr; // Loopy V, T
u8 fX, oamAddr; // Fine X, OAM address
Ctrl ctrl; // PPUCTRL ($2000) register
Mask mask; // PPUMASK ($2001) register
Status status; // PPUSTATUS ($2002) register
u8 nt, at, bgL, bgH, atShiftL, atShiftH; u16 bgShiftL, bgShiftH; // Background latches, shift registers
bool atLatchL, atLatchH;
int scanline, dot; bool frameOdd; // Rendering counters
inline bool rendering() { return mask.bg || mask.spr; }
inline int spr_height() { return ctrl.sprSz ? 16 : 8; }
// Get CIRAM address according to mirroring
u16 nt_mirror(u16 addr) {
switch (mirroring) {
case VERTICAL: return addr % 0x800;
case HORIZONTAL: return ((addr / 2) & 0x400) + (addr % 0x400);
default: return addr - 0x2000;
}
}
void set_mirroring(Mirroring mode) { mirroring = mode; }
// Access PPU memory
u8 rd(u16 addr) {
switch (addr) {
case 0x0000 ... 0x1FFF: return Cartridge::chr_access<0>(addr); // CHR-ROM/RAM
case 0x2000 ... 0x3EFF: return ciRam[nt_mirror(addr)]; // Nametables
case 0x3F00 ... 0x3FFF: // Palettes
if ((addr & 0x13) == 0x10) addr &= ~0x10;
return cgRam[addr & 0x1F] & (mask.gray ? 0x30 : 0xFF);
default: return 0;
}
}
void wr(u16 addr, u8 v) {
switch (addr) {
case 0x0000 ... 0x1FFF: Cartridge::chr_access<1>(addr, v); break; // CHR-ROM/RAM
case 0x2000 ... 0x3EFF: ciRam[nt_mirror(addr)] = v; break; // Nametables
case 0x3F00 ... 0x3FFF: // Palettes
if ((addr & 0x13) == 0x10) addr &= ~0x10;
cgRam[addr & 0x1F] = v; break;
}
}
// Access PPU through registers
template <bool write> u8 access(u16 index, u8 v) {
static u8 res, buffer; // VRAM read buffer
static bool latch; // Detect second reading
// Write into register
if (write) {
res = v;
switch (index) {
case 0: ctrl.r = v; tAddr.nt = ctrl.nt; break; // PPUCTRL ($2000)
case 1: mask.r = v; break; // PPUMASK ($2001)
case 3: oamAddr = v; break; // OAMADDR ($2003)
case 4: oamMem[oamAddr++] = v; break; // OAMDATA ($2004)
case 5: // PPUSCROLL ($2005)
if (!latch) { fX = v & 7; tAddr.cX = v >> 3; } // First write
else { tAddr.fY = v & 7; tAddr.cY = v >> 3; } // Second write
latch = !latch; break;
case 6: // PPUADDR ($2006)
if (!latch) { tAddr.h = v & 0x3F; } // First write
else { tAddr.l = v; vAddr.r = tAddr.r; } // Second write
latch = !latch; break;
case 7: wr(vAddr.addr, v); vAddr.addr += ctrl.incr ? 32 : 1; // PPUDATA ($2007)
}
}
else { // Read from register
switch (index) { // PPUSTATUS ($2002)
case 2: res = (res & 0x1F) | status.r; status.vBlank = 0; latch = 0; break;
case 4: res = oamMem[oamAddr]; break; // OAMDATA ($2004)
case 7: // PPUDATA ($2007)
if (vAddr.addr <= 0x3EFF) res = buffer, buffer = rd(vAddr.addr);
else res = buffer = rd(vAddr.addr), vAddr.addr += ctrl.incr ? 32 : 1;
}
}
return res;
}
template u8 access<0>(u16, u8); template u8 access<1>(u16, u8);
// Calculate graphics addresses
inline u16 nt_addr() { return 0x2000 | (vAddr.r & 0xFFF); }
inline u16 at_addr() { return 0x23C0 | (vAddr.nt << 10) | ((vAddr.cY / 4) << 3) | (vAddr.cX / 4); }
inline u16 bg_addr() { return (ctrl.bgTbl * 0x1000) + (nt * 16) + vAddr.fY; }
// Increment the scroll by one pixel
inline void h_scroll() { if (!rendering()) return; if (vAddr.cX == 31) vAddr.r ^= 0x41F; else vAddr.cX++; }
inline void v_scroll() {
if (!rendering()) return;
if (vAddr.fY < 7) vAddr.fY++;
else {
vAddr.fY = 0;
if (vAddr.cY == 31) vAddr.cY = 0;
else if (vAddr.cY == 29) { vAddr.cY = 0; vAddr.nt ^= 0b10; }
else vAddr.cY++;
}
}
// Copy scrolling data from loopy T to loopy V
inline void h_update() { if (!rendering()) return; vAddr.r = (vAddr.r & ~0x041F) | (tAddr.r & 0x041F); }
inline void v_update() { if (!rendering()) return; vAddr.r = (vAddr.r & ~0x7BE0) | (tAddr.r & 0x7BE0); }
// Put new data into the shift registers
inline void reload_shift() {
bgShiftL = (bgShiftL & 0xFF00) | bgL, bgShiftH = (bgShiftH & 0xFF00) | bgH;
atLatchL = (at & 1), atLatchH = (at & 2);
}
// Clear secondary OAM
void clear_oam() {
for (int i = 0; i < 8; i++) {
secOam[i].id = 64;
secOam[i].y = secOam[i].tile = secOam[i].attr = secOam[i].x = 0xFF;
secOam[i].dataL = secOam[i].dataH = 0;
}
}
// Fill secondary OAM with the sprite infos for the next scanline
void eval_sprites() {
int n = 0;
for (int i = 0; i < 64; i++) {
int line = (scanline == 261 ? -1 : scanline) - oamMem[i*4 + 0];
// If the sprite is in the scanline, copy its properties into secondary OAM
if (line >= 0 and line < spr_height()) {
secOam[n].id = i;
secOam[n].y = oamMem[i*4 + 0];
secOam[n].tile = oamMem[i*4 + 1];
secOam[n].attr = oamMem[i*4 + 2];
secOam[n].x = oamMem[i*4 + 3];
if (++n >= 8) { status.sprOvf = true; break; }
}
}
}
// Load the sprite info into primary OAM and fetch their tile data
void load_sprites() {
u16 addr;
for (int i = 0; i < 8; i++) {
oam[i] = secOam[i]; // Copy secondary OAM into primary
// Different address modes depending on the sprite height
if (spr_height() == 16) addr = ((oam[i].tile & 1) * 0x1000) + ((oam[i].tile & ~1) * 16);
else addr = (ctrl.sprTbl * 0x1000) + (oam[i].tile * 16);
unsigned sprY = (scanline - oam[i].y) % spr_height(); // Line inside the sprite
if (oam[i].attr & 0x80) sprY ^= spr_height() - 1; // Vertical flip
addr += sprY + (sprY & 8); // Select the second tile if on 8x16
oam[i].dataL = rd(addr + 0), oam[i].dataH = rd(addr + 8);
}
}
// Process a pixel, draw it if it's on screen
void pixel() {
u8 palette = 0, objPalette = 0;
bool objPriority = 0;
int x = dot - 2;
if (scanline < 240 and x >= 0 and x < 256) {
if (mask.bg and not (!mask.bgLeft && x < 8)) { // Background
palette = (NTH_BIT(bgShiftH, 15 - fX) << 1) | NTH_BIT(bgShiftL, 15 - fX);
if (palette) palette |= ((NTH_BIT(atShiftH, 7 - fX) << 1) | NTH_BIT(atShiftL, 7 - fX)) << 2;
}
if (mask.spr and not (!mask.sprLeft && x < 8)) { // Sprites
for (int i = 7; i >= 0; i--) {
if (oam[i].id == 64) continue; // Void entry
unsigned sprX = x - oam[i].x;
if (sprX >= 8) continue; // Not in range
if (oam[i].attr & 0x40) sprX ^= 7; // Horizontal flip
u8 sprPalette = (NTH_BIT(oam[i].dataH, 7 - sprX) << 1) | NTH_BIT(oam[i].dataL, 7 - sprX);
if (sprPalette == 0) continue; // Transparent pixel
if (oam[i].id == 0 && palette && x != 255) status.sprHit = true;
sprPalette |= (oam[i].attr & 3) << 2;
objPalette = sprPalette + 16;
objPriority = oam[i].attr & 0x20;
}
}
if (objPalette && (palette == 0 || objPriority == 0)) palette = objPalette; // Evaluate priority
pixels[scanline*256 + x] = nesRgb[rd(0x3F00 + (rendering() ? palette : 0))];
}
// Perform background shifts
bgShiftL <<= 1, bgShiftH <<= 1;
atShiftL = (atShiftL << 1) | atLatchL, atShiftH = (atShiftH << 1) | atLatchH;
}
// Execute a cycle of a scanline
template<Scanline s> void scanline_cycle() {
static u16 addr;
if (s == NMI and dot == 1) { status.vBlank = true; if (ctrl.nmi) CPU::set_nmi(); }
else if (s == POST and dot == 0) GUI::new_frame(pixels);
else if (s == VISIBLE or s == PRE) {
switch (dot) { // Sprites
case 1: clear_oam(); if (s == PRE) { status.sprOvf = status.sprHit = false; } break;
case 257: eval_sprites(); break;
case 321: load_sprites(); break;
}
switch (dot) { // Background
case 2 ... 255: case 322 ... 337:
pixel();
switch (dot % 8) {
// Nametable
case 1: addr = nt_addr(); reload_shift(); break;
case 2: nt = rd(addr); break;
// Attribute
case 3: addr = at_addr(); break;
case 4: at = rd(addr); if (vAddr.cY & 2) at >>= 4;
if (vAddr.cX & 2) at >>= 2; break;
// Background (low bits)
case 5: addr = bg_addr(); break;
case 6: bgL = rd(addr); break;
// Background (high bits)
case 7: addr += 8; break;
case 0: bgH = rd(addr); h_scroll(); break;
} break;
case 256: pixel(); bgH = rd(addr); v_scroll(); break; // Vertical bump
case 257: pixel(); reload_shift(); h_update(); break; // Update horizontal position
case 280 ... 304: if (s == PRE) v_update(); break; // Update vertical position
// No shift reloading
case 1: addr = nt_addr(); if (s == PRE) status.vBlank = false; break;
case 321: case 339: addr = nt_addr(); break;
// Nametable fetch instead of attribute
case 338: nt = rd(addr); break;
case 340: nt = rd(addr); if (s == PRE && rendering() && frameOdd) dot++;
}
if (dot == 260 && rendering()) Cartridge::signal_scanline(); // Signal scanline to mapper
}
}
// Execute a PPU cycle
void step() {
switch (scanline) {
case 0 ... 239: scanline_cycle<VISIBLE>(); break;
case 240: scanline_cycle<POST>(); break;
case 241: scanline_cycle<NMI>(); break;
case 261: scanline_cycle<PRE>(); break;
}
if (++dot > 340) { dot %= 341; if (++scanline > 261) scanline = 0, frameOdd ^= 1; } // Update dot and scanline counters
}
void reset() {
frameOdd = false;
scanline = dot = 0;
ctrl.r = mask.r = status.r = 0;
memset(pixels, 0x00, sizeof(pixels)); memset(ciRam, 0xFF, sizeof(ciRam)); memset(oamMem, 0x00, sizeof(oamMem));
}
}
namespace Cartridge {
Mapper* mapper = nullptr; // Mapper chip
// PRG-ROM access
template <bool wr> u8 access(u16 addr, u8 v) { return !wr ? mapper->read(addr) : mapper->write(addr, v); }
template u8 access<0>(u16, u8); template u8 access<1>(u16, u8);
// CHR-ROM/RAM access
template <bool wr> u8 chr_access(u16 addr, u8 v) { return !wr ? mapper->chr_read(addr) : mapper->chr_write(addr, v); }
template u8 chr_access<0>(u16, u8); template u8 chr_access<1>(u16, u8);
void signal_scanline() { mapper->signal_scanline(); }
// Load the ROM from a file.
void load(const char* fileName) {
FILE* f = fopen(fileName, "rb");
fseek(f, 0, SEEK_END);
int size = ftell(f);
fseek(f, 0, SEEK_SET);
u8* rom = new u8[size];
fread(rom, size, 1, f);
fclose(f);
int mapperNum = (rom[7] & 0xF0) | (rom[6] >> 4);
if (mapper != nullptr) delete mapper;
switch (mapperNum) {
case 0: mapper = new Mapper0(rom); break;
case 1: mapper = new Mapper1(rom); break;
case 2: mapper = new Mapper2(rom); break;
case 3: mapper = new Mapper3(rom); break;
case 4: mapper = new Mapper4(rom); break;
}
CPU::power(), PPU::reset();
}
}
namespace Joypad {
u8 joypad_bits[2]; // Joypad shift registers
bool strobe; // Joypad strobe latch
u8 read_state(int n) { // Read joypad state (NES register format)
if (strobe) return 0x40 | (GUI::get_joypad_state(n) & 1); // When strobe is high, it keeps reading A
// Get the status of a button and shift the register
u8 j = 0x40 | (joypad_bits[n] & 1);
joypad_bits[n] = 0x80 | (joypad_bits[n] >> 1);
return j;
}
void write_strobe(bool v) {
// Read the joypad data on strobe's transition 1 -> 0
if (strobe and !v) for (int i = 0; i < 2; i++) joypad_bits[i] = GUI::get_joypad_state(i);
strobe = v;
}
}
namespace GUI {
// SDL structures
SDL_Window* window;
SDL_Renderer* renderer;
SDL_Texture* gameTexture;
u8 const* keys;
SDL_Scancode KEY_A = SDL_SCANCODE_A, KEY_B = SDL_SCANCODE_S, KEY_SELECT = SDL_SCANCODE_SPACE, KEY_START = SDL_SCANCODE_RETURN;
SDL_Scancode KEY_UP = SDL_SCANCODE_UP, KEY_DOWN = SDL_SCANCODE_DOWN, KEY_LEFT = SDL_SCANCODE_LEFT, KEY_RIGHT = SDL_SCANCODE_RIGHT;
// Initialize GUI
void init() {
// Initialize graphics system
SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_JOYSTICK);
SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "linear");
// Initialize graphics structures
window = SDL_CreateWindow("BadNES", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, WIDTH, HEIGHT, 0);
renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
SDL_RenderSetLogicalSize(renderer, WIDTH, HEIGHT);
gameTexture = SDL_CreateTexture (renderer, SDL_PIXELFORMAT_ARGB8888, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);
keys = SDL_GetKeyboardState(0);
}
// Get the joypad state from SDL
u8 get_joypad_state(int n) {
const int DEAD_ZONE = 8000;
u8 j = 0;
j |= keys[KEY_A] << 0; j |= keys[KEY_B] << 1; j |= keys[KEY_SELECT] << 2; j |= keys[KEY_START] << 3;
j |= keys[KEY_UP] << 4; j |= keys[KEY_DOWN] << 5; j |= keys[KEY_LEFT] << 6; j |= keys[KEY_RIGHT] << 7;
return j;
}
// Send the rendered frame to the GUI
void new_frame(u32* pixels) { SDL_UpdateTexture(gameTexture, NULL, pixels, WIDTH * sizeof(u32)); }
// Render the screen
void render() {
SDL_RenderClear(renderer);
// Draw the NES screen
SDL_RenderCopy(renderer, gameTexture, NULL, NULL);
SDL_RenderPresent(renderer);
}
// Run the emulator
void run(const char* file) {
SDL_Event e;
// Framerate control
u32 frameStart, frameTime;
const int FPS = 60;
const int DELAY = 1000.0f / FPS;
Cartridge::load(file);
while (1) {
frameStart = SDL_GetTicks();
// Handle events
while (SDL_PollEvent(&e)) {
if (e.type == SDL_QUIT) return;
}
CPU::run_frame();
render();
// Wait to mantain framerate
frameTime = SDL_GetTicks() - frameStart;
if (frameTime < DELAY) SDL_Delay((int)(DELAY - frameTime));
}
}
}
int main(int argc, char *argv[]) {
GUI::init();
GUI::run(argv[1]);
}