mmc3.cpp

struct MMC3 : Chip {

bool chr_mode;
bool prg_mode;
uint3 bank_select;
uint8 prg_bank[2];
uint8 chr_bank[6];
bool mirror;
bool ram_enable;
bool ram_write_protect;
uint8 irq_latch;
uint8 irq_counter;
bool irq_enable;
unsigned irq_delay;
bool irq_line;

uint16 chr_abus;

void main() {
  while(true) {
    if(scheduler.sync == Scheduler::SynchronizeMode::All) {
      scheduler.exit(Scheduler::ExitReason::SynchronizeEvent);
    }

    if(irq_delay) irq_delay--;
    cpu.set_irq_line(irq_line);
    tick();
  }
}

void irq_test(unsigned addr) {
  if(!(chr_abus & 0x1000) && (addr & 0x1000)) {
    if(irq_delay == 0) {
      if(irq_counter == 0) {
        irq_counter = irq_latch;
      } else if(--irq_counter == 0) {
        if(irq_enable) irq_line = 1;
      }
    }
    irq_delay = 6;
  }
  chr_abus = addr;
}

unsigned prg_addr(unsigned addr) const {
  switch((addr >> 13) & 3) {
  case 0:
    if(prg_mode == 1) return (0x3e << 13) | (addr & 0x1fff);
    return (prg_bank[0] << 13) | (addr & 0x1fff);
  case 1:
    return (prg_bank[1] << 13) | (addr & 0x1fff);
  case 2:
    if(prg_mode == 0) return (0x3e << 13) | (addr & 0x1fff);
    return (prg_bank[0] << 13) | (addr & 0x1fff);
  case 3:
    return (0x3f << 13) | (addr & 0x1fff);
  }
}

unsigned chr_addr(unsigned addr) const {
  if(chr_mode == 0) {
    if(addr <= 0x07ff) return (chr_bank[0] << 10) | (addr & 0x07ff);
    if(addr <= 0x0fff) return (chr_bank[1] << 10) | (addr & 0x07ff);
    if(addr <= 0x13ff) return (chr_bank[2] << 10) | (addr & 0x03ff);
    if(addr <= 0x17ff) return (chr_bank[3] << 10) | (addr & 0x03ff);
    if(addr <= 0x1bff) return (chr_bank[4] << 10) | (addr & 0x03ff);
    if(addr <= 0x1fff) return (chr_bank[5] << 10) | (addr & 0x03ff);
  } else {
    if(addr <= 0x03ff) return (chr_bank[2] << 10) | (addr & 0x03ff);
    if(addr <= 0x07ff) return (chr_bank[3] << 10) | (addr & 0x03ff);
    if(addr <= 0x0bff) return (chr_bank[4] << 10) | (addr & 0x03ff);
    if(addr <= 0x0fff) return (chr_bank[5] << 10) | (addr & 0x03ff);
    if(addr <= 0x17ff) return (chr_bank[0] << 10) | (addr & 0x07ff);
    if(addr <= 0x1fff) return (chr_bank[1] << 10) | (addr & 0x07ff);
  }
}

unsigned ciram_addr(unsigned addr) const {
  if(mirror == 0) return ((addr & 0x0400) >> 0) | (addr & 0x03ff);
  if(mirror == 1) return ((addr & 0x0800) >> 1) | (addr & 0x03ff);
}

uint8 ram_read(unsigned addr) {
  if(ram_enable) return board.prgram.data[addr & 0x1fff];
  return 0x00;
}

void ram_write(unsigned addr, uint8 data) {
  if(ram_enable && !ram_write_protect) board.prgram.data[addr & 0x1fff] = data;
}

void reg_write(unsigned addr, uint8 data) {
  switch(addr & 0xe001) {
  case 0x8000:
    chr_mode = data & 0x80;
    prg_mode = data & 0x40;
    bank_select = data & 0x07;
    break;

  case 0x8001:
    switch(bank_select) {
    case 0: chr_bank[0] = data & ~1; break;
    case 1: chr_bank[1] = data & ~1; break;
    case 2: chr_bank[2] = data; break;
    case 3: chr_bank[3] = data; break;
    case 4: chr_bank[4] = data; break;
    case 5: chr_bank[5] = data; break;
    case 6: prg_bank[0] = data & 0x3f; break;
    case 7: prg_bank[1] = data & 0x3f; break;
    }
    break;

  case 0xa000:
    mirror = data & 0x01;
    break;

  case 0xa001:
    ram_enable = data & 0x80;
    ram_write_protect = data & 0x40;
    break;

  case 0xc000:
    irq_latch = data;
    break;

  case 0xc001:
    irq_counter = 0;
    break;

  case 0xe000:
    irq_enable = false;
    irq_line = 0;
    break;

  case 0xe001:
    irq_enable = true;
    break;
  }
}

void power() {
}

void reset() {
  chr_mode = 0;
  prg_mode = 0;
  bank_select = 0;
  prg_bank[0] = 0;
  prg_bank[1] = 0;
  chr_bank[0] = 0;
  chr_bank[1] = 0;
  chr_bank[2] = 0;
  chr_bank[3] = 0;
  chr_bank[4] = 0;
  chr_bank[5] = 0;
  mirror = 0;
  ram_enable = 1;
  ram_write_protect = 0;
  irq_latch = 0;
  irq_counter = 0;
  irq_enable = false;
  irq_delay = 0;
  irq_line = 0;

  chr_abus = 0;
}

void serialize(serializer& s) {
  s.integer(chr_mode);
  s.integer(prg_mode);
  s.integer(bank_select);
  s.array(prg_bank);
  s.array(chr_bank);
  s.integer(mirror);
  s.integer(ram_enable);
  s.integer(ram_write_protect);
  s.integer(irq_latch);
  s.integer(irq_counter);
  s.integer(irq_enable);
  s.integer(irq_delay);
  s.integer(irq_line);

  s.integer(chr_abus);
}

MMC3(Board& board) : Chip(board) {
}

};