struct VRC3 : Chip {
  VRC3(Board& board) : Chip(board) {
  }

  auto main() -> void {
    if(irq_enable) {
      if(irq_mode == 0) {  //16-bit
        if(++irq_counter.w == 0) {
          irq_line = 1;
          irq_enable = irq_acknowledge;
          irq_counter.w = irq_latch;
        }
      }
      if(irq_mode == 1) {  //8-bit
        if(++irq_counter.l == 0) {
          irq_line = 1;
          irq_enable = irq_acknowledge;
          irq_counter.l = irq_latch;
        }
      }
    }

    cpu.set_irq_line(irq_line);
    tick();
  }

  auto prg_addr(uint addr) const -> uint {
    uint bank = (addr < 0xc000 ? (uint)prg_bank : 0x0f);
    return (bank * 0x4000) + (addr & 0x3fff);
  }

  auto reg_write(uint addr, uint8 data) -> void {
    switch(addr & 0xf000) {
    case 0x8000: irq_latch = (irq_latch & 0xfff0) | ((data & 0x0f) <<  0); break;
    case 0x9000: irq_latch = (irq_latch & 0xff0f) | ((data & 0x0f) <<  4); break;
    case 0xa000: irq_latch = (irq_latch & 0xf0ff) | ((data & 0x0f) <<  8); break;
    case 0xb000: irq_latch = (irq_latch & 0x0fff) | ((data & 0x0f) << 12); break;

    case 0xc000:
      irq_mode = data & 0x04;
      irq_enable = data & 0x02;
      irq_acknowledge = data & 0x01;
      if(irq_enable) irq_counter.w = irq_latch;
      break;

    case 0xd000:
      irq_line = 0;
      irq_enable = irq_acknowledge;
      break;

    case 0xf000:
      prg_bank = data & 0x0f;
      break;
    }
  }

  auto power() -> void {
  }

  auto reset() -> void {
    prg_bank = 0;
    irq_mode = 0;
    irq_enable = 0;
    irq_acknowledge = 0;
    irq_latch = 0;
    irq_counter.w = 0;
    irq_line = 0;
  }

  auto serialize(serializer& s) -> void {
    s.integer(prg_bank);
    s.integer(irq_mode);
    s.integer(irq_enable);
    s.integer(irq_acknowledge);
    s.integer(irq_latch);
    s.integer(irq_counter.w);
    s.integer(irq_line);
  }

  uint4 prg_bank;
  bool irq_mode;
  bool irq_enable;
  bool irq_acknowledge;
  uint16 irq_latch;
  struct {
    union {
      uint16_t w;
      struct { uint8_t order_lsb2(l, h); };
    };
  } irq_counter;
  bool irq_line;
};