bsnes/higan/fc/cartridge/chip/vrc7.cpp

//Konami VRC7
//Yamaha YM2413 OPLL audio - not emulated

struct VRC7 : Chip {
  VRC7(Board& board) : Chip(board) {
  }

  auto main() -> void {
    if(irq_enable) {
      if(irq_mode == 0) {
        irq_scalar -= 3;
        if(irq_scalar <= 0) {
          irq_scalar += 341;
          if(irq_counter == 0xff) {
            irq_counter = irq_latch;
            irq_line = 1;
          } else {
            irq_counter++;
          }
        }
      }

      if(irq_mode == 1) {
        if(irq_counter == 0xff) {
          irq_counter = irq_latch;
          irq_line = 1;
        } else {
          irq_counter++;
        }
      }
    }
    cpu.irqLine(irq_line);

    tick();
  }

  auto reg_write(uint addr, uint8 data) -> void {
    switch(addr) {
    case 0x8000: prg_bank[0] = data; break;
    case 0x8010: prg_bank[1] = data; break;
    case 0x9000: prg_bank[2] = data; break;
    case 0x9010: break;  //APU addr port
    case 0x9030: break;  //APU data port
    case 0xa000: chr_bank[0] = data; break;
    case 0xa010: chr_bank[1] = data; break;
    case 0xb000: chr_bank[2] = data; break;
    case 0xb010: chr_bank[3] = data; break;
    case 0xc000: chr_bank[4] = data; break;
    case 0xc010: chr_bank[5] = data; break;
    case 0xd000: chr_bank[6] = data; break;
    case 0xd010: chr_bank[7] = data; break;
    case 0xe000: mirror = data & 0x03; break;

    case 0xe010:
      irq_latch = data;
      break;

    case 0xf000:
      irq_mode = data & 0x04;
      irq_enable = data & 0x02;
      irq_acknowledge = data & 0x01;
      if(irq_enable) {
        irq_counter = irq_latch;
        irq_scalar = 341;
      }
      irq_line = 0;
      break;

    case 0xf010:
      irq_enable = irq_acknowledge;
      irq_line = 0;
      break;
    }
  }

  auto prg_addr(uint addr) const -> uint {
    uint bank = 0;
    switch(addr & 0xe000) {
    case 0x8000: bank = prg_bank[0]; break;
    case 0xa000: bank = prg_bank[1]; break;
    case 0xc000: bank = prg_bank[2]; break;
    case 0xe000: bank = 0xff; break;
    }
    return (bank * 0x2000) + (addr & 0x1fff);
  }

  auto chr_addr(uint addr) const -> uint {
    uint bank = chr_bank[addr / 0x0400];
    return (bank * 0x0400) + (addr & 0x03ff);
  }

  auto ciram_addr(uint addr) const -> uint {
    switch(mirror) {
    case 0: return ((addr & 0x0400) >> 0) | (addr & 0x03ff);  //vertical mirroring
    case 1: return ((addr & 0x0800) >> 1) | (addr & 0x03ff);  //horizontal mirroring
    case 2: return 0x0000 | (addr & 0x03ff);                  //one-screen mirroring (first)
    case 3: return 0x0400 | (addr & 0x03ff);                  //one-screen mirroring (second)
    }
  }

  auto power() -> void {
  }

  auto reset() -> void {
    for(auto& n : prg_bank) n = 0;
    for(auto& n : chr_bank) n = 0;
    mirror = 0;

    irq_latch = 0;
    irq_mode = 0;
    irq_enable = 0;
    irq_acknowledge = 0;

    irq_counter = 0;
    irq_scalar = 0;
    irq_line = 0;
  }

  auto serialize(serializer& s) -> void {
    s.array(prg_bank);
    s.array(chr_bank);
    s.integer(mirror);

    s.integer(irq_latch);
    s.integer(irq_mode);
    s.integer(irq_enable);
    s.integer(irq_acknowledge);

    s.integer(irq_counter);
    s.integer(irq_scalar);
    s.integer(irq_line);
  }

  uint8 prg_bank[3];
  uint8 chr_bank[8];
  uint2 mirror;

  uint8 irq_latch;
  bool irq_mode;
  bool irq_enable;
  bool irq_acknowledge;

  uint8 irq_counter;
  int irq_scalar;
  bool irq_line;
};