auto VDC::vramRead(uint16 addr) -> uint16 {
  if(addr.bit(15)) return 0x00;
  return vram[addr];
}

auto VDC::vramWrite(uint16 addr, uint16 data) -> void {
  if(addr.bit(15)) return;
  vram[addr] = data;
}

auto VDC::read(uint11 addr) -> uint8 {
  bool a0 = addr.bit(0);
  if(!addr.bit(10)) {
    //VDC
    if(addr.bit(1) == 0) {
      //SR
      if(a0) return 0x00;
      uint8 data;
      data.bit(0) = irq.pendingCollision;
      data.bit(1) = irq.pendingOverflow;
      data.bit(2) = irq.pendingLineCoincidence;
      data.bit(3) = irq.pendingTransferSATB;
      data.bit(4) = irq.pendingTransferVRAM;
      data.bit(5) = irq.pendingVblank;
      irq.lower();
      return data;
    }

    if(addr.bit(1) == 1) {
      if(io.address == 0x02) {
        //VRR
        uint8 data = io.vramDataRead.byte(a0);
        if(a0) {
          io.vramAddressRead += io.vramAddressIncrement;
          io.vramDataRead = vramRead(io.vramAddressRead);
        }
        return data;
      }
    }
  } else {
    //VCE
    if(addr.bits(0,2) == 0x04) {
      //CTR
      uint8 data = cram[io.colorAddress].bits(0,7);
      return data;
    }

    if(addr.bits(0,2) == 0x05) {
      //CTR
      uint8 data = cram[io.colorAddress].bit(0);
      io.colorAddress++;
      return data;
    }
  }

  return 0x00;
}

auto VDC::write(uint11 addr, uint8 data) -> void {
  bool a0 = addr.bit(0);
  if(!addr.bit(10)) {
    //VDC
    if(addr.bit(1) == 0) {
      //AR
      if(a0) return;
      io.address = data.bits(0,4);
      return;
    }

    if(addr.bit(1) == 1) {
      if(io.address == 0x00) {
        //MAWR
        io.vramAddressWrite.byte(a0) = data;
        return;
      }

      if(io.address == 0x01) {
        //MARR
        io.vramAddressRead.byte(a0) = data;
        io.vramDataRead = vramRead(io.vramAddressRead);
        return;
      }

      if(io.address == 0x02) {
        //VWR
        io.vramDataWrite.byte(a0) = data;
        if(a0) {
          vramWrite(io.vramAddressWrite, io.vramDataWrite);
          io.vramAddressWrite += io.vramAddressIncrement;
        }
        return;
      }

      if(io.address == 0x05) {
        //CR
        if(!a0) {
          irq.enableCollision = data.bit(0);
          irq.enableOverflow = data.bit(1);
          irq.enableLineCoincidence = data.bit(2);
          irq.enableVblank = data.bit(3);
          io.externalSync = data.bits(4,5);
          sprite.enable = data.bit(6);
          background.enable = data.bit(7);
        } else {
          io.displayOutput = data.bits(0,1);
          io.dramRefresh = data.bit(2);
          if(data.bits(3,4) == 0) io.vramAddressIncrement = 0x01;
          if(data.bits(3,4) == 1) io.vramAddressIncrement = 0x20;
          if(data.bits(3,4) == 2) io.vramAddressIncrement = 0x40;
          if(data.bits(3,4) == 3) io.vramAddressIncrement = 0x80;
        }
        return;
      }

      if(io.address == 0x06) {
        //RCR
        io.lineCoincidence.byte(a0) = data;
        return;
      }

      if(io.address == 0x07) {
        //BXR
        background.hscroll.byte(a0) = data;
        return;
      }

      if(io.address == 0x08) {
        //BYR
        background.vscroll.byte(a0) = data;
        background.voffset = background.vscroll;
        return;
      }

      if(io.address == 0x09) {
        //MWR
        if(a0) return;
        io.vramAccess = data.bits(0,1);
        io.spriteAccess = data.bits(2,3);
        if(data.bits(4,5) == 0) background.width =  32;
        if(data.bits(4,5) == 1) background.width =  64;
        if(data.bits(4,5) == 2) background.width = 128;
        if(data.bits(4,5) == 3) background.width = 128;
        if(data.bit(6) == 0) background.height = 32;
        if(data.bit(6) == 1) background.height = 64;
        io.cgMode = data.bit(7);
        return;
      }

      if(io.address == 0x0a) {
        //HSR
        if(!a0) {
          io.horizontalSyncWidth = data.bits(0,4);
        } else {
          io.horizontalDisplayStart = data.bits(0,6);
        }
        return;
      }

      if(io.address == 0x0b) {
        //HDR
        if(!a0) {
          io.horizontalDisplayWidth = data.bits(0,6);
        } else {
          io.horizontalDisplayEnd = data.bits(0,6);
        }
        return;
      }

      if(io.address == 0x0c) {
        //VPR
        if(!a0) {
          io.verticalSyncWidth = data.bits(0,4);
        } else {
          io.verticalDisplayStart = data.bits(0,7);
        }
        return;
      }

      if(io.address == 0x0d) {
        //VDR
        io.verticalDisplayWidth.byte(a0) = data;
        return;
      }

      if(io.address == 0x0e) {
        //VCR
        if(a0) return;
        io.verticalDisplayEnd = data.bits(0,7);
        return;
      }

      if(io.address == 0x0f) {
        //DCR
        if(a0) return;
        irq.enableTransferVRAM = data.bit(0);
        irq.enableTransferSATB = data.bit(1);
        dma.sourceIncrementMode = data.bit(2);
        dma.targetIncrementMode = data.bit(3);
        dma.satbRepeat = data.bit(4);
        return;
      }

      if(io.address == 0x10) {
        //SOUR
        dma.source.byte(a0) = data;
        return;
      }

      if(io.address == 0x11) {
        //DESR
        dma.target.byte(a0) = data;
        return;
      }

      if(io.address == 0x12) {
        //LENR
        dma.length.byte(a0) = data;
        if(a0) dma.vramStart();
        return;
      }

      if(io.address == 0x13) {
        //DVSSR
        dma.satbSource.byte(a0) = data;
        if(a0) dma.satbQueue();
        return;
      }
    }
  } else {
    //VCE
    if(addr.bits(0,2) == 0x00) {
      //CR
      io.divisionRatio = data.bits(0,1);
      io.colorBlur = data.bit(2);
      io.grayscale = data.bit(7);
      return;
    }

    if(addr.bits(0,2) == 0x02) {
      //CTA
      io.colorAddress.bits(0,7) = data.bits(0,7);
      return;
    }

    if(addr.bits(0,2) == 0x03) {
      //CTA
      io.colorAddress.bit(8) = data.bit(0);
      return;
    }

    if(addr.bits(0,2) == 0x04) {
      //CTW
      cram[io.colorAddress].bits(0,7) = data.bits(0,7);
      return;
    }

    if(addr.bits(0,2) == 0x05) {
      //CTW
      cram[io.colorAddress].bit(8) = data.bit(0);
      io.colorAddress++;
      return;
    }
  }
}