auto CPU::DMA::readWord(u32 address) -> u32 {
  uint32 data = 0;
  uint32 c = address >> 4 & 7;

  //DnMADR: DMA Base Address
  if((address & 0xffff'ff0f) == 0x1f80'1080 && c < 7) {
    data.bit(0,23) = channel[c].address;
  }

  //DnBCR: DMA Block Control
  if((address & 0xffff'ff0f) == 0x1f80'1084 && c < 7) {
    data.bit( 0,15) = channel[c].length;
    data.bit(16,31) = channel[c].blocks;
  }

  //DnCHCR: DMA Channel Control
  if((address & 0xffff'ff0f) == 0x1f80'1088 && c < 7) {
    data.bit( 0)    = channel[c].direction;
    data.bit( 1)    = channel[c].step;
    data.bit( 2)    = channel[c].chopping.enable;
    data.bit( 9,10) = channel[c].synchronization;
    data.bit(16,18) = channel[c].chopping.dmaWindow;
    data.bit(20,22) = channel[c].chopping.cpuWindow;
    data.bit(24)    = channel[c].enable;
    data.bit(28)    = channel[c].trigger;
    data.bit(29,30) = channel[c].unknown;
  }

  //DPCR: DMA Control
  if(address == 0x1f80'10f0) {
    data.bit( 0, 2) = channel[0].priority;
    data.bit( 3)    = channel[0].masterEnable;
    data.bit( 4, 6) = channel[1].priority;
    data.bit( 7)    = channel[1].masterEnable;
    data.bit( 8,10) = channel[2].priority;
    data.bit(11)    = channel[2].masterEnable;
    data.bit(12,14) = channel[3].priority;
    data.bit(15)    = channel[3].masterEnable;
    data.bit(16,18) = channel[4].priority;
    data.bit(19)    = channel[4].masterEnable;
    data.bit(20,22) = channel[5].priority;
    data.bit(23)    = channel[5].masterEnable;
    data.bit(24,26) = channel[6].priority;
    data.bit(27)    = channel[6].masterEnable;
  }

  //DICR: DMA Interrupt
  if(address == 0x1f80'10f4) {
    data.bit( 0, 5) = irq.unknown;
    data.bit(16)    = channel[0].irq.enable;
    data.bit(17)    = channel[1].irq.enable;
    data.bit(18)    = channel[2].irq.enable;
    data.bit(19)    = channel[3].irq.enable;
    data.bit(20)    = channel[4].irq.enable;
    data.bit(21)    = channel[5].irq.enable;
    data.bit(22)    = channel[6].irq.enable;
    data.bit(23)    =            irq.enable;
    data.bit(24)    = channel[0].irq.flag;
    data.bit(25)    = channel[1].irq.flag;
    data.bit(26)    = channel[2].irq.flag;
    data.bit(27)    = channel[3].irq.flag;
    data.bit(28)    = channel[4].irq.flag;
    data.bit(29)    = channel[5].irq.flag;
    data.bit(30)    = channel[6].irq.flag;
    data.bit(31)    = irq.flag;
  }

  return data;
}

auto CPU::DMA::writeWord(u32 address, u32 value) -> void {
  uint32 data = value;
  uint32 c = address >> 4 & 7;

  //DnMADR: DMA Base Address
  if((address & 0xffff'ff8f) == 0x1f80'1080 && c < 7) {
    channel[c].address = data.bit(0,23);
  }

  //DnBCR: DMA Block Control
  if((address & 0xffff'ff8f) == 0x1f80'1084 && c < 7) {
    channel[c].length = data.bit( 0,15);
    channel[c].blocks = data.bit(16,31);
  }

  //DnCHCR: DMA Channel Control
  if((address & 0xffff'ff8f) == 0x1f80'1088 && c < 7) {
    channel[c].direction          = data.bit( 0);
    channel[c].step               = data.bit( 1);
    channel[c].chopping.enable    = data.bit( 2);
    channel[c].synchronization    = data.bit( 9,10);
    channel[c].chopping.dmaWindow = data.bit(16,18);
    channel[c].chopping.cpuWindow = data.bit(20,22);
    channel[c].enable             = data.bit(24);
    channel[c].trigger            = data.bit(28);
    channel[c].unknown            = data.bit(29,30);

  //print(c, " ", channel[c].direction, " ", channel[c].synchronization, " ", hex(channel[c].address, 8L), "\n");

    if(channel[c].active()) {
      if(channel[c].synchronization == 0) transferLinear(c);
      if(channel[c].synchronization == 1) transferLinear(c);
      if(channel[c].synchronization == 2) transferLinked(c);
    }
  }

  //DPCR: DMA Control
  if(address == 0x1f80'10f0) {
    channel[0].priority     = data.bit( 0, 2);
    channel[0].masterEnable = data.bit( 3);
    channel[1].priority     = data.bit( 4, 6);
    channel[1].masterEnable = data.bit( 7);
    channel[2].priority     = data.bit( 8,10);
    channel[2].masterEnable = data.bit(11);
    channel[3].priority     = data.bit(12,14);
    channel[3].masterEnable = data.bit(15);
    channel[4].priority     = data.bit(16,18);
    channel[4].masterEnable = data.bit(19);
    channel[5].priority     = data.bit(20,22);
    channel[5].masterEnable = data.bit(23);
    channel[6].priority     = data.bit(24,26);
    channel[6].masterEnable = data.bit(27);
  }

  //DICR: DMA Interrupt
  if(address == 0x1f80'10f4) {
               irq.unknown = data.bit( 0,5);
               irq.force   = data.bit(15);
    channel[0].irq.enable  = data.bit(16);
    channel[1].irq.enable  = data.bit(17);
    channel[2].irq.enable  = data.bit(18);
    channel[3].irq.enable  = data.bit(19);
    channel[4].irq.enable  = data.bit(20);
    channel[5].irq.enable  = data.bit(21);
    channel[6].irq.enable  = data.bit(22);
               irq.enable  = data.bit(23);
    if(data.bit(24)) channel[0].irq.flag = 0;
    if(data.bit(25)) channel[1].irq.flag = 0;
    if(data.bit(26)) channel[2].irq.flag = 0;
    if(data.bit(27)) channel[3].irq.flag = 0;
    if(data.bit(28)) channel[4].irq.flag = 0;
    if(data.bit(29)) channel[5].irq.flag = 0;
    if(data.bit(30)) channel[6].irq.flag = 0;
    pollIRQ();
  }
}

auto CPU::DMA::transferLinear(uint c) -> void {
  u32 address = channel[c].address;
  u16 blocks  = channel[c].synchronization == 0 ? uint16(1) : channel[c].blocks;

  do {
    u16 length = channel[c].length;
    do {
      if(channel[c].direction == 0) {
        u32 data = 0;
        if(c == 6) {
          data = address - 4 & 0xfffffc;    //point to previous entry
          if(length == 1) data = 0xffffff;  //end of ordering table
        }
        bus.writeWord(address, data);
      }

      if(channel[c].direction == 1) {
        u32 data = bus.readWord(address);
        address += 4;
      }

      if(channel[c].step == 0) address += 4;
      if(channel[c].step == 1) address -= 4;
    } while(--length);
  } while(--blocks);
  channel[c].enable  = 0;
  channel[c].trigger = 0;
}

auto CPU::DMA::transferLinked(uint c) -> void {
  if(channel[c].direction == 0) return;  //invalid direction for this mode

  u32 address = channel[c].address;
  u32 timeout = 0x40000;  //unverified; prevents potential infinite loop
  do {
    u32 header = bus.readWord(address);

    for(uint count : range(header >> 24)) {
      address += 4;
      u32 data = bus.readWord(address);

      if(c == 2) {
      //print("gpu ", hex(data, 8L), "\n");
      }
    }

    address = header & 0xffffff;
    if(address & 0x800000) break;
  } while(--timeout);
}

auto CPU::DMA::pollIRQ() -> void {
  irq.flag = irq.force;
  if(!irq.enable) return;
  for(uint n : range(7)) {
    if(channel[n].irq.flag & channel[n].irq.enable) irq.flag = 1;
  }
}

auto CPU::DMA::power(bool reset) -> void {
  for(uint n : range(7)) {
    channel[n].priority = 1 + n;
    channel[n].masterEnable = 0;
  }
}

auto CPU::DMA::Channel::active() const -> bool {
  if(synchronization == 0) return enable && trigger;
  return enable;
}