private void ChangeMode(LcdMode newMode)
{
_currentMode = newMode;
_counter = 0;
if (newMode == LcdMode.OamSearch)
{
if (_stat.OamSearchInterruptEnabled.Value)
{
_lcdStatusInterrupt.Trigger();
}
}
else if (newMode == LcdMode.DataTransfer)
{
// Do nothing.
}
else if (newMode == LcdMode.HorizontalBlank)
{
RenderScanline(_ly.Value);
if (_stat.HBlankInterruptEnabled.Value)
{
_lcdStatusInterrupt.Trigger();
}
}
else if (newMode == LcdMode.VerticalBlank)
{
//Console.WriteLine($"Vblank after {_globalCounter - _lastVblank} cycles.");
_lastVblank = _globalCounter;
OnCompletedFrame();
_vblankInterrupt.Trigger();
// TODO does vblank really have two interrupts?
if (_stat.VBlankInterruptEnabled.Value)
{
_vblankInterrupt.Trigger();
}
}
}
void SetStatLcdMode(LcdMode mode)
{
stat = (byte)((stat & 0xFC) | (byte)mode);
}
void SetLcdMode(LcdMode mode)
{
this.lcdMode = mode;
SetStatLcdMode(mode);
}
public override void Update(uint cycleCount)
{
if (_oamDma.Status != OamDmaStatus.Inactive)
{
UpdateOamDma(cycleCount);
}
// only run lcd controller update if display is enabled
if (!_displayEnabled)
{
return;
}
_frameClock += cycleCount;
// LCD runs for 70224 cpu cycles a frame, 456 cycles a scanline and 154 total scanlines
// 10 of the scanlines are VBlank and the rest are the active portion of the cycle
// mode 2, 3 and 0 occur in he first 65664 cycles of a frame (70224 - 4560)
if (_frameClock < 65664)
{
// Mode 2 - OAM read, 77-83 cycles of frame
if ((_frameClock % 456) < 80)
{
if (_lcdMode != LcdMode.OamRead)
{
// We've just entered OAM read so we're at the beginning of the line,
// increment the current scanline unless we're coming from VBlank, then
// don't inrecement because we've just set it to 0
if (_lcdMode != LcdMode.VBlank)
{
_currentScanline++;
CompareScanlineValue();
}
_lcdMode = LcdMode.OamRead;
// raise OAM stat interrupt if requested
if ((_lcdStatus & 0x20) == 0x20)
{
_interruptController.RequestInterrupt(Interrupt.LCDCStatus);
}
}
}
// Mode 3 - OAM and VRAM read, 162-175 cycles of frame
else if ((_frameClock % 456) < 252)
{
if (_lcdMode != LcdMode.VramRead)
{
_lcdMode = LcdMode.VramRead;
}
}
// Mode 0 - HBlank, 201-207 cycles of frame
else
{
if (_lcdMode != LcdMode.HBlank)
{
_lcdMode = LcdMode.HBlank;
// raise hblank stat interrupt if requested
if ((_lcdStatus & 0x08) == 0x08)
{
_interruptController.RequestInterrupt(Interrupt.LCDCStatus);
}
RenderScanline();
}
}
}
// Mode 1 - VBlank
else
{
// are we entering vblank from another mode?
if (_lcdMode != LcdMode.VBlank)
{
_lcdMode = LcdMode.VBlank;
_currentScanline++;
CompareScanlineValue();
// count 10 scanlines in vblank, include any already pushing into vblank timing
_vblankClock = _frameClock - 65664;
// raise vblank stat interrupt if requested
if ((_lcdStatus & 0x10) == 0x10)
{
_interruptController.RequestInterrupt(Interrupt.LCDCStatus);
}
// raise vblank interrupt
_interruptController.RequestInterrupt(Interrupt.VBlank);
//DEBUG_DumpVramTiles();
// we've just entered vblank so the rendering for the frame is finished
// present the screen data
_frameSink?.AppendFrame(_screenData);
// clear the _screenData for the next frame
Array.Clear(_screenData, 0, _screenData.Length);
}
// processing vblank
else
{
_vblankClock += cycleCount;
if (_vblankClock >= 456)
{
_vblankClock -= 456;
_currentScanline++;
if (_currentScanline > 153)
{
_frameClock -= 70224;
_currentScanline = 0;
}
CompareScanlineValue();
}
}
}
}
public void WriteByte(ushort address, byte value)
{
SynchroniseWithSystemClock();
// 0x8000 - 0x9FFF - vram
if (address >= 0x8000 && address <= 0x9fff)
{
// cannot access vram in mode 3
if (_lcdMode == LcdMode.VramRead)
{
return;
}
_vram[address & 0x1FFF] = value;
// invalidate the tile cache for any tiles updated
if (address < 0x9800)
{
_updateTileCache = true;
_tileCacheInvalid[(address & 0x1FF0) >> 4] = true;
}
}
// 0xFE00 - 0xFE9F - OAM memory
else if (address >= 0xFE00 && address <= 0xFE9F)
{
// cannot access oam in mode 2 or 3
if (_lcdMode == LcdMode.OamRead || _lcdMode == LcdMode.VramRead || !_oamDma.OamAvailable)
{
return;
}
_oam[address & 0xFF] = value;
}
else
{
switch (address)
{
case Registers.LCDC:
_lcdControl = value;
bool enableDisplay = (_lcdControl & 0x80) == 0x80;
// are we being asked to turn on the display and if so are we currently off?
if (enableDisplay && !_displayEnabled)
{
// lcd starts in mode 2 when enabled
_displayEnabled = true;
_lcdMode = LcdMode.OamRead;
CompareScanlineValue();
}
// reset LY when display is disabled
else if (!enableDisplay && _displayEnabled)
{
_displayEnabled = false;
_currentScanline = 0;
_frameClock = 0;
_lcdMode = 0;
}
_windowTileBaseAddress = (ushort)((_lcdControl & 0x40) == 0x40 ? 0x9C00 : 0x9800);
_windowEnabled = (_lcdControl & 0x20) == 0x20;
_backgroundCharBaseAddress = (ushort)((_lcdControl & 0x10) == 0x10 ? 0x8000 : 0x8800);
// if the background char data is in the range 0x8800 - 0x97FF then tile identifiers are signed
_signedCharIdentifier = _backgroundCharBaseAddress == 0x8800;
_backgroundTileBaseAddress = (ushort)((_lcdControl & 0x08) == 0x08 ? 0x9C00 : 0x9800);
_spriteHeight = (_lcdControl & 0x04) == 0x04 ? 16 : 8;
_spritesEnabled = (_lcdControl & 0x02) == 0x02;
_backgroundEnabled = (_lcdControl & 0x01) == 0x01;
break;
case Registers.STAT:
// capture lcd interrupt selection from value
// interrupt selection stored in bits 6-3, preserve bits 0-2
// and mask bits 6-3 from value passed in
_lcdStatus = (byte)((_lcdStatus & 0x07) | (value & 0x78));
// a write to the LY = LYC match flag (bit 2) clears the flag
if ((value & 0x04) == 0x04)
{
unchecked { _lcdStatus &= (byte)~0x04; }
}
break;
case Registers.SCY:
_scrollY = value;
break;
case Registers.SCX:
_scrollX = value;
break;
case Registers.LYC:
_scanlineCompare = value;
break;
case Registers.DMA:
_oamDma.Source = (ushort)(value << 8);
_oamDma.Status = OamDmaStatus.Requested;
break;
case Registers.BGP:
_bgp = value;
_backgroundPalette = ExtractPaletteData(_bgp, 0);
break;
case Registers.OBP0:
_obp0 = value;
// extract sprite palette data, start from index 1, palette entry 00 is always 00
_spritePalette[0] = ExtractPaletteData(_obp0, 1);
break;
case Registers.OBP1:
_obp1 = value;
// extract sprite palette data, start from index 1, palette entry 00 is always 00
_spritePalette[1] = ExtractPaletteData(_obp1, 1);
break;
case Registers.WY:
_windowY = value;
break;
case Registers.WX:
_windowX = value;
break;
default:
throw new ArgumentOutOfRangeException("address");
}
}
}
