S3Trio64.cpp

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/* ES40 emulator.
 * Copyright (C) 2007-2008 by the ES40 Emulator Project
 *
 * WWW    : http://sourceforge.net/projects/es40
 * E-mail : camiel@camicom.com
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 * 
 * Although this is not required, the author would appreciate being notified of, 
 * and receiving any modifications you may make to the source code that might serve
 * the general public.
 */

#include "StdAfx.h"
#include "S3Trio64.h"
#include "System.h"
#include "AliM1543C.h"
#include "gui/gui.h"

static unsigned old_iHeight = 0, old_iWidth = 0, old_MSL = 0;

static const u8 ccdat[16][4] = {
  {0x00, 0x00, 0x00, 0x00},
  {0xff, 0x00, 0x00, 0x00},
  {0x00, 0xff, 0x00, 0x00},
  {0xff, 0xff, 0x00, 0x00},
  {0x00, 0x00, 0xff, 0x00},
  {0xff, 0x00, 0xff, 0x00},
  {0x00, 0xff, 0xff, 0x00},
  {0xff, 0xff, 0xff, 0x00},
  {0x00, 0x00, 0x00, 0xff},
  {0xff, 0x00, 0x00, 0xff},
  {0x00, 0xff, 0x00, 0xff},
  {0xff, 0xff, 0x00, 0xff},
  {0x00, 0x00, 0xff, 0xff},
  {0xff, 0x00, 0xff, 0xff},
  {0x00, 0xff, 0xff, 0xff},
  {0xff, 0xff, 0xff, 0xff},
};

#define SET_TILE_UPDATED(xtile, ytile, value)                    \
  do                                                             \
  {                                                              \
    if(((xtile) < BX_NUM_X_TILES) && ((ytile) < BX_NUM_Y_TILES)) \
      state.vga_tile_updated[(xtile)][(ytile)] = value;          \
  } while(0)

#define GET_TILE_UPDATED(xtile, ytile) \
    ((((xtile) < BX_NUM_X_TILES) && ((ytile) < BX_NUM_Y_TILES)) ? state.vga_tile_updated[(xtile)][(ytile)] : 0)

  void CS3Trio64::run()
{
  try
  {
    // initialize the GUI (and let it know our tilesize)
    bx_gui->init(state.x_tilesize, state.y_tilesize);
    for(;;)
    {
      // Terminate thread if StopThread is set to true
      if(StopThread)
        return;
      // Handle GUI events (100 times per second)
      for (int i=0;i<10;i++)
      {
        bx_gui->lock();
        bx_gui->handle_events();
        bx_gui->unlock();
        Poco::Thread::sleep(10);
      }
      //Update the screen (10 times per second)
      bx_gui->lock();
      update();
      bx_gui->flush();
      bx_gui->unlock();
    }
  }

  catch(Poco::Exception & e)
  {
    printf("Exception in S3 thread: %s.\n", e.displayText().c_str());

    // Let the thread die...
  }
}

static unsigned int rom_max;

static u8           option_rom[65536];

static u32                 s3_cfg_data[64] = {
  /*00*/ 0x88115333,            // CFID: vendor + device
  /*04*/ 0x011f0000,            // CFCS: command + status
  /*08*/ 0x03000002,            // CFRV: class + revision
  /*0c*/ 0x00000000,            // CFLT: latency timer + cache line size
  /*10*/ 0xf8000000,            // BAR0: FB
  /*14*/ 0x00000000,            // BAR1:
  /*18*/ 0x00000000,            // BAR2:
  /*1c*/ 0x00000000,            // BAR3:
  /*20*/ 0x00000000,            // BAR4:
  /*24*/ 0x00000000,            // BAR5:
  /*28*/ 0x00000000,            // CCIC: CardBus
  /*2c*/ 0x00000000,            // CSID: subsystem + vendor
  /*30*/ 0x00000000,            // BAR6: expansion rom base
  /*34*/ 0x00000000,            // CCAP: capabilities pointer
  /*38*/ 0x00000000,
  /*3c*/ 0x281401ff,            // CFIT: interrupt configuration
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};

static u32                 s3_cfg_mask[64] = {
  /*00*/ 0x00000000,            // CFID: vendor + device
  /*04*/ 0x0000ffff,            // CFCS: command + status
  /*08*/ 0x00000000,            // CFRV: class + revision
  /*0c*/ 0x0000ffff,            // CFLT: latency timer + cache line size
  /*10*/ 0xfc000000,            // BAR0: FB
  /*14*/ 0x00000000,            // BAR1:
  /*18*/ 0x00000000,            // BAR2:
  /*1c*/ 0x00000000,            // BAR3:
  /*20*/ 0x00000000,            // BAR4:
  /*24*/ 0x00000000,            // BAR5:
  /*28*/ 0x00000000,            // CCIC: CardBus
  /*2c*/ 0x00000000,            // CSID: subsystem + vendor
  /*30*/ 0x00000000,            // BAR6: expansion rom base
  /*34*/ 0x00000000,            // CCAP: capabilities pointer
  /*38*/ 0x00000000,
  /*3c*/ 0x000000ff,            // CFIT: interrupt configuration
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};

CS3Trio64::CS3Trio64(CConfigurator* cfg, CSystem* c, int pcibus, int pcidev) : CVGA(cfg, c, pcibus, pcidev)
{ }

void CS3Trio64::init()
{
  // Register PCI device
  add_function(0, s3_cfg_data, s3_cfg_mask);

  int i;

  // Initialize all state variables to 0
  memset((void*) &state, 0, sizeof(state));

  // Register VGA I/O ports at 3b4, 3b5, 3ba, 3c0..cf, 3d4, 3d5, 3da
  add_legacy_io(1, 0x3b4, 2);
  add_legacy_io(3, 0x3ba, 2);
  add_legacy_io(2, 0x3c0, 16);
  add_legacy_io(8, 0x3d4, 2);
  add_legacy_io(9, 0x3da, 1);

  /* The VGA BIOS we use sends text messages to port 0x500.
     We listen for these messages at port 500. */
  add_legacy_io(7, 0x500, 1);
  bios_message_size = 0;
  bios_message[0] = '\0';

  // Legacy video address space: A0000 -> bffff
  add_legacy_mem(4, 0xa0000, 128 * 1024);

  // Reset the base PCI device
  ResetPCI();

  /* The configuration file variable "rom" should point to a VGA BIOS
     image. If not, try "vgabios.bin". */
  FILE*   rom = fopen(myCfg->get_text_value("rom", "vgabios.bin"), "rb");
  if(!rom)
  {
    FAILURE_1(FileNotFound, "s3 rom file %s not found",
              myCfg->get_text_value("rom", "vgabios.bin"));
  }

  rom_max = (unsigned) fread(option_rom, 1, 65536, rom);
  fclose(rom);

  // Option ROM address space: C0000
  add_legacy_mem(5, 0xc0000, rom_max);

  state.vga_enabled = 1;
  state.misc_output.color_emulation = 1;
  state.misc_output.enable_ram = 1;
  state.misc_output.horiz_sync_pol = 1;
  state.misc_output.vert_sync_pol = 1;

  state.attribute_ctrl.mode_ctrl.enable_line_graphics = 1;

  state.line_offset = 80;
  state.line_compare = 1023;
  state.vertical_display_end = 399;

  state.attribute_ctrl.video_enabled = 1;
  state.attribute_ctrl.color_plane_enable = 0x0f;

  state.pel.dac_state = 0x01;
  state.pel.mask = 0xff;

  state.graphics_ctrl.memory_mapping = 2; // monochrome text mode

  state.sequencer.reset1 = 1;
  state.sequencer.reset2 = 1;
  state.sequencer.extended_mem = 1;       // display mem greater than 64K
  state.sequencer.odd_even = 1;           // use sequential addressing mode

  state.memsize = 0x40000;
  state.memory = new u8[state.memsize];
  memset(state.memory, 0, state.memsize);

  state.last_bpp = 8;

  state.CRTC.reg[0x09] = 16;
  state.graphics_ctrl.memory_mapping = 3; // color text mode
  state.vga_mem_updated = 1;

  myThread = 0;

  printf("%s: $Id: S3Trio64.cpp,v 1.18 2008/03/25 10:20:35 iamcamiel Exp $\n",
         devid_string);
}

void CS3Trio64::start_threads()
{
  if(!myThread)
  {
    myThread = new Poco::Thread("s3");
    printf(" %s", myThread->getName().c_str());
    StopThread = false;
    myThread->start(*this);
  }
}

void CS3Trio64::stop_threads()
{
  // Signal the thread to stop
  StopThread = true;
  if(myThread)
  {
    printf(" %s", myThread->getName().c_str());
    // Wait for the thread to end execution
    myThread->join();
    // And delete the Thread object
    delete myThread;
    myThread = 0;
  }
}

CS3Trio64::~CS3Trio64()
{
  stop_threads();
}

u32 CS3Trio64::ReadMem_Legacy(int index, u32 address, int dsize)
{
  u32 data = 0;
  switch(index)
  {
  // IO Port 0x3b4
  case 1: 
    data = io_read(address + 0x3b4, dsize);
    break;
  
  // IO Port 0x3c0..0x3cf
  case 2: 
    data = io_read(address + 0x3c0, dsize);
    break;
  
  // IO Port 0x3ba
  case 3: 
    data = io_read(address + 0x3ba, dsize);
    break;

  // VGA Memory
  case 4: 
    data = legacy_read(address, dsize);
    break;

  // ROM
  case 5: 
    data = rom_read(address, dsize);
    break;

  // IO Port 0x3d4
  case 8:
    data = io_read(address + 0x3d4, dsize);
    break;

  // IO Port 0x3da
  case 9:
    data = io_read(address + 0x3da, dsize);
    break;
  }

  return data;
}

void CS3Trio64::WriteMem_Legacy(int index, u32 address, int dsize, u32 data)
{
  switch(index)
  {
  // IO Port 0x3b4
  case 1:
    io_write(address + 0x3b4, dsize, data);
    return;

  // IO Port 0x3c0..0x3cf
  case 2:
    io_write(address + 0x3c0, dsize, data);
    return;

  // IO Port 0x3ba
  case 3:
    io_write(address + 0x3ba, dsize, data);
    return;

  // VGA Memory
  case 4:
    legacy_write(address, dsize, data);
    return;

  // BIOS Message IO Port (0x500)
  case 7:
    bios_message[bios_message_size++] = (char) data & 0xff;
    if(((data & 0xff) == 0x0a) || ((data & 0xff) == 0x0d))
    {
      if(bios_message_size > 1)
      {
        bios_message[bios_message_size - 1] = '\0';
        printf("s3: %s\n", bios_message);
      }

      bios_message_size = 0;
    }

    return;

  // IO Port 0x3d4
  case 8:
    io_write(address + 0x3d4, dsize, data);
    return;

  // IO Port 0x3da
  case 9:
    io_write(address + 0x3da, dsize, data);
    return;
  }
}

u32 CS3Trio64::ReadMem_Bar(int func, int bar, u32 address, int dsize)
{
  switch(bar)
  {
  // PCI memory range
  case 0: 
    return mem_read(address, dsize);
  }

  return 0;
}

void CS3Trio64::WriteMem_Bar(int func, int bar, u32 address, int dsize, u32 data)
{
  switch(bar)
  {
  // PCI Memory range
  case 0: 
    mem_write(address, dsize, data); 
    return;
  }
}

void CS3Trio64::check_state()
{
  if(myThread && !myThread->isRunning())
    FAILURE(Thread, "S3 thread has died");
}

static u32  s3_magic1 = 0x53338811;
static u32  s3_magic2 = 0x88115333;

int CS3Trio64::SaveState(FILE* f)
{
  long  ss = sizeof(state);
  int   res;

  if(res = CPCIDevice::SaveState(f))
    return res;

  fwrite(&s3_magic1, sizeof(u32), 1, f);
  fwrite(&ss, sizeof(long), 1, f);
  fwrite(&state, sizeof(state), 1, f);
  fwrite(&s3_magic2, sizeof(u32), 1, f);
  printf("%s: %d bytes saved.\n", devid_string, (int) ss);
  return 0;
}

int CS3Trio64::RestoreState(FILE* f)
{
  long    ss;
  u32     m1;
  u32     m2;
  int     res;
  size_t  r;

  if(res = CPCIDevice::RestoreState(f))
    return res;

  r = fread(&m1, sizeof(u32), 1, f);
  if(r != 1)
  {
    printf("%s: unexpected end of file!\n", devid_string);
    return -1;
  }

  if(m1 != s3_magic1)
  {
    printf("%s: MAGIC 1 does not match!\n", devid_string);
    return -1;
  }

  fread(&ss, sizeof(long), 1, f);
  if(r != 1)
  {
    printf("%s: unexpected end of file!\n", devid_string);
    return -1;
  }

  if(ss != sizeof(state))
  {
    printf("%s: STRUCT SIZE does not match!\n", devid_string);
    return -1;
  }

  fread(&state, sizeof(state), 1, f);
  if(r != 1)
  {
    printf("%s: unexpected end of file!\n", devid_string);
    return -1;
  }

  r = fread(&m2, sizeof(u32), 1, f);
  if(r != 1)
  {
    printf("%s: unexpected end of file!\n", devid_string);
    return -1;
  }

  if(m2 != s3_magic2)
  {
    printf("%s: MAGIC 1 does not match!\n", devid_string);
    return -1;
  }

  printf("%s: %d bytes restored.\n", devid_string, (int) ss);
  return 0;
}

u32 CS3Trio64::mem_read(u32 address, int dsize)
{
  u32 data = 0;

  //printf("S3 mem read: %" LL "x, %d, %" LL "x   \n", address, dsize, data);
  return data;
}

void CS3Trio64::mem_write(u32 address, int dsize, u32 data)
{

  //printf("S3 mem write: %" LL "x, %d, %" LL "x   \n", address, dsize, data);
  switch(dsize)
  {
  case 8:
  case 16:
  case 32:
    break;
  }
}

u32 CS3Trio64::legacy_read(u32 address, int dsize)
{
  u32 data = 0;
  switch(dsize)
  {
  case 32:
    data |= (u64) vga_mem_read((u32) address + 0xA0003) << 24;
    data |= (u64) vga_mem_read((u32) address + 0xA0002) << 16;

  case 16:
    data |= (u64) vga_mem_read((u32) address + 0xA0001) << 8;

  case 8:
    data |= (u64) vga_mem_read((u32) address + 0xA0000);
  }

  //  //printf("S3 legacy read: %" LL "x, %d, %" LL "x   \n", address, dsize, data);
  return data;
}

void CS3Trio64::legacy_write(u32 address, int dsize, u32 data)
{

  //  //printf("S3 legacy write: %" LL "x, %d, %" LL "x   \n", address, dsize, data);
  switch(dsize)
  {
  case 32:
    vga_mem_write((u32) address + 0xA0002, (u8) (data >> 16));
    vga_mem_write((u32) address + 0xA0003, (u8) (data >> 24));

  case 16:
    vga_mem_write((u32) address + 0xA0001, (u8) (data >> 8));

  case 8:
    vga_mem_write((u32) address + 0xA0000, (u8) (data));
  }
}

u32 CS3Trio64::rom_read(u32 address, int dsize)
{
  u32   data = 0x00;
  u8*   x = (u8*) option_rom;
  if(address <= rom_max)
  {
    x += address;
    switch(dsize)
    {
    case 8:   data = (u32) endian_8((*((u8*) x)) & 0xff); break;
    case 16:  data = (u32) endian_16((*((u16*) x)) & 0xffff); break;
    case 32:  data = (u32) endian_32((*((u32*) x)) & 0xffffffff); break;
    }

    //printf("S3 rom read: %" LL "x, %d, %" LL "x\n", address, dsize,data);
  }
  else
  {

    //printf("S3 (BAD) rom read: %" LL "x, %d, %" LL "x\n", address, dsize,data);
  }

  return data;
}

u32 CS3Trio64::io_read(u32 address, int dsize)
{
  u32 data = 0;
  if(dsize != 8)
    FAILURE(InvalidArgument, "Unsupported dsize");

  switch(address)
  {
  case 0x3c0:
    data = read_b_3c0();
    break;

  case 0x3c1:
    data = read_b_3c1();
    break;

  case 0x3c2:
    data = read_b_3c2();
    break;

  case 0x3c3:
    data = read_b_3c3();
    break;

  case 0x3c4:
    data = read_b_3c4();
    break;

  case 0x3c5:
    data = read_b_3c5();
    break;

  case 0x3c9:
    data = read_b_3c9();
    break;

  case 0x3ca:
    data = read_b_3ca();
    break;

  case 0x3cc:
    data = read_b_3cc();
    break;

  case 0x3cf:
    data = read_b_3cf();
    break;

  case 0x3b4:
  case 0x3d4:
    data = read_b_3d4();
    break;

  case 0x3b5:
  case 0x3d5:
    data = read_b_3d5();
    break;

  case 0x3ba:
  case 0x3da:
    data = read_b_3da();
    break;

  default:
    FAILURE_1(NotImplemented, "Unhandled port %x read", address);
  }

  //printf("S3 io read: %" LL "x, %d, %" LL "x   \n", address, dsize, data);
  return data;
}

void CS3Trio64::io_write(u32 address, int dsize, u32 data)
{

  //  printf("S3 io write: %" LL "x, %d, %" LL "x   \n", address+VGA_BASE, dsize, data);
  switch(dsize)
  {
  case 8:
    io_write_b(address, (u8) data);
    break;

  case 16:
    io_write_b(address, (u8) data);
    io_write_b(address + 1, (u8) (data >> 8));
    break;

  default:
    FAILURE(InvalidArgument, "Weird IO size");
  }
}

void CS3Trio64::io_write_b(u32 address, u8 data)
{
  switch(address)
  {
  case 0x3c0:
    write_b_3c0(data);
    break;

  case 0x3c2:
    write_b_3c2(data);
    break;

  case 0x3c4:
    write_b_3c4(data);
    break;

  case 0x3c5:
    write_b_3c5(data);
    break;

  case 0x3c6:
    write_b_3c6(data);
    break;

  case 0x3c7:
    write_b_3c7(data);
    break;

  case 0x3c8:
    write_b_3c8(data);
    break;

  case 0x3c9:
    write_b_3c9(data);
    break;

  case 0x3ce:
    write_b_3ce(data);
    break;

  case 0x3cf:
    write_b_3cf(data);
    break;

  case 0x3b4:
  case 0x3d4:
    write_b_3d4(data);
    break;

  case 0x3b5:
  case 0x3d5:
    write_b_3d5(data);
    break;

  default:
    FAILURE_1(NotImplemented, "Unhandled port %x write", address);
  }
}

void CS3Trio64::write_b_3c0(u8 value)
{
  // Variables to save old state (to detect transitions)
  bool  prev_video_enabled;
  bool  prev_line_graphics;
  bool  prev_int_pal_size;

  /* The flip-flop determines whether the write goes to the index-register
     (address) or the data-register. */
  if(state.attribute_ctrl.flip_flop == 0)
  { 
    // Write goes to the index-register.

    /* The index register also has a bit that controls whether video
       output is enabled or not.
       We check this bit, and compare it to it's previous state, to 
       determine whether we need to perform an enable or disable 
       transition. */
    prev_video_enabled = state.attribute_ctrl.video_enabled;
    state.attribute_ctrl.video_enabled = (value >> 5) & 0x01;
#if defined(DEBUG_VGA)
    printf("io write 3c0: video_enabled = %u   \n",
           (unsigned) state.attribute_ctrl.video_enabled);
#endif
    if(state.attribute_ctrl.video_enabled == 0)
    {
      if (prev_video_enabled)
      {
#if defined(DEBUG_VGA)
        printf("found disable transition   \n");
#endif
        // Video output has been disabled. Clear the screen.
        bx_gui->lock();
        bx_gui->clear_screen();
        bx_gui->unlock();
      }
    }
    else if(!prev_video_enabled)
    {
#if defined(DEBUG_VGA)
      printf("found enable transition   \n");
#endif
      // Video output has been enabled. Draw the screen.
      redraw_area(0, 0, old_iWidth, old_iHeight);
    }

    // Determine what register should be addressed.
    value &= 0x1f;  /* address = bits 0..4 */
    state.attribute_ctrl.address = value;

    /* Registers 0x00..0x0f are palette selection registers. 
       Write a debugging message for all other registers. */
#if defined(DEBUG_VGA)
    if (value>0x0f)
      printf("io write 3c0: address mode reg=%u   \n", (unsigned) value);
#endif
  }
  else
  { 
    // Write should go to the data-register.

    // Registers 0x00..0x0f are palette selection registers.
    if (state.attribute_ctrl.address<=0x0f)
    {
      // Update palette selection only of there is a change.
      if(value != state.attribute_ctrl.palette_reg[state.attribute_ctrl.
           address])
      {
        // Update the palette selection.
        state.attribute_ctrl.palette_reg[state.attribute_ctrl.address] = value;
        // Requires redrawing the screen.
        redraw_area(0, 0, old_iWidth, old_iHeight);
      }
    }
    else
    {
      switch(state.attribute_ctrl.address)
      {
      // Mode control register
      case 0x10:
        prev_line_graphics = state.attribute_ctrl.mode_ctrl.enable_line_graphics;
        prev_int_pal_size = state.attribute_ctrl.mode_ctrl.internal_palette_size;
        state.attribute_ctrl.mode_ctrl.graphics_alpha = (value >> 0) & 0x01;
        state.attribute_ctrl.mode_ctrl.display_type = (value >> 1) & 0x01;
        state.attribute_ctrl.mode_ctrl.enable_line_graphics = (value >> 2) & 0x01;
        state.attribute_ctrl.mode_ctrl.blink_intensity = (value >> 3) & 0x01;
        state.attribute_ctrl.mode_ctrl.pixel_panning_compat = (value >> 5) & 0x01;
        state.attribute_ctrl.mode_ctrl.pixel_clock_select = (value >> 6) & 0x01;
        state.attribute_ctrl.mode_ctrl.internal_palette_size = (value >> 7) & 0x01;
        if(((value >> 2) & 0x01) != prev_line_graphics)
        {
          bx_gui->lock();
          bx_gui->set_text_charmap(&state.memory[0x20000 + state.charmap_address]);
          bx_gui->unlock();
          state.vga_mem_updated = 1;
        }

        if(((value >> 7) & 0x01) != prev_int_pal_size)
        {
          redraw_area(0, 0, old_iWidth, old_iHeight);
        }

#if defined(DEBUG_VGA)
        printf("io write 3c0: mode control: %02x h   \n", (unsigned) value);
#endif
        break;

      // Overscan Color Register
      case 0x11:
        /* We don't do anything with this. Our display doesn't
           show the overscan part of the normal monitor. */
        state.attribute_ctrl.overscan_color = (value & 0x3f);
#if defined(DEBUG_VGA)
        printf("io write 3c0: overscan color = %02x   \n", (unsigned) value);
#endif
        break;

      // Color Plane Enable Register
      case 0x12:
        state.attribute_ctrl.color_plane_enable = (value & 0x0f);
        redraw_area(0, 0, old_iWidth, old_iHeight);
#if defined(DEBUG_VGA)
        printf("io write 3c0: color plane enable = %02x   \n", (unsigned) value);
#endif
        break;

      // Horizontal Pixel Panning Register
      case 0x13:
        state.attribute_ctrl.horiz_pel_panning = (value & 0x0f);
        redraw_area(0, 0, old_iWidth, old_iHeight);
#if defined(DEBUG_VGA)
        printf("io write 3c0: horiz pel panning = %02x   \n", (unsigned) value);
#endif
        break;

      // Color Select Register
      case 0x14:
        state.attribute_ctrl.color_select = (value & 0x0f);
        redraw_area(0, 0, old_iWidth, old_iHeight);
#if defined(DEBUG_VGA)
        printf("io write 3c0: color select = %02x   \n",
               (unsigned) state.attribute_ctrl.color_select);
#endif
        break;

      default:
        FAILURE_1(NotImplemented, "io write 3c0: data-write mode %02x h",
                  (unsigned) state.attribute_ctrl.address);
      }
    }
  }

  // Flip the flip-flop
  state.attribute_ctrl.flip_flop = !state.attribute_ctrl.flip_flop;
}

void CS3Trio64::write_b_3c2(u8 value)
{
  state.misc_output.color_emulation = (value >> 0) & 0x01;
  state.misc_output.enable_ram = (value >> 1) & 0x01;
  state.misc_output.clock_select = (value >> 2) & 0x03;
  state.misc_output.select_high_bank = (value >> 5) & 0x01;
  state.misc_output.horiz_sync_pol = (value >> 6) & 0x01;
  state.misc_output.vert_sync_pol = (value >> 7) & 0x01;
#if defined(DEBUG_VGA)
  printf("io write 3c2:   \n");
  printf("  color_emulation = %u   \n",
         (unsigned) state.misc_output.color_emulation);
  printf("  enable_ram = %u   \n", (unsigned) state.misc_output.enable_ram);
  printf("  clock_select = %u   \n", (unsigned) state.misc_output.clock_select);
  printf("  select_high_bank = %u   \n",
         (unsigned) state.misc_output.select_high_bank);
  printf("  horiz_sync_pol = %u   \n",
         (unsigned) state.misc_output.horiz_sync_pol);
  printf("  vert_sync_pol = %u   \n", (unsigned) state.misc_output.vert_sync_pol);
#endif
}

void CS3Trio64::write_b_3c4(u8 value)
{
  state.sequencer.index = value;
}

void CS3Trio64::write_b_3c5(u8 value)
{
  unsigned  i;
  u8        charmap1;
  u8        charmap2;

  switch(state.sequencer.index)
  {
  // Sequencer: reset register
  case 0:
#if defined(DEBUG_VGA)
    printf("write 0x3c5: sequencer reset: value=0x%02x   \n", (unsigned) value);
#endif
    if(state.sequencer.reset1 && ((value & 0x01) == 0))
    {
      state.sequencer.char_map_select = 0;
      state.charmap_address = 0;
      bx_gui->lock();
      bx_gui->set_text_charmap(&state.memory[0x20000 + state.charmap_address]);
      bx_gui->unlock();
      state.vga_mem_updated = 1;
    }

    state.sequencer.reset1 = (value >> 0) & 0x01;
    state.sequencer.reset2 = (value >> 1) & 0x01;
    break;

  // Sequencer: clocking mode register
  case 1:
#if defined(DEBUG_VGA)
    printf("io write 3c5=%02x: clocking mode reg: ignoring   \n",
           (unsigned) value);
#endif
    state.sequencer.reg1 = value & 0x3f;
    state.x_dotclockdiv2 = ((value & 0x08) > 0);
    break;

  // Sequencer: map mask register
  case 2:
    state.sequencer.map_mask = (value & 0x0f);
    for(i = 0; i < 4; i++)
      state.sequencer.map_mask_bit[i] = (value >> i) & 0x01;
    break;

  // Sequencer: character map select register
  case 3:
    state.sequencer.char_map_select = value;
    charmap1 = value & 0x13;
    if(charmap1 > 3)
      charmap1 = (charmap1 & 3) + 4;
    charmap2 = (value & 0x2C) >> 2;
    if(charmap2 > 3)
      charmap2 = (charmap2 & 3) + 4;
    if(state.CRTC.reg[0x09] > 0)
    {
      state.charmap_address = (charmap1 << 13);
      bx_gui->lock();
      bx_gui->set_text_charmap(&state.memory[0x20000 + state.charmap_address]);
      bx_gui->unlock();
      state.vga_mem_updated = 1;
    }

    if(charmap2 != charmap1)
      printf("char map select: #2=%d (unused)   \n", charmap2);
    break;

  // Sequencer: memory mode register
  case 4:
    state.sequencer.extended_mem = (value >> 1) & 0x01;
    state.sequencer.odd_even = (value >> 2) & 0x01;
    state.sequencer.chain_four = (value >> 3) & 0x01;

#if defined(DEBUG_VGA)
    printf("io write 3c5: index 4:   \n");
    printf("  extended_mem %u   \n", (unsigned) state.sequencer.extended_mem);
    printf("  odd_even %u   \n", (unsigned) state.sequencer.odd_even);
    printf("  chain_four %u   \n", (unsigned) state.sequencer.chain_four);
#endif
    break;

  default:
    FAILURE_1(NotImplemented, "io write 3c5: index %u unhandled",
              (unsigned) state.sequencer.index);
  }
}

void CS3Trio64::write_b_3c6(u8 value)
{
  state.pel.mask = value;
#if defined(DEBUG_VGA)
  if(state.pel.mask != 0xff)
    printf("io write 3c6: PEL mask=0x%02x != 0xFF   \n", value);
#endif

  // state.pel.mask should be and'd with final value before
  // indexing into color register state.pel.data[]
}

void CS3Trio64::write_b_3c7(u8 value)
{
  state.pel.read_data_register = value;
  state.pel.read_data_cycle = 0;
  state.pel.dac_state = 0x03;
}

void CS3Trio64::write_b_3c8(u8 value)
{
  state.pel.write_data_register = value;
  state.pel.write_data_cycle = 0;
  state.pel.dac_state = 0x00;
}

void CS3Trio64::write_b_3c9(u8 value)
{
  switch(state.pel.write_data_cycle)
  {
  case 0:
    state.pel.data[state.pel.write_data_register].red = value;
    break;

  case 1:
    state.pel.data[state.pel.write_data_register].green = value;
    break;

  case 2:
    {
      state.pel.data[state.pel.write_data_register].blue = value;
      // Palette write complete. Check if value has changed
      bx_gui->lock();
      bool  changed = bx_gui->palette_change(state.pel.write_data_register,
                                             state.pel.data[state.pel.write_data_register].red << 2,
                                             state.pel.data[state.pel.write_data_register].green << 2,
                                             state.pel.data[state.pel.write_data_register].blue << 2);
      bx_gui->unlock();
      // If palette value has changed, redraw the screen.
      if(changed)
        redraw_area(0, 0, old_iWidth, old_iHeight);
    }
    break;
  }

  // Move on to next RGB component
  state.pel.write_data_cycle++;

  // palette entry complete, move on to next one
  if(state.pel.write_data_cycle >= 3)
  {

    //BX_INFO(("state.pel.data[%u] {r=%u, g=%u, b=%u}",
    //  (unsigned) state.pel.write_data_register,
    //  (unsigned) state.pel.data[state.pel.write_data_register].red,
    //  (unsigned) state.pel.data[state.pel.write_data_register].green,
    //  (unsigned) state.pel.data[state.pel.write_data_register].blue);
    state.pel.write_data_cycle = 0;
    state.pel.write_data_register++;
  }
}

void CS3Trio64::write_b_3ce(u8 value)
{
#if defined(DEBUG_VGA)
  if(value > 0x08)  /* ??? */
    printf("io write: 3ce: value > 8   \n");
#endif
  state.graphics_ctrl.index = value;
}

void CS3Trio64::write_b_3cf(u8 value)
{
  u8    prev_memory_mapping;
  bool  prev_graphics_alpha;
  bool  prev_chain_odd_even;

  /* Graphics Controller Registers 00..08 */
  switch(state.graphics_ctrl.index)
  {
  case 0:           /* Set/Reset */
    state.graphics_ctrl.set_reset = value & 0x0f;
    break;

  case 1:           /* Enable Set/Reset */
    state.graphics_ctrl.enable_set_reset = value & 0x0f;
    break;

  case 2:           /* Color Compare */
    state.graphics_ctrl.color_compare = value & 0x0f;
    break;

  case 3:           /* Data Rotate */
    state.graphics_ctrl.data_rotate = value & 0x07;

    /* ??? is this bits 3..4 or 4..5 */
    state.graphics_ctrl.raster_op = (value >> 3) & 0x03;  /* ??? */
    break;

  case 4:     /* Read Map Select */
    state.graphics_ctrl.read_map_select = value & 0x03;
#if defined(DEBUG_VGA)
    printf("io write to 03cf = %02x (RMS)   \n", (unsigned) value);
#endif
    break;

  case 5:     /* Mode */
    state.graphics_ctrl.write_mode = value & 0x03;
    state.graphics_ctrl.read_mode = (value >> 3) & 0x01;
    state.graphics_ctrl.odd_even = (value >> 4) & 0x01;
    state.graphics_ctrl.shift_reg = (value >> 5) & 0x03;

#if defined(DEBUG_VGA)
    if(state.graphics_ctrl.odd_even)
      printf("io write: 3cf: reg 05: value = %02xh   \n", (unsigned) value);
    if(state.graphics_ctrl.shift_reg)
      printf("io write: 3cf: reg 05: value = %02xh   \n", (unsigned) value);
#endif
    break;

  case 6:     /* Miscellaneous */
    prev_graphics_alpha = state.graphics_ctrl.graphics_alpha;
    prev_chain_odd_even = state.graphics_ctrl.chain_odd_even;
    prev_memory_mapping = state.graphics_ctrl.memory_mapping;

    state.graphics_ctrl.graphics_alpha = value & 0x01;
    state.graphics_ctrl.chain_odd_even = (value >> 1) & 0x01;
    state.graphics_ctrl.memory_mapping = (value >> 2) & 0x03;
#if defined(DEBUG_VGA)
    printf("memory_mapping set to %u   \n",
           (unsigned) state.graphics_ctrl.memory_mapping);
    printf("graphics mode set to %u   \n",
           (unsigned) state.graphics_ctrl.graphics_alpha);
    printf("odd_even mode set to %u   \n",
           (unsigned) state.graphics_ctrl.odd_even);
    printf("io write: 3cf: reg 06: value = %02xh   \n", (unsigned) value);
#endif
    if(prev_memory_mapping != state.graphics_ctrl.memory_mapping)
    {
      redraw_area(0, 0, old_iWidth, old_iHeight);
    }

    if(prev_graphics_alpha != state.graphics_ctrl.graphics_alpha)
    {
      redraw_area(0, 0, old_iWidth, old_iHeight);
      old_iHeight = 0;
    }
    break;

  case 7:     /* Color Don't Care */
    state.graphics_ctrl.color_dont_care = value & 0x0f;
    break;

  case 8:     /* Bit Mask */
    state.graphics_ctrl.bitmask = value;
    break;

  default:

    /* ??? */
    FAILURE_1(NotImplemented, "io write: 3cf: index %u unhandled",
              (unsigned) state.graphics_ctrl.index);
  }
}

void CS3Trio64::write_b_3d4(u8 value)
{
  state.CRTC.address = value & 0x7f;
#if defined(DEBUG_VGA)
  if(state.CRTC.address > 0x18)
    printf("write: invalid CRTC register 0x%02x selected",
           (unsigned) state.CRTC.address);
#endif
}

void CS3Trio64::write_b_3d5(u8 value)
{

  /* CRTC Registers */
  if(state.CRTC.address > 0x18)
  {
#if defined(DEBUG_VGA)
    printf("write: invalid CRTC register 0x%02x ignored",
           (unsigned) state.CRTC.address);
#endif
    return;
  }

  if(state.CRTC.write_protect && (state.CRTC.address < 0x08))
  {
    if(state.CRTC.address == 0x07)
    {
      state.CRTC.reg[state.CRTC.address] &= ~0x10;
      state.CRTC.reg[state.CRTC.address] |= (value & 0x10);
      state.line_compare &= 0x2ff;
      if(state.CRTC.reg[0x07] & 0x10)
        state.line_compare |= 0x100;
      redraw_area(0, 0, old_iWidth, old_iHeight);
      return;
    }
    else
    {
      return;
    }
  }

  if(value != state.CRTC.reg[state.CRTC.address])
  {
    state.CRTC.reg[state.CRTC.address] = value;
    switch(state.CRTC.address)
    {
    case 0x07:
      state.vertical_display_end &= 0xff;
      if(state.CRTC.reg[0x07] & 0x02)
        state.vertical_display_end |= 0x100;
      if(state.CRTC.reg[0x07] & 0x40)
        state.vertical_display_end |= 0x200;
      state.line_compare &= 0x2ff;
      if(state.CRTC.reg[0x07] & 0x10)
        state.line_compare |= 0x100;
      redraw_area(0, 0, old_iWidth, old_iHeight);
      break;

    case 0x08:

      // Vertical pel panning change
      redraw_area(0, 0, old_iWidth, old_iHeight);
      break;

    case 0x09:
      state.y_doublescan = ((value & 0x9f) > 0);
      state.line_compare &= 0x1ff;
      if(state.CRTC.reg[0x09] & 0x40)
        state.line_compare |= 0x200;
      redraw_area(0, 0, old_iWidth, old_iHeight);
      break;

    case 0x0A:
    case 0x0B:
    case 0x0E:
    case 0x0F:

      // Cursor size / location change
      state.vga_mem_updated = 1;
      break;

    case 0x0C:
    case 0x0D:

      // Start address change
      if(state.graphics_ctrl.graphics_alpha)
      {
        redraw_area(0, 0, old_iWidth, old_iHeight);
      }
      else
      {
        state.vga_mem_updated = 1;
      }
      break;

    case 0x12:
      state.vertical_display_end &= 0x300;
      state.vertical_display_end |= state.CRTC.reg[0x12];
      break;

    case 0x13:
    case 0x14:
    case 0x17:

      // Line offset change
      state.line_offset = state.CRTC.reg[0x13] << 1;
      if(state.CRTC.reg[0x14] & 0x40)
        state.line_offset <<= 2;
      else if((state.CRTC.reg[0x17] & 0x40) == 0)
        state.line_offset <<= 1;
      redraw_area(0, 0, old_iWidth, old_iHeight);
      break;

    case 0x18:
      state.line_compare &= 0x300;
      state.line_compare |= state.CRTC.reg[0x18];
      redraw_area(0, 0, old_iWidth, old_iHeight);
      break;
    }
  }
}

u8 CS3Trio64::read_b_3c0()
{
  if(state.attribute_ctrl.flip_flop == 0)
  {

    //BX_INFO(("io read: 0x3c0: flip_flop = 0"));
    return(state.attribute_ctrl.video_enabled << 5) | state.attribute_ctrl.address;
  }
  else
  {
    FAILURE(NotImplemented, "io read: 0x3c0: flip_flop != 0");
  }
}

u8 CS3Trio64::read_b_3c1()
{
  u8  retval;
  switch(state.attribute_ctrl.address)
  {
  case 0x00:
  case 0x01:
  case 0x02:
  case 0x03:
  case 0x04:
  case 0x05:
  case 0x06:
  case 0x07:
  case 0x08:
  case 0x09:
  case 0x0a:
  case 0x0b:
  case 0x0c:
  case 0x0d:
  case 0x0e:
  case 0x0f:
    retval = state.attribute_ctrl.palette_reg[state.attribute_ctrl.address];
    return(retval);
    break;

  case 0x10:  /* mode control register */
    retval = (state.attribute_ctrl.mode_ctrl.graphics_alpha << 0) |
      (state.attribute_ctrl.mode_ctrl.display_type << 1) |
        (state.attribute_ctrl.mode_ctrl.enable_line_graphics << 2) |
          (state.attribute_ctrl.mode_ctrl.blink_intensity << 3) |
            (state.attribute_ctrl.mode_ctrl.pixel_panning_compat << 5) |
              (state.attribute_ctrl.mode_ctrl.pixel_clock_select << 6) |
                (state.attribute_ctrl.mode_ctrl.internal_palette_size << 7);
    return(retval);
    break;

  case 0x11:  /* overscan color register */
    return(state.attribute_ctrl.overscan_color);
    break;

  case 0x12:  /* color plane enable */
    return(state.attribute_ctrl.color_plane_enable);
    break;

  case 0x13:  /* horizontal PEL panning register */
    return(state.attribute_ctrl.horiz_pel_panning);
    break;

  case 0x14:  /* color select register */
    return(state.attribute_ctrl.color_select);
    break;

  default:
    FAILURE_1(NotImplemented, "io read: 0x3c1: unknown register 0x%02x",
              (unsigned) state.attribute_ctrl.address);
  }
}

u8 CS3Trio64::read_b_3c2()
{
  return 0;   // input status register
}

u8 CS3Trio64::read_b_3c3()
{
  return state.vga_enabled;
}

u8 CS3Trio64::read_b_3c4()
{
  return state.sequencer.index;
}

u8 CS3Trio64::read_b_3c5()
{
  switch(state.sequencer.index)
  {
  case 0:     /* sequencer: reset */
#if defined(DEBUG_VGA)
    BX_DEBUG(("io read 0x3c5: sequencer reset"));
#endif
    return(state.sequencer.reset1 ? 1 : 0) | (state.sequencer.reset2 ? 2 : 0);
    break;

  case 1:     /* sequencer: clocking mode */
#if defined(DEBUG_VGA)
    BX_DEBUG(("io read 0x3c5: sequencer clocking mode"));
#endif
    return state.sequencer.reg1;
    break;

  case 2:     /* sequencer: map mask register */
    return state.sequencer.map_mask;
    break;

  case 3:     /* sequencer: character map select register */
    return state.sequencer.char_map_select;
    break;

  case 4:     /* sequencer: memory mode register */
    return(state.sequencer.extended_mem << 1) |
      (state.sequencer.odd_even << 2) |
      (state.sequencer.chain_four << 3);
    break;

  default:
    FAILURE_1(NotImplemented, "io read 0x3c5: index %u unhandled",
              (unsigned) state.sequencer.index);
  }
}

u8 CS3Trio64::read_b_3c9()
{
  u8  retval;
  if(state.pel.dac_state == 0x03)
  {
    switch(state.pel.read_data_cycle)
    {
    case 0:   retval = state.pel.data[state.pel.read_data_register].red; break;
    case 1:   retval = state.pel.data[state.pel.read_data_register].green; break;
    case 2:   retval = state.pel.data[state.pel.read_data_register].blue; break;
    default:  retval = 0; // keep compiler happy
    }

    state.pel.read_data_cycle++;
    if(state.pel.read_data_cycle >= 3)
    {
      state.pel.read_data_cycle = 0;
      state.pel.read_data_register++;
    }
  }
  else
  {
    retval = 0x3f;
  }

  return retval;
}

u8 CS3Trio64::read_b_3ca()
{
  return 0;
}

u8 CS3Trio64::read_b_3cc()
{

  /* Miscellaneous Output / Graphics 1 Position ??? */
  return((state.misc_output.color_emulation & 0x01) << 0) |
    ((state.misc_output.enable_ram & 0x01) << 1) |
      ((state.misc_output.clock_select & 0x03) << 2) |
        ((state.misc_output.select_high_bank & 0x01) << 5) |
          ((state.misc_output.horiz_sync_pol & 0x01) << 6) |
            ((state.misc_output.vert_sync_pol & 0x01) << 7);
}

u8 CS3Trio64::read_b_3cf()
{
  u8  retval;
  switch(state.graphics_ctrl.index)
  {
  case 0:               /* Set/Reset */
    return(state.graphics_ctrl.set_reset);
    break;

  case 1:               /* Enable Set/Reset */
    return(state.graphics_ctrl.enable_set_reset);
    break;

  case 2:               /* Color Compare */
    return(state.graphics_ctrl.color_compare);
    break;

  case 3:               /* Data Rotate */
    retval = ((state.graphics_ctrl.raster_op & 0x03) << 3) | ((state.graphics_ctrl.data_rotate & 0x07) << 0);
    return(retval);
    break;

  case 4:               /* Read Map Select */
    return(state.graphics_ctrl.read_map_select);
    break;

  case 5:               /* Mode */
    retval = ((state.graphics_ctrl.shift_reg & 0x03) << 5) |
      ((state.graphics_ctrl.odd_even & 0x01) << 4) |
        ((state.graphics_ctrl.read_mode & 0x01) << 3) |
          ((state.graphics_ctrl.write_mode & 0x03) << 0);

#if defined(DEBUG_VGA)
    if(state.graphics_ctrl.odd_even || state.graphics_ctrl.shift_reg)
      BX_DEBUG(("io read 0x3cf: reg 05 = 0x%02x", (unsigned) retval));
#endif
    return(retval);
    break;

  case 6:               /* Miscellaneous */
    return((state.graphics_ctrl.memory_mapping & 0x03) << 2) |
      ((state.graphics_ctrl.odd_even & 0x01) << 1) |
        ((state.graphics_ctrl.graphics_alpha & 0x01) << 0);
    break;

  case 7:               /* Color Don't Care */
    return(state.graphics_ctrl.color_dont_care);
    break;

  case 8:               /* Bit Mask */
    return(state.graphics_ctrl.bitmask);
    break;

  default:
    FAILURE_1(NotImplemented, "io read: 0x3cf: index %u unhandled",
              (unsigned) state.graphics_ctrl.index);
  }
}

u8 CS3Trio64::read_b_3d4()
{
  return state.CRTC.address;
}

u8 CS3Trio64::read_b_3d5()
{
  if(state.CRTC.address > 0x18)
  {
    FAILURE_1(NotImplemented, "io read: invalid CRTC register 0x%02x   \n",
              (unsigned) state.CRTC.address);
  }

  return state.CRTC.reg[state.CRTC.address];
}

u8 CS3Trio64::read_b_3da()
{

  /* Input Status 1 (color emulation modes) */
  u8  retval = 0;

  // bit3: Vertical Retrace
  //       0 = display is in the display mode
  //       1 = display is in the vertical retrace mode
  // bit0: Display Enable
  //       0 = display is in the display mode
  //       1 = display is not in the display mode; either the
  //           horizontal or vertical retrace period is active
  // using 72 Hz vertical frequency

  /*** TO DO ??? ***
       usec = bx_pc_system.time_usec();
       switch ( ( state.misc_output.vert_sync_pol << 1) | state.misc_output.horiz_sync_pol )
       {
         case 0: vertres = 200; break;
         case 1: vertres = 400; break;
         case 2: vertres = 350; break;
         default: vertres = 480; break;
       }
       if ((usec % 13888) < 70) {
         vert_retrace = 1;
       }
       if ((usec % (13888 / vertres)) == 0) {
         horiz_retrace = 1;
       }
 
       if (horiz_retrace || vert_retrace)
         retval = 0x01;
       if (vert_retrace)
         retval |= 0x08;
 
       *** TO DO ??? ***/

  /* reading this port resets the flip-flop to address mode */
  state.attribute_ctrl.flip_flop = 0;
  return retval;
}

u8 CS3Trio64::get_actl_palette_idx(u8 index)
{
  return state.attribute_ctrl.palette_reg[index];
}

void CS3Trio64::redraw_area(unsigned x0, unsigned y0, unsigned width,
                            unsigned height)
{
  unsigned  xti;

  unsigned  yti;

  unsigned  xt0;

  unsigned  xt1;

  unsigned  yt0;

  unsigned  yt1;

  unsigned  xmax;

  unsigned  ymax;

  if((width == 0) || (height == 0))
  {
    return;
  }

  state.vga_mem_updated = 1;

  if(state.graphics_ctrl.graphics_alpha)
  {

    // graphics mode
    xmax = old_iWidth;
    ymax = old_iHeight;
    xt0 = x0 / X_TILESIZE;
    yt0 = y0 / Y_TILESIZE;
    if(x0 < xmax)
    {
      xt1 = (x0 + width - 1) / X_TILESIZE;
    }
    else
    {
      xt1 = (xmax - 1) / X_TILESIZE;
    }

    if(y0 < ymax)
    {
      yt1 = (y0 + height - 1) / Y_TILESIZE;
    }
    else
    {
      yt1 = (ymax - 1) / Y_TILESIZE;
    }

    for(yti = yt0; yti <= yt1; yti++)
    {
      for(xti = xt0; xti <= xt1; xti++)
      {
        SET_TILE_UPDATED(xti, yti, 1);
      }
    }
  }
  else
  {

    // text mode
    memset(state.text_snapshot, 0, sizeof(state.text_snapshot));
  }
}

void CS3Trio64::update(void)
{
  unsigned  iHeight;

  unsigned  iWidth;

  /* no screen update necessary */
  if(state.vga_mem_updated == 0)
    return;

  /* skip screen update when vga/video is disabled or the sequencer is in reset mode */
  if(!state.vga_enabled || !state.attribute_ctrl.video_enabled
   || !state.sequencer.reset2 || !state.sequencer.reset1) return;

  // fields that effect the way video memory is serialized into screen output:
  // GRAPHICS CONTROLLER:
  //   state.graphics_ctrl.shift_reg:
  //     0: output data in standard VGA format or CGA-compatible 640x200 2 color
  //        graphics mode (mode 6)
  //     1: output data in CGA-compatible 320x200 4 color graphics mode
  //        (modes 4 & 5)
  //     2: output data 8 bits at a time from the 4 bit planes
  //        (mode 13 and variants like modeX)
  // if (state.vga_mem_updated==0 || state.attribute_ctrl.video_enabled == 0)
  if(state.graphics_ctrl.graphics_alpha)
  {
    u8            color;
    unsigned      bit_no;
    unsigned      r;
    unsigned      c;
    unsigned      x;
    unsigned      y;
    unsigned long byte_offset;
    unsigned long start_addr;
    unsigned      xc;
    unsigned      yc;
    unsigned      xti;
    unsigned      yti;

    start_addr = (state.CRTC.reg[0x0c] << 8) | state.CRTC.reg[0x0d];

    //BX_DEBUG(("update: shiftreg=%u, chain4=%u, mapping=%u",
    //  (unsigned) state.graphics_ctrl.shift_reg,
    //  (unsigned) state.sequencer.chain_four,
    //  (unsigned) state.graphics_ctrl.memory_mapping);
    determine_screen_dimensions(&iHeight, &iWidth);
    if((iWidth != old_iWidth) || (iHeight != old_iHeight) || (state.last_bpp > 8))
    {
      bx_gui->dimension_update(iWidth, iHeight);
      old_iWidth = iWidth;
      old_iHeight = iHeight;
      state.last_bpp = 8;
    }

    switch(state.graphics_ctrl.shift_reg)
    {
    case 0:
      u8 attribute, palette_reg_val, DAC_regno;

      unsigned long line_compare;
      u8*           plane0;
      u8 *plane1;
      u8 *plane2;
      u8 *plane3;

      if(state.graphics_ctrl.memory_mapping == 3)
      {                 // CGA 640x200x2
        for(yc = 0, yti = 0; yc < iHeight; yc += Y_TILESIZE, yti++)
        {
          for(xc = 0, xti = 0; xc < iWidth; xc += X_TILESIZE, xti++)
          {
            if(GET_TILE_UPDATED(xti, yti))
            {
              for(r = 0; r < Y_TILESIZE; r++)
              {
                y = yc + r;
                if(state.y_doublescan)
                  y >>= 1;
                for(c = 0; c < X_TILESIZE; c++)
                {
                  x = xc + c;

                  /* 0 or 0x2000 */
                  byte_offset = start_addr + ((y & 1) << 13);

                  /* to the start of the line */
                  byte_offset += (320 / 4) * (y / 2);

                  /* to the byte start */
                  byte_offset += (x / 8);

                  bit_no = 7 - (x % 8);
                  palette_reg_val = (((state.memory[byte_offset]) >> bit_no) & 1);
                  DAC_regno = state.attribute_ctrl.palette_reg[palette_reg_val];
                  state.tile[r * X_TILESIZE + c] = DAC_regno;
                }
              }

              SET_TILE_UPDATED(xti, yti, 0);
              bx_gui->graphics_tile_update(state.tile, xc, yc);
            }
          }
        }
      }
      else
      {                 // output data in serial fashion with each display plane
        // output on its associated serial output.  Standard EGA/VGA format
        plane0 = &state.memory[0 << 16];
        plane1 = &state.memory[1 << 16];
        plane2 = &state.memory[2 << 16];
        plane3 = &state.memory[3 << 16];
        line_compare = state.line_compare;
        if(state.y_doublescan)
          line_compare >>= 1;

        for(yc = 0, yti = 0; yc < iHeight; yc += Y_TILESIZE, yti++)
        {
          for(xc = 0, xti = 0; xc < iWidth; xc += X_TILESIZE, xti++)
          {
            if(GET_TILE_UPDATED(xti, yti))
            {
              for(r = 0; r < Y_TILESIZE; r++)
              {
                y = yc + r;
                if(state.y_doublescan)
                  y >>= 1;
                for(c = 0; c < X_TILESIZE; c++)
                {
                  x = xc + c;
                  if(state.x_dotclockdiv2)
                    x >>= 1;
                  bit_no = 7 - (x % 8);
                  if(y > line_compare)
                  {
                    byte_offset = x / 8 + ((y - line_compare - 1) * state.line_offset);
                  }
                  else
                  {
                    byte_offset = start_addr + x / 8 + (y * state.line_offset);
                  }

                  attribute = (((plane0[byte_offset] >> bit_no) & 0x01) << 0) |
                    (((plane1[byte_offset] >> bit_no) & 0x01) << 1) |
                      (((plane2[byte_offset] >> bit_no) & 0x01) << 2) |
                        (((plane3[byte_offset] >> bit_no) & 0x01) << 3);

                  attribute &= state.attribute_ctrl.color_plane_enable;

                  // undocumented feature ???: colors 0..7 high intensity, colors 8..15 blinking
                  // using low/high intensity. Blinking is not implemented yet.
                  if(state.attribute_ctrl.mode_ctrl.blink_intensity)
                    attribute ^= 0x08;
                  palette_reg_val = state.attribute_ctrl.palette_reg[attribute];
                  if(state.attribute_ctrl.mode_ctrl.internal_palette_size)
                  {

                    // use 4 lower bits from palette register
                    // use 4 higher bits from color select register
                    // 16 banks of 16-color registers
                    DAC_regno = (palette_reg_val & 0x0f) | (state.attribute_ctrl.color_select << 4);
                  }
                  else
                  {

                    // use 6 lower bits from palette register
                    // use 2 higher bits from color select register
                    // 4 banks of 64-color registers
                    DAC_regno = (palette_reg_val & 0x3f) | ((state.attribute_ctrl.color_select & 0x0c) << 4);
                  }

                  // DAC_regno &= video DAC mask register ???
                  state.tile[r * X_TILESIZE + c] = DAC_regno;
                }
              }

              SET_TILE_UPDATED(xti, yti, 0);
              bx_gui->graphics_tile_update(state.tile, xc, yc);
            }
          }
        }
      }
      break;            // case 0

    case 1:             // output the data in a CGA-compatible 320x200 4 color graphics
      // mode.  (modes 4 & 5)

      /* CGA 320x200x4 start */
      for(yc = 0, yti = 0; yc < iHeight; yc += Y_TILESIZE, yti++)
      {
        for(xc = 0, xti = 0; xc < iWidth; xc += X_TILESIZE, xti++)
        {
          if(GET_TILE_UPDATED(xti, yti))
          {
            for(r = 0; r < Y_TILESIZE; r++)
            {
              y = yc + r;
              if(state.y_doublescan)
                y >>= 1;
              for(c = 0; c < X_TILESIZE; c++)
              {
                x = xc + c;
                if(state.x_dotclockdiv2)
                  x >>= 1;

                /* 0 or 0x2000 */
                byte_offset = start_addr + ((y & 1) << 13);

                /* to the start of the line */
                byte_offset += (320 / 4) * (y / 2);

                /* to the byte start */
                byte_offset += (x / 4);

                attribute = 6 - 2 * (x % 4);
                palette_reg_val = (state.memory[byte_offset]) >> attribute;
                palette_reg_val &= 3;
                DAC_regno = state.attribute_ctrl.palette_reg[palette_reg_val];
                state.tile[r * X_TILESIZE + c] = DAC_regno;
              }
            }

            SET_TILE_UPDATED(xti, yti, 0);
            bx_gui->graphics_tile_update(state.tile, xc, yc);
          }
        }
      }

      /* CGA 320x200x4 end */
      break;            // case 1

    case 2:             // output the data eight bits at a time from the 4 bit plane

    // (format for VGA mode 13 hex)
    case 3:             // FIXME: is this really the same ???
      if(state.sequencer.chain_four)
      {
        unsigned long pixely;

        unsigned long pixelx;

        unsigned long plane;

        if(state.misc_output.select_high_bank != 1)
        {
          FAILURE(NotImplemented, "update: select_high_bank != 1   \n");
        }

        for(yc = 0, yti = 0; yc < iHeight; yc += Y_TILESIZE, yti++)
        {
          for(xc = 0, xti = 0; xc < iWidth; xc += X_TILESIZE, xti++)
          {
            if(GET_TILE_UPDATED(xti, yti))
            {
              for(r = 0; r < Y_TILESIZE; r++)
              {
                pixely = yc + r;
                if(state.y_doublescan)
                  pixely >>= 1;
                for(c = 0; c < X_TILESIZE; c++)
                {
                  pixelx = (xc + c) >> 1;
                  plane = (pixelx % 4);
                  byte_offset = start_addr + (plane * 65536) + (pixely * state.line_offset) + (pixelx &~0x03);
                  color = state.memory[byte_offset];
                  state.tile[r * X_TILESIZE + c] = color;
                }
              }

              SET_TILE_UPDATED(xti, yti, 0);
              bx_gui->graphics_tile_update(state.tile, xc, yc);
            }
          }
        }
      }
      else
      {                 // chain_four == 0, modeX
        unsigned long pixely;

        // chain_four == 0, modeX
        unsigned long pixelx;

        // chain_four == 0, modeX
        unsigned long plane;

        for(yc = 0, yti = 0; yc < iHeight; yc += Y_TILESIZE, yti++)
        {
          for(xc = 0, xti = 0; xc < iWidth; xc += X_TILESIZE, xti++)
          {
            if(GET_TILE_UPDATED(xti, yti))
            {
              for(r = 0; r < Y_TILESIZE; r++)
              {
                pixely = yc + r;
                if(state.y_doublescan)
                  pixely >>= 1;
                for(c = 0; c < X_TILESIZE; c++)
                {
                  pixelx = (xc + c) >> 1;
                  plane = (pixelx % 4);
                  byte_offset = (plane * 65536) + (pixely * state.line_offset) + (pixelx >> 2);
                  color = state.memory[start_addr + byte_offset];
                  state.tile[r * X_TILESIZE + c] = color;
                }
              }

              SET_TILE_UPDATED(xti, yti, 0);
              bx_gui->graphics_tile_update(state.tile, xc, yc);
            }
          }
        }
      }
      break;            // case 2

    default:
      FAILURE_1(NotImplemented, "update: shift_reg == %u   \n",
                (unsigned) state.graphics_ctrl.shift_reg);
    }

    state.vga_mem_updated = 0;
    return;
  }
  else
  {                     // text mode
    unsigned long   start_address;
    unsigned long   cursor_address;
    unsigned long   cursor_x;
    unsigned long   cursor_y;
    bx_vga_tminfo_t tm_info;
    unsigned        VDE;
    unsigned        MSL;
    unsigned        cols;
    unsigned        rows;
    unsigned        cWidth;

    tm_info.start_address = 2 * ((state.CRTC.reg[12] << 8) + state.CRTC.reg[13]);
    tm_info.cs_start = state.CRTC.reg[0x0a] & 0x3f;
    tm_info.cs_end = state.CRTC.reg[0x0b] & 0x1f;
    tm_info.line_offset = state.CRTC.reg[0x13] << 2;
    tm_info.line_compare = state.line_compare;
    tm_info.h_panning = state.attribute_ctrl.horiz_pel_panning & 0x0f;
    tm_info.v_panning = state.CRTC.reg[0x08] & 0x1f;
    tm_info.line_graphics = state.attribute_ctrl.mode_ctrl.enable_line_graphics;
    tm_info.split_hpanning = state.attribute_ctrl.mode_ctrl.pixel_panning_compat;
    if((state.sequencer.reg1 & 0x01) == 0)
    {
      if(tm_info.h_panning >= 8)
        tm_info.h_panning = 0;
      else
        tm_info.h_panning++;
    }
    else
    {
      tm_info.h_panning &= 0x07;
    }

    // Verticle Display End: find out how many lines are displayed
    VDE = state.vertical_display_end;

    // Maximum Scan Line: height of character cell
    MSL = state.CRTC.reg[0x09] & 0x1f;
    if(MSL == 0)
    {
#if defined(DEBUG_VGA)
      BX_ERROR(("character height = 1, skipping text update"));
#endif
      return;
    }

    cols = state.CRTC.reg[1] + 1;
    if((MSL == 1) && (VDE == 399))
    {

      // emulated CGA graphics mode 160x100x16 colors
      MSL = 3;
    }

    rows = (VDE + 1) / (MSL + 1);
    if(rows > BX_MAX_TEXT_LINES)
    {
      BX_PANIC(("text rows>%d: %d", BX_MAX_TEXT_LINES, rows));
      return;
    }

    cWidth = ((state.sequencer.reg1 & 0x01) == 1) ? 8 : 9;
    iWidth = cWidth * cols;
    iHeight = VDE + 1;
    if((iWidth != old_iWidth) || (iHeight != old_iHeight) || (MSL != old_MSL)
     || (state.last_bpp > 8))
    {
      bx_gui->dimension_update(iWidth, iHeight, MSL + 1, cWidth);
      old_iWidth = iWidth;
      old_iHeight = iHeight;
      old_MSL = MSL;
      state.last_bpp = 8;
    }

    // pass old text snapshot & new VGA memory contents
    start_address = 2 * ((state.CRTC.reg[12] << 8) + state.CRTC.reg[13]);
    cursor_address = 2 * ((state.CRTC.reg[0x0e] << 8) + state.CRTC.reg[0x0f]);
    if(cursor_address < start_address)
    {
      cursor_x = 0xffff;
      cursor_y = 0xffff;
    }
    else
    {
      cursor_x = ((cursor_address - start_address) / 2) % (iWidth / cWidth);
      cursor_y = ((cursor_address - start_address) / 2) / (iWidth / cWidth);
    }

    bx_gui->text_update(state.text_snapshot, &state.memory[start_address],
                        cursor_x, cursor_y, tm_info, rows);

    // screen updated, copy new VGA memory contents into text snapshot
    memcpy(state.text_snapshot, &state.memory[start_address], 2 * cols * rows);
    state.vga_mem_updated = 0;
  }
}

void CS3Trio64::determine_screen_dimensions(unsigned*  piHeight,
                                            unsigned*  piWidth)
{
  int ai[0x20];
  int i;
  int h;
  int v;
  for(i = 0; i < 0x20; i++)
    ai[i] = state.CRTC.reg[i];

  h = (ai[1] + 1) * 8;
  v = (ai[18] | ((ai[7] & 0x02) << 7) | ((ai[7] & 0x40) << 3)) + 1;

  if(state.graphics_ctrl.shift_reg == 0)
  {
    *piWidth = 640;
    *piHeight = 480;

    if(state.CRTC.reg[6] == 0xBF)
    {
      if(state.CRTC.reg[23] == 0xA3 && state.CRTC.reg[20] == 0x40
       && state.CRTC.reg[9] == 0x41)
      {
        *piWidth = 320;
        *piHeight = 240;
      }
      else
      {
        if(state.x_dotclockdiv2)
          h <<= 1;
        *piWidth = h;
        *piHeight = v;
      }
    }
    else if((h >= 640) && (v >= 480))
    {
      *piWidth = h;
      *piHeight = v;
    }
  }
  else if(state.graphics_ctrl.shift_reg == 2)
  {
    if(state.sequencer.chain_four)
    {
      *piWidth = h;
      *piHeight = v;
    }
    else
    {
      *piWidth = h;
      *piHeight = v;
    }
  }
  else
  {
    if(state.x_dotclockdiv2)
      h <<= 1;
    *piWidth = h;
    *piHeight = v;
  }
}

u8 CS3Trio64::vga_mem_read(u32 addr)
{
  u32   offset;
  u8*   plane0;
  u8 *plane1;
  u8 *plane2;
  u8 *plane3;
  u8    retval = 0;

  switch(state.graphics_ctrl.memory_mapping)
  {
  case 1:               // 0xA0000 .. 0xAFFFF
    if(addr > 0xAFFFF)
      return 0xff;
    offset = addr & 0xFFFF;
    break;

  case 2:               // 0xB0000 .. 0xB7FFF
    if((addr < 0xB0000) || (addr > 0xB7FFF))
      return 0xff;
    offset = addr & 0x7FFF;
    break;

  case 3:               // 0xB8000 .. 0xBFFFF
    if(addr < 0xB8000)
      return 0xff;
    offset = addr & 0x7FFF;
    break;

  default:              // 0xA0000 .. 0xBFFFF
    offset = addr & 0x1FFFF;
  }

  if(state.sequencer.chain_four)
  {

    // Mode 13h: 320 x 200 256 color mode: chained pixel representation
    return state.memory[(offset &~0x03) + (offset % 4) * 65536];
  }

  plane0 = &state.memory[0 << 16];
  plane1 = &state.memory[1 << 16];
  plane2 = &state.memory[2 << 16];
  plane3 = &state.memory[3 << 16];

  /* addr between 0xA0000 and 0xAFFFF */
  switch(state.graphics_ctrl.read_mode)
  {
  case 0:               /* read mode 0 */
    state.graphics_ctrl.latch[0] = plane0[offset];
    state.graphics_ctrl.latch[1] = plane1[offset];
    state.graphics_ctrl.latch[2] = plane2[offset];
    state.graphics_ctrl.latch[3] = plane3[offset];
    retval = state.graphics_ctrl.latch[state.graphics_ctrl.read_map_select];
    break;

  case 1:               /* read mode 1 */
    {
      u8  color_compare;

      u8  color_dont_care;
      u8  latch0;
      u8  latch1;
      u8  latch2;
      u8  latch3;

      color_compare = state.graphics_ctrl.color_compare & 0x0f;
      color_dont_care = state.graphics_ctrl.color_dont_care & 0x0f;
      latch0 = state.graphics_ctrl.latch[0] = plane0[offset];
      latch1 = state.graphics_ctrl.latch[1] = plane1[offset];
      latch2 = state.graphics_ctrl.latch[2] = plane2[offset];
      latch3 = state.graphics_ctrl.latch[3] = plane3[offset];

      latch0 ^= ccdat[color_compare][0];
      latch1 ^= ccdat[color_compare][1];
      latch2 ^= ccdat[color_compare][2];
      latch3 ^= ccdat[color_compare][3];

      latch0 &= ccdat[color_dont_care][0];
      latch1 &= ccdat[color_dont_care][1];
      latch2 &= ccdat[color_dont_care][2];
      latch3 &= ccdat[color_dont_care][3];

      retval = ~(latch0 | latch1 | latch2 | latch3);
    }
    break;
  }

  return retval;
}

void CS3Trio64::vga_mem_write(u32 addr, u8 value)
{
  u32       offset;
  u8        new_val[4];
  unsigned  start_addr;
  u8*       plane0;
  u8 *plane1;
  u8 *plane2;
  u8 *plane3;

  /* The memory_mapping bits of the graphics controller determine 
   * what window of VGA memory is available.
   *
   *  00: 0xA0000 .. 0xBFFFF (128K)
   *  01: 0xA0000 .. 0xAFFFF (64K) (also used for VGA text mode)
   *  02: 0xB0000 .. 0xB7FFF (32K)
   *  03: 0xB8000 .. 0xBFFFF (32K) (also used for CGA text mode)
   */
  switch(state.graphics_ctrl.memory_mapping)
  {
  // 0xA0000 .. 0xAFFFF
  case 1:
    if(addr > 0xAFFFF)
      return;
    offset = addr - 0xA0000;
    break;

  // 0xB0000 .. 0xB7FFF
  case 2:
    if((addr < 0xB0000) || (addr > 0xB7FFF))
      return;
    offset = addr - 0xB0000;
    break;

  // 0xB8000 .. 0xBFFFF
  case 3:
    if(addr < 0xB8000)
      return;
    offset = addr - 0xB8000;
    break;

  // 0xA0000 .. 0xBFFFF
  default:
    offset = addr - 0xA0000;
  }

  start_addr = (state.CRTC.reg[0x0c] << 8) | state.CRTC.reg[0x0d];

  if(state.graphics_ctrl.graphics_alpha)
  {
    if(state.graphics_ctrl.memory_mapping == 3)
    {                   
      // Text mode, and memory 0xB8000 .. 0xBFFFF selected => CGA text mode
      unsigned  x_tileno;
      unsigned  x_tileno2;
      unsigned  y_tileno;

      /* CGA 320x200x4 / 640x200x2 start */
      state.memory[offset] = value;
      offset -= start_addr;
      if(offset >= 0x2000)
      {
        y_tileno = offset - 0x2000;
        y_tileno /= (320 / 4);
        y_tileno <<= 1; //2 * y_tileno;
        y_tileno++;
        x_tileno = (offset - 0x2000) % (320 / 4);
        x_tileno <<= 2; //*= 4;
      }
      else
      {
        y_tileno = offset / (320 / 4);
        y_tileno <<= 1; //2 * y_tileno;
        x_tileno = offset % (320 / 4);
        x_tileno <<= 2; //*=4;
      }

      x_tileno2 = x_tileno;
      if(state.graphics_ctrl.shift_reg == 0)
      {
        x_tileno *= 2;
        x_tileno2 += 7;
      }
      else
      {
        x_tileno2 += 3;
      }

      if(state.x_dotclockdiv2)
      {
        x_tileno /= (X_TILESIZE / 2);
        x_tileno2 /= (X_TILESIZE / 2);
      }
      else
      {
        x_tileno /= X_TILESIZE;
        x_tileno2 /= X_TILESIZE;
      }

      if(state.y_doublescan)
      {
        y_tileno /= (Y_TILESIZE / 2);
      }
      else
      {
        y_tileno /= Y_TILESIZE;
      }

      state.vga_mem_updated = 1;
      SET_TILE_UPDATED(x_tileno, y_tileno, 1);
      if(x_tileno2 != x_tileno)
      {
        SET_TILE_UPDATED(x_tileno2, y_tileno, 1);
      }

      return;

      /* CGA 320x200x4 / 640x200x2 end */
    }
    
    if(state.graphics_ctrl.memory_mapping != 1)
    {
      FAILURE_1(NotImplemented, "mem_write: graphics: mapping = %u  \n",
                (unsigned) state.graphics_ctrl.memory_mapping);
    }

    if(state.sequencer.chain_four)
    {
      unsigned  x_tileno;

      unsigned  y_tileno;

      // 320 x 200 256 color mode: chained pixel representation
      state.memory[(offset &~0x03) + (offset % 4) * 65536] = value;
      if(state.line_offset > 0)
      {
        offset -= start_addr;
        x_tileno = (offset % state.line_offset) / (X_TILESIZE / 2);
        if(state.y_doublescan)
        {
          y_tileno = (offset / state.line_offset) / (Y_TILESIZE / 2);
        }
        else
        {
          y_tileno = (offset / state.line_offset) / Y_TILESIZE;
        }

        state.vga_mem_updated = 1;
        SET_TILE_UPDATED(x_tileno, y_tileno, 1);
      }

      return;
    }
  }

  /* addr between 0xA0000 and 0xAFFFF */
  plane0 = &state.memory[0 << 16];
  plane1 = &state.memory[1 << 16];
  plane2 = &state.memory[2 << 16];
  plane3 = &state.memory[3 << 16];

  switch(state.graphics_ctrl.write_mode)
  {
    unsigned  i;
  // Write mode 0
  case 0:
    {
      /* Write Mode 0 is the standard and most general write mode. 
       * While the other write modes are designed to perform a specific 
       * task, this mode can be used to perform most tasks as all five 
       * operations are performed on the data:
       *   - The data byte from the host is first rotated as specified
       *     by the Rotate Count field, then is replicated across all
       *     four planes.
       *   - Then the Enable Set/Reset field selects which planes will
       *     receive their values from the host data and which will
       *     receive their data from that plane's Set/Reset field
       *     location.
       *   - Then the operation specified by the Logical Operation
       *     field is performed on the resulting data and the data in
       *     the read latches.
       *   - The Bit Mask field is then used to select between the
       *     resulting data and data from the latch register. 
       *   - Finally, the resulting data is written to the display
       *     memory planes enabled in the Memory Plane Write Enable
       *     field. 
       *   .
       */
      const u8  bitmask = state.graphics_ctrl.bitmask;
      const u8  set_reset = state.graphics_ctrl.set_reset;
      const u8  enable_set_reset = state.graphics_ctrl.enable_set_reset;

      /* perform rotate on CPU data in case its needed */
      if(state.graphics_ctrl.data_rotate)
      {
        value = (value >> state.graphics_ctrl.data_rotate) | (value << (8 - state.graphics_ctrl.data_rotate));
      }

      new_val[0] = state.graphics_ctrl.latch[0] &~bitmask;
      new_val[1] = state.graphics_ctrl.latch[1] &~bitmask;
      new_val[2] = state.graphics_ctrl.latch[2] &~bitmask;
      new_val[3] = state.graphics_ctrl.latch[3] &~bitmask;
      switch(state.graphics_ctrl.raster_op)
      {
      case 0: // replace
        new_val[0] |=
          (
            (enable_set_reset & 1) ? ((set_reset & 1) ? bitmask : 0) :
              (value & bitmask)
          );
        new_val[1] |=
          (
            (enable_set_reset & 2) ? ((set_reset & 2) ? bitmask : 0) :
              (value & bitmask)
          );
        new_val[2] |=
          (
            (enable_set_reset & 4) ? ((set_reset & 4) ? bitmask : 0) :
              (value & bitmask)
          );
        new_val[3] |=
          (
            (enable_set_reset & 8) ? ((set_reset & 8) ? bitmask : 0) :
              (value & bitmask)
          );
        break;

      case 1: // AND
        new_val[0] |=
          (
            (enable_set_reset & 1) ?
              ((set_reset & 1) ? (state.graphics_ctrl.latch[0] & bitmask) : 0) :
                (value & state.graphics_ctrl.latch[0]) & bitmask
          );
        new_val[1] |=
          (
            (enable_set_reset & 2) ?
              ((set_reset & 2) ? (state.graphics_ctrl.latch[1] & bitmask) : 0) :
                (value & state.graphics_ctrl.latch[1]) & bitmask
          );
        new_val[2] |=
          (
            (enable_set_reset & 4) ?
              ((set_reset & 4) ? (state.graphics_ctrl.latch[2] & bitmask) : 0) :
                (value & state.graphics_ctrl.latch[2]) & bitmask
          );
        new_val[3] |=
          (
            (enable_set_reset & 8) ?
              ((set_reset & 8) ? (state.graphics_ctrl.latch[3] & bitmask) : 0) :
                (value & state.graphics_ctrl.latch[3]) & bitmask
          );
        break;

      case 2: // OR
        new_val[0] |=
          (
            (enable_set_reset & 1) ?
              (
                (set_reset & 1) ? bitmask :
                  (state.graphics_ctrl.latch[0] & bitmask)
              ) : ((value | state.graphics_ctrl.latch[0]) & bitmask)
          );
        new_val[1] |=
          (
            (enable_set_reset & 2) ?
              (
                (set_reset & 2) ? bitmask :
                  (state.graphics_ctrl.latch[1] & bitmask)
              ) : ((value | state.graphics_ctrl.latch[1]) & bitmask)
          );
        new_val[2] |=
          (
            (enable_set_reset & 4) ?
              (
                (set_reset & 4) ? bitmask :
                  (state.graphics_ctrl.latch[2] & bitmask)
              ) : ((value | state.graphics_ctrl.latch[2]) & bitmask)
          );
        new_val[3] |=
          (
            (enable_set_reset & 8) ?
              (
                (set_reset & 8) ? bitmask :
                  (state.graphics_ctrl.latch[3] & bitmask)
              ) : ((value | state.graphics_ctrl.latch[3]) & bitmask)
          );
        break;

      case 3: // XOR
        new_val[0] |=
          (
            (enable_set_reset & 1) ?
              (
                (set_reset & 1) ? (~state.graphics_ctrl.latch[0] & bitmask) :
                  (state.graphics_ctrl.latch[0] & bitmask)
              ) : (value ^ state.graphics_ctrl.latch[0]) & bitmask
          );
        new_val[1] |=
          (
            (enable_set_reset & 2) ?
              (
                (set_reset & 2) ? (~state.graphics_ctrl.latch[1] & bitmask) :
                  (state.graphics_ctrl.latch[1] & bitmask)
              ) : (value ^ state.graphics_ctrl.latch[1]) & bitmask
          );
        new_val[2] |=
          (
            (enable_set_reset & 4) ?
              (
                (set_reset & 4) ? (~state.graphics_ctrl.latch[2] & bitmask) :
                  (state.graphics_ctrl.latch[2] & bitmask)
              ) : (value ^ state.graphics_ctrl.latch[2]) & bitmask
          );
        new_val[3] |=
          (
            (enable_set_reset & 8) ?
              (
                (set_reset & 8) ? (~state.graphics_ctrl.latch[3] & bitmask) :
                  (state.graphics_ctrl.latch[3] & bitmask)
              ) : (value ^ state.graphics_ctrl.latch[3]) & bitmask
          );
        break;

      default:
        FAILURE_1(NotImplemented, "vga_mem_write: write mode 0: op = %u",
                  (unsigned) state.graphics_ctrl.raster_op);
      }
    }
    break;

  // Write mode 1
  case 1:
    /* Write Mode 1 is used to transfer the data in the latches
     * register directly to the screen, affected only by the
     * Memory Plane Write Enable field. This can facilitate
     * rapid transfer of data on byte boundaries from one area
     * of video memory to another or filling areas of the
     * display with a pattern of 8 pixels. 
     * When Write Mode 0 is used with the Bit Mask field set to 
     * 00000000b the operation of the hardware is identical to 
     * this mode.
     */
    for(i = 0; i < 4; i++)
    {
      new_val[i] = state.graphics_ctrl.latch[i];
    }
    break;

  // Write mode 2
  case 2:
    {
      /* Write Mode 2 is used to unpack a pixel value packed into
       * the lower 4 bits of the host data byte into the 4 display
       * planes:
       *   - In the byte from the host, the bit representing each
       *     plane will be replicated across all 8 bits of the
       *     corresponding planes.
       *   - Then the operation specified by the Logical Operation
       *     field is performed on the resulting data and the data
       *     in the read latches.
       *   - The Bit Mask field is then used to select between the
       *     resulting data and data from the latch register. 
       *   - Finally, the resulting data is written to the display
       *     memory planes enabled in the Memory Plane Write Enable
       *     field.
       *   .
       */
      const u8  bitmask = state.graphics_ctrl.bitmask;

      new_val[0] = state.graphics_ctrl.latch[0] &~bitmask;
      new_val[1] = state.graphics_ctrl.latch[1] &~bitmask;
      new_val[2] = state.graphics_ctrl.latch[2] &~bitmask;
      new_val[3] = state.graphics_ctrl.latch[3] &~bitmask;
      switch(state.graphics_ctrl.raster_op)
      {
      case 0: // write
        new_val[0] |= (value & 1) ? bitmask : 0;
        new_val[1] |= (value & 2) ? bitmask : 0;
        new_val[2] |= (value & 4) ? bitmask : 0;
        new_val[3] |= (value & 8) ? bitmask : 0;
        break;

      case 1: // AND
        new_val[0] |= (value & 1) ? (state.graphics_ctrl.latch[0] & bitmask) : 0;
        new_val[1] |= (value & 2) ? (state.graphics_ctrl.latch[1] & bitmask) : 0;
        new_val[2] |= (value & 4) ? (state.graphics_ctrl.latch[2] & bitmask) : 0;
        new_val[3] |= (value & 8) ? (state.graphics_ctrl.latch[3] & bitmask) : 0;
        break;

      case 2: // OR
        new_val[0] |= (value & 1) ? bitmask : (state.graphics_ctrl.latch[0] & bitmask);
        new_val[1] |= (value & 2) ? bitmask : (state.graphics_ctrl.latch[1] & bitmask);
        new_val[2] |= (value & 4) ? bitmask : (state.graphics_ctrl.latch[2] & bitmask);
        new_val[3] |= (value & 8) ? bitmask : (state.graphics_ctrl.latch[3] & bitmask);
        break;

      case 3: // XOR
        new_val[0] |= (value & 1) ? (~state.graphics_ctrl.latch[0] & bitmask) : (state.graphics_ctrl.latch[0] & bitmask);
        new_val[1] |= (value & 2) ? (~state.graphics_ctrl.latch[1] & bitmask) : (state.graphics_ctrl.latch[1] & bitmask);
        new_val[2] |= (value & 4) ? (~state.graphics_ctrl.latch[2] & bitmask) : (state.graphics_ctrl.latch[2] & bitmask);
        new_val[3] |= (value & 8) ? (~state.graphics_ctrl.latch[3] & bitmask) : (state.graphics_ctrl.latch[3] & bitmask);
        break;
      }
    }
    break;

  // Write mode 3
  case 3:
    {
      /* Write Mode 3 is used when the color written is fairly
       * constant but the Bit Mask field needs to be changed
       * frequently, such as when drawing single color lines or
       * text: 
       *   - The value of the Set/Reset field is expanded as if
       *     the Enable Set/Reset field were set to 1111b,
       *     regardless of its actual value.
       *   - The host data is first rotated as specified by the
       *     Rotate Count field, then is ANDed with the Bit
       *     Mask field.
       *   - The resulting value is used where the Bit Mask
       *     field normally would be used, selecting data from
       *     either the expansion of the Set/Reset field or the
       *     latch register.
       *   - Finally, the resulting data is written to the
       *     display memory planes enabled in the Memory Plane
       *     Write Enable field.
       *   .
       */
      const u8  bitmask = state.graphics_ctrl.bitmask & value;
      const u8  set_reset = state.graphics_ctrl.set_reset;

      /* perform rotate on CPU data */
      if(state.graphics_ctrl.data_rotate)
      {
        value = (value >> state.graphics_ctrl.data_rotate) | (value << (8 - state.graphics_ctrl.data_rotate));
      }

      new_val[0] = state.graphics_ctrl.latch[0] &~bitmask;
      new_val[1] = state.graphics_ctrl.latch[1] &~bitmask;
      new_val[2] = state.graphics_ctrl.latch[2] &~bitmask;
      new_val[3] = state.graphics_ctrl.latch[3] &~bitmask;

      value &= bitmask;

      switch(state.graphics_ctrl.raster_op)
      {
      case 0: // write
        new_val[0] |= (set_reset & 1) ? value : 0;
        new_val[1] |= (set_reset & 2) ? value : 0;
        new_val[2] |= (set_reset & 4) ? value : 0;
        new_val[3] |= (set_reset & 8) ? value : 0;
        break;

      case 1: // AND
        new_val[0] |= ((set_reset & 1) ? value : 0) & state.graphics_ctrl.latch[0];
        new_val[1] |= ((set_reset & 2) ? value : 0) & state.graphics_ctrl.latch[1];
        new_val[2] |= ((set_reset & 4) ? value : 0) & state.graphics_ctrl.latch[2];
        new_val[3] |= ((set_reset & 8) ? value : 0) & state.graphics_ctrl.latch[3];
        break;

      case 2: // OR
        new_val[0] |= ((set_reset & 1) ? value : 0) | state.graphics_ctrl.latch[0];
        new_val[1] |= ((set_reset & 2) ? value : 0) | state.graphics_ctrl.latch[1];
        new_val[2] |= ((set_reset & 4) ? value : 0) | state.graphics_ctrl.latch[2];
        new_val[3] |= ((set_reset & 8) ? value : 0) | state.graphics_ctrl.latch[3];
        break;

      case 3: // XOR
        new_val[0] |= ((set_reset & 1) ? value : 0) ^ state.graphics_ctrl.latch[0];
        new_val[1] |= ((set_reset & 2) ? value : 0) ^ state.graphics_ctrl.latch[1];
        new_val[2] |= ((set_reset & 4) ? value : 0) ^ state.graphics_ctrl.latch[2];
        new_val[3] |= ((set_reset & 8) ? value : 0) ^ state.graphics_ctrl.latch[3];
        break;
      }
    }
    break;

  default:
    FAILURE_1(NotImplemented, "vga_mem_write: write mode %u ?",
              (unsigned) state.graphics_ctrl.write_mode);
  }

  // state.sequencer.map_mask determines which bitplanes the write should actually go to
  if(state.sequencer.map_mask & 0x0f)
  {
    state.vga_mem_updated = 1;
    if(state.sequencer.map_mask & 0x01)
      plane0[offset] = new_val[0];
    if(state.sequencer.map_mask & 0x02)
      plane1[offset] = new_val[1];
    if(state.sequencer.map_mask & 0x04)
    {
      // Plane 2 contains the character map
      if((offset & 0xe000) == state.charmap_address)
      {

        //printf("Updating character map %04x with %02x...\n  ", (offset & 0x1fff), new_val[2]);
        bx_gui->lock();
        bx_gui->set_text_charbyte((u16) (offset & 0x1fff), new_val[2]);
        bx_gui->unlock();
      }

      plane2[offset] = new_val[2];
    }

    if(state.sequencer.map_mask & 0x08)
      plane3[offset] = new_val[3];

    unsigned  x_tileno;

    unsigned  y_tileno;

    if(state.graphics_ctrl.shift_reg == 2)
    {
      offset -= start_addr;
      x_tileno = (offset % state.line_offset) * 4 / (X_TILESIZE / 2);
      if(state.y_doublescan)
      {
        y_tileno = (offset / state.line_offset) / (Y_TILESIZE / 2);
      }
      else
      {
        y_tileno = (offset / state.line_offset) / Y_TILESIZE;
      }

      SET_TILE_UPDATED(x_tileno, y_tileno, 1);
    }
    else
    {
      if(state.line_compare < state.vertical_display_end)
      {
        if(state.line_offset > 0)
        {
          if(state.x_dotclockdiv2)
          {
            x_tileno = (offset % state.line_offset) / (X_TILESIZE / 16);
          }
          else
          {
            x_tileno = (offset % state.line_offset) / (X_TILESIZE / 8);
          }

          if(state.y_doublescan)
          {
            y_tileno =
              (
                (offset / state.line_offset) *
                2 +
                state.line_compare +
                1
              ) /
              Y_TILESIZE;
          }
          else
          {
            y_tileno = ((offset / state.line_offset) + state.line_compare + 1) / Y_TILESIZE;
          }

          SET_TILE_UPDATED(x_tileno, y_tileno, 1);
        }
      }

      if(offset >= start_addr)
      {
        offset -= start_addr;
        if(state.line_offset > 0)
        {
          if(state.x_dotclockdiv2)
          {
            x_tileno = (offset % state.line_offset) / (X_TILESIZE / 16);
          }
          else
          {
            x_tileno = (offset % state.line_offset) / (X_TILESIZE / 8);
          }

          if(state.y_doublescan)
          {
            y_tileno = (offset / state.line_offset) / (Y_TILESIZE / 2);
          }
          else
          {
            y_tileno = (offset / state.line_offset) / Y_TILESIZE;
          }

          SET_TILE_UPDATED(x_tileno, y_tileno, 1);
        }
      }
    }
  }
}

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