Palacios Public Git Repository

To checkout Palacios execute

  git clone http://v3vee.org/palacios/palacios.web/palacios.git
This will give you the master branch. You probably want the devel branch or one of the release branches. To switch to the devel branch, simply execute
  cd palacios
  git checkout --track -b devel origin/devel
The other branches are similar.


Cleanup and sanity-checking of endianness, dead code, unchecked returns (Coverity...
[palacios.git] / palacios / src / devices / vga.c
index 0aa991e..1cf1179 100644 (file)
 #include <palacios/vmm_types.h>
 #include <palacios/vm_guest_mem.h>
 #include <palacios/vmm_io.h>
+#include <interfaces/vmm_graphics_console.h>
 
 #include "vga_regs.h"
 
+#ifndef V3_CONFIG_DEBUG_VGA
+#undef PrintDebug
+#define PrintDebug(fmt, args...)
+#endif
+
+#define DEBUG_MEM_DATA    0
+#define DEBUG_DEEP_MEM    0
+#define DEBUG_DEEP_RENDER 0
+
+
 #define MEM_REGION_START 0xa0000
 #define MEM_REGION_END   0xc0000
 #define MEM_REGION_NUM_PAGES (((MEM_REGION_END)-(MEM_REGION_START))/4096)
 #define MAP_SIZE 65536
 #define MAP_NUM  4
 
-typedef uint8_t *vga_map; // points to MAP_SIZE data
-
-/* HACK HACK HACK */
 
-struct fb_info {
-    uint32_t rows;
-    uint32_t cols;
-    uint32_t bitsperpixel;
-};
-
-struct fb {
-    struct fb_info *info;
-    uint8_t * data;
-};
-
-//extern
-struct fb *palacios_linux_fb_hack_pointer;
+typedef uint8_t *vga_map; // points to MAP_SIZE data
 
-/* HACK HACK HACK */
+#define VGA_MAXX 1024
+#define VGA_MAXY 768
 
 
 #define VGA_MISC_OUT_READ 0x3cc
@@ -94,6 +91,22 @@ struct fb *palacios_linux_fb_hack_pointer;
 
 #define VGA_DAC_NUM_ENTRIES 256
 
+
+#define VGA_FONT_WIDTH      8
+#define VGA_MAX_FONT_HEIGHT 32
+
+struct vga_render_model {
+  uint32_t   model;  // composite the following
+
+#define VGA_DRIVEN_PERIODIC_RENDERING 0x1  // render after n GPU updates
+#define CONSOLE_ADVISORY_RENDERING    0x2  // ask console if we should render following an update
+#define CONSOLE_DRIVEN_RENDERING      0x4  // have console tell us when to render
+
+  uint32_t   updates_before_render;   // defaults to the following
+
+#define DEFAULT_UPDATES_BEFORE_RENDER   1000
+};
+
 struct vga_misc_regs {
     /* Read: 0x3cc; Write: 0x3c2 */
     struct vga_misc_out_reg        vga_misc_out;
@@ -160,7 +173,7 @@ struct vga_crt_controller_regs {
     /* index 8 */
     struct vga_preset_row_scan_reg vga_preset_row_scan;
     /* index 9 */
-    struct vga_max_row_scan_reg vga_row_scan;
+    struct vga_max_row_scan_reg vga_max_row_scan;
     /* index 10 */
     struct vga_cursor_start_reg vga_cursor_start;
     /* index 11 */
@@ -178,7 +191,7 @@ struct vga_crt_controller_regs {
     /* index 17 */
     struct vga_vertical_retrace_end_reg vga_vertical_retrace_end;
     /* index 18 */
-    vga_vertical_display_enable_end_reg vga_vertical_display_enable;
+    vga_vertical_display_enable_end_reg vga_vertical_display_enable_end;
     /* index 19 */
     vga_offset_reg vga_offset;
     /* index 20 */
@@ -280,9 +293,16 @@ struct vga_dac_regs {
     
 
 struct vga_internal {
-    struct vm_device *dev;  
-    
+    struct vm_device *dev; 
+
     bool passthrough;
+    bool skip_next_passthrough_out; // for word access 
+
+    struct v3_frame_buffer_spec  target_spec;
+    v3_graphics_console_t host_cons;
+    struct vga_render_model render_model;
+
+    uint32_t updates_since_render;
 
     struct frame_buf *framebuf; // we render to this
     
@@ -322,6 +342,765 @@ struct vga_internal {
 };
 
 
+typedef enum {PLANAR_SHIFT, PACKED_SHIFT, C256_SHIFT} shift_mode_t;
+
+
+static void find_text_char_dim(struct vga_internal *vga, uint32_t *w, uint32_t *h)
+{
+    *w = (vga->vga_sequencer.vga_clocking_mode.dot8 ? 8 : 9);
+
+    *h = vga->vga_crt_controller.vga_max_row_scan.max_scan_line+1;
+
+}
+
+static void find_text_res(struct vga_internal *vga, uint32_t *width, uint32_t *height)
+{
+    uint32_t vert_lsb, vert_msb;
+    uint32_t ph;
+    uint32_t ch, cw;
+
+    *width = (vga->vga_crt_controller.vga_horizontal_display_enable_end + 1) 
+       - vga->vga_crt_controller.vga_end_horizontal_blanking.display_enable_skew;
+
+    vert_lsb = vga->vga_crt_controller.vga_vertical_display_enable_end; // 8 bits here
+    vert_msb = (vga->vga_crt_controller.vga_overflow.vertical_disp_enable_end9 << 1)  // 2 bits here
+       + (vga->vga_crt_controller.vga_overflow.vertical_disp_enable_end8);
+              
+    ph  = ( (vert_msb << 8) + vert_lsb + 1) ; // pixels high (scanlines)
+
+    find_text_char_dim(vga,&cw, &ch);
+
+    *height = ph / ch; 
+
+}
+
+
+static void find_text_data_start(struct vga_internal *vga, void **data)
+{
+    uint32_t offset;
+
+    offset = vga->vga_crt_controller.vga_start_address_high;
+    offset <<= 8;
+    offset += vga->vga_crt_controller.vga_start_address_low;
+
+    *data = vga->map[0]+offset;
+
+}
+
+
+static void find_text_attr_start(struct vga_internal *vga, void **data)
+{
+    uint32_t offset;
+
+    offset = vga->vga_crt_controller.vga_start_address_high;
+    offset <<= 8;
+    offset += vga->vga_crt_controller.vga_start_address_low;
+
+    *data = vga->map[1]+offset;
+
+}
+
+static void find_text_cursor_pos(struct vga_internal *vga, uint32_t *x, uint32_t *y, void **data)
+{
+    uint32_t w,h;
+    uint32_t offset;
+    uint32_t charsin;
+    void *buf;
+
+    find_text_res(vga,&w,&h);
+
+    find_text_data_start(vga,&buf);
+
+    offset = vga->vga_crt_controller.vga_cursor_location_high;
+    offset <<= 8;
+    offset += vga->vga_crt_controller.vga_cursor_location_low;
+
+    *data = vga->map[0]+offset;
+
+    charsin = (uint32_t)(*data - buf);
+    
+    *x = charsin % w;
+    *y = charsin / w;
+        
+}
+
+
+static void find_text_font_start(struct vga_internal *vga, void **data, uint8_t char_map)
+{
+    uint32_t mapa_offset, mapb_offset;
+
+
+    switch (char_map) { 
+       case 0:
+           mapa_offset = (vga->vga_sequencer.vga_char_map_select.char_map_a_sel_lsb << 1)
+                          + vga->vga_sequencer.vga_char_map_select.char_map_a_sel_msb ;
+           *data = vga->map[2] + mapa_offset;
+           break;
+           
+       case 1:
+           mapb_offset = (vga->vga_sequencer.vga_char_map_select.char_map_b_sel_lsb << 1)
+                          + vga->vga_sequencer.vga_char_map_select.char_map_b_sel_msb ;
+           *data = vga->map[2] + mapb_offset;
+           break;
+       default:
+           PrintError(VM_NONE, VCORE_NONE, "vga: unknown char_map given to find_text_font_start\n");
+           break;
+           
+    }
+}
+
+static int extended_fontset(struct vga_internal *vga)
+{
+    if (vga->vga_sequencer.vga_mem_mode.extended_memory &&
+       ! ( (vga->vga_sequencer.vga_char_map_select.char_map_a_sel_lsb 
+            == vga->vga_sequencer.vga_char_map_select.char_map_b_sel_lsb) &&
+           (vga->vga_sequencer.vga_char_map_select.char_map_a_sel_msb 
+            == vga->vga_sequencer.vga_char_map_select.char_map_b_sel_msb))) { 
+       return 1;
+    } else {
+       return 0;
+    }
+
+}
+
+static int blinking(struct vga_internal *vga)
+{
+    return vga->vga_attribute_controller.vga_attribute_mode_control.enable_blink;
+}
+
+
+static void find_graphics_data_starting_offset(struct vga_internal *vga, uint32_t *offset)
+{
+
+    *offset = vga->vga_crt_controller.vga_start_address_high;
+    *offset <<= 8;
+    *offset += vga->vga_crt_controller.vga_start_address_low;
+}
+
+
+static void find_shift_mode(struct vga_internal *vga, shift_mode_t *mode)
+{
+    if (vga->vga_graphics_controller.vga_graphics_mode.c256) { 
+       *mode=C256_SHIFT;
+    } else {
+       if (vga->vga_graphics_controller.vga_graphics_mode.shift_reg_mode) {
+           *mode=PACKED_SHIFT;
+       } else {
+           *mode=PLANAR_SHIFT;
+       }
+    }
+}
+
+
+static void find_graphics_res(struct vga_internal *vga, uint32_t *width, uint32_t *height)
+{
+    uint32_t vert_lsb, vert_msb;
+
+    *width = ((vga->vga_crt_controller.vga_horizontal_display_enable_end + 1) 
+             - vga->vga_crt_controller.vga_end_horizontal_blanking.display_enable_skew);
+
+    *width *= (vga->vga_sequencer.vga_clocking_mode.dot8 ? 8 : 9);
+
+    vert_lsb = vga->vga_crt_controller.vga_vertical_display_enable_end; // 8 bits here
+    vert_msb = (vga->vga_crt_controller.vga_overflow.vertical_disp_enable_end9 << 1)  // 2 bits here
+       + (vga->vga_crt_controller.vga_overflow.vertical_disp_enable_end8);
+              
+    *height  = ( (vert_msb << 8) + vert_lsb + 1) ; // pixels high (scanlines)
+
+    // At this point we have the resolution in dot clocks across and scanlines top-to-bottom
+    // This is usually the resolution in pixels, but it can be monkeyed with
+    // at least in the following ways
+
+    // vga sequencer dot clock divide by two 
+    if (vga->vga_sequencer.vga_clocking_mode.dot_clock) { 
+       *width/=2;
+       *height/=2;
+    }
+
+    // crt_controller.max_row_scan.double_scan => each row twice for 200=>400
+    if (vga->vga_crt_controller.vga_max_row_scan.double_scan) { 
+       *height/=2;
+    }
+    
+    // crt_controller.crt_mode_control.count_by_two => pixels twice as wide as normal
+    if (vga->vga_crt_controller.vga_crt_mode_control.count_by_two) { 
+       *width /= 2;
+    }
+
+    // crt_controller.crt_mode_control.horizontal_retrace_select => pixels twice as tall as normal
+    if (vga->vga_crt_controller.vga_crt_mode_control.horizontal_retrace_select) { 
+       *height /= 2;
+    }
+    
+}
+
+
+static void find_graphics_cursor_pos(struct vga_internal *vga, uint32_t *x, uint32_t *y)
+{
+    // todo
+    *x=*y=0;
+}
+
+
+static void dac_lookup_24bit_color(struct vga_internal *vga,
+                                  uint8_t entry,
+                                  uint8_t *red,
+                                  uint8_t *green,
+                                  uint8_t *blue)
+{
+    // use internal or external palette?
+
+    vga_palette_reg *r = &(vga->vga_dac.vga_dac_palette[entry]);
+
+    // converting from 6 bits to 8 bits so << 2
+    *red = (*r & 0x3f) << 2;
+    *green = ((*r >> 8) & 0x3f) << 2;
+    *blue = ((*r >> 16) & 0x3f) << 2;
+
+}
+
+
+/*
+  Colors work like this:
+
+  4 bit modes:   index is to the internal palette on the attribute controller
+                 that supplies 6 bits, but we need 8 to index the dac
+                2 more (the msbs) are supplied from the color select register
+                 we can optionally overwrite bits 5 and 4 from the color
+                select register as well, depending on a selection bit
+                in the mode control register.   The result of all this is
+                8 bit index for the dac
+
+  8 bit modes:   the attribute controller passes the index straight through
+                 to the DAC.
+
+
+  The DAC translates from the 8 bit index into 6 bits per color channel
+  (18 bit color).   We mulitply by 4 to get 24 bit color.
+*/
+
+static void find_24bit_color(struct vga_internal *vga, 
+                            uint8_t val,
+                            uint8_t *red,
+                            uint8_t *green,
+                            uint8_t *blue)
+{
+    uint8_t di;  // ultimate dac index
+
+    if (vga->vga_attribute_controller.vga_attribute_mode_control.pixel_width) { 
+       // 8 bit mode does right to the DAC
+       di=val;
+    } else {
+       struct vga_internal_palette_reg pr = vga->vga_attribute_controller.vga_internal_palette[val%16];
+       di = pr.palette_data;
+       
+       // Fix bits 5-4 if needed
+       if (vga->vga_attribute_controller.vga_attribute_mode_control.p54_select) { 
+           di &= ~0x30;  // clear 5-4
+           di |= vga->vga_attribute_controller.vga_color_select.sc4 << 4;
+           di |= vga->vga_attribute_controller.vga_color_select.sc5 << 5;
+       }
+
+       // We must always produce bits 6 and 7
+       di &= ~0xc0; // clear 7-6
+       di |= vga->vga_attribute_controller.vga_color_select.sc6 << 6;
+       di |= vga->vga_attribute_controller.vga_color_select.sc7 << 7;
+    }
+       
+    dac_lookup_24bit_color(vga,di,red,green,blue);
+}
+       
+static void render_graphics(struct vga_internal *vga, void *fb)
+{
+
+    struct v3_frame_buffer_spec *spec = &(vga->target_spec);
+
+    uint32_t gw, gh; // graphics w/h
+    uint32_t fw, fh; // fb w/h
+    uint32_t rgw, rgh;  // region we can actually show on the frame buffer
+    
+
+    uint32_t fx, fy;     // pixel position within the frame buffer
+    
+    uint32_t offset;     // offset into the maps
+    uint8_t  m;        // map
+    uint8_t  p;          // pixel in the current map byte  (0..7)
+
+    uint8_t r,g,b;  // looked up colors for entry
+
+    void    *pixel;   // current pixel in the fb
+    uint8_t *red;     // and the channels in the pixel
+    uint8_t *green;   //
+    uint8_t *blue;    //
+
+    uint8_t db[4]; // 4 bytes read at a time
+    uint8_t pb[8]; // 8 pixels assembled at a time
+
+    shift_mode_t sm;   // shift mode
+
+    uint32_t cur_x, cur_y;
+    
+
+    find_graphics_res(vga,&gw,&gh);
+
+    find_shift_mode(vga,&sm);
+
+    find_graphics_cursor_pos(vga,&cur_x,&cur_y);
+
+    find_graphics_data_starting_offset(vga,&offset);
+
+    fw = spec->width;
+    fh = spec->height;
+
+
+    PrintDebug(VM_NONE, VCORE_NONE, "vga: attempting graphics render (%s): graphics_res=(%u,%u), fb_res=(%u,%u), "
+               "fb=0x%p offset=0x%x\n",
+              sm == PLANAR_SHIFT ? "planar shift" : 
+              sm == PACKED_SHIFT ? "packed shift" : 
+              sm == C256_SHIFT ? "color256 shift" : "UNKNOWN",
+              gw,gh,fw,fh,fb,offset);
+
+    // First we need to clip to what we can actually show
+    rgw = gw < fw ? gw : fw;
+    rgh = gh < fh ? gh : fh;
+
+    if (gw%8) { 
+       PrintError(VM_NONE, VCORE_NONE, "vga: warning: graphics width is not a multiple of 8\n");
+    }
+
+
+
+    // Now we scan across by row
+    for (fy=0;fy<gh;fy++) { 
+       // by column
+       for (fx=0;fx<gw;
+            fx += (sm==C256_SHIFT ? 4 : 8) , offset++ ) { 
+
+           // if any of these pixels are in the rendger region
+           if (fy < rgh && fx < rgw) {
+               // assemble all 4 or 8 pixels
+               
+               // fetch the data bytes
+               for (m=0;m<4;m++) { 
+                   db[m]=*((uint8_t*)(vga->map[m]+offset));
+               }
+                
+               // assemble
+               switch (sm) { 
+                   case PLANAR_SHIFT:
+                       for (p=0;p<8;p++) { 
+                           pb[p]= 
+                               (( db[0] >> 7) & 0x1) |
+                               (( db[1] >> 6) & 0x2) |
+                               (( db[2] >> 5) & 0x4) |
+                               (( db[3] >> 4) & 0x8) ;
+                           
+                           for (m=0;m<4;m++) { 
+                               db[m] <<= 1;
+                           }
+                       }
+                       break;
+                       
+                   case PACKED_SHIFT:
+                       // first 4 pixels use planes 0 and 2
+                       for (p=0;p<4;p++) { 
+                           pb[p] = 
+                               ((db[2] >> 4) & 0xc) |
+                               ((db[0] >> 6) & 0x3) ;
+                           db[2] <<= 2;
+                           db[0] <<= 2;
+                       }
+                       
+                       // next 4 pixels use planes 1 and 3
+                       for (p=4;p<8;p++) { 
+                           pb[p] = 
+                               ((db[3] >> 4) & 0xc) |
+                               ((db[1] >> 6) & 0x3) ;
+                           db[3] <<= 2;
+                           db[1] <<= 2;
+                       }
+                       break;
+
+                   case C256_SHIFT:
+                       // this one is either very bizarre or as simple as this
+                       for (p=0;p<4;p++) { 
+                           pb[p] = db[p];
+                       }
+                       break;
+               }
+
+               // draw each pixel
+               for (p=0;p< (sm==C256_SHIFT ? 4 : 8);p++) { 
+                   
+                   // find its color
+                   find_24bit_color(vga,pb[p],&r,&g,&b);
+               
+                   // find its position in the framebuffer;
+                   pixel =  fb + (((fx + p) + (fy*spec->width)) * spec->bytes_per_pixel);
+                   red = pixel + spec->red_offset;
+                   green = pixel + spec->green_offset;
+                   blue = pixel + spec->blue_offset;
+
+                   // draw it
+                   *red=r;
+                   *green=g;
+                   *blue=b;
+               }
+           }
+       }
+    }
+    
+    PrintDebug(VM_NONE, VCORE_NONE, "vga: render done\n");
+}
+
+
+static void render_text_cursor(struct vga_internal *vga, void *fb)
+{
+}
+
+
+
+
+//
+// A variant of this function could render to
+// a text console interface as well
+//
+static void render_text(struct vga_internal *vga, void *fb)
+{
+    // line graphics enable bit means to  dupe column 8 to 9 when
+    // in 9 dot wide mode
+    // otherwise 9th dot is background
+
+    struct v3_frame_buffer_spec *spec = &(vga->target_spec);
+
+    uint32_t gw, gh; // graphics w/h
+    uint32_t tw, th; // text w/h
+    uint32_t rtw, rth; // rendered text w/h
+    uint32_t cw, ch; // char font w/h including 8/9
+    uint32_t fw, fh; // fb w/h
+
+    uint32_t px, py; // cursor position
+    
+    uint32_t x, y, l, p; // text location, line and pixel within the char
+    uint32_t fx, fy;     // pixel position within the frame buffer
+    
+    uint8_t *text_start; 
+    uint8_t *text;    // points to current char
+    uint8_t *attr;    // and its matching attribute
+    uint8_t *curs;    // to where the cursor is
+    uint8_t *font;    // to where the current font is
+
+    uint8_t fg_entry; // foreground color entry
+    uint8_t bg_entry; // background color entry
+    uint8_t fgr,fgg,fgb;    // looked up  foreground colors
+    uint8_t bgr,bgg,bgb;    // looked up  bg colors
+
+    uint8_t ct, ca;   // the current char and attribute
+    struct vga_attribute_byte a; // decoded attribute
+
+    void *pixel;      // current pixel in the fb
+    uint8_t *red;     // and the channels in the pixel
+    uint8_t *green;   //
+    uint8_t *blue;    //
+
+    
+
+    find_graphics_res(vga,&gw,&gh);
+    find_text_res(vga,&tw,&th);
+    find_text_char_dim(vga,&cw,&ch);
+    fw = spec->width;
+    fh = spec->height;
+
+    find_text_cursor_pos(vga,&px,&py,(void**)&curs);
+    find_text_data_start(vga,(void**)&text);
+    find_text_attr_start(vga,(void**)&attr);
+
+    find_text_font_start(vga,(void**)&font,0); // will need to switch this as we go since it is part of attr
+
+    PrintDebug(VM_NONE, VCORE_NONE, "vga: attempting text render: graphics_res=(%u,%u), fb_res=(%u,%u), text_res=(%u,%u), "
+              "char_res=(%u,%u), cursor=(%u,%u) font=0x%p, text=0x%p, attr=0x%p, curs=0x%p, fb=0x%p"
+              "graphics extension=%u, extended_fontset=%d, blinking=%d\n",
+              gw,gh,fw,fh,tw,th,cw,ch,px,py,font,text,attr,curs,fb,
+              vga->vga_attribute_controller.vga_attribute_mode_control.enable_line_graphics_char_code,
+              extended_fontset(vga), blinking(vga));
+
+    text_start=text;
+
+    // First we need to clip to what we can actually show
+    rtw = tw < fw/cw ? tw : fw/cw;
+    rth = th < fh/ch ? th : fh/ch;
+
+    PrintDebug(VM_NONE, VCORE_NONE, "\n");
+
+    // Now let's scan by char across the whole thing
+    for (y=0;y<th;y++) { 
+       for (x=0;x<tw;x++, text++, attr++) { 
+           if (x < rtw && y < rth) { 
+               // grab the character and attribute for the position
+               ct = *text; 
+               ca = *attr;  
+               a.val = ca;
+
+               PrintDebug(VM_NONE, VCORE_NONE, "%c",ct);
+
+               // find the character's font bitmap (one byte per row)
+               find_text_font_start(vga,(void**)&font,
+                                    extended_fontset(vga) ? a.foreground_intensity_or_font_select : 0 ); 
+
+               font += ct * ((VGA_MAX_FONT_HEIGHT * VGA_FONT_WIDTH)/8);
+
+               // Now let's find out what colors we will be using
+               // foreground
+               
+               if (!extended_fontset(vga)) { 
+                   fg_entry = a.foreground_intensity_or_font_select << 3;
+               } else {
+                   fg_entry = 0;
+               }
+               fg_entry |= a.fore;
+
+               find_24bit_color(vga,fg_entry,&fgr,&fgg,&fgb);
+
+               if (!blinking(vga)) { 
+                   bg_entry = a.blinking_or_bg_intensity << 3;
+               } else {
+                   bg_entry = 0;
+               }
+               bg_entry |= a.back;
+               
+               find_24bit_color(vga,bg_entry,&bgr,&bgg,&bgb);
+
+               // Draw the character
+               for (l=0; l<ch; l++, font++) {
+                   uint8_t frow = *font;  // this is the row of of the font map
+                   for (p=0;p<cw;p++) {
+                       uint8_t fbit;
+                       
+                       // a char can be 9 bits wide, but the font map
+                       // is only 8 bits wide, which means we need to know where to
+                       // get the 9th bit
+                       if (p >= 8) { 
+                           // We get it from the font map if
+                           // its line line graphics mode and its a graphics char
+                           // otherwise it's the background color
+                           if (vga->vga_attribute_controller.vga_attribute_mode_control.enable_line_graphics_char_code
+                               && ct>=0xc0 && ct<=0xdf ) { 
+                               fbit = frow & 0x1;
+                           } else {
+                               fbit = 0;
+                           }
+                       } else {
+                           fbit= (frow >> (7-p) ) & 0x1;
+                       }
+                       
+                       // We are now at the pixel level, with fbit being the pixel we draw (color+attr or bg+attr)
+                       // For now, we will draw it as black/white
+
+                       // find its position in the framebuffer;
+                       fx = x*cw + p;
+                       fy = y*ch + l;
+                       pixel =  fb + ((fx + (fy*spec->width)) * spec->bytes_per_pixel);
+                       red = pixel + spec->red_offset;
+                       green = pixel + spec->green_offset;
+                       blue = pixel + spec->blue_offset;
+
+                       // Are we on the cursor?
+                       // if so, let's negate this pixel to invert the cell
+                       if (curs==text) { 
+                           fbit^=0x1;
+                       }
+                       // update the framebuffer
+                       if (fbit) { 
+                           *red=fgr; 
+                           *green=fgg;
+                           *blue=fgb;
+                       } else {
+                           *red=bgr;
+                           *green=bgg;
+                           *blue=bgb;
+                       }
+                   }
+               }
+           }
+       }
+       PrintDebug(VM_NONE, VCORE_NONE, "\n");
+    }
+
+}
+
+                       
+                       
+
+
+static void render_test(struct vga_internal *vga, void *fb)
+{
+    struct v3_frame_buffer_spec *s;
+
+    s=&(vga->target_spec);
+
+    if (fb && s->height>=480 && s->width>=640 ) { 
+       uint8_t color = (uint8_t)(vga->updates_since_render);
+       
+       uint32_t x, y;
+       
+       for (y=0;y<480;y++) {
+           for (x=0;x<640;x++) { 
+               void *pixel = fb + ((x + (y*s->width)) * s->bytes_per_pixel);
+               uint8_t *red = pixel + s->red_offset;
+               uint8_t *green = pixel + s->green_offset;
+               uint8_t *blue = pixel + s->blue_offset;
+               
+               if (y<(480/4)) { 
+                   *red=color+x;
+                   *green=0;
+                   *blue=0;
+               } else if (y<(480/2)) { 
+                   *red=0;
+                   *green=color+x;
+                   *blue=0;
+               } else if (y<(3*(480/4))) { 
+                   *red=0;
+                   *green=0;
+                   *blue=color+x;
+               } else {
+                   *red=*green=*blue=color+x;
+               }
+           }
+       }
+    }
+}
+
+static void render_black(struct vga_internal *vga, void *fb)
+{
+    struct v3_frame_buffer_spec *s;
+
+    s=&(vga->target_spec);
+
+    memset(fb,0,s->height*s->width*s->bytes_per_pixel);
+}
+
+static void render_maps(struct vga_internal *vga, void *fb)
+{
+
+    struct v3_frame_buffer_spec *s;
+    
+
+    s=&(vga->target_spec);
+
+    if (fb && s->height>=768 && s->width>=1024 ) { 
+       // we draw the maps next, each being a 256x256 block appearing 32 pixels below the display block
+       uint8_t m;
+       uint32_t x,y;
+       uint8_t *b;
+       
+       for (m=0;m<4;m++) { 
+           b=(vga->map[m]);
+           for (y=480+32;y<768;y++) { 
+               for (x=m*256;x<(m+1)*256;x++,b++) { 
+                   void *pixel = fb + ((x + (y*s->width)) * s->bytes_per_pixel);
+                   uint8_t *red = pixel + s->red_offset;
+                   uint8_t *green = pixel + s->green_offset;
+                   uint8_t *blue = pixel + s->blue_offset;
+                   
+                   *red=*green=*blue=*b;
+               }
+           }
+       }
+    }
+}
+
+static int render_core(struct vga_internal *vga)
+{
+  void *fb;
+
+  PrintDebug(VM_NONE, VCORE_NONE, "vga: render on update %u\n",vga->updates_since_render);
+  
+  fb = v3_graphics_console_get_frame_buffer_data_rw(vga->host_cons,&(vga->target_spec));
+  
+  if (!(vga->vga_sequencer.vga_clocking_mode.screen_off)) {
+    if (vga->vga_attribute_controller.vga_attribute_mode_control.graphics) { 
+      render_graphics(vga,fb);
+    } else {
+         render_text(vga,fb);
+         render_text_cursor(vga,fb);
+       }
+  } else {
+    render_black(vga,fb);
+  }
+  
+  if (0) { render_test(vga,fb); }
+  
+  // always render maps for now 
+  render_maps(vga,fb);
+  
+  v3_graphics_console_release_frame_buffer_data_rw(vga->host_cons);
+  
+  vga->updates_since_render=0;
+  
+  return 0;
+
+}
+    
+
+static int render(struct vga_internal *vga)
+{
+
+    vga->updates_since_render++;
+
+
+    if (vga->host_cons) { 
+      int do_render=0;
+      
+      if ((vga->render_model.model & VGA_DRIVEN_PERIODIC_RENDERING)
+         &&
+         (vga->updates_since_render > vga->render_model.updates_before_render)) {
+       PrintDebug(VM_NONE, VCORE_NONE, "vga: render due to periodic\n");
+       
+       do_render = 1;
+      }
+      
+      if ((vga->render_model.model & CONSOLE_ADVISORY_RENDERING) 
+         &&
+         (v3_graphics_console_inform_update(vga->host_cons) > 0) ) { 
+
+        PrintDebug(VM_NONE, VCORE_NONE, "vga: render due to advisory\n");
+
+       do_render = 1;
+      }
+
+      // note that CONSOLE_DRIVEN_RENDERING is handled via the render_callback() function
+      
+      if (do_render) { 
+       return render_core(vga);
+      } else {
+       return 0;
+      }
+    }
+    return 0;
+    
+}
+
+
+static int render_callback(v3_graphics_console_t cons,
+                          void *priv)
+{
+  struct vga_internal *vga = (struct vga_internal *) priv;
+  
+  PrintDebug(VM_NONE, VCORE_NONE, "vga: render due to callback\n");
+
+  return render_core(vga);
+}
+
+static int update_callback(v3_graphics_console_t cons,
+                          void *priv)
+{
+  struct vga_internal *vga = (struct vga_internal *) priv;
+  
+  return vga->updates_since_render>0;
+}
+
+
+
 static void get_mem_region(struct vga_internal *vga, uint64_t *mem_start, uint64_t *mem_end) 
 {
     switch (vga->vga_graphics_controller.vga_misc.memory_map) { 
@@ -344,19 +1123,61 @@ static void get_mem_region(struct vga_internal *vga, uint64_t *mem_start, uint64
     }
 }
 
-static uint64_t find_offset(struct vga_internal *vga, addr_t guest_addr)
+static uint64_t find_offset_write(struct vga_internal *vga, addr_t guest_addr)
 {
     uint64_t mem_start, mem_end;
+    uint64_t size;
     
     mem_start=mem_end=0;
     
     get_mem_region(vga, &mem_start, &mem_end);
+    
+    size=(mem_end-mem_start > 65536 ? 65536 : (mem_end-mem_start)); 
 
-    return (guest_addr-mem_start) % (mem_end-mem_start > 65536 ? 65536 : (mem_end-mem_start)); 
-
+    if (vga->vga_sequencer.vga_mem_mode.odd_even) { 
+      // NOT odd/even mode
+      return (guest_addr-mem_start) % size;
+    } else {
+       // odd/even mode
+      return ((guest_addr-mem_start) >> 1 ) % size;
+    }
 }
 
+
+
     
+// Determines which maps should be enabled for this single byte write
+// and what the increment (actually 1/increment for the copy loop
+//
+//  memory_mode.odd_even == 0 => even address = maps 0 and 2 enabled; 1,3 otherwise
+//  
+static uint8_t find_map_write(struct vga_internal *vga, addr_t guest_addr)
+{
+    uint8_t mm = vga->vga_sequencer.vga_map_mask.val;
+
+    if (vga->vga_sequencer.vga_mem_mode.odd_even) { 
+      // NOT odd/even mode
+      return mm;
+    } else {
+      // odd/even mode
+      if (guest_addr & 0x1) { 
+       return mm & 0xa;  // 0x1010
+      } else {
+       return mm & 0x5;  // 0x0101
+      }
+    }
+}
+
+static uint8_t find_increment_write(struct vga_internal *vga, addr_t new_guest_addr)
+{
+  if (vga->vga_sequencer.vga_mem_mode.odd_even) { 
+    // NOT odd/even mode
+    return 1;
+  } else {
+    return !(new_guest_addr & 0x1);
+  }
+}
+
 
 
 static int vga_write(struct guest_info * core, 
@@ -368,14 +1189,35 @@ static int vga_write(struct guest_info * core,
     struct vm_device *dev = (struct vm_device *)priv_data;
     struct vga_internal *vga = (struct vga_internal *) dev->private_data;
 
-    PrintDebug("vga: memory write: guest_addr=0x%p len=%u\n",(void*)guest_addr, length);
+    PrintDebug(core->vm_info, core, "vga: memory write: guest_addr=0x%p len=%u write_mode=%d first_byte=0x%x\n",
+              (void*)guest_addr, length, vga->vga_graphics_controller.vga_graphics_mode.write_mode, *(uint8_t*)src);
 
     if (vga->passthrough) { 
+       PrintDebug(core->vm_info, core, "vga: passthrough write to 0x%p\n", V3_VAddr((void*)guest_addr));
        memcpy(V3_VAddr((void*)guest_addr),src,length);
     }
     
+#if DEBUG_MEM_DATA
+    int i;
+    PrintDebug(core->vm_info, core, "vga: data written was 0x");
+    for (i=0;i<length;i++) {
+       uint8_t c= ((char*)src)[i];
+       PrintDebug(core->vm_info, core, "%.2x", c);
+    }
+    PrintDebug(core->vm_info, core, " \"");
+    for (i=0;i<length;i++) {
+       char c= ((char*)src)[i];
+       PrintDebug(core->vm_info, core, "%c", (c>='a' && c<='z') || (c>='A' && c<='Z') || (c>='0' && c<='9') || (c==' ') ? c : '.');
+    }
+    PrintDebug(core->vm_info, core, "\"\n");
+#endif
+
     /* Write mode determine by Graphics Mode Register (Index 05h).writemode */
-    
+
+
+    // probably could just reduce this to the datapath itself instead
+    // of following the programmer's perspective... 
+
     switch (vga->vga_graphics_controller.vga_graphics_mode.write_mode) {
        case 0: {
            
@@ -398,30 +1240,49 @@ static int vga_write(struct guest_info * core,
            uint8_t ror = vga->vga_graphics_controller.vga_data_rotate.rotate_count;
            uint8_t func = vga->vga_graphics_controller.vga_data_rotate.function;
            
-           offset = find_offset(vga, guest_addr);
+           offset = find_offset_write(vga, guest_addr);
 
-           PrintDebug("vga: mode 0 write, offset=0x%llx, ror=%u, func=%u\n", offset,ror,func);
+#if DEBUG_DEEP_MEM
+           PrintDebug(core->vm_info, core, "vga: mode 0 write, offset=0x%llx, ror=%u, func=%u\n", offset,ror,func);
+#endif
 
-           for (i=0;i<length;i++,offset++) { 
+           for (i=0;i<length;i++,offset+=find_increment_write(vga,guest_addr+i)) { 
                // now for each map
                uint8_t sr = vga->vga_graphics_controller.vga_set_reset.val & 0xf;
                uint8_t esr = vga->vga_graphics_controller.vga_enable_set_reset.val &0xf;
                uint8_t bm = vga->vga_graphics_controller.vga_bit_mask;
-               uint8_t mm = vga->vga_sequencer.vga_map_mask.val;
+               uint8_t mm = find_map_write(vga,guest_addr+i);
 
-               for (mapnum=0;mapnum<4;mapnum++, sr>>=1, esr>>=1, bm>>=1, mm>>=1) { 
+#if DEBUG_DEEP_MEM
+               PrintDebug(core->vm_info, core, "vga: write i=%u, mm=0x%x, bm=0x%x sr=0x%x esr=0x%x offset=0x%x\n",i,(unsigned int)mm,(unsigned int)bm, (unsigned int)sr, (unsigned int)esr,(unsigned int)offset);
+#endif
+
+               for (mapnum=0;mapnum<4;mapnum++, sr>>=1, esr>>=1, mm>>=1) { 
                    vga_map map = vga->map[mapnum];
                    uint8_t data = ((uint8_t *)src)[i];
                    uint8_t latchval = vga->latch[mapnum];
-                       
+                   
+#if DEBUG_DEEP_MEM
+                   PrintDebug(core->vm_info, core, "vga: raw data=0x%x\n",data);
+#endif
                    // rotate data right
-                   data = (data>>ror) | data<<(8-ror);
-
+                   if (ror) { 
+                       data = (data>>ror) | (data<<(8-ror));
+                   }
+                   
+#if DEBUG_DEEP_MEM
+                   PrintDebug(core->vm_info, core, "vga: data after ror=0x%x\n",data);
+#endif
                    // use SR bit if ESR is on for this map
-                   if (esr & 0x1) { 
-                       data = (uint8_t)((((sint8_t)(sr&0x1))<<7)>>7);  // expand sr bit
+                   if (esr & 0x1) {
+                       data = (sr&0x1) * -1;
+                       
                    }
                    
+#if DEBUG_DEEP_MEM
+                   PrintDebug(core->vm_info, core, "vga: data after esrr=0x%x\n",data);
+#endif
+                   
                    // Apply function
                    switch (func) { 
                        case 0: // NOP
@@ -436,19 +1297,26 @@ static int vga_write(struct guest_info * core,
                            data ^= latchval;
                            break;
                    }
-                           
-                   // mux between latch and alu output
-                   if (bm & 0x1) { 
-                       // use alu output, which is in data
-                   } else {
-                       // use latch value
-                       data=latchval;
-                   }
+                   
+#if DEBUG_DEEP_MEM
+                   PrintDebug(core->vm_info, core, "vga: data after func=0x%x\n",data);
+#endif
+                   
+                   // mux between the data byte and the latch byte on
+                   // a per-bit basis
+                   data = (bm & data) | ((~bm) & latchval);
+                   
+
+#if DEBUG_DEEP_MEM
+                   PrintDebug(core->vm_info, core, "vga: data after bm mux=0x%x\n",data);
+#endif
                    
                    // selective write
                    if (mm & 0x1) { 
                        // write to this map
-                       PrintDebug("vga: write map %u offset 0x%p map=0x%p pointer=0x%p\n",mapnum,(void*)offset,map,&(map[offset]));
+#if DEBUG_DEEP_MEM
+                       PrintDebug(core->vm_info, core, "vga: write map %u offset 0x%p map=0x%p pointer=0x%p\n",mapnum,(void*)offset,map,&(map[offset]));
+#endif
                        map[offset] = data;
                    } else {
                        // skip this map
@@ -469,14 +1337,16 @@ static int vga_write(struct guest_info * core,
 
            int i;
 
-           uint64_t offset = find_offset(vga,guest_addr);
+           uint64_t offset = find_offset_write(vga,guest_addr);
 
-           PrintDebug("vga: mode 1 write, offset=0x%llx\n", offset);
+#if DEBUG_DEEP_MEM
+           PrintDebug(core->vm_info, core, "vga: mode 1 write, offset=0x%llx\n", offset);
+#endif
 
-           for (i=0;i<length;i++,offset++) { 
+           for (i=0;i<length;i++,offset+=find_increment_write(vga,guest_addr+i)) { 
 
                uint8_t mapnum;
-               uint8_t mm = vga->vga_sequencer.vga_map_mask.val;
+               uint8_t mm = find_map_write(vga,guest_addr+i);
 
                for (mapnum=0;mapnum<4;mapnum++,  mm>>=1) { 
                    vga_map map = vga->map[mapnum];
@@ -510,24 +1380,26 @@ static int vga_write(struct guest_info * core,
 
            uint8_t func = vga->vga_graphics_controller.vga_data_rotate.function;
            
-           offset = find_offset(vga, guest_addr);
+           offset = find_offset_write(vga, guest_addr);
 
-           PrintDebug("vga: mode 2 write, offset=0x%llx, func=%u\n", offset,func);
+#if DEBUG_DEEP_MEM
+           PrintDebug(core->vm_info, core, "vga: mode 2 write, offset=0x%llx, func=%u\n", offset,func);
+#endif
 
-           for (i=0;i<length;i++,offset++) { 
+           for (i=0;i<length;i++,offset+=find_increment_write(vga,guest_addr+i)) { 
                // now for each map
                uint8_t bm = vga->vga_graphics_controller.vga_bit_mask;
-               uint8_t mm = vga->vga_sequencer.vga_map_mask.val;
+               uint8_t mm = find_map_write(vga,guest_addr+i);
 
-               for (mapnum=0;mapnum<4;mapnum++,  bm>>=1, mm>>=1) { 
+               for (mapnum=0;mapnum<4;mapnum++,  mm>>=1) { 
                    vga_map map = vga->map[mapnum];
                    uint8_t data = ((uint8_t *)src)[i];
                    uint8_t latchval = vga->latch[mapnum];
                        
                    // expand relevant bit to 8 bit
-                   // it's basically esr=1, sr=bit from write
-                   data = (uint8_t)(((sint8_t)(((data>>mapnum)&0x1)<<7))>>7);
-                   
+                   // it's basically esr=1, sr=bit from mode 0 write
+                   data = ((data>>mapnum)&0x1) * -1;
+                       
                    // Apply function
                    switch (func) { 
                        case 0: // NOP
@@ -542,14 +1414,9 @@ static int vga_write(struct guest_info * core,
                            data ^= latchval;
                            break;
                    }
-                           
+
                    // mux between latch and alu output
-                   if (bm & 0x1) { 
-                       // use alu output, which is in data
-                   } else {
-                       // use latch value
-                       data=latchval;
-                   }
+                   data = (bm & data) | ((~bm) & latchval);
                    
                    // selective write
                    if (mm & 0x1) { 
@@ -581,34 +1448,35 @@ static int vga_write(struct guest_info * core,
 
            uint8_t ror = vga->vga_graphics_controller.vga_data_rotate.rotate_count;
            
-           offset = find_offset(vga, guest_addr);
+           offset = find_offset_write(vga, guest_addr);
 
-           PrintDebug("vga: mode 3 write, offset=0x%llx, ror=%u\n", offset,ror);
+           PrintDebug(core->vm_info, core, "vga: mode 3 write, offset=0x%llx, ror=%u\n", offset,ror);
 
-           for (i=0;i<length;i++,offset++) { 
+           for (i=0;i<length;i++,offset+=find_increment_write(vga,guest_addr+i)) { 
                // now for each map
                uint8_t data = ((uint8_t *)src)[i];
 
-               data = (data>>ror) | data<<(8-ror);
+               if (ror) {
+                   data = (data>>ror) | (data<<(8-ror));
+               }
 
+               // Note here that the bitmask is the register AND the data
+               // the data written by the system is used for no other purpose
                uint8_t bm = vga->vga_graphics_controller.vga_bit_mask & data;
+
                uint8_t sr = vga->vga_graphics_controller.vga_set_reset.val & 0xf;
-               uint8_t mm = vga->vga_sequencer.vga_map_mask.val;
 
-               for (mapnum=0;mapnum<4;mapnum++, sr>>=1, bm>>=1, mm>>=1) { 
+               uint8_t mm = find_map_write(vga,guest_addr+i);
+
+               for (mapnum=0;mapnum<4;mapnum++, sr>>=1, mm>>=1) { 
                    vga_map map = vga->map[mapnum];
                    uint8_t latchval = vga->latch[mapnum];
                        
-                   data = (uint8_t)((((sint8_t)(sr&0x1))<<7)>>7);  // expand sr bit
-                   
-                   
+                   // expand SR bit - that's the data we're going to use
+                   data = (sr&0x1) * -1;
+
                    // mux between latch and alu output
-                   if (bm & 0x1) { 
-                       // use alu output, which is in data
-                   } else {
-                       // use latch value
-                       data=latchval;
-                   }
+                   data = (bm & data) | ((~bm) & latchval);
                    
                    // selective write
                    if (mm & 0x1) { 
@@ -625,50 +1493,81 @@ static int vga_write(struct guest_info * core,
 
            // There is no default
     }
+
+    render(vga);
     
     return length;
 }
 
-    //    PrintError("vga: vga_write UNIMPLEMENTED\n");
-
-/*
-up to 256K mapped through a window of 128K
-
-most cards support linear mode as well
-
-Need to implement readability too
-
-Write extended memory bit to enable all 256K: 
-
-   Sequencer Memory Mode Register (Index 04h) . extended memory
-
-Must enable writes before effects happen:
-  
-  Miscellaneous Output Register (Read at 3CCh, Write at 3C2h).ram enable
 
-Choose which addresses are supported for CPU writes:
 
-Miscellaneous Graphics Register (Index 06h).memory map select
-00b -- A0000h-BFFFFh (128K region)
-01b -- A0000h-AFFFFh (64K region)
-10b -- B0000h-B7FFFh (32K region)
-11b -- B8000h-BFFFFh (32K region)
+static uint64_t find_offset_read(struct vga_internal *vga, addr_t guest_addr)
+{
+    uint64_t mem_start, mem_end;
+    uint64_t size;
+    
+    mem_start=mem_end=0;
+    
+    get_mem_region(vga, &mem_start, &mem_end);
+    
+    size=(mem_end-mem_start > 65536 ? 65536 : (mem_end-mem_start)); 
 
-There are three addressing modes: Chain 4, Odd/Even mode, and normal mode:
+    if (!vga->vga_sequencer.vga_mem_mode.odd_even) { 
+      // odd/even mode takes priority
+      return ((guest_addr-mem_start) >> 1 ) % size;
+    } 
 
-Chain 4: This mode is used for MCGA emulation in the 320x200 256-color mode. The address is mapped to memory MOD 4 (shifted right 2 places.)
+    if (vga->vga_sequencer.vga_mem_mode.chain4) {
+      // otherwise chain4 if it's on
+      return ((guest_addr - mem_start) >> 2) % size;
+    }
 
-Memory model: 64K 32 bit locations; divided into 4 64K bit planes
+    // and what you would expect if neither are on
+    return (guest_addr-mem_start) % size;
+}
 
+// Given this address
+// which specific map should we write into?
+// Note that unlike with find_map_write, here we are looking
+// for a single map number, not a bit vector of maps to be selected
+static uint8_t find_map_read(struct vga_internal *vga, addr_t guest_addr)
+{
+    uint64_t mem_start, mem_end;
+    
+    mem_start=mem_end=0;
+    
+    get_mem_region(vga, &mem_start, &mem_end);
+    
+    if (!vga->vga_sequencer.vga_mem_mode.odd_even) { 
+      // odd-even mode
+      // last bit tells us map 0 or 1
+      return (guest_addr-mem_start) & 0x1; 
+    } 
 
-   
+    if (vga->vga_sequencer.vga_mem_mode.chain4) {
+      // otherwise chain4 if it's on
+      // last two bits
+      return (guest_addr - mem_start) & 0x3;
+    }
 
+    // and what you would expect if neither are on
+    // note that it's not the same as a write!
+    return vga->vga_graphics_controller.vga_read_map_select.map_select;
+}
 
-Assume linear framebuffer, starting at address buf:
+static uint8_t find_increment_read(struct vga_internal *vga, addr_t new_guest_addr)
+{
 
-*/
+  if (!vga->vga_sequencer.vga_mem_mode.odd_even) { 
+    // odd-even mode
+    return !(new_guest_addr & 0x1); 
+  } 
 
+  if (vga->vga_sequencer.vga_mem_mode.chain4) { 
+    return !(new_guest_addr & 0x3);
+  } 
+  return 1;
+}
 
 
 static int vga_read(struct guest_info * core, 
@@ -679,15 +1578,12 @@ static int vga_read(struct guest_info * core,
 {
     struct vm_device *dev = (struct vm_device *)priv_data;
     struct vga_internal *vga = (struct vga_internal *) dev->private_data;
+    
 
-    PrintDebug("vga: memory read: guest_addr=0x%p len=%u\n",(void*)guest_addr, length);
-
-
-    if (vga->passthrough) { 
-       memcpy(dst,V3_VAddr((void*)guest_addr),length);
-    }
+    PrintDebug(core->vm_info, core, "vga: memory read: guest_addr=0x%p len=%u read_mode=%d\n",(void*)guest_addr, length,
+              vga->vga_graphics_controller.vga_graphics_mode.read_mode);
 
-               
+        
    
     /*
       Reading, 2 modes, set via Graphics Mode Register (index 05h).Read Mode:
@@ -695,24 +1591,32 @@ static int vga_read(struct guest_info * core,
     switch (vga->vga_graphics_controller.vga_graphics_mode.read_mode) { 
        case 0: {
            /*      0 - a byte from ONE of the 4 planes is returned; 
-                   which plane is determined by Read Map Select (Read Map Select Register (Index 04h)) */
+                   which plane is determined by Read Map Select (Read Map Select Register (Index 04h))
+                   OR by odd/even chaining OR by chain4 chaining
+           */
            uint8_t  mapnum;
            uint64_t offset;
-           
-           mapnum = vga->vga_graphics_controller.vga_read_map_select.map_select;
-           offset = find_offset(vga,guest_addr);
-           
-           if (offset>=65536) { 
-               PrintError("vga: read to offset=%llu map=%u (%u bytes)\n",offset,mapnum,length);
-           }
+           uint32_t i;
 
-           memcpy(dst,(vga->map[mapnum])+offset,length);
+           offset = find_offset_read(vga,guest_addr);
+           
+#if DEBUG_DEEP_MEM
+           PrintDebug(core->vm_info, core, "vga: mode 0 read, offset=0x%llx\n",offset);
+#endif
+           for (i=0;i<length;i++,offset+=find_increment_read(vga,guest_addr+i)) { 
+
+             mapnum = find_map_read(vga,guest_addr+i);
+
+             // the data returned
+             ((uint8_t*)dst)[i] = *(vga->map[mapnum]+offset);
+             
+             // need to load all latches even though we are 
+             // returning data from only the selected map
+             for (mapnum=0;mapnum<4;mapnum++) { 
+               vga->latch[mapnum] = *(vga->map[mapnum]+offset);
+             }
 
-           // load the latches with the last item read
-           for (mapnum=0;mapnum<4;mapnum++) { 
-               vga->latch[mapnum] = vga->map[mapnum][offset+length-1];
            }
-           
        
        }
            break;
@@ -726,70 +1630,70 @@ static int vga_read(struct guest_info * core,
 
            */
            int i;
-
-           uint8_t cc=vga->vga_graphics_controller.vga_color_compare.val & 0xf ;
-           uint8_t dc=vga->vga_graphics_controller.vga_color_dont_care.val & 0xf;
-
-           uint8_t  mapnum;
            uint64_t offset;
-           uint8_t  byte;
-           uint8_t  bits;
-           
-           offset = find_offset(vga,guest_addr);
-           
-           for (i=0;i<length;i++,offset++) { 
-               vga_map map;
-               byte=0;
-               for (mapnum=0;mapnum<4;mapnum++) { 
-                   map = vga->map[mapnum];
-                   if ( (dc>>mapnum)&0x1 ) { // don't care
-                       bits=0;
-                   } else {
-                       // lower 4 bits
-                       bits = (map[offset]&0xf) == cc;
-                       bits <<= 1;
-                       // upper 4 bits
-                       bits |= (((map[offset]>>4))&0xf) == cc;
-                   }
-                   // not clear whether it is 0..k or k..0
-                   byte<<=2;
-                   byte|=bits;
-               }
-           }
+           
+           offset = find_offset_read(vga,guest_addr);
 
-           // load the latches with the last item read
-           for (mapnum=0;mapnum<4;mapnum++) { 
-               vga->latch[mapnum] = vga->map[mapnum][offset+length-1];
+#if DEBUG_DEEP_MEM
+           PrintDebug(core->vm_info, core, "vga: mode 1 read, offset=0x%llx\n",offset);
+#endif
+               
+           for (i=0;i<length;i++,offset+=find_increment_read(vga,guest_addr+i)) { 
+             uint8_t mapnum;
+             uint8_t mapcalc=0xff;
+             
+             uint8_t cc=vga->vga_graphics_controller.vga_color_compare.val & 0xf ;
+             uint8_t dc=vga->vga_graphics_controller.vga_color_dont_care.val & 0xf;
+             
+             for (mapnum=0;mapnum<4;mapnum++, cc>>=1, dc>>=1) { 
+               if (dc&0x1) {  // dc is active low; 1=we do care
+                 mapcalc &= (cc * -1) & *(vga->map[mapnum]+offset);
+               }
+               // do latch load
+               vga->latch[mapnum] = *(vga->map[mapnum]+offset);
+             }
+             // write back the comparison result (for 8 pixels)
+             ((uint8_t *)dst)[i]=mapcalc;
            }
 
        }
+
            break;
            // there is no default
     }
 
-    return length;
-
-}
+    if (vga->passthrough) { 
+       PrintDebug(core->vm_info, core, "vga: passthrough read from 0x%p\n",V3_VAddr((void*)guest_addr));
+       memcpy(dst,V3_VAddr((void*)guest_addr),length);
+    }
 
 
+#if DEBUG_MEM_DATA
+    int i;
+    PrintDebug(core->vm_info, core, "vga: data read is 0x");
+    for (i=0;i<length;i++) {
+       uint8_t c= ((char*)dst)[i];
+       PrintDebug(core->vm_info, core, "%.2x", c);
+    }
+    PrintDebug(core->vm_info, core, " \"");
+    for (i=0;i<length;i++) {
+       char c= ((char*)dst)[i];
+       PrintDebug(core->vm_info, core, "%c", (c>='a' && c<='z') || (c>='A' && c<='Z') || (c>='0' && c<='9') || (c==' ') ? c : '.');
+    }
+    PrintDebug(core->vm_info, core, "\"\n");
+#endif
 
-static int render(struct vga_internal *vga)
-{
-    PrintError("vga: render UNIMPLEMENTED\n");
+    return length;
 
-    if (!palacios_linux_fb_hack_pointer) { 
-       return 0;
-    }
+}
 
 
 
-    return 0;
-}
 
 
 #define ERR_WRONG_SIZE(op,reg,len,min,max)     \
     if (((len)<(min)) || ((len)>(max))) {       \
-       PrintError("vga: %s of %s wrong size (%d bytes, but only %d to %d allowed)\n",(op),(reg),(len),(min),(max)); \
+       PrintError(core->vm_info, core, "vga: %s of %s wrong size (%d bytes, but only %d to %d allowed)\n",(op),(reg),(len),(min),(max)); \
        return -1; \
 }
        
@@ -805,7 +1709,7 @@ static inline void passthrough_io_in(uint16_t port, void * dest, uint_t length)
            *(uint32_t *)dest = v3_indw(port);
            break;
        default:
-           PrintError("vga: unsupported passthrough io in size %u\n",length);
+           PrintError(VM_NONE, VCORE_NONE, "vga: unsupported passthrough io in size %u\n",length);
            break;
     }
 }
@@ -823,7 +1727,7 @@ static inline void passthrough_io_out(uint16_t port, const void * src, uint_t le
            v3_outdw(port, *(uint32_t *)src);
            break;
        default:
-           PrintError("vga: unsupported passthrough io out size %u\n",length);
+           PrintError(VM_NONE, VCORE_NONE, "vga: unsupported passthrough io out size %u\n",length);
            break;
     }
 }
@@ -832,9 +1736,13 @@ static inline void passthrough_io_out(uint16_t port, const void * src, uint_t le
     do { if ((vga)->passthrough) { passthrough_io_in(port,dest,len); } } while (0)
 
 #define PASSTHROUGH_IO_OUT(vga,port,src,len)                           \
-    do { if ((vga)->passthrough) { passthrough_io_in(port,src,len); } } while (0)
-               
+    do { if ((vga)->passthrough && (!(vga)->skip_next_passthrough_out)) { passthrough_io_out(port,src,len); } (vga)->skip_next_passthrough_out=false; } while (0)
 
+#define PASSTHROUGH_IO_SKIP_NEXT_OUT(vga)                                      \
+    do { if ((vga)->passthrough) { (vga)->skip_next_passthrough_out=true; } } while (0)
+               
+#define PASSTHROUGH_READ_CHECK(vga,inter,pass) \
+    do { if ((vga)->passthrough) { if ((inter)!=(pass)) { PrintError(core->vm_info, core, "vga: passthrough error: passthrough value read is 0x%x, but internal value read is 0x%x\n",(pass),(inter)); } } } while (0)
 
 static int misc_out_read(struct guest_info *core, 
                         uint16_t port, 
@@ -844,13 +1752,15 @@ static int misc_out_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
 
-    PrintDebug("vga: misc out read data=0x%x\n", vga->vga_misc.vga_misc_out.val);
+    PrintDebug(core->vm_info, core, "vga: misc out read data=0x%x\n", vga->vga_misc.vga_misc_out.val);
 
     ERR_WRONG_SIZE("read","misc out",len,1,1);
-    
+   
+    *((uint8_t*)dest) = vga->vga_misc.vga_misc_out.val;
+
     PASSTHROUGH_IO_IN(vga,port,dest,len);
 
-    *((uint8_t*)dest) = vga->vga_misc.vga_misc_out.val;
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_misc.vga_misc_out.val,*((uint8_t*)dest));
 
     return len;
 }
@@ -863,7 +1773,7 @@ static int misc_out_write(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
     
-    PrintDebug("vga: misc out write data=0x%x\n", *((uint8_t*)src));
+    PrintDebug(core->vm_info, core, "vga: misc out write data=0x%x\n", *((uint8_t*)src));
        
     ERR_WRONG_SIZE("write","misc out",len,1,1);
 
@@ -886,13 +1796,15 @@ static int input_stat0_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
 
-    PrintDebug("vga: input stat0  read data=0x%x\n", vga->vga_misc.vga_input_stat0.val);
+    PrintDebug(core->vm_info, core, "vga: input stat0  read data=0x%x\n", vga->vga_misc.vga_input_stat0.val);
 
     ERR_WRONG_SIZE("read","input stat0",len,1,1);
 
+    *((uint8_t*)dest) = vga->vga_misc.vga_input_stat0.val;
+
     PASSTHROUGH_IO_IN(vga,port,dest,len);
 
-    *((uint8_t*)dest) = vga->vga_misc.vga_input_stat0.val;
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_misc.vga_input_stat0.val,*(uint8_t*)dest);
 
     return len;
 }
@@ -906,22 +1818,47 @@ static int input_stat1_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
 
-    PrintDebug("vga: input stat0 (%s) read data=0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: input stat0 (%s) read data=0x%x\n", 
               port==0x3ba ? "mono" : "color",
               vga->vga_misc.vga_input_stat1.val);
 
     ERR_WRONG_SIZE("read","input stat1",len,1,1);
 
-    PASSTHROUGH_IO_IN(vga,port,dest,len);
 
     *((uint8_t*)dest) = vga->vga_misc.vga_input_stat1.val;
 
+    // Pretend that horizontal and vertical blanking
+    // is occurring
+    if (!vga->vga_misc.vga_input_stat1.disp_en) {
+
+        // if not blanking, start horizontal blanking
+        vga->vga_misc.vga_input_stat1.disp_en = 1;
+        vga->vga_misc.vga_input_stat1.vert_retrace = 0;
+
+    } else {
+
+        if (!vga->vga_misc.vga_input_stat1.vert_retrace) {
+            // if not vertical blanking, then now vertical blanking
+            vga->vga_misc.vga_input_stat1.disp_en = 1;
+            vga->vga_misc.vga_input_stat1.vert_retrace = 1;
+        } else { 
+            // if vertical blanking, now not blanking
+            vga->vga_misc.vga_input_stat1.disp_en = 0;
+            vga->vga_misc.vga_input_stat1.vert_retrace = 0;
+        }
+
+    }
+
     // Stunningly, reading stat1 is also a way to reset
     // the state of attribute controller address/data flipflop
     // That is some mighty fine crack the designers were smoking.
     
     vga->vga_attribute_controller.state=ATTR_ADDR;
 
+    PASSTHROUGH_IO_IN(vga,port,dest,len);
+
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_misc.vga_input_stat1.val,*(uint8_t*)dest);
+
     return len;
 }
                         
@@ -934,15 +1871,18 @@ static int feature_control_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
 
-    PrintDebug("vga: feature control  read data=0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: feature control  read data=0x%x\n", 
               vga->vga_misc.vga_feature_control.val);
 
     ERR_WRONG_SIZE("read","feature control",len,1,1);
 
-    PASSTHROUGH_IO_IN(vga,port,dest,len);
 
     *((uint8_t*)dest) = vga->vga_misc.vga_feature_control.val;
 
+    PASSTHROUGH_IO_IN(vga,port,dest,len);
+
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_misc.vga_feature_control.val,*(uint8_t*)dest);
+
     return len;
 }
 
@@ -954,7 +1894,7 @@ static int feature_control_write(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
     
-    PrintDebug("vga: feature control (%s) write data=0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: feature control (%s) write data=0x%x\n", 
               port==0x3ba ? "mono" : "color",
               *((uint8_t*)src));
        
@@ -978,14 +1918,16 @@ static int video_subsys_enable_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
 
-    PrintDebug("vga: video subsys enable read data=0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: video subsys enable read data=0x%x\n", 
               vga->vga_misc.vga_video_subsys_enable.val);
 
     ERR_WRONG_SIZE("read","video subsys enable",len,1,1);
 
+    *((uint8_t*)dest) = vga->vga_misc.vga_video_subsys_enable.val;
+
     PASSTHROUGH_IO_IN(vga,port,dest,len);
 
-    *((uint8_t*)dest) = vga->vga_misc.vga_video_subsys_enable.val;
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_misc.vga_video_subsys_enable.val,*(uint8_t*)dest);
 
     return len;
 }
@@ -998,7 +1940,7 @@ static int video_subsys_enable_write(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
     
-    PrintDebug("vga: video subsys enable write data=0x%x\n", *((uint8_t*)src));
+    PrintDebug(core->vm_info, core, "vga: video subsys enable write data=0x%x\n", *((uint8_t*)src));
        
     ERR_WRONG_SIZE("write","video subsys enable",len,1,1);
     
@@ -1019,14 +1961,16 @@ static int sequencer_address_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
 
-    PrintDebug("vga: sequencer address read data=0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: sequencer address read data=0x%x\n", 
               vga->vga_sequencer.vga_sequencer_addr.val);
 
     ERR_WRONG_SIZE("read","vga sequencer addr",len,1,1);
 
+    *((uint8_t*)dest) = vga->vga_sequencer.vga_sequencer_addr.val;
+
     PASSTHROUGH_IO_IN(vga,port,dest,len);
 
-    *((uint8_t*)dest) = vga->vga_sequencer.vga_sequencer_addr.val;
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_sequencer.vga_sequencer_addr.val,*(uint8_t*)dest);
 
     return len;
 }
@@ -1044,14 +1988,19 @@ static int sequencer_data_write(struct guest_info *core,
     data=*((uint8_t*)src);
     index=vga->vga_sequencer.vga_sequencer_addr.val;  // should mask probably
     
-    PrintDebug("vga: sequencer write data (index=%d) with 0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: sequencer write data (index=%d) with 0x%x\n", 
               index, data);
     
     ERR_WRONG_SIZE("write","vga sequencer data",len,1,1);
     
     PASSTHROUGH_IO_OUT(vga,port,src,len);
 
-    vga->vga_sequencer.vga_sequencer_regs[index] = data;
+
+    if (index>=VGA_SEQUENCER_NUM) { 
+       PrintError(core->vm_info, core, "vga: sequencer data write is for invalid index %d, ignoring\n",index);
+    } else {
+       vga->vga_sequencer.vga_sequencer_regs[index] = data;
+    }
 
     render(vga);
     
@@ -1069,28 +2018,23 @@ static int sequencer_address_write(struct guest_info *core,
 
     new_addr=*((uint8_t*)src);
 
-    PrintDebug("vga: sequencer address write data=0x%x len=%u\n", new_addr,len);
+    PrintDebug(core->vm_info, core, "vga: sequencer address write data=0x%x len=%u\n", len==1 ? *((uint8_t*)src) : len==2 ? *((uint16_t*)src) : *((uint32_t*)src), len);
 
     ERR_WRONG_SIZE("write","vga sequencer addr",len,1,2);
 
-    PASSTHROUGH_IO_OUT(vga,port,src,1);
-
-    if (new_addr>VGA_SEQUENCER_NUM) {
-       PrintError("vga: ignoring change of sequencer address to %u (>%u)\n",
-                  new_addr, VGA_SEQUENCER_NUM);
-       //return -1;
-    } else {
-       vga->vga_sequencer.vga_sequencer_addr.val =  *((uint8_t*)src) ;
-       if (len==2) { 
-           // second byte is the data
-           if (sequencer_data_write(core,port,src+1,1,vga)!=1) { 
-               PrintError("vga: write of data failed\n");
-               return -1;
-           }
+    PASSTHROUGH_IO_OUT(vga,port,src,len);
+    
+    vga->vga_sequencer.vga_sequencer_addr.val =  *((uint8_t*)src) ;
+    
+    if (len==2) { 
+       PASSTHROUGH_IO_SKIP_NEXT_OUT(vga);
+       // second byte is the data
+       if (sequencer_data_write(core,port,src+1,1,vga)!=1) { 
+           PrintError(core->vm_info, core, "vga: write of data failed\n");
+           return -1;
        }
     }
 
-
     return len;
 }
 
@@ -1105,16 +2049,24 @@ static int sequencer_data_read(struct guest_info *core,
     uint8_t data;
 
     index=vga->vga_sequencer.vga_sequencer_addr.val;  // should mask probably
-    data=vga->vga_sequencer.vga_sequencer_regs[index];
+
+    if (index>=VGA_SEQUENCER_NUM) { 
+       data=0;
+       PrintError(core->vm_info, core, "vga: sequencer data read at invalid index %d, returning zero\n",index);
+    } else {
+       data=vga->vga_sequencer.vga_sequencer_regs[index];
+    }
+
+    PrintDebug(core->vm_info, core, "vga: sequencer data read data (index=%d) = 0x%x\n", 
+                  index, data);
     
-    PrintDebug("vga: sequencer data read data (index=%d) = 0x%x\n", 
-              index, data);
+    ERR_WRONG_SIZE("read","vga sequencer data",len,1,1);
 
-    ERR_WRONG_SIZE("read","vga sequenver data",len,1,1);
+    *((uint8_t*)dest) = data;
 
     PASSTHROUGH_IO_IN(vga,port,dest,len);
 
-    *((uint8_t*)dest) = data;
+    PASSTHROUGH_READ_CHECK(vga,data,*(uint8_t*)dest);
 
     return len;
 }
@@ -1131,15 +2083,17 @@ static int crt_controller_address_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
 
-    PrintDebug("vga: crt controller (%s) address read data=0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: crt controller (%s) address read data=0x%x\n", 
               port==0x3b4 ? "mono" : "color",
               vga->vga_crt_controller.vga_crt_addr.val);
 
     ERR_WRONG_SIZE("read","vga crt controller addr",len,1,1);
 
+    *((uint8_t*)dest) = vga->vga_crt_controller.vga_crt_addr.val;
+
     PASSTHROUGH_IO_IN(vga,port,dest,len);
 
-    *((uint8_t*)dest) = vga->vga_crt_controller.vga_crt_addr.val;
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_crt_controller.vga_crt_addr.val,*(uint8_t*)dest);
 
     return len;
 }
@@ -1158,7 +2112,7 @@ static int crt_controller_data_write(struct guest_info *core,
 
     index=vga->vga_crt_controller.vga_crt_addr.val;  // should mask probably
     
-    PrintDebug("vga: crt controller (%s) write data (index=%d) with 0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: crt controller (%s) write data (index=%d) with 0x%x\n", 
               port==0x3b5 ? "mono" : "color",
               index, data);
 
@@ -1166,7 +2120,16 @@ static int crt_controller_data_write(struct guest_info *core,
 
     PASSTHROUGH_IO_OUT(vga,port,src,len);
 
-    vga->vga_crt_controller.vga_crt_controller_regs[index] = data;
+    if (index>=VGA_CRT_CONTROLLER_NUM) { 
+        PrintError(core->vm_info, core, "vga; crt controller write is for illegal index %d, ignoring\n",index);
+    } else {
+        vga->vga_crt_controller.vga_crt_controller_regs[index] = data;
+        if (index == 17) {
+            if (vga->vga_crt_controller.vga_vertical_retrace_end.enable_vertical_interrupt) {
+                PrintError(core->vm_info, core, "vga: vertical_retrace_interrupt_enabled is unsupported -- no interrupts will occur!\n");
+            }
+        }
+    }
 
     render(vga);
 
@@ -1184,30 +2147,25 @@ static int crt_controller_address_write(struct guest_info *core,
 
     new_addr=*((uint8_t*)src);
 
-    PrintDebug("vga: crt controller (%s) address write data=0x%x len=%u\n", 
+    PrintDebug(core->vm_info, core, "vga: crt controller (%s) address write data=0x%x len=%u\n", 
               port==0x3b4 ? "mono" : "color",
-              new_addr,len);
+              len==1 ? *((uint8_t*)src) : len==2 ? *((uint16_t*)src) : *((uint32_t*)src), len);
 
     ERR_WRONG_SIZE("write","vga crt controller addr",len,1,2);
 
-    PASSTHROUGH_IO_OUT(vga,port,src,1);
+    PASSTHROUGH_IO_OUT(vga,port,src,len);
 
-    if (new_addr>VGA_CRT_CONTROLLER_NUM) {
-       PrintError("vga: ignoring change of crt controller address to %u (>%u)\n",
-                  new_addr, VGA_CRT_CONTROLLER_NUM);
-       //return -1;
-    } else {
-       vga->vga_crt_controller.vga_crt_addr.val =  *((uint8_t*)src) ;
-       if (len==2) { 
-           // second byte is the data
-           if (crt_controller_data_write(core,port,src+1,1,vga)!=1) { 
-               PrintError("vga: write of data failed\n");
-               return -1;
-           }
+    vga->vga_crt_controller.vga_crt_addr.val =  *((uint8_t*)src) ;
+       
+    if (len==2) { 
+       PASSTHROUGH_IO_SKIP_NEXT_OUT(vga);
+       // second byte is the data
+       if (crt_controller_data_write(core,port,src+1,1,vga)!=1) { 
+           PrintError(core->vm_info, core, "vga: write of data failed\n");
+           return -1;
        }
-
     }
-
+    
     return len;
 }
 
@@ -1222,17 +2180,23 @@ static int crt_controller_data_read(struct guest_info *core,
     uint8_t data;
 
     index=vga->vga_crt_controller.vga_crt_addr.val;  // should mask probably
-    data=vga->vga_crt_controller.vga_crt_controller_regs[index];
     
-    PrintDebug("vga: crt controller data (%s) read data (index=%d) = 0x%x\n", 
-              port==0x3b5 ? "mono" : "color",
-              index, data);
+    if (index>=VGA_CRT_CONTROLLER_NUM) { 
+       data=0;
+       PrintError(core->vm_info, core, "vga: crt controller data read for illegal index %d, returning zero\n",index);
+    } else {
+       data=vga->vga_crt_controller.vga_crt_controller_regs[index];
+    }
 
+    PrintDebug(core->vm_info, core, "vga: crt controller data (index=%d) = 0x%x\n",index,data);
+    
     ERR_WRONG_SIZE("read","vga crt controller data",len,1,1);
 
+    *((uint8_t*)dest) = data;
+
     PASSTHROUGH_IO_IN(vga,port,dest,len);
 
-    *((uint8_t*)dest) = data;
+    PASSTHROUGH_READ_CHECK(vga,data,*(uint8_t *)dest);
 
     return len;
 }
@@ -1247,14 +2211,16 @@ static int graphics_controller_address_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
     
-    PrintDebug("vga: graphics controller address read data=0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: graphics controller address read data=0x%x\n", 
               vga->vga_graphics_controller.vga_graphics_ctrl_addr.val);
 
     ERR_WRONG_SIZE("read","vga graphics controller addr",len,1,1);
 
+    *((uint8_t*)dest) = vga->vga_graphics_controller.vga_graphics_ctrl_addr.val;
+
     PASSTHROUGH_IO_IN(vga,port,dest,len);
 
-    *((uint8_t*)dest) = vga->vga_graphics_controller.vga_graphics_ctrl_addr.val;
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_graphics_controller.vga_graphics_ctrl_addr.val,*(uint8_t*)dest);
 
     return len;
 }
@@ -1272,14 +2238,19 @@ static int graphics_controller_data_write(struct guest_info *core,
     data=*((uint8_t*)src);
     index=vga->vga_graphics_controller.vga_graphics_ctrl_addr.val;  // should mask probably
     
-    PrintDebug("vga: graphics_controller write data (index=%d) with 0x%x\n", 
+
+    PrintDebug(core->vm_info, core, "vga: graphics_controller write data (index=%d) with 0x%x\n", 
               index, data);
     
     ERR_WRONG_SIZE("write","vga graphics controller data",len,1,1);
     
     PASSTHROUGH_IO_OUT(vga,port,src,len);
 
-    vga->vga_graphics_controller.vga_graphics_controller_regs[index] = data;
+    if (index>=VGA_GRAPHICS_CONTROLLER_NUM) { 
+       PrintError(core->vm_info, core, "vga: graphics controller write for illegal index %d ignored\n",index);
+    } else {
+       vga->vga_graphics_controller.vga_graphics_controller_regs[index] = data;
+    }
 
     render(vga);
     
@@ -1297,26 +2268,24 @@ static int graphics_controller_address_write(struct guest_info *core,
 
     new_addr=*((uint8_t*)src);
 
-    PrintDebug("vga: graphics controller address write data=0x%x len=%u\n", new_addr,len);
+    PrintDebug(core->vm_info, core, "vga: graphics controller address write data=0x%x len=%u\n", 
+              len==1 ? *((uint8_t*)src) : len==2 ? *((uint16_t*)src) : *((uint32_t*)src), len);
 
     ERR_WRONG_SIZE("write","vga graphics controller addr",len,1,2);
 
-    PASSTHROUGH_IO_OUT(vga,port,src,1);
+    PASSTHROUGH_IO_OUT(vga,port,src,len);
 
-    if (new_addr>VGA_GRAPHICS_CONTROLLER_NUM) {
-       PrintError("vga: ignoring change of graphics controller address to %u (>%u)\n",
-                  new_addr, VGA_GRAPHICS_CONTROLLER_NUM);
-       //return -1;
-    } else {
-       vga->vga_graphics_controller.vga_graphics_ctrl_addr.val =  *((uint8_t*)src) ;
-       if (len==2) { 
-           // second byte is the data
-           if (graphics_controller_data_write(core,port,src+1,1,vga)!=1) { 
-               PrintError("vga: write of data failed\n");
-               return -1;
-           }
+    vga->vga_graphics_controller.vga_graphics_ctrl_addr.val =  *((uint8_t*)src) ;
+
+    if (len==2) { 
+       PASSTHROUGH_IO_SKIP_NEXT_OUT(vga);
+       // second byte is the data
+       if (graphics_controller_data_write(core,port,src+1,1,vga)!=1) { 
+           PrintError(core->vm_info, core, "vga: write of data failed\n");
+           return -1;
        }
     }
+
     return len;
 }
 
@@ -1331,17 +2300,26 @@ static int graphics_controller_data_read(struct guest_info *core,
     uint8_t data;
 
     index=vga->vga_graphics_controller.vga_graphics_ctrl_addr.val;  // should mask probably
-    data=vga->vga_graphics_controller.vga_graphics_controller_regs[index];
+
+
+    if (index>=VGA_GRAPHICS_CONTROLLER_NUM) { 
+       data=0;
+       PrintError(core->vm_info, core, "vga: graphics controller data read from illegal index %d, returning zero\n",index);
+    } else {
+       data=vga->vga_graphics_controller.vga_graphics_controller_regs[index];
+    }
     
-    PrintDebug("vga: graphics controller data read data (index=%d) = 0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: graphics controller data read data (index=%d) = 0x%x\n", 
               index, data);
 
     ERR_WRONG_SIZE("read","vga graphics controller data",len,1,1);
 
-    PASSTHROUGH_IO_IN(vga,port,dest,len);
-
     *((uint8_t*)dest) = data;
 
+    PASSTHROUGH_IO_IN(vga,port,dest,len);
+
+    PASSTHROUGH_READ_CHECK(vga,data,*(uint8_t*)dest);
+    
     return len;
 }
 
@@ -1358,14 +2336,16 @@ static int attribute_controller_address_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
     
-    PrintDebug("vga: attribute controller address read data=0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: attribute controller address read data=0x%x\n", 
               vga->vga_attribute_controller.vga_attribute_controller_addr.val);
 
     ERR_WRONG_SIZE("read","vga attribute  controller addr",len,1,1);
 
+    *((uint8_t*)dest) = vga->vga_attribute_controller.vga_attribute_controller_addr.val;
+
     PASSTHROUGH_IO_IN(vga,port,dest,len);
 
-    *((uint8_t*)dest) = vga->vga_attribute_controller.vga_attribute_controller_addr.val;
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_attribute_controller.vga_attribute_controller_addr.val,*(uint8_t*)dest);
 
     // Reading the attribute controller does not change the state
 
@@ -1385,19 +2365,14 @@ static int attribute_controller_address_and_data_write(struct guest_info *core,
        uint8_t new_addr = *((uint8_t*)src);
        // We are to treat this as an address write, and flip state
        // to expect data ON THIS SAME PORT
-       PrintDebug("vga: attribute controller address write data=0x%x\n", new_addr);
+       PrintDebug(core->vm_info, core, "vga: attribute controller address write data=0x%x\n", new_addr);
        
        ERR_WRONG_SIZE("write","vga attribute controller addr",len,1,1);
 
        PASSTHROUGH_IO_OUT(vga,port,src,len);
 
-       if (new_addr>VGA_ATTRIBUTE_CONTROLLER_NUM) {
-           PrintError("vga: ignoring change of attribute controller address to %u (>%u)\n",
-                      new_addr, VGA_ATTRIBUTE_CONTROLLER_NUM);
-           //return -1;
-       } else {
-           vga->vga_attribute_controller.vga_attribute_controller_addr.val =  *((uint8_t*)src) ;
-       }
+       vga->vga_attribute_controller.vga_attribute_controller_addr.val =  new_addr;
+
        vga->vga_attribute_controller.state=ATTR_DATA;
        return len;
 
@@ -1406,13 +2381,17 @@ static int attribute_controller_address_and_data_write(struct guest_info *core,
        uint8_t data = *((uint8_t*)src);
        uint8_t index=vga->vga_attribute_controller.vga_attribute_controller_addr.val;  // should mask probably
 
-       PrintDebug("vga: attribute controller data write index %d with data=0x%x\n", index,data);
+       PrintDebug(core->vm_info, core, "vga: attribute controller data write index %d with data=0x%x\n", index,data);
        
        ERR_WRONG_SIZE("write","vga attribute controller data",len,1,1);
 
        PASSTHROUGH_IO_OUT(vga,port,src,len);
        
-       vga->vga_attribute_controller.vga_attribute_controller_regs[index] = data;
+       if (index>=VGA_ATTRIBUTE_CONTROLLER_NUM) { 
+           PrintError(core->vm_info, core, "vga: attribute controller write to illegal index %d ignored\n",index);
+       } else {
+           vga->vga_attribute_controller.vga_attribute_controller_regs[index] = data;
+       }
        
        vga->vga_attribute_controller.state=ATTR_ADDR;
        
@@ -1434,16 +2413,24 @@ static int attribute_controller_data_read(struct guest_info *core,
     uint8_t data;
 
     index=vga->vga_attribute_controller.vga_attribute_controller_addr.val;  // should mask probably
-    data=vga->vga_attribute_controller.vga_attribute_controller_regs[index];
+
+    if (index>=VGA_ATTRIBUTE_CONTROLLER_NUM) { 
+       data=0;
+       PrintError(core->vm_info, core, "vga: attribute controller read of illegal index %d, returning zero\n",index);
+    } else {
+       data=vga->vga_attribute_controller.vga_attribute_controller_regs[index];
+    }
     
-    PrintDebug("vga: attribute controller data read data (index=%d) = 0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: attribute controller data read data (index=%d) = 0x%x\n", 
               index, data);
 
     ERR_WRONG_SIZE("read","vga attribute controller data",len,1,1);
 
+    *((uint8_t*)dest) = data;
+
     PASSTHROUGH_IO_IN(vga,port,dest,len);
 
-    *((uint8_t*)dest) = data;
+    PASSTHROUGH_READ_CHECK(vga,data,*(uint8_t*)dest);
 
     return len;
 }
@@ -1462,15 +2449,18 @@ static int dac_write_address_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
     
-    PrintDebug("vga: dac write address read data=0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: dac write address read data=0x%x\n", 
               vga->vga_dac.vga_dac_write_addr);
 
     ERR_WRONG_SIZE("read","vga dac write addr",len,1,1);
 
-    PASSTHROUGH_IO_IN(vga,port,dest,len);
 
     *((uint8_t*)dest) = vga->vga_dac.vga_dac_write_addr;
 
+    PASSTHROUGH_IO_IN(vga,port,dest,len);
+    
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_dac.vga_dac_write_addr,*(uint8_t*)dest);
+
     // This read does not reset the state machine
 
     return len;
@@ -1487,7 +2477,7 @@ static int dac_write_address_write(struct guest_info *core,
 
     new_addr=*((uint8_t*)src);
 
-    PrintDebug("vga: dac write address write data=0x%x\n", new_addr);
+    PrintDebug(core->vm_info, core, "vga: dac write address write data=0x%x\n", new_addr);
 
     ERR_WRONG_SIZE("write","vga dac write addr",len,1,1);
 
@@ -1514,15 +2504,17 @@ static int dac_read_address_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
     
-    PrintDebug("vga: dac read address read data=0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: dac read address read data=0x%x\n", 
               vga->vga_dac.vga_dac_read_addr);
 
     ERR_WRONG_SIZE("read","vga dac read addr",len,1,1);
 
-    PASSTHROUGH_IO_IN(vga,port,dest,len);
-
     *((uint8_t*)dest) = vga->vga_dac.vga_dac_read_addr;
 
+    PASSTHROUGH_IO_IN(vga,port,dest,len);
+
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_dac.vga_dac_read_addr,*(uint8_t*)dest);
+    
     // This read does not reset the state machine
 
     return len;
@@ -1539,7 +2531,7 @@ static int dac_read_address_write(struct guest_info *core,
 
     new_addr=*((uint8_t*)src);
 
-    PrintDebug("vga: dac read address write data=0x%x\n", new_addr);
+    PrintDebug(core->vm_info, core, "vga: dac read address write data=0x%x\n", new_addr);
 
     ERR_WRONG_SIZE("write","vga dac read addr",len,1,1);
 
@@ -1570,25 +2562,27 @@ static int dac_data_read(struct guest_info *core,
     uint8_t data;
     
     if (vga->vga_dac.state!=DAC_READ) { 
-       PrintError("vga: dac data read while in other state\n");
+       PrintError(core->vm_info, core, "vga: dac data read while in other state\n");
        // results undefined, so we continue
     }
 
     ERR_WRONG_SIZE("read","vga dac read data",len,1,1);
 
-    PASSTHROUGH_IO_IN(vga,port,dest,len);
-
     curreg = vga->vga_dac.vga_dac_read_addr;
     curchannel = vga->vga_dac.channel;
     data = (vga->vga_dac.vga_dac_palette[curreg] >> curchannel*8) & 0x3f;
 
-    PrintDebug("vga: dac reg %u [%s] = 0x%x\n",
+    PrintDebug(core->vm_info, core, "vga: dac reg %u [%s] = 0x%x\n",
               curreg, 
               curchannel == 0 ? "RED" : curchannel == 1 ? "GREEN" 
                           : curchannel==2 ? "BLUE" : "BAD CHANNEL", 
               data);
 
     *((uint8_t*)dest) = data;
+
+    PASSTHROUGH_IO_IN(vga,port,dest,len);
+
+    PASSTHROUGH_READ_CHECK(vga,data,*(uint8_t*)dest);
     
     curchannel = (curchannel+1)%3;
     vga->vga_dac.channel=curchannel;
@@ -1617,7 +2611,7 @@ static int dac_data_write(struct guest_info *core,
     vga_palette_reg mask32;
     
     if (vga->vga_dac.state!=DAC_WRITE) { 
-       PrintError("vga: dac data write while in other state\n");
+       PrintError(core->vm_info, core, "vga: dac data write while in other state\n");
        // results undefined, so we continue
     }
 
@@ -1629,7 +2623,7 @@ static int dac_data_write(struct guest_info *core,
     curchannel = vga->vga_dac.channel;
     data = *((uint8_t *)src);
 
-    PrintDebug("vga: dac reg %u [%s] write with 0x%x\n",
+    PrintDebug(core->vm_info, core, "vga: dac reg %u [%s] write with 0x%x\n",
               curreg, 
               curchannel == 0 ? "RED" : curchannel == 1 ? "GREEN" 
                           : curchannel==2 ? "BLUE" : "BAD CHANNEL", 
@@ -1665,14 +2659,16 @@ static int dac_pixel_mask_read(struct guest_info *core,
 {
     struct vga_internal *vga = (struct vga_internal *) priv_data;
     
-    PrintDebug("vga: dac pixel mask read data=0x%x\n", 
+    PrintDebug(core->vm_info, core, "vga: dac pixel mask read data=0x%x\n", 
               vga->vga_dac.vga_pixel_mask);
 
     ERR_WRONG_SIZE("read","vga pixel mask",len,1,1);
 
+    *((uint8_t*)dest) = vga->vga_dac.vga_pixel_mask;
+
     PASSTHROUGH_IO_IN(vga,port,dest,len);
 
-    *((uint8_t*)dest) = vga->vga_dac.vga_pixel_mask;
+    PASSTHROUGH_READ_CHECK(vga,vga->vga_dac.vga_pixel_mask,*(uint8_t*)dest);
 
     return len;
 }
@@ -1688,7 +2684,7 @@ static int dac_pixel_mask_write(struct guest_info *core,
 
     new_data=*((uint8_t*)src);
 
-    PrintDebug("vga: dac pixel mask write data=0x%x\n", new_data);
+    PrintDebug(core->vm_info, core, "vga: dac pixel mask write data=0x%x\n", new_data);
 
     ERR_WRONG_SIZE("write","pixel mask",len,1,1);
 
@@ -1701,9 +2697,10 @@ static int dac_pixel_mask_write(struct guest_info *core,
 
 static int init_vga(struct vga_internal *vga)
 {
-    // TODO: startup spec of register contents, if any
-    PrintError("vga: init_vga is UNIMPLEMTED\n");
-    return 0;
+  // TODO: startup spec of register contents, if any
+  vga->vga_misc.vga_input_stat1.val = 0x1;  // display enable, not in retrace
+
+  return 0;
 }
 
 static int free_vga(struct vga_internal *vga) 
@@ -1766,6 +2763,10 @@ static int free_vga(struct vga_internal *vga)
     ret |= v3_dev_unhook_io(dev, VGA_DAC_PIXEL_MASK);
 
 
+    if (vga->host_cons) { 
+       v3_graphics_console_close(vga->host_cons);
+    }
+
     V3_Free(vga);
 
     return 0;
@@ -1783,45 +2784,107 @@ static int vga_init(struct v3_vm_info * vm, v3_cfg_tree_t * cfg) {
 
     char * dev_id = v3_cfg_val(cfg, "ID");
     char * passthrough = v3_cfg_val(cfg, "passthrough");
+    char * hostframebuf = v3_cfg_val(cfg, "hostframebuf");
 
-    // DETERMINE THE FRAMEBUFFER AND SET IT EARLY
-    // FRAMEBUFFER IS SUPPLIED BY THE BACKEND
-
-    PrintDebug("vga: init_device\n");
+    PrintDebug(vm, VCORE_NONE, "vga: init_device\n");
 
     vga = (struct vga_internal *)V3_Malloc(sizeof(struct vga_internal));
 
     if (!vga) { 
-       PrintError("vga: cannot allocate\n");
+       PrintError(vm, VCORE_NONE, "vga: cannot allocate\n");
        return -1;
     }
 
     memset(vga, 0, sizeof(struct vga_internal));
 
+    vga->render_model.model = CONSOLE_DRIVEN_RENDERING | VGA_DRIVEN_PERIODIC_RENDERING;
+    vga->render_model.updates_before_render = DEFAULT_UPDATES_BEFORE_RENDER;
+
     if (passthrough && strcasecmp(passthrough,"enable")==0) {
-       PrintDebug("vga: enabling passthrough\n");
+       PrintDebug(vm, VCORE_NONE, "vga: enabling passthrough\n");
        vga->passthrough=true;
+       vga->skip_next_passthrough_out=false;
+    }
+
+
+    if (hostframebuf && strcasecmp(hostframebuf,"enable")==0) { 
+       struct v3_frame_buffer_spec req;
+
+       PrintDebug(vm, VCORE_NONE, "vga: enabling host frame buffer console (GRAPHICS_CONSOLE)\n");
+
+       memset(&req,0,sizeof(struct v3_frame_buffer_spec));
+       memset(&(vga->target_spec),0,sizeof(struct v3_frame_buffer_spec));
+
+       req.height=VGA_MAXY;
+       req.width=VGA_MAXX;
+       req.bytes_per_pixel=4;
+       req.bits_per_channel=8;
+       req.red_offset=0;
+       req.green_offset=1;
+       req.blue_offset=2;
+       
+
+       vga->host_cons = v3_graphics_console_open(vm,&req,&(vga->target_spec));
+
+       if (!vga->host_cons) { 
+           PrintError(vm, VCORE_NONE, "vga: unable to open host OS's graphics console\n");
+           free_vga(vga);
+           return -1;
+       }
+
+       if (memcmp(&req,&(vga->target_spec),sizeof(req))) {
+           PrintDebug(vm, VCORE_NONE, "vga: warning: target spec differs from requested spec\n");
+           PrintDebug(vm, VCORE_NONE, "vga: request: %u by %u by %u with %u bpc and r,g,b at %u, %u, %u\n", req.width, req.height, req.bytes_per_pixel, req.bits_per_channel, req.red_offset, req.green_offset, req.blue_offset);
+           PrintDebug(vm, VCORE_NONE, "vga: response: %u by %u by %u with %u bpc and r,g,b at %u, %u, %u\n", vga->target_spec.width, vga->target_spec.height, vga->target_spec.bytes_per_pixel, vga->target_spec.bits_per_channel, vga->target_spec.red_offset, vga->target_spec.green_offset, vga->target_spec.blue_offset);
+
+       }
+
+       if (vga->render_model.model & CONSOLE_DRIVEN_RENDERING) { 
+         V3_Print(vm, VCORE_NONE, "vga: enabling console-driven rendering\n");
+         if (v3_graphics_console_register_render_request(vga->host_cons, render_callback, vga)!=0) { 
+           PrintError(vm, VCORE_NONE, "vga: cannot enable console-driven rendering\n");
+           free_vga(vga);
+           return -1;
+         }
+       }
+       
+       V3_Print(vm, VCORE_NONE, "vga: enabling console inquiry for updates\n");
+       if (v3_graphics_console_register_update_inquire(vga->host_cons, update_callback, vga)!=0) { 
+         PrintError(vm, VCORE_NONE, "vga: cannot enable console inquiry for updates\n");
+         free_vga(vga);
+         return -1;
+       }
+   }
+
+    if (!vga->passthrough && !vga->host_cons) { 
+       V3_Print(vm, VCORE_NONE, "vga: neither passthrough nor host console are enabled - no way to display anything!\n");
     }
 
+
     // No memory store is allocated since we will use a full memory hook
     // The VGA maps can be read as well as written
     // Reads also affect writes, since they are how you fill the latches
 
     // Now allocate the maps
     for (i=0;i<MAP_NUM;i++) { 
-       vga->map[i] = (vga_map) V3_VAddr((void*)V3_AllocPages(MAP_SIZE/4096));
-       if (!(vga->map[i])) {
-           PrintError("vga: cannot allocate maps\n");
+       void *temp;
+
+       temp = (void*)V3_AllocPages(MAP_SIZE/4096);
+       if (!temp) { 
+           PrintError(vm, VCORE_NONE, "vga: cannot allocate maps\n");
            free_vga(vga);
            return -1;
        }
+
+       vga->map[i] = (vga_map) V3_VAddr(temp);
+
        memset(vga->map[i],0,MAP_SIZE);
     }
     
     struct vm_device * dev = v3_add_device(vm, dev_id, &dev_ops, vga);
     
     if (dev == NULL) {
-       PrintError("Could not attach device %s\n", dev_id);
+       PrintError(vm, VCORE_NONE, "Could not attach device %s\n", dev_id);
        free_vga(vga);
        return -1;
     }
@@ -1833,7 +2896,7 @@ static int vga_init(struct v3_vm_info * vm, v3_cfg_tree_t * cfg) {
                         &vga_read, 
                         &vga_write,
                         dev) == -1) {
-       PrintError("vga: memory book failed\n");
+       PrintError(vm, VCORE_NONE, "vga: memory book failed\n");
        v3_remove_device(dev);
        return -1;
     }
@@ -1877,14 +2940,14 @@ static int vga_init(struct v3_vm_info * vm, v3_cfg_tree_t * cfg) {
     ret |= v3_dev_hook_io(dev, VGA_DAC_PIXEL_MASK, &dac_pixel_mask_read, &dac_pixel_mask_write);
 
     if (ret != 0) {
-       PrintError("vga: Error allocating VGA I/O ports\n");
+       PrintError(vm, VCORE_NONE, "vga: Error allocating VGA I/O ports\n");
        v3_remove_device(dev);
        return -1;
     }
 
     init_vga(vga);
 
-    PrintDebug("vga: successfully added and initialized, waiting for framebuffer attach\n");
+    PrintDebug(vm, VCORE_NONE, "vga: successfully added and initialized.\n");
 
     return 0;