diff --git a/bochs/iodev/display/svga_cirrus.cc b/bochs/iodev/display/svga_cirrus.cc
index aada78ed1..aac754f40 100644
--- a/bochs/iodev/display/svga_cirrus.cc
+++ b/bochs/iodev/display/svga_cirrus.cc
@@ -257,7 +257,7 @@ void bx_svga_cirrus_c::init_vga_extension(void)
   BX_CIRRUS_THIS put("CIRRUS");
   // initialize SVGA stuffs.
   BX_CIRRUS_THIS bx_vgacore_c::init_iohandlers(svga_read_handler, svga_write_handler);
-  BX_CIRRUS_THIS bx_vgacore_c::init_systemtimer(svga_timer_handler, svga_param_handler);
+  BX_CIRRUS_THIS bx_vgacore_c::init_systemtimer();
   BX_CIRRUS_THIS pci_enabled = SIM->is_pci_device("cirrus");
   BX_CIRRUS_THIS svga_init_members();
 #if BX_SUPPORT_PCI
@@ -440,7 +440,7 @@ void bx_svga_cirrus_c::after_restore_state(void)
                                     BX_CIRRUS_THIS s.pel.data[i].blue<<2);
     }
     BX_CIRRUS_THIS svga_needs_update_mode = 1;
-    BX_CIRRUS_THIS svga_update();
+    BX_CIRRUS_THIS update();
   }
 }
 
@@ -807,22 +807,6 @@ void bx_svga_cirrus_c::get_text_snapshot(Bit8u **text_snapshot,
   BX_CIRRUS_THIS bx_vgacore_c::get_text_snapshot(text_snapshot,txHeight,txWidth);
 }
 
-Bit64s bx_svga_cirrus_c::svga_param_handler(bx_param_c *param, int set, Bit64s val)
-{
-  if (set) {
-    Bit32u update_interval = (Bit32u)(1000000 / val);
-    BX_INFO(("Changing timer interval to %d", update_interval));
-    BX_CIRRUS_THIS svga_timer_handler(theSvga);
-    bx_virt_timer.activate_timer(BX_CIRRUS_THIS timer_id, update_interval, 1);
-    if (update_interval < 300000) {
-      BX_CIRRUS_THIS s.blink_counter = 300000 / (unsigned)update_interval;
-    } else {
-      BX_CIRRUS_THIS s.blink_counter = 1;
-    }
-  }
-  return val;
-}
-
 Bit32u bx_svga_cirrus_c::svga_read_handler(void *this_ptr, Bit32u address, unsigned io_len)
 {
 #if !BX_USE_CIRRUS_SMF
@@ -1001,37 +985,6 @@ void bx_svga_cirrus_c::svga_write(Bit32u address, Bit32u value, unsigned io_len)
   VGA_WRITE(address,value,io_len);
 }
 
-void bx_svga_cirrus_c::refresh_display(void *this_ptr, bx_bool redraw)
-{
-#if BX_SUPPORT_PCI
-  if (BX_CIRRUS_THIS s.vga_override && (BX_CIRRUS_THIS s.nvgadev != NULL)) {
-    BX_CIRRUS_THIS s.nvgadev->refresh_display(BX_CIRRUS_THIS s.nvgadev, redraw);
-    return;
-  }
-#endif
-  if (redraw) {
-    redraw_area(0, 0, BX_CIRRUS_THIS s.last_xres, BX_CIRRUS_THIS s.last_yres);
-  }
-  svga_timer_handler(this_ptr);
-}
-
-void bx_svga_cirrus_c::svga_timer_handler(void *this_ptr)
-{
-#if !BX_USE_CIRRUS_SMF
-  bx_svga_cirrus_c *class_ptr = (bx_svga_cirrus_c *) this_ptr;
-  class_ptr->svga_timer();
-}
-
-void bx_svga_cirrus_c::svga_timer(void)
-{
-#else // !BX_USE_CIRRUS_SMF
-  UNUSED(this_ptr);
-#endif // !BX_USE_CIRRUS_SMF
-
-  BX_CIRRUS_THIS svga_update();
-  bx_gui->flush();
-}
-
 void bx_svga_cirrus_c::svga_modeupdate(void)
 {
   Bit32u iTopOffset, iWidth, iHeight;
@@ -1214,16 +1167,10 @@ void bx_svga_cirrus_c::draw_hardware_cursor(unsigned xc, unsigned yc, bx_svga_ti
   }
 }
 
-void bx_svga_cirrus_c::svga_update(void)
+void bx_svga_cirrus_c::update(void)
 {
   unsigned width, height, pitch;
 
-#if BX_SUPPORT_PCI
-  if (BX_CIRRUS_THIS s.vga_override && (BX_CIRRUS_THIS s.nvgadev != NULL)) {
-    BX_CIRRUS_THIS s.nvgadev->update();
-    return;
-  }
-#endif
   /* skip screen update when the sequencer is in reset mode or video is disabled */
   if (! BX_CIRRUS_THIS s.sequencer.reset1 ||
       ! BX_CIRRUS_THIS s.sequencer.reset2 ||
diff --git a/bochs/iodev/display/svga_cirrus.h b/bochs/iodev/display/svga_cirrus.h
index 5fc7a0fbe..0e817dac9 100644
--- a/bochs/iodev/display/svga_cirrus.h
+++ b/bochs/iodev/display/svga_cirrus.h
@@ -70,7 +70,6 @@ public:
 
   virtual void init_vga_extension(void);
   virtual void reset(unsigned type);
-  virtual void refresh_display(void *this_ptr, bx_bool redraw);
   virtual void redraw_area(unsigned x0, unsigned y0,
                            unsigned width, unsigned height);
   virtual Bit8u mem_read(bx_phy_address addr);
@@ -87,6 +86,9 @@ public:
   virtual void debug_dump(int argc, char **argv);
 #endif
 
+protected:
+  virtual void update(void);
+
 private:
   static Bit32u svga_read_handler(void *this_ptr, Bit32u address, unsigned io_len);
   static void   svga_write_handler(void *this_ptr, Bit32u address, Bit32u value, unsigned io_len);
@@ -97,11 +99,7 @@ private:
   BX_CIRRUS_SMF void mem_write_mode4and5_8bpp(Bit8u mode, Bit32u offset, Bit8u value);
   BX_CIRRUS_SMF void mem_write_mode4and5_16bpp(Bit8u mode, Bit32u offset, Bit8u value);
 
-  static void   svga_timer_handler(void *);
-  static Bit64s svga_param_handler(bx_param_c *param, int set, Bit64s val);
-  BX_CIRRUS_SMF void   svga_timer(void);
   BX_CIRRUS_SMF void   svga_modeupdate(void);
-  BX_CIRRUS_SMF void   svga_update(void);
 
   BX_CIRRUS_SMF void   svga_init_members();
 
diff --git a/bochs/iodev/display/vga.cc b/bochs/iodev/display/vga.cc
index 370117e48..6c95309ab 100644
--- a/bochs/iodev/display/vga.cc
+++ b/bochs/iodev/display/vga.cc
@@ -92,7 +92,7 @@ void bx_vga_c::init_vga_extension(void)
   Bit16u max_xres, max_yres, max_bpp;
 
   BX_VGA_THIS init_iohandlers(read_handler, write_handler);
-  BX_VGA_THIS init_systemtimer(timer_handler, vga_param_handler);
+  BX_VGA_THIS init_systemtimer();
   BX_VGA_THIS pci_enabled = SIM->is_pci_device("pcivga");
 
   // The following is for the VBE display extension
@@ -100,7 +100,7 @@ void bx_vga_c::init_vga_extension(void)
   BX_VGA_THIS vbe.enabled = 0;
   BX_VGA_THIS vbe.dac_8bit = 0;
   BX_VGA_THIS vbe.base_address = 0x0000;
-  if (!strcmp(SIM->get_param_string(BXPN_VGA_EXTENSION)->getptr(), "vbe")) {
+  if (!strcmp(BX_VGA_THIS vgaext->getptr(), "vbe")) {
     BX_VGA_THIS put("BXVGA");
     for (addr=VBE_DISPI_IOPORT_INDEX; addr<=VBE_DISPI_IOPORT_DATA; addr++) {
       DEV_register_ioread_handler(this, vbe_read_handler, addr, "vga video", 7);
@@ -326,64 +326,10 @@ void bx_vga_c::write(Bit32u address, Bit32u value, unsigned io_len, bx_bool no_l
   }
 }
 
-Bit64s bx_vga_c::vga_param_handler(bx_param_c *param, int set, Bit64s val)
-{
-  // handler for runtime parameter 'vga: update_freq'
-  if (set) {
-    Bit32u update_interval = (Bit32u)(1000000 / val);
-    BX_INFO(("Changing timer interval to %d", update_interval));
-    BX_VGA_THIS timer_handler(theVga);
-    bx_virt_timer.activate_timer(BX_VGA_THIS timer_id, update_interval, 1);
-    if (update_interval < 300000) {
-      BX_VGA_THIS s.blink_counter = 300000 / (unsigned)update_interval;
-    } else {
-      BX_VGA_THIS s.blink_counter = 1;
-    }
-  }
-  return val;
-}
-
-void bx_vga_c::refresh_display(void *this_ptr, bx_bool redraw)
-{
-#if BX_SUPPORT_PCI
-  if (BX_VGA_THIS s.vga_override && (BX_VGA_THIS s.nvgadev != NULL)) {
-    BX_VGA_THIS s.nvgadev->refresh_display(BX_VGA_THIS s.nvgadev, redraw);
-    return;
-  }
-#endif
-  if (redraw) {
-    redraw_area(0, 0, BX_VGA_THIS s.last_xres, BX_VGA_THIS s.last_yres);
-  }
-  timer_handler(this_ptr);
-}
-
-void bx_vga_c::timer_handler(void *this_ptr)
-{
-#if BX_USE_VGA_SMF == 0
-  bx_vga_c *class_ptr = (bx_vga_c *) this_ptr;
-  class_ptr->timer();
-}
-
-void bx_vga_c::timer(void)
-{
-#else
-  UNUSED(this_ptr);
-#endif
-
-  update();
-  bx_gui->flush();
-}
-
 void bx_vga_c::update(void)
 {
   unsigned iHeight, iWidth;
 
-#if BX_SUPPORT_PCI
-  if (BX_VGA_THIS s.vga_override && (BX_VGA_THIS s.nvgadev != NULL)) {
-    BX_VGA_THIS s.nvgadev->update();
-    return;
-  }
-#endif
   if (BX_VGA_THIS vbe.enabled) {
     /* no screen update necessary */
     if ((BX_VGA_THIS s.vga_mem_updated==0) && BX_VGA_THIS s.graphics_ctrl.graphics_alpha)
diff --git a/bochs/iodev/display/vga.h b/bochs/iodev/display/vga.h
index 058e2678d..8d8573641 100644
--- a/bochs/iodev/display/vga.h
+++ b/bochs/iodev/display/vga.h
@@ -105,12 +105,6 @@ public:
                              unsigned width, unsigned height);
 
   virtual void   init_vga_extension(void);
-  virtual void   refresh_display(void *this_ptr, bx_bool redraw);
-
-  static void     timer_handler(void *);
-#if BX_USE_VGA_SMF == 0
-  BX_VGA_SMF void timer(void);
-#endif
 
 #if BX_SUPPORT_PCI
   virtual void pci_write_handler(Bit8u address, Bit32u value, unsigned io_len);
@@ -119,8 +113,6 @@ public:
   virtual void debug_dump(int argc, char **argv);
 #endif
 
-  static Bit64s   vga_param_handler(bx_param_c *param, int set, Bit64s val);
-
 protected:
   static void   write_handler(void *this_ptr, Bit32u address, Bit32u value, unsigned io_len);
 #if BX_USE_VGA_SMF
@@ -128,7 +120,7 @@ protected:
 #endif
   void  write(Bit32u address, Bit32u value, unsigned io_len, bx_bool no_log);
 
-  BX_VGA_SMF void update(void);
+  virtual void update(void);
 
   // Bochs VBE section
 #if BX_SUPPORT_PCI
diff --git a/bochs/iodev/display/vgacore.cc b/bochs/iodev/display/vgacore.cc
index 78f480521..c37179136 100644
--- a/bochs/iodev/display/vgacore.cc
+++ b/bochs/iodev/display/vgacore.cc
@@ -100,6 +100,7 @@ void bx_vgacore_c::init(void)
 {
   unsigned x,y;
 
+  BX_VGA_THIS vgaext = SIM->get_param_string(BXPN_VGA_EXTENSION);
   BX_VGA_THIS extension_init = 0;
   BX_VGA_THIS pci_enabled = 0;
 
@@ -116,10 +117,8 @@ void bx_vgacore_c::init(void)
     for (x = 0; x < BX_VGA_THIS s.num_x_tiles; x++)
       SET_TILE_UPDATED(x, y, 0);
 
-  char *strptr = SIM->get_param_string(BXPN_VGA_EXTENSION)->getptr();
-  if (!BX_VGA_THIS extension_init &&
-      (strlen(strptr) > 0) && strcmp(strptr, "none")) {
-    BX_PANIC(("unknown display extension: %s", strptr));
+  if (!BX_VGA_THIS extension_init && !BX_VGA_THIS vgaext->isempty()) {
+    BX_PANIC(("unknown display extension: %s", BX_VGA_THIS vgaext->getptr()));
   }
   if (!BX_VGA_THIS pci_enabled) {
     BX_MEM(0)->load_ROM(SIM->get_param_string(BXPN_VGA_ROM_PATH)->getptr(), 0xc0000, 1);
@@ -128,8 +127,6 @@ void bx_vgacore_c::init(void)
 
 void bx_vgacore_c::init_standard_vga(void)
 {
-  char *extname;
-
   // initialize VGA controllers and other internal stuff
   BX_VGA_THIS s.vga_enabled = 1;
   BX_VGA_THIS s.misc_output.color_emulation  = 1;
@@ -165,8 +162,7 @@ void bx_vgacore_c::init_standard_vga(void)
   BX_VGA_THIS s.vga_override = 0;
 
   // initialize memory, handlers and timer (depending on extension)
-  extname = SIM->get_param_string(BXPN_VGA_EXTENSION)->getptr();
-  if ((strlen(extname) == 0) || (!strcmp(extname, "none"))) {
+  if (BX_VGA_THIS vgaext->isempty()) {
     BX_VGA_THIS s.memsize = 0x40000;
     if (BX_VGA_THIS s.memory == NULL)
       BX_VGA_THIS s.memory = new Bit8u[BX_VGA_THIS s.memsize];
@@ -257,16 +253,17 @@ void bx_vgacore_c::init_iohandlers(bx_read_handler_t f_read, bx_write_handler_t
   }
 }
 
-void bx_vgacore_c::init_systemtimer(bx_timer_handler_t f_timer, param_event_handler f_param)
+void bx_vgacore_c::init_systemtimer(void)
 {
   BX_VGA_THIS realtime = SIM->get_param_bool(BXPN_VGA_REALTIME)->get();
   bx_param_num_c *vga_update_freq = SIM->get_param_num(BXPN_VGA_UPDATE_FREQUENCY);
   Bit32u update_interval = (Bit32u)(1000000 / vga_update_freq->get());
   BX_INFO(("interval=%u, mode=%s", update_interval, BX_VGA_THIS realtime ? "realtime":"standard"));
   if (BX_VGA_THIS timer_id == BX_NULL_TIMER_HANDLE) {
-    BX_VGA_THIS timer_id = bx_virt_timer.register_timer(this, f_timer,
+    BX_VGA_THIS timer_id = bx_virt_timer.register_timer(this, vga_timer_handler,
        update_interval, 1, 1, BX_VGA_THIS realtime, "vga");
-    vga_update_freq->set_handler(f_param);
+    vga_update_freq->set_handler(vga_param_handler);
+    vga_update_freq->set_device_param(this);
   }
   // VGA text mode cursor blink frequency 1.875 Hz
   if (update_interval < 266666) {
@@ -2377,3 +2374,52 @@ void bx_vgacore_c::redraw_area(unsigned x0, unsigned y0, unsigned width, unsigne
            sizeof(BX_VGA_THIS s.text_snapshot));
   }
 }
+
+void bx_vgacore_c::refresh_display(void *this_ptr, bx_bool redraw)
+{
+  bx_vgacore_c *vgadev = (bx_vgacore_c *) this_ptr;
+#if BX_SUPPORT_PCI
+  if (vgadev->s.vga_override && (vgadev->s.nvgadev != NULL)) {
+    vgadev->s.nvgadev->refresh_display(vgadev->s.nvgadev, redraw);
+    return;
+  }
+#endif
+  if (redraw) {
+    redraw_area(0, 0, vgadev->s.last_xres, vgadev->s.last_yres);
+  }
+  vga_timer_handler(vgadev);
+}
+
+void bx_vgacore_c::vga_timer_handler(void *this_ptr)
+{
+  bx_vgacore_c *vgadev = (bx_vgacore_c *) this_ptr;
+#if BX_SUPPORT_PCI
+  if (vgadev->s.vga_override && (vgadev->s.nvgadev != NULL)) {
+    vgadev->s.nvgadev->update();
+    return;
+  }
+#endif
+  vgadev->update();
+  bx_gui->flush();
+}
+
+#undef LOG_THIS
+#define LOG_THIS vgadev->
+
+Bit64s bx_vgacore_c::vga_param_handler(bx_param_c *param, int set, Bit64s val)
+{
+  // handler for runtime parameter 'vga: update_freq'
+  if (set) {
+    Bit32u update_interval = (Bit32u)(1000000 / val);
+    bx_vgacore_c *vgadev = (bx_vgacore_c *)param->get_device_param();
+    BX_INFO(("Changing timer interval to %d", update_interval));
+    vga_timer_handler(vgadev);
+    bx_virt_timer.activate_timer(vgadev->timer_id, update_interval, 1);
+    if (update_interval < 266666) {
+      vgadev->s.blink_counter = 266666 / (unsigned)update_interval;
+    } else {
+      vgadev->s.blink_counter = 1;
+    }
+  }
+  return val;
+}
diff --git a/bochs/iodev/display/vgacore.h b/bochs/iodev/display/vgacore.h
index 59bf83f3f..f05b35a69 100644
--- a/bochs/iodev/display/vgacore.h
+++ b/bochs/iodev/display/vgacore.h
@@ -65,7 +65,6 @@ public:
   static bx_bool mem_write_handler(bx_phy_address addr, unsigned len, void *data, void *param);
   virtual Bit8u  mem_read(bx_phy_address addr);
   virtual void   mem_write(bx_phy_address addr, Bit8u value);
-  virtual void   refresh_display(void *this_ptr, bx_bool redraw) {}
   virtual void   set_override(bx_bool enabled, void *dev);
   virtual void   register_state(bx_list_c *parent);
   virtual void   after_restore_state(void);
@@ -75,16 +74,19 @@ public:
 
   virtual void   redraw_area(unsigned x0, unsigned y0,
                              unsigned width, unsigned height);
-
+  virtual void   refresh_display(void *this_ptr, bx_bool redraw);
   virtual void   get_text_snapshot(Bit8u **text_snapshot, unsigned *txHeight,
                                    unsigned *txWidth);
   virtual void   init_vga_extension(void) {}
 
+  static void    vga_timer_handler(void *);
+  static Bit64s  vga_param_handler(bx_param_c *param, int set, Bit64s val);
+
 protected:
   void init_standard_vga(void);
   void init_gui(void);
   void init_iohandlers(bx_read_handler_t f_read, bx_write_handler_t f_write);
-  void init_systemtimer(bx_timer_handler_t f_timer, param_event_handler f_param);
+  void init_systemtimer();
 
   static Bit32u read_handler(void *this_ptr, Bit32u address, unsigned io_len);
   static void   write_handler(void *this_ptr, Bit32u address, Bit32u value, unsigned io_len);
@@ -93,7 +95,7 @@ protected:
   void   write(Bit32u address, Bit32u value, unsigned io_len, bx_bool no_log);
 
   Bit8u get_vga_pixel(Bit16u x, Bit16u y, Bit16u saddr, Bit16u lc, bx_bool bs, Bit8u **plane);
-  void update(void);
+  virtual void update(void);
   void determine_screen_dimensions(unsigned *piHeight, unsigned *piWidth);
   void calculate_retrace_timing(void);
   bx_bool skip_update(void);
@@ -238,6 +240,7 @@ protected:
 
   int timer_id;
   bx_bool realtime;
+  bx_param_string_c *vgaext;
   bx_bool extension_init;
   bx_bool pci_enabled;
 };
diff --git a/bochs/iodev/display/voodoo.cc b/bochs/iodev/display/voodoo.cc
index c28226d66..f34ec4727 100644
--- a/bochs/iodev/display/voodoo.cc
+++ b/bochs/iodev/display/voodoo.cc
@@ -633,6 +633,7 @@ void bx_voodoo_c::refresh_display(void *this_ptr, bx_bool redraw)
     redraw_area(0, 0, v->fbi.width, v->fbi.height);
   }
   vertical_timer_handler(this_ptr);
+  update();
 }
 
 void bx_voodoo_c::vertical_timer_handler(void *this_ptr)