diff --git a/nemu/src/device/vga.c b/nemu/src/device/vga.c
index 7b9c26d..44313aa 100644
--- a/nemu/src/device/vga.c
+++ b/nemu/src/device/vga.c
@@ -33,7 +33,6 @@ static uint32_t screen_size() {
 
 static void *vmem = NULL;
 static uint32_t *vgactl_port_base = NULL;
-static uint32_t *sync_reg = NULL;
 
 #ifdef CONFIG_VGA_SHOW_SCREEN
 #ifndef CONFIG_TARGET_AM
@@ -75,10 +74,10 @@ static inline void update_screen() {
 void vga_update_screen() {
   // TODO: call `update_screen()` when the sync register is non-zero,
   // then zero out the sync register
-  if (*sync_reg != 0) {
-    printf("Update Screen\n");
+  if (vgactl_port_base[1] != 0) {
+    // printf("Update Screen\n");
     update_screen();
-    *sync_reg = 0;
+    vgactl_port_base[1] = 0;
   }
 }
 
@@ -91,9 +90,6 @@ void init_vga() {
   add_mmio_map("vgactl", CONFIG_VGA_CTL_MMIO, vgactl_port_base, 8, NULL);
 #endif
 
-  sync_reg = (uint32_t*)new_space(8);
-  add_mmio_map("sync", CONFIG_VGA_CTL_MMIO + 8, sync_reg, 8, NULL);
-
   vmem = new_space(screen_size());
   add_mmio_map("vmem", CONFIG_FB_ADDR, vmem, screen_size(), NULL);
   IFDEF(CONFIG_VGA_SHOW_SCREEN, init_screen());