diff --git a/presets/atari7800/dlist.c b/presets/atari7800/dlist.c
index 86d23f14..42640551 100644
--- a/presets/atari7800/dlist.c
+++ b/presets/atari7800/dlist.c
@@ -3,57 +3,131 @@
 
 #include <string.h>
 
-byte DL[16][64];
-
-DLLEntry DLL[16];
-
 //#link "chr_font.s"
 
-char* hello = "\2\4\6\0\220\222\102";
+//#link "generic8x16.s"
 
-void setup_dll() {
+#define SLOTHEIGHT 16
+#define DOUBLEBUFFER
+
+#ifdef DOUBLEBUFFER
+#define NUMSLOTS 32
+#define SLOTSIZE 32
+byte slot0 = 0;
+#else
+#define NUMSLOTS 16
+#define SLOTSIZE 64
+const byte slot0 = 0;
+#endif
+
+
+byte DL[NUMSLOTS][SLOTSIZE];
+byte DL_len[NUMSLOTS];
+DLLEntry DLL[NUMSLOTS];
+
+void dll_clear() {
+  byte i;
+  for (i=slot0; i<slot0+16; i++) {
+    DL[i][1] = 0;
+    DL_len[i] = 0;
+  }
+}
+
+#ifdef DOUBLEBUFFER
+void dll_swap() {
+  slot0 ^= 16;
+  if (!slot0) {
+    MARIA.DPPH = (word)(DLL+16)>>8;
+    MARIA.DPPL = (byte)(DLL+16);
+  } else {
+    MARIA.DPPH = (word)DLL>>8;
+    MARIA.DPPL = (byte)DLL;
+  }
+}
+#endif
+
+void* dll_alloc(byte slot, byte len) {
+  byte dlofs;
+  slot &= NUMSLOTS-1;
+  dlofs = DL_len[slot];
+  DL_len[slot] += len;
+  DL[slot][dlofs+len+1] = 0;
+  return &DL[slot][dlofs];
+}
+
+void dll_add_sprite(word addr, byte x, byte y, byte wpal) {
+  byte slot = (y >> 4) | slot0;
+  register DL4Entry* dl = (DL4Entry*) dll_alloc(slot, 4);
+  dl->data_lo = (byte)addr;
+  dl->data_hi = (byte)(addr>>8) + (y & 15);
+  dl->xpos = x;
+  dl->width_pal = wpal;
+  if (y & 15) {
+    DL4Entry* dl2 = (DL4Entry*) dll_alloc(slot+1, 4);
+    *dl2 = *dl;
+    dl2->data_hi -= SLOTHEIGHT;
+  }
+}
+
+void dll_add_string(const char* str, byte x, byte y, byte wpal) {
+  byte slot = (y >> 4) | slot0;
+  register DL5Entry* dl = (DL5Entry*) dll_alloc(slot, 5);
+  dl->data_lo = (byte)str;
+  dl->data_hi = (word)str>>8;
+  dl->flags = DL5_INDIRECT;
+  dl->width_pal = wpal;
+  dl->xpos = x;
+}
+
+void dll_setup() {
   byte i;
-  // set up DLL
   byte* dlptr = &DL[0][0];
-  DLLEntry *dll = &DLL[0];
-  for (i=0; i<16; i++) {
-    dll->offset_flags = DLL_H16 | (16-1);
+  register DLLEntry *dll = &DLL[0];
+  for (i=0; i<NUMSLOTS; i++) {
+    dll->offset_flags = DLL_H16 | (SLOTHEIGHT-1);
     dll->dl_hi = (word)dlptr>>8;
     dll->dl_lo = (byte)dlptr;
     dlptr += sizeof(DL[0]);
     dll++;
   }
-  memset(DL, 0, sizeof(DL));
+  dll_clear();
+#ifdef DOUBLEBUFFER
+  dll_swap();
+  dll_clear();
+#endif
 }
 
+char* hello = "\2\4\6\0\220\222\102";
+
 void main() {
+  byte i;
+  byte y = 0;
 
-  setup_dll();
+  dll_setup();
   
-  // set up display list
-  {
-    DL5Entry dl5;
-    dl5.data_hi = (word)hello>>8;
-    dl5.data_lo = (word)hello;
-    dl5.flags = DL5_INDIRECT;
-    dl5.width_pal = 32-8;
-    dl5.xpos = 32;
-    memcpy(DL[2], &dl5, sizeof(dl5));
-  }
-
   // activate DMA
   MARIA.CHARBASE = 0x80;
   MARIA.DPPH = (word)DLL>>8;
   MARIA.DPPL = (byte)DLL;
   MARIA.CTRL = CTRL_DMA_ON | CTRL_DBLBYTE | CTRL_160AB;
-  MARIA.P0C1 = 0x2f;
-  MARIA.P0C2 = 0x1f;
-  MARIA.P0C3 = 0xf;
+  MARIA.P0C1 = 0x8f;
+  MARIA.P0C2 = 0x4f;
+  MARIA.P0C3 = 0x1f;
+  MARIA.P1C1 = 0x34;
+  MARIA.P1C2 = 0x28;
+  MARIA.P1C3 = 0x1f;
+  MARIA.BACKGRND = 0;
 
   while (1) {
     while ((MARIA.MSTAT & MSTAT_VBLANK) == 0) ;
+    dll_swap();
+    dll_clear();
+    dll_add_string(hello, y+32, 32, DL_WP(8,0));
+    for (i=0; i<8; i++) {
+      dll_add_sprite(0xa068, i*4, i*16+y, DL_WP(4,1));
+      dll_add_sprite(0xa06c, i*8+y, i*16, DL_WP(4,1));
+    }
     while ((MARIA.MSTAT & MSTAT_VBLANK) != 0) ;
-    MARIA.BACKGRND = 0;
-    DL[2][4]++;
+    y++;
   }
 }
diff --git a/src/baseplatform.ts b/src/baseplatform.ts
index 333dd13f..2d44b264 100644
--- a/src/baseplatform.ts
+++ b/src/baseplatform.ts
@@ -273,13 +273,13 @@ export abstract class BaseDebugPlatform extends BasePlatform {
       this.debugTargetClock -= this.debugClock;
       this.debugClock = 0;
     }
-    this.frameCount++;
   }
   postFrame() {
     // reload debug state at end of frame after breakpoint
     if (this.debugCallback && this.debugBreakState) {
       this.loadState(this.debugBreakState);
     }
+    this.frameCount++;
   }
   pollControls() {
   }
@@ -361,6 +361,7 @@ export abstract class BaseDebugPlatform extends BasePlatform {
     });
   }
   runToVsync() {
+    this.restartDebugging();
     var frame0 = this.frameCount;
     this.runEval( () : boolean => {
       return this.frameCount > frame0;