diff --git a/include/gb.h b/include/gb.h
index ced4190..63c03ab 100644
--- a/include/gb.h
+++ b/include/gb.h
@@ -102,13 +102,33 @@ typedef struct oam_scan_table {
 	ut8 addr;
 } OAMScanTable;
 
+typedef struct pixel_fifo_t {
+	ut64 data;
+	ut32 fetch;
+	ut32 obj_fetch;
+	ut8 shift_out;	//lower nibble is sourch info, pallet, color
+			// 0b....spcc
+#if 0
+bg	-	00
+win	-	01
+obj p0	-	10
+obj p1	-	11
+#endif
+	ut8 n_fpixel;	//number of pixel that are currently in the upper half of the fifo - 1
+	ut8 x;
+	ut8 y;
+} PixelFifo;
+
 typedef struct gb_dmg_ppu_t {
 	GBPixBuf *pixbuf;
 	ut64 seek;
 	ut8 buf[GB_PPU_N_REGS];
 	OAMScanTable ost;
+	PixelFifo fifo;
 	int reg_fd;
 	int vram_fd;
+	ut32 vram_mapid;
+	ut32 oam_mapid;
 } GBPPU;
 
 typedef struct gameboy_t {
diff --git a/io/ppu.c b/io/ppu.c
index 353665f..63a4e89 100644
--- a/io/ppu.c
+++ b/io/ppu.c
@@ -145,7 +145,7 @@ static ut32 gb_ppu_oam_scan_update (GB *gb, ut32 cycles) {
 		if (gb->ppu->ost.n_entries < 10) {
 			ut8 yx[2];
 			r_io_fd_read_at (gb->io, gb->dma->oam_fd, (ut64)gb->ppu->ost.addr, yx, 2);
-			if ((yx[0] <= ly) && (ly < (yx[0] + height))) {
+			if ((yx[0] <= ly) && (ly < (yx[0] + height)) && yx[1]) {
 				gb->ppu->ost.data[gb->ppu->ost.n_entries] =
 					(gb->ppu->ost.addr << 8) | yx[1];
 				gb->ppu->ost.n_entries++;
@@ -158,10 +158,38 @@ beach:
 	if (gb->ppu->ost.addr == 0xa0) {
 		//indicate next mode
 		gb->ppu->buf[GB_PPU_STAT] |= GB_PPU_STAT_MODE_RENDER;
+		RIOMap *vram = r_io_map_get (gb->io, gb->ppu->vram_mapid);
+		vram->perm = 0;	//disable vram access for rendering
 	}
 	return cycles;
 }
 
+static void gb_ppu_pixel_fifo_merge_opixels (PixelFifo *pxf, bool priority) {
+	ut32 pixels = pxf->data >> 32;
+	ut32 newpixels = 0;
+	ut32 i;
+	for (i = 0; i < 8; i++) {
+		if (!(pixels & (0x3 << 28))) {
+			newpixels = (newpixels << 4) |
+				((pxf->obj_fetch & (0xf << ((i - 1) << 2))) >> ((i - 1) << 2));
+			pixels = pixels << 4;
+			continue;
+		}
+	}
+}
+
+static ut32 gb_ppu_render_update (GB *gb, ut32 cycles) {
+	return 0;
+}
+
+static ut32 gb_ppu_hblank_update (GB *gb, ut32 cycles) {
+	return 0;
+}
+
+static ut32 gb_ppu_vblank_update (GB *gb, ut32 cycles) {
+	return 0;
+}
+
 void gb_ppu_update (GB *gb, ut32 cycles) {
 	while (cycles) {
 		switch (gb->ppu->buf[GB_PPU_STAT] & GB_PPU_STAT_MODE_MASK) {
@@ -169,10 +197,13 @@ void gb_ppu_update (GB *gb, ut32 cycles) {
 			cycles = gb_ppu_oam_scan_update (gb, cycles);
 			break;
 		case GB_PPU_STAT_MODE_RENDER:
+			cycles = gb_ppu_render_update (gb, cycles);
 			break;
 		case GB_PPU_STAT_MODE_HBLANK:
+			cycles = gb_ppu_hblank_update (gb, cycles);
 			break;
 		case GB_PPU_STAT_MODE_VBLANK:
+			cycles = gb_ppu_vblank_update (gb, cycles);
 			break;
 		}
 	}