diff --git a/common.mk b/common.mk
index 1e5f937..afe9b63 100644
--- a/common.mk
+++ b/common.mk
@@ -1,10 +1,10 @@
 LIB ?= .
+OPT ?= -Og
 
 AARCH = --isa=sh2 --big
 AFLAGS = -g -gdwarf-4
-CFLAGS = -I$(LIB)
 CFLAGS += -ffunction-sections -fshort-enums -ffreestanding -nostdlib
-CFLAGS += -Wall -Werror -Wfatal-errors -Wno-error=unused-variable -g -gdwarf-4 -Og
+CFLAGS += -Wall -Werror -Wfatal-errors -Wno-error=unused-variable -g -gdwarf-4 $(OPT)
 CXXFLAGS = -fno-exceptions -fno-rtti
 CARCH = -m2 -mb
 
@@ -16,8 +16,6 @@ LD = $(TARGET)ld
 OBJCOPY = $(TARGET)objcopy
 OBJDUMP = $(TARGET)objdump
 
-all: main.iso
-
 $(LIB)/sys_%.o: $(LIB)/segasmp/lib/sys_%.o
 	$(OBJCOPY) -I coff-sh -O elf32-sh -g \
 		--rename-section .text=.text.$* \
@@ -42,9 +40,6 @@ SYS_IP_OBJ += $(LIB)/smpsys.o
 %.o: %.cpp
 	$(CXX) $(CFLAGS) $(CXXFLAGS) $(CARCH) -c $< -o $@
 
-%.elf:
-	$(LD) --print-memory-usage -T $(LIB)/sys_ip.lds $^ -o $@
-
 %.bin: %.elf
 	$(OBJCOPY) -O binary $< $@
 
@@ -54,11 +49,11 @@ SYS_IP_OBJ += $(LIB)/smpsys.o
 		--rename-section .data=.rodata,alloc,load,readonly,data,contents \
 		$< $@
 
-sys_ip.elf: $(SYS_IP_OBJ)
+%.elf:
+	$(LD) --print-memory-usage -T $(LIB)/sh2.lds $^ -o $@
 
-main.elf: $(MAIN_OBJ)
-	$(LD) --print-memory-usage \
-	-T $(LIB)/sh2.lds $^ -o $@
+sys_ip.elf: $(SYS_IP_OBJ)
+	$(LD) --print-memory-usage -T $(LIB)/sys_ip.lds $^ -o $@
 
 # mkisofs sorts file names alphabetically, it does not place the files in the
 # generated directory descriptors the order given on the command-line.
@@ -78,7 +73,7 @@ main.elf: $(MAIN_OBJ)
 # that do check this).
 #
 # `-graft-points` is used to enable the "path grafting" pathspec syntax.
-main.iso: main.bin sys_ip.bin
+%.iso: %.bin sys_ip.bin
 	mkisofs \
 		-sysid "SEGA SEGASATURN" \
 		-volid "SAMPLE_GAME_TITLE" \
@@ -92,11 +87,16 @@ main.iso: main.bin sys_ip.bin
 		-G sys_ip.bin \
 		-o $@ \
 		-graft-points \
-		/0main.bin=./main.bin \
+		/0${<}=./${<} \
 		/=$(LIB)/segasmp/smp_cpy.txt \
 		/=$(LIB)/segasmp/smp_abs.txt \
 		/=$(LIB)/segasmp/smp_bib.txt
 
+%.cue: %.iso
+	@echo "FILE \"${<}\" BINARY" > $@
+	@echo "  TRACK 01 MODE1/2048" >> $@
+	@echo "    INDEX 01 00:00:00" >> $@
+
 clean:
 	rm -f *.iso *.o *.bin *.elf
 
diff --git a/main.cue b/main.cue
deleted file mode 100644
index ce51c75..0000000
--- a/main.cue
+++ /dev/null
@@ -1,3 +0,0 @@
-FILE "main.iso" BINARY
-  TRACK 01 MODE1/2048
-    INDEX 01 00:00:00
diff --git a/sh2.h b/sh2.h
index 1041d10..4560ff8 100644
--- a/sh2.h
+++ b/sh2.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "type.h"
 
 typedef struct sh2_reg {
@@ -98,6 +100,7 @@ typedef struct sh2_reg {
 static_assert((sizeof (struct sh2_reg)) == 0x200);
 static_assert((offsetof (struct sh2_reg, OCRAB)) == 0x014);
 static_assert((offsetof (struct sh2_reg, BCR1)) == 0x1e0);
+static_assert((offsetof (struct sh2_reg, DVSR)) == 0x100);
 
 struct sh2 {
   sh2_reg reg;
diff --git a/vdp2.h b/vdp2.h
index c54b23a..4911de9 100644
--- a/vdp2.h
+++ b/vdp2.h
@@ -101,8 +101,13 @@ typedef struct vdp2_reg {
   reg16 SCYN3;  /* SCREEN SCROLL VALUE (NBG3, VERTICAL) */
   reg16 ZMCTL;  /* REDUCTION ENABLE */
   reg16 SCRCTL; /* LINE AND VERTICAL CELL SCROLL CONTROL (NBGO, NBG1) */
-  reg16 VCSTAU; /* VERTICAL CELL SCROLL TABLE ADDRESS (NBGO, NBG1) */
-  reg16 VCSTAL; /* VERTICAL CELL SCROLL TABLE ADDRESS (NBGO, NBG1) */
+  union {
+    struct {
+      reg16 VCSTAU; /* VERTICAL CELL SCROLL TABLE ADDRESS (NBGO, NBG1) */
+      reg16 VCSTAL; /* VERTICAL CELL SCROLL TABLE ADDRESS (NBGO, NBG1) */
+    };
+    reg32 VCSTA;
+  };
   reg16 LSTA0U; /* LINE SCROLL TABLE ADDRESS (NBG0) */
   reg16 LSTA0L; /* LINE SCROLL TABLE ADDRESS (NBG0) */
   reg16 LSTA1U; /* LINE SCROLL TABLE ADDRESS (NBG1) */