CPU and GPU Reg Funcs Decomp (#16)

* decomp/doc cpu funcs and gpu reg funcs

* use Cpu32 macro funcs

* address review comments

* decomp SetBGOBJEnableFlags

15 files changed, 510 insertions, 693 deletions

diff --git a/asm/code_800B540.s b/asm/code_800B540.s
deleted file mode 100644
index 2ac2395..0000000
--- a/asm/code_800B540.s
+++ /dev/null
@@ -1,88 +0,0 @@
-	.include "constants/gba_constants.inc"
-	.include "asm/macros.inc"
-
-	.syntax unified
-
-	.text
-
-	thumb_func_start sub_800B540
-sub_800B540:
-	push {r4,lr}
-	ldr r1, _0800B5C8
-	movs r2, 0
-	adds r0, r1, 0
-	adds r0, 0x14
-_0800B54A:
-	str r2, [r0]
-	subs r0, 0x4
-	cmp r0, r1
-	bge _0800B54A
-	bl nullsub_17
-	bl sub_800BD08
-	ldr r1, _0800B5CC
-_0800B55C:
-	ldrh r0, [r1]
-	cmp r0, 0x9F
-	bls _0800B55C
-	ldr r4, _0800B5D0
-	ldrh r0, [r4]
-	movs r1, 0x45
-	eors r0, r1
-	strh r0, [r4]
-	movs r2, 0x80
-	lsls r2, 19
-	ldrb r0, [r2]
-	movs r1, 0x80
-	orrs r0, r1
-	strb r0, [r2]
-	ldr r0, _0800B5D4
-	bl sub_800B6B0
-	ldr r1, _0800B5D8
-	movs r0, 0xC1
-	lsls r0, 16
-	str r0, [r1]
-	ldrh r0, [r4]
-	ldr r2, _0800B5DC
-	adds r1, r2, 0
-	orrs r0, r1
-	strh r0, [r4]
-	ldr r1, _0800B5E0
-	movs r0, 0x28
-	strh r0, [r1]
-	ldr r1, _0800B5E4
-	movs r2, 0x1
-	negs r2, r2
-	adds r0, r2, 0
-	strh r0, [r1]
-	ldr r1, _0800B5E8
-	movs r0, 0
-	strh r0, [r1]
-	bl sub_800D6AC
-	bl sub_800D7D0
-	ldr r1, _0800B5EC
-	movs r0, 0x1
-	strb r0, [r1]
-	bl EnableInterrupts
-	ldr r1, _0800B5CC
-_0800B5BA:
-	ldrh r0, [r1]
-	cmp r0, 0x9F
-	bls _0800B5BA
-	pop {r4}
-	pop {r0}
-	bx r0
-	.align 2, 0
-_0800B5C8: .4byte gUnknown_202D5F0
-_0800B5CC: .4byte 0x04000006
-_0800B5D0: .4byte 0x04000200
-_0800B5D4: .4byte gUnknown_80B9C00
-_0800B5D8: .4byte 0x0400010c
-_0800B5DC: .4byte 0x00002045
-_0800B5E0: .4byte 0x04000004
-_0800B5E4: .4byte gUnknown_203B0AE
-_0800B5E8: .4byte gUnknown_203B0AC
-_0800B5EC: .4byte gInterruptsEnabled
-	thumb_func_end sub_800B540
-
-
-	.align 2, 0 @ Don't pad with nop.
diff --git a/asm/code_800B5F0.s b/asm/code_800B5F0.s
index cb44c31..b30e371 100644
--- a/asm/code_800B5F0.s
+++ b/asm/code_800B5F0.s
@@ -651,126 +651,4 @@ _0800BC08: .4byte 0x00008304
 _0800BC0C: .4byte 0x04000208
 	thumb_func_end sub_800BB44
 
-	thumb_func_start nullsub_17
-nullsub_17:
-	bx lr
-	thumb_func_end nullsub_17
-
-	thumb_func_start UpdateBGControlRegisters
-UpdateBGControlRegisters:
-	push {r4,lr}
-	sub sp, 0x10
-	ldr r0, _0800BC2C
-	ldrb r0, [r0]
-	cmp r0, 0x1
-	bne _0800BC30
-	str r0, [sp]
-	movs r0, 0x2
-	str r0, [sp, 0x4]
-	movs r0, 0
-	b _0800BC3A
-	.align 2, 0
-_0800BC2C: .4byte gUnknown_202D7FE
-_0800BC30:
-	movs r0, 0
-	str r0, [sp]
-	movs r0, 0x1
-	str r0, [sp, 0x4]
-	movs r0, 0x2
-_0800BC3A:
-	str r0, [sp, 0x8]
-	movs r0, 0x3
-	str r0, [sp, 0xC]
-	ldr r1, _0800BCA8
-	ldr r2, _0800BCAC
-	ldrh r0, [r2, 0x4]
-	strh r0, [r1]
-	adds r1, 0x2
-	ldrh r0, [r2, 0x6]
-	strh r0, [r1]
-	adds r1, 0x2
-	ldr r2, _0800BCB0
-	ldrh r0, [r2, 0x4]
-	strh r0, [r1]
-	adds r1, 0x2
-	ldrh r0, [r2, 0x6]
-	strh r0, [r1]
-	adds r1, 0x2
-	ldr r3, _0800BCB4
-	ldrh r0, [r3, 0x4]
-	strh r0, [r1]
-	adds r1, 0x2
-	ldrh r0, [r3, 0x6]
-	strh r0, [r1]
-	adds r1, 0x2
-	ldr r2, _0800BCB8
-	ldrh r0, [r2, 0x4]
-	strh r0, [r1]
-	adds r1, 0x2
-	ldrh r0, [r2, 0x6]
-	strh r0, [r1]
-	ldr r2, _0800BCBC
-	ldr r0, [sp]
-	movs r4, 0xB0
-	lsls r4, 6
-	adds r1, r4, 0
-	orrs r0, r1
-	strh r0, [r2]
-	adds r2, 0x2
-	ldr r0, [sp, 0x4]
-	movs r4, 0xB4
-	lsls r4, 6
-	adds r1, r4, 0
-	orrs r0, r1
-	strh r0, [r2]
-	ldrh r1, [r3, 0x2]
-	movs r0, 0x80
-	lsls r0, 8
-	cmp r1, r0
-	bne _0800BCC8
-	ldr r0, _0800BCC0
-	ldr r1, [sp, 0x8]
-	ldr r3, _0800BCC4
-	adds r2, r3, 0
-	b _0800BCD2
-	.align 2, 0
-_0800BCA8: .4byte 0x04000010
-_0800BCAC: .4byte gUnknown_202D698
-_0800BCB0: .4byte gUnknown_202D6A0
-_0800BCB4: .4byte gUnknown_202D6A8
-_0800BCB8: .4byte gUnknown_202D6B0
-_0800BCBC: .4byte 0x04000008
-_0800BCC0: .4byte 0x0400000c
-_0800BCC4: .4byte 0x00002e08
-_0800BCC8:
-	ldr r0, _0800BCF4
-	ldr r1, [sp, 0x8]
-	movs r4, 0xB8
-	lsls r4, 6
-	adds r2, r4, 0
-_0800BCD2:
-	orrs r1, r2
-	strh r1, [r0]
-	ldr r2, _0800BCF8
-	ldr r0, [sp, 0xC]
-	ldr r3, _0800BCFC
-	adds r1, r3, 0
-	orrs r0, r1
-	strh r0, [r2]
-	ldr r1, _0800BD00
-	ldr r0, _0800BD04
-	ldrh r0, [r0]
-	strh r0, [r1]
-	add sp, 0x10
-	pop {r4}
-	pop {r0}
-	bx r0
-	.align 2, 0
-_0800BCF4: .4byte 0x0400000c
-_0800BCF8: .4byte 0x0400000e
-_0800BCFC: .4byte 0x00002f08
-_0800BD00: .4byte 0x04000050
-_0800BD04: .4byte gUnknown_202D7FC
-	thumb_func_end UpdateBGControlRegisters
-
 	.align 2, 0 @ Don't pad with nop.
diff --git a/asm/code_800C9CC.s b/asm/code_800C9CC.s
deleted file mode 100644
index 8f34a57..0000000
--- a/asm/code_800C9CC.s
+++ /dev/null
@@ -1,249 +0,0 @@
-	.include "constants/gba_constants.inc"
-	.include "asm/macros.inc"
-
-	.syntax unified
-
-	.text	
-
-	thumb_func_start sub_800CD64
-sub_800CD64:
-	ldr r2, _0800CD7C
-	strb r1, [r2]
-	ldr r2, _0800CD80
-	negs r1, r0
-	orrs r1, r0
-	asrs r1, 31
-	movs r3, 0x80
-	lsls r3, 8
-	adds r0, r3, 0
-	ands r1, r0
-	strh r1, [r2, 0x2]
-	bx lr
-	.align 2, 0
-_0800CD7C: .4byte gUnknown_202D7FE
-_0800CD80: .4byte gUnknown_202D6A8
-	thumb_func_end sub_800CD64
-
-	thumb_func_start SetBGOBJEnableFlags
-SetBGOBJEnableFlags:
-	push {r4,lr}
-	movs r3, 0x80
-	lsls r3, 19
-	ldrh r1, [r3]
-	ldr r2, _0800CDA4
-	ands r2, r1
-	lsls r0, 8
-	movs r4, 0xF8
-	lsls r4, 5
-	adds r1, r4, 0
-	bics r1, r0
-	orrs r2, r1
-	strh r2, [r3]
-	pop {r4}
-	pop {r0}
-	bx r0
-	.align 2, 0
-_0800CDA4: .4byte 0x0000e0ff
-	thumb_func_end SetBGOBJEnableFlags
-
-	thumb_func_start sub_800CDA8
-sub_800CDA8:
-	ldr r1, _0800CDBC
-	str r0, [r1]
-	ldr r2, _0800CDC0
-	ldr r1, _0800CDC4
-	lsls r0, 1
-	adds r0, r1
-	ldrh r0, [r0]
-	strh r0, [r2]
-	bx lr
-	.align 2, 0
-_0800CDBC: .4byte gUnknown_202D800
-_0800CDC0: .4byte gUnknown_202D7FC
-_0800CDC4: .4byte gUnknown_203B0BE
-	thumb_func_end sub_800CDA8
-
-	thumb_func_start sub_800CDC8
-sub_800CDC8:
-	ldr r0, _0800CDD0
-	ldr r0, [r0]
-	bx lr
-	.align 2, 0
-_0800CDD0: .4byte gUnknown_202D800
-	thumb_func_end sub_800CDC8
-
-	thumb_func_start SetWindowTitle
-SetWindowTitle:
-	bx lr
-	thumb_func_end SetWindowTitle
-
-	thumb_func_start nullsub_23
-nullsub_23:
-	bx lr
-	thumb_func_end nullsub_23
-
-	thumb_func_start nullsub_182
-nullsub_182:
-	bx lr
-	thumb_func_end nullsub_182
-
-	thumb_func_start sub_800CDE0
-sub_800CDE0:
-	movs r0, 0x1
-	bx lr
-	thumb_func_end sub_800CDE0
-
-	thumb_func_start CpuCopy
-CpuCopy:
-	push {lr}
-	adds r3, r0, 0
-	cmp r2, 0
-	bge _0800CDEE
-	adds r2, 0x3
-_0800CDEE:
-	lsls r2, 9
-	lsrs r2, 11
-	movs r0, 0x80
-	lsls r0, 19
-	orrs r2, r0
-	adds r0, r1, 0
-	adds r1, r3, 0
-	bl CpuSet
-	pop {r0}
-	bx r0
-	thumb_func_end CpuCopy
-
-	thumb_func_start CpuClear
-CpuClear:
-	push {lr}
-	sub sp, 0x4
-	adds r3, r0, 0
-	movs r0, 0
-	str r0, [sp]
-	cmp r1, 0
-	bge _0800CE14
-	adds r1, 0x3
-_0800CE14:
-	lsls r2, r1, 9
-	lsrs r2, 11
-	movs r0, 0xA0
-	lsls r0, 19
-	orrs r2, r0
-	mov r0, sp
-	adds r1, r3, 0
-	bl CpuSet
-	add sp, 0x4
-	pop {r0}
-	bx r0
-	thumb_func_end CpuClear
-
-	thumb_func_start CpuFill
-CpuFill:
-	push {lr}
-	sub sp, 0x4
-	adds r3, r0, 0
-	str r1, [sp]
-	cmp r2, 0
-	bge _0800CE3A
-	adds r2, 0x3
-_0800CE3A:
-	lsls r2, 9
-	lsrs r2, 11
-	movs r0, 0xA0
-	lsls r0, 19
-	orrs r2, r0
-	mov r0, sp
-	adds r1, r3, 0
-	bl CpuSet
-	add sp, 0x4
-	pop {r0}
-	bx r0
-	thumb_func_end CpuFill
-
-	thumb_func_start sub_800CE54
-sub_800CE54:
-	push {lr}
-	ldr r2, _0800CEC0
-	ldrh r0, [r2]
-	movs r3, 0x80
-	lsls r3, 8
-	adds r1, r3, 0
-	orrs r0, r1
-	ldr r1, _0800CEC4
-	ands r0, r1
-	strh r0, [r2]
-	mov r8, r8
-	mov r8, r8
-	mov r8, r8
-	mov r8, r8
-	ldr r1, _0800CEC8
-	ands r0, r1
-	strh r0, [r2]
-	ldr r1, _0800CECC
-	ldr r2, _0800CED0
-	adds r0, r2, 0
-	strh r0, [r1]
-	adds r1, 0x2
-	movs r0, 0x3D
-	strh r0, [r1]
-	adds r1, 0x6
-	ldr r0, _0800CED4
-	ldrh r0, [r0]
-	strh r0, [r1]
-	adds r1, 0x2
-	ldr r0, _0800CED8
-	ldrh r0, [r0]
-	strh r0, [r1]
-	ldr r0, _0800CEDC
-	ldrb r1, [r0]
-	cmp r1, 0
-	beq _0800CEF4
-	ldr r1, _0800CEE0
-	ldr r0, _0800CEE4
-	ldr r2, [r0]
-	adds r0, r2, 0x4
-	str r0, [r1]
-	ldr r3, _0800CEE8
-	str r3, [r1, 0x4]
-	ldr r0, _0800CEEC
-	str r0, [r1, 0x8]
-	ldr r0, [r1, 0x8]
-	ldrh r0, [r2]
-	strh r0, [r3]
-	subs r1, 0x6E
-	ldrh r0, [r2, 0x2]
-	strh r0, [r1]
-	ldr r0, _0800CEF0
-	movs r1, 0xA0
-	b _0800CEFE
-	.align 2, 0
-_0800CEC0: .4byte 0x040000ba
-_0800CEC4: .4byte 0x0000cdff
-_0800CEC8: .4byte 0x00007fff
-_0800CECC: .4byte 0x04000048
-_0800CED0: .4byte 0x00003f3f
-_0800CED4: .4byte gUnknown_202D7FC
-_0800CED8: .4byte gUnknown_202D7FA
-_0800CEDC: .4byte gUnknown_2026E38
-_0800CEE0: .4byte 0x040000b0
-_0800CEE4: .4byte gUnknown_2026E3C
-_0800CEE8: .4byte 0x04000040
-_0800CEEC: .4byte 0xa2600002
-_0800CEF0: .4byte 0x04000044
-_0800CEF4:
-	ldr r0, _0800CF08
-	strh r1, [r0]
-	adds r0, 0x2
-	strh r1, [r0]
-	adds r0, 0x2
-_0800CEFE:
-	strh r1, [r0]
-	adds r0, 0x2
-	strh r1, [r0]
-	pop {r0}
-	bx r0
-	.align 2, 0
-_0800CF08: .4byte 0x04000040
-	thumb_func_end sub_800CE54
-
-        .align 2,0
diff --git a/asm/code_800D090.s b/asm/code_800D090.s
index a77aeab..3fd539a 100644
--- a/asm/code_800D090.s
+++ b/asm/code_800D090.s
@@ -7522,7 +7522,7 @@ sub_8010960:
 	adds r1, r5
 	movs r2, 0
 	ldrsh r1, [r1, r2]
-	bl sub_800CCA0
+	bl SetBG2RegOffsets
 	ldr r1, [r6]
 	adds r4, r1, r4
 	movs r2, 0
@@ -7530,7 +7530,7 @@ sub_8010960:
 	adds r1, r5
 	movs r2, 0
 	ldrsh r1, [r1, r2]
-	bl sub_800CCAC
+	bl SetBG3RegOffsets
 	movs r0, 0x1
 	bl sub_8010A88
 	bl sub_8010A00
@@ -9139,7 +9139,7 @@ sub_801169C:
 	adds r1, r6
 	movs r3, 0
 	ldrsh r1, [r1, r3]
-	bl sub_800CCA0
+	bl SetBG2RegOffsets
 	ldr r1, [r5]
 	adds r4, r1, r4
 	movs r2, 0
@@ -9147,7 +9147,7 @@ sub_801169C:
 	adds r1, r6
 	movs r3, 0
 	ldrsh r1, [r1, r3]
-	bl sub_800CCAC
+	bl SetBG3RegOffsets
 	bl sub_8010F28
 	bl sub_80111C4
 	lsls r0, 24
diff --git a/asm/code_803D110.s b/asm/code_803D110.s
index 55aaf57..f5f9425 100644
--- a/asm/code_803D110.s
+++ b/asm/code_803D110.s
@@ -2567,7 +2567,7 @@ sub_803E490:
 	adds r1, r4
 	movs r2, 0
 	ldrsh r1, [r1, r2]
-	bl sub_800CCA0
+	bl SetBG2RegOffsets
 	b _0803E4FC
 	.align 2, 0
 _0803E4D8: .4byte gUnknown_202EDD4
@@ -2582,7 +2582,7 @@ _0803E4EC:
 	strb r0, [r1]
 	movs r0, 0
 	movs r1, 0
-	bl sub_800CCA0
+	bl SetBG2RegOffsets
 _0803E4FC:
 	ldr r4, _0803E62C
 	ldr r2, [r4]
@@ -2598,7 +2598,7 @@ _0803E4FC:
 	adds r2, r3
 	ldr r2, [r2]
 	subs r1, r2
-	bl sub_800CCAC
+	bl SetBG3RegOffsets
 	bl sub_806CC10
 	bl sub_804522C
 	bl sub_803F9CC
diff --git a/asm/code_80A26CC.s b/asm/code_80A26CC.s
index ebc16bc..20676d2 100644
--- a/asm/code_80A26CC.s
+++ b/asm/code_80A26CC.s
@@ -4386,12 +4386,12 @@ _080A4998: .4byte 0x00000536
 _080A499C:
 	ldr r0, [r4, 0x48]
 	ldr r1, [r4, 0x4C]
-	bl sub_800CCA0
+	bl SetBG2RegOffsets
 	b _080A49AE
 _080A49A6:
 	ldr r0, [r4, 0x48]
 	ldr r1, [r4, 0x4C]
-	bl sub_800CCAC
+	bl SetBG3RegOffsets
 _080A49AE:
 	adds r6, 0x1
 	adds r5, 0x1
diff --git a/include/bg.h b/include/bg.h
new file mode 100644
index 0000000..376fb6f
--- /dev/null
+++ b/include/bg.h
@@ -0,0 +1,18 @@
+struct BGControlStruct
+{
+    u16 padding;
+    u16 unk2;
+    s16 hofs;
+    s16 vofs;
+};
+
+void SetBG0RegOffsets(s32 xoffset, s32 yoffset);
+void SetBG1RegOffsets(s32 xoffset, s32 yoffset);
+void SetBG2RegOffsets(s32 xoffset, s32 yoffset);
+void SetBG3RegOffsets(s32 xoffset, s32 yoffset);
+void SetBGRegOffsets(s32 reg, u32 xoffset, s32 yoffset);
+void SetBGRegXOffset(s32 reg, s32 offset);
+void SetBGRegYOffset(s32 reg, s32 offset);
+void UpdateBGControlRegisters(void);
+void SetBGOBJEnableFlags(u32 mask);
+
diff --git a/include/gba/io_reg.h b/include/gba/io_reg.h
index 6dbe5e8..2453645 100644
--- a/include/gba/io_reg.h
+++ b/include/gba/io_reg.h
@@ -538,6 +538,41 @@
 #define BGCNT_AFF512x512        0x8000
 #define BGCNT_AFF1024x1024      0xC000
 
+// WININ/OUT
+#define WININ_WIN0_BG0      (1 << 0)
+#define WININ_WIN0_BG1      (1 << 1)
+#define WININ_WIN0_BG2      (1 << 2)
+#define WININ_WIN0_BG3      (1 << 3)
+#define WININ_WIN0_BG_ALL   (WININ_WIN0_BG0 | WININ_WIN0_BG1 | WININ_WIN0_BG2 | WININ_WIN0_BG3)
+#define WININ_WIN0_OBJ      (1 << 4)
+#define WININ_WIN0_CLR      (1 << 5)
+#define WININ_WIN0_ALL      (WININ_WIN0_BG_ALL | WININ_WIN0_OBJ | WININ_WIN0_CLR)
+#define WININ_WIN1_BG0      (1 << 8)
+#define WININ_WIN1_BG1      (1 << 9)
+#define WININ_WIN1_BG2      (1 << 10)
+#define WININ_WIN1_BG3      (1 << 11)
+#define WININ_WIN1_BG_ALL   (WININ_WIN1_BG0 | WININ_WIN1_BG1 | WININ_WIN1_BG2 | WININ_WIN1_BG3)
+#define WININ_WIN1_OBJ      (1 << 12)
+#define WININ_WIN1_CLR      (1 << 13)
+#define WININ_WIN1_ALL      (WININ_WIN1_BG_ALL | WININ_WIN1_OBJ | WININ_WIN1_CLR)
+
+#define WINOUT_WIN01_BG0    (1 << 0)
+#define WINOUT_WIN01_BG1    (1 << 1)
+#define WINOUT_WIN01_BG2    (1 << 2)
+#define WINOUT_WIN01_BG3    (1 << 3)
+#define WINOUT_WIN01_BG_ALL (WINOUT_WIN01_BG0 | WINOUT_WIN01_BG1 | WINOUT_WIN01_BG2 | WINOUT_WIN01_BG3)
+#define WINOUT_WIN01_OBJ    (1 << 4)
+#define WINOUT_WIN01_CLR    (1 << 5)
+#define WINOUT_WIN01_ALL    (WINOUT_WIN01_BG_ALL | WINOUT_WIN01_OBJ | WINOUT_WIN01_CLR)
+#define WINOUT_WINOBJ_BG0   (1 << 8)
+#define WINOUT_WINOBJ_BG1   (1 << 9)
+#define WINOUT_WINOBJ_BG2   (1 << 10)
+#define WINOUT_WINOBJ_BG3   (1 << 11)
+#define WINOUT_WINOBJ_BG_ALL (WINOUT_WINOBJ_BG0 | WINOUT_WINOBJ_BG1 | WINOUT_WINOBJ_BG2 | WINOUT_WINOBJ_BG3)
+#define WINOUT_WINOBJ_OBJ   (1 << 12)
+#define WINOUT_WINOBJ_CLR   (1 << 13)
+#define WINOUT_WINOBJ_ALL   (WINOUT_WINOBJ_BG_ALL | WINOUT_WINOBJ_OBJ | WINOUT_WINOBJ_CLR)
+
 // BLDCNT
 // Bits 0-5 select layers for the 1st target
 #define BLDCNT_TGT1_BG0      (1 << 0)
diff --git a/ld_script.txt b/ld_script.txt
index 5acc3f0..1d675cd 100755
--- a/ld_script.txt
+++ b/ld_script.txt
@@ -68,14 +68,12 @@ SECTIONS {
         asm/code_8009804.o(.text);
         src/file_system.o(.text);
         src/main.o(.text);
-        asm/code_800B540.o(.text);
-        src/code_800B5F0.o(.text);
         asm/code_800B5F0.o(.text);
         src/music_pre.o(.text);
         asm/music.o(.text);
         src/music.o(.text);
         src/code_800C9CC.o(.text);
-        asm/code_800C9CC.o(.text);
+        src/cpu.o(.text);
         src/flash.o(.text);
         src/code_800D090.o(.text);
         asm/code_800D090.o(.text);
diff --git a/src/code_2.c b/src/code_2.c
index 4e778e7..fcec96d 100644
--- a/src/code_2.c
+++ b/src/code_2.c
@@ -2,6 +2,7 @@
 #include "file_system.h"
 #include "friend_area.h"
 #include "input.h"
+#include "bg.h"
 
 extern void InitHeap(void);
 extern void NDS_DebugInit(void);
@@ -37,8 +38,6 @@ extern void sub_80097B0(void);
 extern void sub_800CDA8(u32);
 extern void sub_800641C(u32, u32, u32);
 extern void LoadTitleScreen(void);
-extern void sub_800CCA0(u32, u32);
-extern void sub_800CCAC(u32, u32);
 extern void SetBGPaletteBufferColorRGB(s32, u8 *, s32, u8 *);
 extern void sub_800BDFC(u32);
 extern void sub_80095CC(u32, u32);
@@ -47,7 +46,6 @@ extern void sub_8012468(void);
 extern u32 sub_8012484(void);
 extern void sub_8012558(void);
 extern u8 sub_80363E0(void);
-extern void SetBGOBJEnableFlags(u32);
 extern void SetUpMenu(void);
 extern u32 UpdateMenu(void);
 extern void CleanUpMenu(void);
@@ -134,8 +132,8 @@ void GameLoop(void)
         sub_800641C(0, 1, 1);
         gUnknown_2026E4E = 0x1000;
         LoadTitleScreen();
-        sub_800CCA0(0, 0);
-        sub_800CCAC(0, 0);
+        SetBG2RegOffsets(0, 0);
+        SetBG3RegOffsets(0, 0);
         gUnknown_2000A80 = 0;
         while (gUnknown_2000A80 < 32) {
             s32 i;
diff --git a/src/code_800B5F0.c b/src/code_800B5F0.c
deleted file mode 100644
index 35b5282..0000000
--- a/src/code_800B5F0.c
+++ /dev/null
@@ -1,99 +0,0 @@
-#include "global.h"
-
-extern bool8 gInterruptsEnabled;
-extern u32 gIntrTable[];
-extern u32 IntrMain;
-extern u8 gUnknown_202D4B8;
-extern u32 gUnknown_202D5F0[];
-
-bool8 EnableInterrupts(void)
-{
-    if(gInterruptsEnabled == FALSE)
-    {
-        return FALSE;
-    }
-
-    if((REG_IME & 1) != 0)
-    {
-        return FALSE;
-    }
-    else
-    {
-        REG_IME = 1;
-        return TRUE;
-    }
-}
-
-bool8 DisableInterrupts(void)
-{
-    if(gInterruptsEnabled == 0)
-    {
-        return FALSE;
-    }
-
-    if((REG_IME & 1) == 0)
-    {
-        return FALSE;
-    }
-    else
-    {
-        REG_IME = 0;
-        return TRUE;
-    }
-
-}
-
-bool8 sub_800B650(void)
-{
-    if(gInterruptsEnabled == FALSE)
-    {
-        return FALSE;
-    }
-
-    if((REG_IME & 1) != 0)
-    {
-        return FALSE;
-    }
-    else
-    {
-        return TRUE;
-    }
-}
-
-void SetInterruptFlag(u16 flag)
-{
-    if(gInterruptsEnabled == FALSE)
-    {
-        return;
-    }
-
-    REG_IME = 0;
-    INTR_CHECK |= flag;
-    REG_IME = 1;
-}
-
-void sub_800B6B0(const u32 *r0)
-{
-    CpuCopy32(r0, &gIntrTable, 0x18); // 0x18 = 0x6 * 4 (0x4f00 is 32 bits)
-    CpuCopy32(&IntrMain, &gUnknown_202D4B8, 0x120); // 0x120 = 0x48 * 4 (0x4f00 is 32 bits)
-    INTR_VECTOR = &gUnknown_202D4B8;
-}
-
-u32 *sub_800B6E8(u32 r0)
-{
-    return &gIntrTable[r0];
-}
-
-u32 sub_800B6F4(u32 r0, u32 r1)
-{
-    u32 temp;
-    u32 interrupt_var;
-
-    interrupt_var = DisableInterrupts();
-    temp = gUnknown_202D5F0[r0];
-    gUnknown_202D5F0[r0] = r1;
-    if(interrupt_var != FALSE){
-        EnableInterrupts();
-    }
-    return temp;
-}
diff --git a/src/code_800C9CC.c b/src/code_800C9CC.c
index ddc49c6..28ce10a 100644
--- a/src/code_800C9CC.c
+++ b/src/code_800C9CC.c
@@ -1,23 +1,17 @@
 #include "global.h"
 #include "input.h"
-
-struct unkStruct_809CC88
-{
-    u16 padding;
-    u16 unk2;
-    u16 unk4;
-    u16 unk6;
-};
+#include "bg.h"
 
 extern u16 gRawKeyInput;
 extern u8 gUnknown_202D6B8;
 extern u8 gUnknown_202D6B9;
 extern u16 gUnknown_202D7FA;
+extern u8 gUnknown_202D7FE;
 
-extern struct unkStruct_809CC88 gUnknown_202D698;
-extern struct unkStruct_809CC88 gUnknown_202D6A0;
-extern struct unkStruct_809CC88 gUnknown_202D6A8;
-extern struct unkStruct_809CC88 gUnknown_202D6B0;
+extern struct BGControlStruct gUnknown_202D698;
+extern struct BGControlStruct gUnknown_202D6A0;
+extern struct BGControlStruct gUnknown_202D6A8;
+extern struct BGControlStruct gUnknown_202D6B0;
 
 void ReadKeyInput(struct Inputs *r0)
 {
@@ -97,122 +91,86 @@ void sub_800CC44(s32 r0, s32 r1)
 
 }
 
-void sub_800CC88(u32 r0, u32 r1)
+void SetBG0RegOffsets(s32 xoffset, s32 yoffset)
 {
-    gUnknown_202D698.unk4 = r0;
-    gUnknown_202D698.unk6 = r1;
+    gUnknown_202D698.hofs = xoffset;
+    gUnknown_202D698.vofs = yoffset;
 }
 
-void sub_800CC94(u32 r0, u32 r1)
+void SetBG1RegOffsets(s32 xoffset, s32 yoffset)
 {
-    gUnknown_202D6A0.unk4 = r0;
-    gUnknown_202D6A0.unk6 = r1;
+    gUnknown_202D6A0.hofs = xoffset;
+    gUnknown_202D6A0.vofs = yoffset;
 }
 
-void sub_800CCA0(u32 r0, u32 r1)
+void SetBG2RegOffsets(s32 xoffset, s32 yoffset)
 {
-    gUnknown_202D6A8.unk4 = r0;
-    gUnknown_202D6A8.unk6 = r1;
+    gUnknown_202D6A8.hofs = xoffset;
+    gUnknown_202D6A8.vofs = yoffset;
 }
 
-void sub_800CCAC(u32 r0, u32 r1)
+void SetBG3RegOffsets(s32 xoffset, s32 yoffset)
 {
-    gUnknown_202D6B0.unk4 = r0;
-    gUnknown_202D6B0.unk6 = r1;
+    gUnknown_202D6B0.hofs = xoffset;
+    gUnknown_202D6B0.vofs = yoffset;
 }
 
-void sub_800CCB8(s32 r0, u32 r1, u32 r2)
+void SetBGRegOffsets(s32 reg, u32 xoffset, s32 yoffset)
 {
-    if(r0 == 1)
-    {
-        goto _0800CCD4;
-    }
-    if(r0 <= 1)
-    {
-        goto _0800CCCA;
-    }
-    if(r0 == 2)
-    {
-        goto _0800CCDE;
+    switch (reg) {
+        default:
+        case 0: return SetBG0RegOffsets(xoffset, yoffset);
+        case 1: return SetBG1RegOffsets(xoffset, yoffset);
+        case 2: return SetBG2RegOffsets(xoffset, yoffset);
+        case 3: return SetBG3RegOffsets(xoffset, yoffset);
     }
-    if(r0 == 3)
-    {
-        goto _0800CCE8;
-    }
-   
-    _0800CCCA:
-        sub_800CC88(r1, r2);
-        return;
-    _0800CCD4:
-        sub_800CC94(r1, r2);
-        return;
-    _0800CCDE:
-        sub_800CCA0(r1, r2);
-        return;
-    _0800CCE8:
-        sub_800CCAC(r1, r2);
 }
 
-void sub_800CCF4(s32 r0, u32 r1)
+void SetBGRegXOffset(s32 reg, s32 offset)
 {
-    if(r0 == 1)
-    {
-        goto _0800CD10;
-    }
-    if(r0 <= 1)
-    {
-        goto _0800CD06;
+    switch (reg) {
+        default:
+        case 0:
+            gUnknown_202D698.hofs = offset;
+            break;
+        case 1:
+            gUnknown_202D6A0.hofs = offset;
+            break;
+        case 2:
+            gUnknown_202D6A8.hofs = offset;
+            break;
+        case 3:
+            gUnknown_202D6B0.hofs = offset;
+            break;
     }
-    if(r0 == 2)
-    {
-        goto _0800CD18;
-    }
-    if(r0 == 3)
-    {
-        goto _0800CD20;
-    }
-
-    _0800CD06:
-        gUnknown_202D698.unk4 = r1;
-        return;
-    _0800CD10:
-        gUnknown_202D6A0.unk4 = r1;
-        return;
-    _0800CD18:
-        gUnknown_202D6A8.unk4 = r1;
-        return;
-    _0800CD20:
-        gUnknown_202D6B0.unk4 = r1;
 }
 
-void sub_800CD2C(s32 r0, u32 r1)
+void SetBGRegYOffset(s32 reg, s32 offset)
 {
-    if(r0 == 1)
-    {
-        goto _0800CD48;
-    }
-    if(r0 <= 1)
-    {
-        goto _0800CD3E;
-    }
-    if(r0 == 2)
-    {
-        goto _0800CD50;
-    }
-    if(r0 == 3)
-    {
-        goto _0800CD58;
+    switch (reg) {
+        default:
+        case 0:
+            gUnknown_202D698.vofs = offset;
+            break;
+        case 1:
+            gUnknown_202D6A0.vofs = offset;
+            break;
+        case 2:
+            gUnknown_202D6A8.vofs = offset;
+            break;
+        case 3:
+            gUnknown_202D6B0.vofs = offset;
+            break;
     }
+}
 
-    _0800CD3E:
-        gUnknown_202D698.unk6 = r1;
-        return;
-    _0800CD48:
-        gUnknown_202D6A0.unk6 = r1;
-        return;
-    _0800CD50:
-        gUnknown_202D6A8.unk6 = r1;
-        return;
-    _0800CD58:
-        gUnknown_202D6B0.unk6 = r1;
+void sub_800CD64(s32 r0, u8 r1)
+{
+    gUnknown_202D7FE = r1;
+    gUnknown_202D6A8.unk2 = r0 ? 0x8000 : 0; 
+}
+
+void SetBGOBJEnableFlags(u32 mask)
+{
+    REG_DISPCNT = (REG_DISPCNT & 0xe0ff) | (~(mask << 8) & (DISPCNT_BG_ALL_ON | DISPCNT_OBJ_ON));
 }
diff --git a/src/cpu.c b/src/cpu.c
new file mode 100644
index 0000000..eb1043a
--- /dev/null
+++ b/src/cpu.c
@@ -0,0 +1,170 @@
+#include "global.h"
+
+extern u32 gUnknown_202D800;
+extern u16 gUnknown_202D7FC; // used to update Blend Count Reg
+extern u16 gUnknown_203B0BE[];
+
+void sub_800CDA8(u32 r0)
+{
+    gUnknown_202D800 = r0;
+    gUnknown_202D7FC = gUnknown_203B0BE[r0];
+}
+
+u32 sub_800CDC8(void)
+{
+    return gUnknown_202D800;
+}
+
+void SetWindowTitle(char *title)
+{
+}
+
+void nullsub_23(void)
+{
+}
+
+void nullsub_182(void)
+{
+}
+
+u32 sub_800CDE0(void)
+{
+    return 1;
+}
+
+void CpuCopy(void* src, void *dest, s32 size)
+{
+    CpuCopy32(dest, src, size);
+}
+
+void CpuClear(void* dest, s32 size)
+{
+    CpuFill32(NULL, dest, size);
+}
+
+void CpuFill(void* src, void *dest, s32 size)
+{
+    CpuFill32(dest, src, size);
+}
+
+#ifdef NONMATCHING
+void sub_800CE54(void)
+{
+    // TODO this is so gross.. looks like a macro or something else but I don't want to deal with this rn
+    REG_DMA0CNT_H = (REG_DMA0CNT_H | DMA_ENABLE) & 0xcdff;
+    asm("mov \tr8, r8");
+    asm("mov \tr8, r8");
+    asm("mov \tr8, r8");
+    asm("mov \tr8, r8");
+    REG_DMA0CNT_H &= 0x7fff;
+
+    // Everything below matches
+
+    REG_WININ = WININ_WIN0_ALL | WININ_WIN1_ALL;
+    REG_WINOUT = WINOUT_WIN01_OBJ | WINOUT_WIN01_CLR | WINOUT_WIN01_BG3 | WINOUT_WIN01_BG2 | WINOUT_WIN01_BG0;
+    REG_BLDCNT = gUnknown_202D7FC;
+    REG_BLDALPHA = gUnknown_202D7FA;
+    if(gUnknown_2026E38 != 0)
+    {
+        DmaSet(0, &gUnknown_2026E3C[2], REG_ADDR_WIN0H, 0xa2600002);
+        REG_WIN0H = gUnknown_2026E3C[0];
+        REG_WIN1H = gUnknown_2026E3C[1];
+        REG_WIN0V = 160;
+        REG_WIN1V = 160;
+    }
+    else
+    {
+        REG_WIN0H = 0;
+        REG_WIN1H = 0;
+        REG_WIN0V = 0;
+        REG_WIN1V = 0;
+    }
+}
+#else
+NAKED
+void sub_800CE54(void)
+{
+	asm_unified("\tpush {lr}\n"
+	"\tldr r2, _0800CEC0\n"
+	"\tldrh r0, [r2]\n"
+	"\tmovs r3, 0x80\n"
+	"\tlsls r3, 8\n"
+	"\tadds r1, r3, 0\n"
+	"\torrs r0, r1\n"
+	"\tldr r1, _0800CEC4\n"
+	"\tands r0, r1\n"
+	"\tstrh r0, [r2]\n"
+	"\tmov r8, r8\n"
+	"\tmov r8, r8\n"
+	"\tmov r8, r8\n"
+	"\tmov r8, r8\n"
+	"\tldr r1, _0800CEC8\n"
+	"\tands r0, r1\n"
+	"\tstrh r0, [r2]\n"
+	"\tldr r1, _0800CECC\n"
+	"\tldr r2, _0800CED0\n"
+	"\tadds r0, r2, 0\n"
+	"\tstrh r0, [r1]\n"
+	"\tadds r1, 0x2\n"
+	"\tmovs r0, 0x3D\n"
+	"\tstrh r0, [r1]\n"
+	"\tadds r1, 0x6\n"
+	"\tldr r0, _0800CED4\n"
+	"\tldrh r0, [r0]\n"
+	"\tstrh r0, [r1]\n"
+	"\tadds r1, 0x2\n"
+	"\tldr r0, _0800CED8\n"
+	"\tldrh r0, [r0]\n"
+	"\tstrh r0, [r1]\n"
+	"\tldr r0, _0800CEDC\n"
+	"\tldrb r1, [r0]\n"
+	"\tcmp r1, 0\n"
+	"\tbeq _0800CEF4\n"
+	"\tldr r1, _0800CEE0\n"
+	"\tldr r0, _0800CEE4\n"
+	"\tldr r2, [r0]\n"
+	"\tadds r0, r2, 0x4\n"
+	"\tstr r0, [r1]\n"
+	"\tldr r3, _0800CEE8\n"
+	"\tstr r3, [r1, 0x4]\n"
+	"\tldr r0, _0800CEEC\n"
+	"\tstr r0, [r1, 0x8]\n"
+	"\tldr r0, [r1, 0x8]\n"
+	"\tldrh r0, [r2]\n"
+	"\tstrh r0, [r3]\n"
+	"\tsubs r1, 0x6E\n"
+	"\tldrh r0, [r2, 0x2]\n"
+	"\tstrh r0, [r1]\n"
+	"\tldr r0, _0800CEF0\n"
+	"\tmovs r1, 0xA0\n"
+	"\tb _0800CEFE\n"
+	"\t.align 2, 0\n"
+"_0800CEC0: .4byte 0x040000ba\n"
+"_0800CEC4: .4byte 0x0000cdff\n"
+"_0800CEC8: .4byte 0x00007fff\n"
+"_0800CECC: .4byte 0x04000048\n"
+"_0800CED0: .4byte 0x00003f3f\n"
+"_0800CED4: .4byte gUnknown_202D7FC\n"
+"_0800CED8: .4byte gUnknown_202D7FA\n"
+"_0800CEDC: .4byte gUnknown_2026E38\n"
+"_0800CEE0: .4byte 0x040000b0\n"
+"_0800CEE4: .4byte gUnknown_2026E3C\n"
+"_0800CEE8: .4byte 0x04000040\n"
+"_0800CEEC: .4byte 0xa2600002\n"
+"_0800CEF0: .4byte 0x04000044\n"
+"_0800CEF4:\n"
+	"\tldr r0, _0800CF08\n"
+	"\tstrh r1, [r0]\n"
+	"\tadds r0, 0x2\n"
+	"\tstrh r1, [r0]\n"
+	"\tadds r0, 0x2\n"
+"_0800CEFE:\n"
+	"\tstrh r1, [r0]\n"
+	"\tadds r0, 0x2\n"
+	"\tstrh r1, [r0]\n"
+	"\tpop {r0}\n"
+	"\tbx r0\n"
+	"\t.align 2, 0\n"
+"_0800CF08: .4byte 0x04000040");
+}
+#endif
diff --git a/src/main.c b/src/main.c
index 687ef6d..2d586a5 100644
--- a/src/main.c
+++ b/src/main.c
@@ -5,8 +5,16 @@
 
 extern char ewram_start[];
 
+extern u8 gUnknown_202D4B8;
+extern void *gUnknown_202D5F0[6];
 extern u16 gUnknown_202D7FC;
 extern u8 gUnknown_202D7FE;
+extern u8 gInterruptsEnabled;
+extern u16 gUnknown_203B0AC;
+extern s16 gUnknown_203B0AE;
+extern u32 gIntrTable[];
+extern u32 IntrMain;
+
 
 extern char alt_203B038[];
 
@@ -21,6 +29,7 @@ extern char unk_code_ram[];
 extern char unk_code_ram_end[];
 
 extern u8 gUnknown_80B9BF1[];
+extern u32 gUnknown_80B9C00;
 
 extern char gUnknown_8270000[];
 
@@ -37,11 +46,20 @@ extern void sub_80057E8(void);
 extern void InitFileSystem(void);
 extern void sub_80098A0(void);
 extern void InitGraphics(void);
-extern void sub_800B6F4(int, void *);
 extern void GameLoop(void);
 extern void Hang(void);
 extern void sub_800CE54(void);
 
+extern void nullsub_17(void);
+extern void sub_800BD08(void); // music initializer
+extern void sub_800D6AC(void);
+extern void sub_800D7D0(void);
+
+bool8 EnableInterrupts(void);
+void InitIntrTable(const u32 *interrupt_table);
+void *sub_800B6F4(u32 index, void * new_callback);
+
+
 void AgbMain(void)
 {
     u8 value[4];
@@ -76,16 +94,16 @@ void AgbMain(void)
     REG_WIN1H = 0;
     REG_WIN0V = 0;
     REG_WIN1V = 0;
-    REG_WININ = 16191;
-    REG_WINOUT = 61;
-    gUnknown_202D7FC = REG_BLDCNT = 15426;
-    REG_BLDALPHA = 1546;
+    REG_WININ = WININ_WIN0_ALL | WININ_WIN1_ALL; // 16191
+    REG_WINOUT = WINOUT_WIN01_BG0 | WINOUT_WIN01_BG2 | WINOUT_WIN01_BG3 | WINOUT_WIN01_OBJ | WINOUT_WIN01_CLR; // 61
+    gUnknown_202D7FC = REG_BLDCNT = BLDCNT_TGT1_BG1 | BLDCNT_EFFECT_BLEND | BLDCNT_TGT2_BG2 | BLDCNT_TGT2_BG3 | BLDCNT_TGT2_BD | BLDCNT_TGT2_OBJ; // 15426
+    REG_BLDALPHA = BLDALPHA_BLEND(10, 6); // 1546
     gUnknown_202D7FE = 0;
-    REG_BG0CNT = 11264;
-    REG_BG1CNT = 11521;
-    REG_BG2CNT = 11786;
-    REG_BG3CNT = 12043;
-    REG_DISPCNT = 32704;
+    REG_BG0CNT = BGCNT_PRIORITY(0) | BGCNT_CHARBASE(0) | BGCNT_WRAP | BGCNT_SCREENBASE(12); // 11264
+    REG_BG1CNT = BGCNT_PRIORITY(1) | BGCNT_CHARBASE(0) | BGCNT_WRAP | BGCNT_SCREENBASE(13); // 11521
+    REG_BG2CNT = BGCNT_PRIORITY(2) | BGCNT_CHARBASE(2) | BGCNT_WRAP | BGCNT_SCREENBASE(14); // 11786
+    REG_BG3CNT = BGCNT_PRIORITY(3) | BGCNT_CHARBASE(2) | BGCNT_WRAP | BGCNT_SCREENBASE(15); // 12043
+    REG_DISPCNT = DISPCNT_WIN1_ON | DISPCNT_WIN0_ON | DISPCNT_OBJ_ON | DISPCNT_BG_ALL_ON | DISPCNT_OBJ_1D_MAP | DISPCNT_FORCED_BLANK; // 32704
     sub_800CDA8(1);
     sub_800B540();
     InitFlash();
@@ -102,7 +120,132 @@ void AgbMain(void)
     sub_80098A0();
     InitGraphics();
     sub_800B6F4(1, sub_800CE54);
-    REG_DISPCNT = 32576;
+    REG_DISPCNT = DISPCNT_WIN1_ON | DISPCNT_WIN0_ON | DISPCNT_OBJ_ON | DISPCNT_BG_ALL_ON | DISPCNT_OBJ_1D_MAP; // 32576
     GameLoop();
     Hang();
 }
+
+void sub_800B540(void)
+{
+    s32 i;
+    for (i = 0; i < 6; i++) {
+        gUnknown_202D5F0[i] = NULL;
+    }
+
+    nullsub_17();
+    sub_800BD08(); // initialize music and stop DMAs
+
+    while(REG_VCOUNT <= 159){}
+
+    REG_IE ^= INTR_FLAG_TIMER3 | INTR_FLAG_VBLANK | INTR_FLAG_VCOUNT; // 0x45
+
+    *(u8*)&REG_DISPCNT |= DISPCNT_FORCED_BLANK; 
+
+    InitIntrTable(&gUnknown_80B9C00); // set up intrrupt vector/table
+
+    REG_TM3CNT = (TIMER_64CLK | TIMER_INTR_ENABLE | TIMER_ENABLE) << 16; 
+
+    REG_IE |= INTR_FLAG_GAMEPAK | INTR_FLAG_TIMER3 | INTR_FLAG_VCOUNT | INTR_FLAG_VBLANK; // 0x2045
+    REG_DISPSTAT = DISPSTAT_VCOUNT_INTR | DISPSTAT_VBLANK_INTR;
+    gUnknown_203B0AE = -1;
+    gUnknown_203B0AC = 0;
+    sub_800D6AC(); // Some other IO REG update func
+    sub_800D7D0(); // Some other IO REG update func
+    gInterruptsEnabled = 1;
+    EnableInterrupts();
+
+    while(REG_VCOUNT <= 159){}
+}
+
+bool8 EnableInterrupts(void)
+{
+    if(!gInterruptsEnabled)
+    {
+        return FALSE;
+    }
+
+    if(REG_IME & 1)
+    {
+        return FALSE;
+    }
+    else
+    {
+        REG_IME = 1;
+        return TRUE;
+    }
+}
+
+bool8 DisableInterrupts(void)
+{
+    if(!gInterruptsEnabled)
+    {
+        return FALSE;
+    }
+
+    if(!(REG_IME & 1))
+    {
+        return FALSE;
+    }
+    else
+    {
+        REG_IME = 0;
+        return TRUE;
+    }
+
+}
+
+bool8 sub_800B650(void)
+{
+    if(!gInterruptsEnabled)
+    {
+        return FALSE;
+    }
+
+    if(REG_IME & 1)
+    {
+        return FALSE;
+    }
+    else
+    {
+        return TRUE;
+    }
+}
+
+void SetInterruptFlag(u16 flag)
+{
+    if(!gInterruptsEnabled)
+    {
+        return;
+    }
+
+    REG_IME = 0;
+    INTR_CHECK |= flag;
+    REG_IME = 1;
+}
+
+void InitIntrTable(const u32 *interrupt_table)
+{
+    CpuCopy32(interrupt_table, &gIntrTable, 0x18); // 0x18 = 0x6 * 4 (0x4f00 is 32 bits)
+    CpuCopy32(&IntrMain, &gUnknown_202D4B8, 0x120); // 0x120 = 0x48 * 4 (0x4f00 is 32 bits)
+    INTR_VECTOR = &gUnknown_202D4B8;
+}
+
+u32 *sub_800B6E8(u32 r0)
+{
+    return &gIntrTable[r0];
+}
+
+void *sub_800B6F4(u32 index, void * new_callback)
+{
+    void *old_callback;
+    u32 interrupt_var;
+
+    interrupt_var = DisableInterrupts();
+    old_callback = gUnknown_202D5F0[index];
+    gUnknown_202D5F0[index] = new_callback;
+    if(interrupt_var){
+        EnableInterrupts();
+    }
+    return old_callback;
+}
+
diff --git a/src/music_pre.c b/src/music_pre.c
index 292f0a8..4260ea1 100644
--- a/src/music_pre.c
+++ b/src/music_pre.c
@@ -1,6 +1,7 @@
 #include "global.h"
 #include "gba/io_reg.h"
 #include "m4a.h"
+#include "bg.h"
 
 extern void nullsub_19(void);
 extern void nullsub_20(u16 songIndex);
@@ -31,8 +32,62 @@ struct unkStruct_3000FD8
 
 extern struct unkStruct_3000FD8 gUnknown_3000FD8[8];
 
+extern u8 gUnknown_202D7FE;
+extern u16 gUnknown_202D7FC;
+extern struct BGControlStruct gUnknown_202D698;
+extern struct BGControlStruct gUnknown_202D6A0;
+extern struct BGControlStruct gUnknown_202D6A8;
+extern struct BGControlStruct gUnknown_202D6B0;
+
 void sub_800BF80(void);
 
+void nullsub_17(void)
+{
+}
+
+void UpdateBGControlRegisters(void)
+{
+    u32 BG[4];
+
+    if(gUnknown_202D7FE == 1)
+    {
+        BG[0] = 1;
+        BG[1] = 2;
+        BG[2] = 0;
+        BG[3] = 3;
+    }
+    else
+    {
+        BG[0] = 0;
+        BG[1] = 1;
+        BG[2] = 2;
+        BG[3] = 3;
+    }
+
+    REG_BG0HOFS = gUnknown_202D698.hofs;
+    REG_BG0VOFS = gUnknown_202D698.vofs;
+    REG_BG1HOFS = gUnknown_202D6A0.hofs;
+    REG_BG1VOFS = gUnknown_202D6A0.vofs;
+    REG_BG2HOFS = gUnknown_202D6A8.hofs;
+    REG_BG2VOFS = gUnknown_202D6A8.vofs;
+    REG_BG3HOFS = gUnknown_202D6B0.hofs;
+    REG_BG3VOFS = gUnknown_202D6B0.vofs;
+
+    REG_BG0CNT = BG[0] | 0xB0 << 6;
+    REG_BG1CNT = BG[1] | 0xB4 << 6;
+    if(gUnknown_202D6A8.unk2 == 0x80 << 8)
+    {
+        REG_BG2CNT = BG[2] | 0x2e08;
+    }
+    else
+    {
+        REG_BG2CNT = BG[2] | 0xB8 << 6;
+    }
+
+    REG_BG3CNT = BG[3] | 0x2f08;
+    REG_BLDCNT = gUnknown_202D7FC;
+}
+
 // Some kind of initializer for music?
 void sub_800BD08(void)
 {