From 76fa7b081687f96493e97350ba5896b07c5cb22a Mon Sep 17 00:00:00 2001
From: Randy Thiemann <randy.thiemann@student.pxl.be>
Date: Fri, 27 Oct 2023 21:37:32 +0200
Subject: [PATCH] Code cleanup and documentation.

---
 bin/DMGTRIS.GBC        | Bin 65536 -> 65536 bytes
 src/banking.asm        |   2 +-
 src/dmgfx.asm          |   1 +
 src/field.asm          | 228 +++++++++++++++++++++++------------------
 src/gbc.asm            |  75 +++++++-------
 src/input.asm          |   4 +
 src/interrupts.asm     |   5 +-
 src/level.asm          |  30 ++----
 src/main.asm           |  14 +--
 src/memory.asm         |   9 +-
 src/rng.asm            |  34 +++---
 src/score.asm          |   5 +-
 src/sfx.asm            | 108 ++++++++-----------
 src/sprites.asm        |  35 +++----
 src/sram.asm           |   5 +-
 src/state_gameplay.asm |   5 +
 src/state_title.asm    |  20 +++-
 src/time.asm           |  41 ++++++++
 18 files changed, 340 insertions(+), 281 deletions(-)

diff --git a/bin/DMGTRIS.GBC b/bin/DMGTRIS.GBC
index 35ad7830f31dd3df5a59c016d7b3a7086d67766b..5c5d58d4113f70b0e303b83f1f13873f8e062d89 100644
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diff --git a/src/banking.asm b/src/banking.asm
index a0ee652..1a621f2 100644
--- a/src/banking.asm
+++ b/src/banking.asm
@@ -25,7 +25,7 @@ INCLUDE "globals.asm"
 SECTION "High Banking Variables", HRAM
 hBankBackup: ds 1
 
-; 0x00, 0x08, 0x10, 0x18, 0x20, 0x28, 0x30, and 0x38
+
 SECTION "Switch Bank", ROM0[$08]
     ; Saves the current bank and switches to the bank in b.
 RSTSwitchBank::
diff --git a/src/dmgfx.asm b/src/dmgfx.asm
index d1665c6..48bb236 100644
--- a/src/dmgfx.asm
+++ b/src/dmgfx.asm
@@ -23,6 +23,7 @@ INCLUDE "globals.asm"
 
 
 SECTION "DMG Intro Effect", ROM0
+    ; Does a small effect on boot with the nintendo logo.
 DoDMGEffect::
     ld a, [wInitialA]
     cp a, $11
diff --git a/src/field.asm b/src/field.asm
index 2edd26a..4e17cc6 100644
--- a/src/field.asm
+++ b/src/field.asm
@@ -62,6 +62,10 @@ hShouldLockIfGrounded: ds 1
 
 
 SECTION "Field Functions", ROM0
+    ; Initializes the field completely blank.
+    ; Initializes the combo counter to 1.
+    ; Initializes the bravo counter to 0.
+    ; Initializes the shadow field.
 FieldInit::
     xor a, a
     ldh [hBravo], a
@@ -69,14 +73,14 @@ FieldInit::
     ldh [hComboCt], a
     ld hl, wField
     ld bc, 10*24
-    ld d, 1
+    ld d, TILE_BLANK
     call UnsafeMemSet
     ld hl, wShadowField
     ld bc, 14*26
     ld d, $FF
     jp UnsafeMemSet
 
-
+    ; Fills the field with the empty tile.
 FieldClear::
     ld hl, wField
     ld bc, 10*24
@@ -84,13 +88,16 @@ FieldClear::
     jp UnsafeMemSet
 
 
+    ; Backs up the field.
+    ; This backup field is used for pausing the game.
 ToBackupField::
-    ld hl, wBackupField
     ld de, wField
+    ld hl, wBackupField
     ld bc, 10*24
     jp UnsafeMemCopy
 
 
+    ; Restores the backup of the field for ending pause mode.
 FromBackupField::
     ld hl, wField
     ld de, wBackupField
@@ -98,6 +105,8 @@ FromBackupField::
     jp UnsafeMemCopy
 
 
+    ; Copies the field to the shadow field.
+    ; This shadow field is used to calculate whether or not the piece can fit.
 ToShadowField::
     ld hl, wField
     ld de, wShadowField+2
@@ -119,6 +128,7 @@ ToShadowField::
     ret
 
 
+    ; Restores the shadow field to the main field.
 FromShadowField:
     ld hl, wField
     ld de, wShadowField+2
@@ -140,9 +150,10 @@ FromShadowField:
     ret
 
 
-    ; This routine will copy wField onto the screen.
+    ; Blits the field onto the tile map.
+    ; On the GBC, this chain calls into a special version that takes
+    ; advantage of the GBC's CPU.
 BlitField::
-    ; Hold on, are we on a gbc?
     ld a, [wInitialA]
     cp a, $11
     jp z, GBCBlitField
@@ -190,39 +201,39 @@ BlitField::
         add hl, bc
     ENDR
 
-    ; This has to finish just before the first LCDC interrupt of the frame or stuff will break in weird ways.
+    ; This function is actually called as the vblank handler for the gameplay state.
+    ; This is why it jumps straight back to the event loop.
     jp EventLoop
 
 
+    ; The current piece ID is used to get the offset into the rotation states
+    ; corresponding to that piece's zero rotation.
 SetPieceData:
     ldh a, [hCurrentPiece]
+    sla a
+    sla a
+    sla a
+    sla a
+    ld c, a
+    ld b, 0
+
     ld hl, sPieceRotationStates
-    ld de, 16
-:   cp a, 0
-    jr z, :+
-    add hl, de
-    dec a
-    jr :-
-:   ld a, l
+    add hl, bc
+    ld a, l
     ldh [hPieceDataBase], a
     ld a, h
     ldh [hPieceDataBase+1], a
 
-    ldh a, [hCurrentPiece]
     ld hl, sPieceFastRotationStates
-    ld de, 16
-:   cp a, 0
-    jr z, :+
-    add hl, de
-    dec a
-    jr :-
-:   ld a, l
+    add hl, bc
+    ld a, l
     ldh [hPieceDataBaseFast], a
     ld a, h
     ldh [hPieceDataBaseFast+1], a
     ret
 
 
+    ; The rotation state is a further offset of 4 bytes.
 SetPieceDataOffset:
     ldh a, [hCurrentPieceRotationState]
     sla a
@@ -248,7 +259,6 @@ XYToSFieldPtr:
     ret
 
 
-
     ; Converts piece Y in B and a piece X in A to a pointer to the field in HL.
 XYToFieldPtr:
     ld hl, wField-2
@@ -266,6 +276,9 @@ XYToFieldPtr:
     ret
 
 
+    ; This function makes HL point to the correct offset into the rotation data.
+    ; This version of the data is used for thorough checking (T, J, and L have
+    ; a middle column exception.)
 GetPieceData:
     ldh a, [hPieceDataBase]
     ld l, a
@@ -273,12 +286,13 @@ GetPieceData:
     ld h, a
     ldh a, [hPieceDataOffset]
     ld c, a
-    xor a, a
-    ld b, a
+    ld b, 0
     add hl, bc
     ret
 
 
+    ; Same as the above but for the fast data. This data is used when the exact
+    ; cell that failed isn't important.
 GetPieceDataFast:
     ldh a, [hPieceDataBaseFast]
     ld l, a
@@ -291,61 +305,12 @@ GetPieceDataFast:
     add hl, bc
     ret
 
-    ; Checks if the piece can fit at the current position, but fast.
-    ; HL should point to the piece's rotation state data.
-    ; DE should be pointing to the right place in the SHADOW field.
-CanPieceFitFast:
-    ld a, [hl+]
-    add a, e
-    ld e, a
-    adc a, d
-    sub e
-    ld d, a
-    ld a, [de]
-    cp a, TILE_FIELD_EMPTY
-    jr z, :+
-    xor a, a
-    ret
-:   ld a, [hl+]
-    add a, e
-    ld e, a
-    adc a, d
-    sub e
-    ld d, a
-    ld a, [de]
-    cp a, TILE_FIELD_EMPTY
-    jr z, :+
-    xor a, a
-    ret
-:   ld a, [hl+]
-    add a, e
-    ld e, a
-    adc a, d
-    sub e
-    ld d, a
-    ld a, [de]
-    cp a, TILE_FIELD_EMPTY
-    jr z, :+
-    xor a, a
-    ret
-:   ld a, [hl+]
-    add a, e
-    ld e, a
-    adc a, d
-    sub e
-    ld d, a
-    ld a, [de]
-    cp a, TILE_FIELD_EMPTY
-    jr z, :+
-    xor a, a
-    ret
-:   ld a, $FF
-    ret
-
 
     ; Checks if the piece can fit at the current position.
     ; HL should point to the piece's rotation state data.
     ; DE should be pointing to the right place in the SHADOW field.
+    ; This will return with $FF in A if the piece fits, or with the
+    ; exact cell that caused the first failure in A.
 CanPieceFit:
     xor a, a
     ld b, a
@@ -503,6 +468,63 @@ CanPieceFit:
     ret
 
 
+    ; Checks if the piece can fit at the current position, but fast.
+    ; HL should point to the piece's fast rotation state data.
+    ; DE should be pointing to the right place in the SHADOW field.
+    ; This will return with $FF in A if the piece fits, or with a non-$FF
+    ; value if it doesn't.
+CanPieceFitFast:
+    ld a, [hl+]
+    add a, e
+    ld e, a
+    adc a, d
+    sub e
+    ld d, a
+    ld a, [de]
+    cp a, TILE_FIELD_EMPTY
+    jr z, :+
+    xor a, a
+    ret
+:   ld a, [hl+]
+    add a, e
+    ld e, a
+    adc a, d
+    sub e
+    ld d, a
+    ld a, [de]
+    cp a, TILE_FIELD_EMPTY
+    jr z, :+
+    xor a, a
+    ret
+:   ld a, [hl+]
+    add a, e
+    ld e, a
+    adc a, d
+    sub e
+    ld d, a
+    ld a, [de]
+    cp a, TILE_FIELD_EMPTY
+    jr z, :+
+    xor a, a
+    ret
+:   ld a, [hl+]
+    add a, e
+    ld e, a
+    adc a, d
+    sub e
+    ld d, a
+    ld a, [de]
+    cp a, TILE_FIELD_EMPTY
+    jr z, :+
+    xor a, a
+    ret
+:   ld a, $FF
+    ret
+
+
+    ; This function will draw the piece even if it can't fit.
+    ; We use this to draw a final failed spawn before going game
+    ; over.
 ForceSpawnPiece::
     call SetPieceData
     call SetPieceDataOffset
@@ -513,8 +535,7 @@ ForceSpawnPiece::
     ld d, h
     ld e, l
     call GetPieceData
-    ld a, GAME_OVER_OTHER
-    ld b, a
+    ld b, GAME_OVER_OTHER
     push hl
     push de
     pop hl
@@ -522,6 +543,8 @@ ForceSpawnPiece::
     jp DrawPiece
 
 
+    ; Initialize the state for a new piece and attempts to spawn it.
+    ; On return, A will be $FF if the piece fit.
 TrySpawnPiece::
     ; Always reset these for a new piece.
     xor a, a
@@ -708,6 +731,8 @@ FindMaxG:
     ret
 
 
+    ; This is the main function that will process input, gravity, and locking.
+    ; It should be ran once per frame as long as lock delay is greater than 0.
 FieldProcess::
     ; **************************************************************
     ; SETUP
@@ -836,7 +861,7 @@ FieldProcess::
     cp a, PIECE_Z
     jr z, .trykickright
 
-    ; I piece only kicks in TGM3/TGW3/EASY/EAWY
+    ; I piece only kicks in ARS2
     cp a, PIECE_I
     jr nz, :+
     ld a, [wRotModeState]
@@ -932,7 +957,7 @@ FieldProcess::
     ldh [hLockDelayForce], a
     jp .norot
 
-    ; In TGM3, TGW3, EASY, and EAWY modes, there are a few other kicks possible.
+    ; In ARS2 mode, there are a few other kicks possible.
 .maybetgm3rot
     ld a, [wRotModeState]
     cp a, ROT_MODE_ARSTI
@@ -1228,6 +1253,7 @@ FieldProcess::
     ld a, $FF
     ldh [hAwardDownBonus], a
     ld a, 20
+    ldh [hWantedG], a
     ld b, a
     ldh a, [hActualG]
     cp a, b
@@ -1260,7 +1286,7 @@ FieldProcess::
 
     ; Gravity?
 :   ldh a, [hCurrentFractionalGravity]
-    cp a, $00
+    cp a, $00 ; 0 is the sentinel value that should be interpreted as "every frame"
     jr z, :+
     ld b, a
     ldh a, [hGravityCtr]
@@ -1443,7 +1469,7 @@ FieldProcess::
     ldh a, [hWantedG]
     cp a, 1
     jr nz, .postghost
-    ld a, [wInitialA]
+    ld a, [wInitialA] ; Let's not do the flickering on the GBC.
     cp a, $11
     jr z, .ghost
     ldh a, [hEvenFrame]
@@ -1481,20 +1507,22 @@ FieldProcess::
     cp a, b
     jr z, .drawpiece
 
-    ; If we're not grounded, draw the piece normally.
-    ldh a, [hGrounded]
-    cp a, $FF
-    jr nz, .drawpiece
-
     ; If the lock delay is 0, draw the piece in the final color.
-    ldh a, [hCurrentPiece]
-    ld b, TILE_PIECE_0+7
-    add a, b
+    ldh a, [hWantedTile]
+    add a, 7
     ldh [hWantedTile], a
     ldh a, [hCurrentLockDelayRemaining]
     cp a, 0
     jr z, .drawpiece
 
+    ; If we're not grounded, draw the piece normally.
+    ldh a, [hWantedTile]
+    sub a, 7
+    ldh [hWantedTile], a
+    ldh a, [hGrounded]
+    cp a, $FF
+    jr nz, .drawpiece
+
     ; Otherwise, look it up.
     call GetTileShade
 
@@ -1515,7 +1543,7 @@ FieldProcess::
     call DrawPiece
     ret
 
-
+    ; Performs a lookup to see how "locked" the piece is.
 GetTileShade:
     ldh a, [hCurrentLockDelay]
     cp a, 30
@@ -1623,6 +1651,8 @@ GetTileShade:
     ret
 
 
+    ; This is called every frame after a piece has been locked until the delay state ends.
+    ; Lines are cleared, levels and score are awarded, and ARE time is waited out.
 FieldDelay::
     ; Switch on the delay state.
     ld a, [wDelayState]
@@ -1661,7 +1691,7 @@ FieldDelay::
     and a, d
     cp a, $FF
     jr z, .skip
-    ld a, DELAY_STATE_LINE_PRE_CLEAR ; If there were line clears, do a line clear delay, then an ARE delay.
+    ld a, DELAY_STATE_LINE_PRE_CLEAR ; If there were line clears, do a line clear delay, then a LINE_ARE delay.
     ld [wDelayState], a
     ldh a, [hCurrentLineClearDelay]
     ldh [hRemainingDelay], a
@@ -1804,7 +1834,7 @@ FieldDelay::
 
 
     ; Line clear delay.
-    ; Count down the delay. If we're out of delay, clear the lines and go to ARE.
+    ; Count down the delay. If we're out of delay, clear the lines and go to LINE_ARE.
 .lineclear
     ldh a, [hRemainingDelay]
     dec a
@@ -1858,12 +1888,12 @@ FieldDelay::
     ldh [hCurrentPiece], a
     call GetNextPiece
 
-
     ; Kill the sound for the next piece.
-    call SFXKill
-    ret
+    jp SFXKill
 
 
+    ; Shifts B into the line clear list.
+    ; Also increments the line clear count.
 AppendClearedLine:
     ldh a, [hLineClearCt]
     inc a
@@ -1879,6 +1909,8 @@ AppendClearedLine:
     ret
 
 
+    ; Scans the field for lines that are completely filled with non-empty spaces.
+    ; Every time one is found, it is added to a list.
 FindClearedLines:
     xor a, a
     ldh [hLineClearCt], a
@@ -1914,7 +1946,7 @@ FindClearedLines:
 
     ret
 
-
+    ; Goes through the list of cleared lines and marks those lines with the "line clear" tile.
 MarkClear:
     ldh a, [hClearedLines]
     cp a, $FF
@@ -1966,10 +1998,10 @@ MarkClear:
     jr nz, :-
     ld bc, 10
     ld d, TILE_CLEARING
-    call UnsafeMemSet
-    ret
+    jp UnsafeMemSet
 
 
+    ; Once again, scans the field for cleared lines, but this time removes them.
 ClearLines:
     ld de, 0
 
diff --git a/src/gbc.asm b/src/gbc.asm
index ae71675..4e5f960 100644
--- a/src/gbc.asm
+++ b/src/gbc.asm
@@ -38,9 +38,11 @@ DEF R3 EQU %0000000000011111
 SECTION "GBC Shadow Tilemap", WRAM0, ALIGN[8]
 wShadowTilemap:: ds 32*32
 
+
 SECTION "GBC Shadow Tile Attributes", WRAM0, ALIGN[8]
 wShadowTileAttrs:: ds 32*32
 
+
 SECTION "GBC Variables", WRAM0
 wOuterReps:: ds 1
 wInnerReps:: ds 1
@@ -48,6 +50,7 @@ wTitlePal:: ds 1
 
 
 SECTION "GBC Functions", ROM0
+    ; Copies the shadow tile attribute map to vram using instant HDMA.
 ToATTR::
     ld a, [wInitialA]
     cp a, $11
@@ -71,38 +74,7 @@ ToATTR::
     ret
 
 
-ToVRAM::
-    ; Bank 1
-    ld a, 1
-    ldh [rVBK], a
-    ld a, HIGH(wShadowTileAttrs)
-    ldh [rHDMA1], a
-    ld a, LOW(wShadowTileAttrs)
-    ldh [rHDMA2], a
-    ld a, HIGH($9800)
-    ldh [rHDMA3], a
-    ld a, LOW($9800)
-    ldh [rHDMA4], a
-    ld a, 40
-    ldh [rHDMA5], a
-
-
-    ; Bank 0
-    ld a, 0
-    ldh [rVBK], a
-    ld a, HIGH(wShadowTilemap)
-    ldh [rHDMA1], a
-    ld a, LOW(wShadowTilemap)
-    ldh [rHDMA2], a
-    ld a, HIGH($9800)
-    ldh [rHDMA3], a
-    ld a, LOW($9800)
-    ldh [rHDMA4], a
-    ld a, 39 | $80
-    ldh [rHDMA5], a
-    jp EventLoop
-
-
+    ; Sets up GBC registers for the title state.
 GBCTitleInit::
     ld a, [wInitialA]
     cp a, $11
@@ -384,7 +356,7 @@ GBCTitleInit::
     ld [wTitlePal], a
     ret
 
-
+    ; Sets the GBC registers for the gameplay state.
 GBCGameplayInit::
     ld a, [wInitialA]
     cp a, $11
@@ -678,6 +650,7 @@ GBCGameplayInit::
     ret
 
 
+    ; Additional GBC effects for the title screen process state.
 GBCTitleProcess::
     ld a, [wInitialA]
     cp a, $11
@@ -725,10 +698,10 @@ GBCTitleProcess::
     ld a, 3
     ld d, a
     ld bc, 32
-    call UnsafeMemSet
-    ret
+    jp UnsafeMemSet
 
 
+    ; Additional GBC effects for the gameplay process state.
 GBCGameplayProcess::
     ld a, [wInitialA]
     cp a, $11
@@ -946,8 +919,38 @@ GBCGameplayProcess::
     ret
 
 
+    ; Copies the shadow tile maps to VRAM using HDMA. The attributes are copied using instant mode
+    ; The tile data is done using hblank mode.
 GBCBlitField::
-    jp ToVRAM
+ToVRAM::
+    ; Bank 1
+    ld a, 1
+    ldh [rVBK], a
+    ld a, HIGH(wShadowTileAttrs)
+    ldh [rHDMA1], a
+    ld a, LOW(wShadowTileAttrs)
+    ldh [rHDMA2], a
+    ld a, HIGH($9800)
+    ldh [rHDMA3], a
+    ld a, LOW($9800)
+    ldh [rHDMA4], a
+    ld a, 40
+    ldh [rHDMA5], a
+
+    ; Bank 0
+    ld a, 0
+    ldh [rVBK], a
+    ld a, HIGH(wShadowTilemap)
+    ldh [rHDMA1], a
+    ld a, LOW(wShadowTilemap)
+    ldh [rHDMA2], a
+    ld a, HIGH($9800)
+    ldh [rHDMA3], a
+    ld a, LOW($9800)
+    ldh [rHDMA4], a
+    ld a, 39 | $80
+    ldh [rHDMA5], a
+    jp EventLoop
 
 
 ENDC
diff --git a/src/input.asm b/src/input.asm
index c8bb681..3199b9a 100644
--- a/src/input.asm
+++ b/src/input.asm
@@ -35,6 +35,7 @@ hSelectState::     ds 1
 
 
 SECTION "Input Functions", ROM0
+    ; Zeroes out all button states.
 InputInit::
     xor a, a
     ldh [hUpState], a
@@ -48,6 +49,9 @@ InputInit::
     ret
 
 
+    ; Gets the current state of all buttons.
+    ; Held buttons are incremented. Buttons that aren't held are reset to 0.
+    ; Left/Right cause Up/Down to be reset as well.
 GetInput::
     ; Get the button state.
 .btns
diff --git a/src/interrupts.asm b/src/interrupts.asm
index d9c18bb..f5de576 100644
--- a/src/interrupts.asm
+++ b/src/interrupts.asm
@@ -27,12 +27,13 @@ hLCDCCtr:: ds 1
 
 
 SECTION "Interrupt Initialization Functions", ROM0
+    ; Zeroes out the interrupt counter.
 IntrInit::
     xor a, a
     ldh [hLCDCCtr], a
     ret
 
-
+    ; Sets up the STAT interrupt.
 InitializeLCDCInterrupt::
     ld a, STATF_LYC
     ldh [rSTAT], a
@@ -49,6 +50,8 @@ InitializeLCDCInterrupt::
 
 
 SECTION "LCDC Interrupt", ROM0[INT_HANDLER_STAT]
+    ; This interrupt handler will be called every 7 scanlines, scrolling up the tile map by 1 line. This has the
+    ; effect of making the tiles appear as 8x7 pixels, and making 20 rows fit on the screen.
 LCDCInterrupt:
     push af
     push hl
diff --git a/src/level.asm b/src/level.asm
index 250fd43..b3d03c1 100644
--- a/src/level.asm
+++ b/src/level.asm
@@ -41,22 +41,11 @@ hPrevHundreds:: ds 1
 
 
 SECTION "Level Functions", ROM0
+    ; Loads the initial state of the speed curve.
 LevelInit::
     xor a, a
-    ldh [hLevel], a
-    ldh [hLevel+1], a
-    ldh [hCLevel], a
-    ldh [hCLevel+1], a
-    ldh [hCLevel+2], a
-    ldh [hCLevel+3], a
-    ldh [hNLevel], a
-    ldh [hNLevel+2], a ; Note +1 is inited later.
-    ldh [hNLevel+3], a
     ldh [hRequiresLineClear], a
 
-    ld a, 1
-    ldh [hNLevel+1], a
-
     ldh a, [hStartSpeed]
     ld l, a
     ldh a, [hStartSpeed+1]
@@ -109,8 +98,8 @@ LevelInit::
     and a, $0F
     ldh [hNLevel], a
 
-    call DoSpeedUp
-    ret
+    jp DoSpeedUp
+
 
     ; Increment level and speed up if necessary. Level increment in E.
     ; Levels may only increment by single digits.
@@ -199,8 +188,7 @@ LevelUp::
     ldh [hLevel+1], a
     call DoSpeedUp
     ld a, SFX_RANKUP
-    call SFXEnqueue
-    ret
+    jp SFXEnqueue
 
 .checknlevel
     ; Make wNLevel make sense.
@@ -306,16 +294,14 @@ LevelUp::
 
 :   ldh a, [hNextSpeedUp+1]
     and a, $0F
-    jr z, :+
+    jr z, DoSpeedUp
     ld hl, hCLevel+3
     cp a, [hl]
-    jr z, :+
-    ret nc
-
-:   call DoSpeedUp
-    ret
+    jr z, DoSpeedUp
+    ret nc  ; This can fall through to the next function here. This is intentional.
 
 
+    ; Iterates over the speed curve and loads the new constants.
 DoSpeedUp:
     ; Load curve ptr.
     ldh a, [hSpeedCurvePtr]
diff --git a/src/main.asm b/src/main.asm
index 9012594..b7000d4 100644
--- a/src/main.asm
+++ b/src/main.asm
@@ -39,10 +39,6 @@ wAlways20GState:: ds 1
 wInitialA:: ds 1
 wInitialB:: ds 1
 wInitialC:: ds 1
-wInitialD:: ds 1
-wInitialE:: ds 1
-wInitialH:: ds 1
-wInitialL:: ds 1
 
 
 SECTION "Stack", WRAM0
@@ -52,6 +48,7 @@ wStackEnd::
 
 
 SECTION "Code Entry Point", ROM0
+    ; Main entry point. Does some set up and then goes into an infinite event loop initialized on the title screen.
 Main::
     ; Load the initial registers. For reasons.
     ld [wInitialA], a
@@ -59,14 +56,6 @@ Main::
     ld [wInitialB], a
     ld a, c
     ld [wInitialC], a
-    ld a, d
-    ld [wInitialD], a
-    ld a, e
-    ld [wInitialE], a
-    ld a, h
-    ld [wInitialH], a
-    ld a, l
-    ld [wInitialL], a
 
     ; Let the DMG have some fun with the initial screen.
     call DoDMGEffect
@@ -128,6 +117,7 @@ Main::
     call SwitchToTitle
 
 
+    ; Event loop time!
 EventLoop::
     ; Play the sound effect, if any.
     call SFXPlay
diff --git a/src/memory.asm b/src/memory.asm
index c43033c..2498619 100644
--- a/src/memory.asm
+++ b/src/memory.asm
@@ -23,7 +23,7 @@ INCLUDE "globals.asm"
 
 
 SECTION "Memory Functions", ROM0
-; Copies data from de to hl, bc bytes
+    ; Copies data from de to hl, bc bytes. Doesn't check for vram access.
 UnsafeMemCopy::
     ld a, [de]
     ld [hl+], a
@@ -35,7 +35,7 @@ UnsafeMemCopy::
     ret
 
 
-; Copies data from de to hl, bc bytes
+    ; Copies data from de to hl, bc bytes. Checks for vram access.
 SafeMemCopy::
     wait_vram
     ld a, [de]
@@ -47,7 +47,8 @@ SafeMemCopy::
     jr nz, SafeMemCopy
     ret
 
-; Sets memory from hl to hl+bc to d
+
+    ; Sets memory from hl to hl+bc to d. Doesn't check for vram access.
 UnsafeMemSet::
     ld [hl], d
     inc hl
@@ -57,6 +58,8 @@ UnsafeMemSet::
     jr nz, UnsafeMemSet
     ret
 
+
+    ; Sets memory from hl to hl+bc to d. Checks for vram access.
 SafeMemSet::
     wait_vram
     ld [hl], d
diff --git a/src/rng.asm b/src/rng.asm
index e608320..c50c297 100644
--- a/src/rng.asm
+++ b/src/rng.asm
@@ -38,6 +38,7 @@ wTGM3WorstDroughtIdx: ds 1
 
 
 section "RNG Functions", ROM0
+    ; Snapshots the initial seed for a game, then initializes the history and piece queue.
 RNGInit::
     ; Do some bit fuckery on the seed using the gameboy's free-running timers.
     ldh a, [rDIV]
@@ -112,8 +113,7 @@ RNGInit::
 
     ; Generate the next 2 to fill up the queue.
     call GetNextPiece
-    call GetNextPiece
-    ret
+    jp GetNextPiece
 
 
     ; Shift the generated piece into the history and save it.
@@ -354,21 +354,27 @@ GetNextTGM3Piece:
     ld [hl], a
     ret
 
-
+    ; Gets the next piece depending on RNG mode.
 GetNextPiece::
+    ld hl, .nextpiecejumps
     ld a, [wRNGModeState]
-    cp a, RNG_MODE_HELL
-    jp z, GetNextHellPiece
-    cp a, RNG_MODE_TGM1
-    jp z, GetNextTGM1Piece
-    cp a, RNG_MODE_TGM2
-    jp z, GetNextTGM2Piece
-    cp a, RNG_MODE_TGM3
-    jp z, GetNextTGM3Piece
-    cp a, RNG_MODE_NES
-    jp z, GetNextNesPiece
+    ld b, 0
+    ld c, a
+    add a, c
+    add a, c
+    ld c, a
+    add hl, bc
+    jp hl
+
+.nextpiecejumps
+    jp GetNextTGM1Piece
+    jp GetNextTGM2Piece
+    jp GetNextTGM3Piece
+    jp GetNextHellPiece
+    jp GetNextNesPiece
 
 
+    ; Tries generating bytes until it gets one in [0; 35)
 Next35Piece:
 :   call NextByte
     and a, $3F
@@ -377,6 +383,7 @@ Next35Piece:
     ret
 
 
+    ; Tries generating bytes until it gets one in [0; 7)
 Next7Piece:
 :   call NextByte
     and a, $07
@@ -385,6 +392,7 @@ Next7Piece:
     ret
 
 
+    ; Cyrcles the RNG returning a random byte in a.
 NextByte:
     ; Load seed
     ld hl, hRNGSeed+3
diff --git a/src/score.asm b/src/score.asm
index ad1d670..8138848 100644
--- a/src/score.asm
+++ b/src/score.asm
@@ -30,6 +30,7 @@ hScoreIncrementHead:: ds 1
 
 
 SECTION "Score Functions", ROM0
+    ; Wipes the score.
 ScoreInit::
     xor a, a
     ldh [hScore], a
@@ -49,6 +50,7 @@ ScoreInit::
     ldh [hScoreIncrementBCD+5], a
     ret
 
+
     ; Increases the current score by the amount in wScoreIncrement.
 IncreaseScore::
     ; Wipe the old BCD score.
@@ -186,8 +188,7 @@ IncreaseScore::
     xor a, a
     ldh [hScore], a
     ld a, SFX_RANKUP
-    call SFXEnqueue
-    ret
+    jp SFXEnqueue
 
 
 ENDC
diff --git a/src/sfx.asm b/src/sfx.asm
index 17d5ed4..3bc1413 100644
--- a/src/sfx.asm
+++ b/src/sfx.asm
@@ -70,8 +70,9 @@ hNoisePlayhead:: ds 2
 
 
 SECTION "SFX Functions", ROM0
-SFXInit::
     ; Audio on, volume on, and enable all channels.
+    ; Zeroes out all playheads and the queue.
+SFXInit::
     ld a, $80
     ldh [rNR52], a
     ld a, $FF
@@ -92,8 +93,8 @@ SFXInit::
     ret
 
 
-SFXPopQueue:
     ; Pop the head of the queue into A, the tail of the queue will be set to $FF.
+SFXPopQueue:
     ldh a, [hPlayQueue]
     ld b, a
     ldh a, [hPlayQueue+1]
@@ -108,8 +109,8 @@ SFXPopQueue:
     ret
 
 
-SFXPushQueue:
     ; Push A onto the tail of the queue, the head of the queue will be pushed off.
+SFXPushQueue:
     ld b, a
     ldh a, [hPlayQueue+1]
     ldh [hPlayQueue], a
@@ -122,18 +123,18 @@ SFXPushQueue:
     ret
 
 
+    ; Process the queue, if there's more to play, it will do so.
 SFXProcessQueue:
     ; Clear the playhead.
     xor a, a
     ldh [hPlayhead], a
     ldh [hPlayhead+1], a
 
+    ; Music will just repeat.
     ldh a, [hPlayQueue]
     cp a, MUSIC_MENU
     jr nz, :+
-    call SFXEnqueue
-    ret
-
+    jr SFXEnqueue
 
     ; Try 4 times to pop a sound effect off the queue.
 :   call SFXPopQueue
@@ -150,10 +151,10 @@ SFXProcessQueue:
     ret z
 
     ; If we got a valid sound effect, then play it.
-    call SFXEnqueue
-    ret
+    jr SFXEnqueue
 
 
+    ; Noise effects use their own playhead that can play at the same time as the normal queue.
 SFXTriggerNoise::
     cp a, SFX_LINE_CLEAR
     jr nz, :+
@@ -191,8 +192,7 @@ SFXEnqueue::
     or a, l
     jr z, :+
     ld a, b
-    call SFXPushQueue
-    ret
+    jr SFXPushQueue
 
     ; Menu music
 :   ld a, b
@@ -203,9 +203,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sMusicMenu)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
-
+    jp SFXPlay
 
     ; Piece jingles.
 :   ld a, b
@@ -215,8 +213,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceI)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_I | SFX_IRS
@@ -225,8 +222,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceIRSI)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_S
@@ -235,8 +231,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceS)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_S | SFX_IRS
@@ -245,8 +240,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceIRSS)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_Z
@@ -255,8 +249,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceZ)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_Z | SFX_IRS
@@ -265,8 +258,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceIRSZ)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_J
@@ -275,8 +267,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceJ)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_J | SFX_IRS
@@ -285,8 +276,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceIRSJ)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_L
@@ -295,8 +285,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceL)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_L | SFX_IRS
@@ -305,8 +294,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceIRSL)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_O
@@ -315,8 +303,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceO)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_O | SFX_IRS
@@ -325,8 +312,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceIRSO)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_T
@@ -335,8 +321,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceT)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   ld a, b
     cp a, PIECE_T | SFX_IRS
@@ -345,9 +330,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXPieceIRST)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
-
+    jp SFXPlay
 
     ; IRS
 :   cp a, SFX_IHS
@@ -356,8 +339,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXIHS)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jp SFXPlay
 
 :   cp a, SFX_IHS | SFX_IRS
     jr nz, :+
@@ -365,9 +347,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXIHSIRS)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
-
+    jp SFXPlay
 
     ; Leveling
 :   cp a, SFX_LEVELLOCK
@@ -376,8 +356,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXLevelLock)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jr SFXPlay
 
 :   cp a, SFX_LEVELUP
     jr nz, :+
@@ -385,9 +364,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXLevelUp)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
-
+    jr SFXPlay
 
     ; Other
 :   cp a, SFX_RANKUP
@@ -396,8 +373,7 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXRankUp)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
+    jr SFXPlay
 
 :   cp a, SFX_READYGO
     ret nz
@@ -405,10 +381,9 @@ SFXEnqueue::
     ldh [hPlayhead], a
     ld a, HIGH(sSFXReadyGo)
     ldh [hPlayhead+1], a
-    call SFXPlay
-    ret
-
+    jr SFXPlay
 
+    ; Kill the non-noise sound and clear the queue.
 SFXKill::
     ; Kill all sound without pops.
     ld a, %00111111
@@ -416,12 +391,10 @@ SFXKill::
     ldh [rNR21], a
     ld a, $FF
     ldh [rNR31], a
-    ;ldh [rNR41], a
     ld a, %01000000
     ldh [rNR14], a
     ldh [rNR24], a
     ldh [rNR34], a
-    ;ldh [rNR44], a
 
     ; Clear the queue.
     ld a, $FF
@@ -435,6 +408,8 @@ SFXKill::
     ret
 
 
+    ; Play routine for the noise channel.
+    ; Must be called every frame.
 SFXPlayNoise::
     ; Get the noise playhead.
     ldh a, [hNoisePlayhead]
@@ -484,11 +459,11 @@ SFXPlayNoise::
     ldh [hNoisePlayhead], a
     ld a, h
     ldh [hNoisePlayhead+1], a
-    rst RSTRestoreBank
-    ret
+    jp RSTRestoreBank
 
 
-    ; This play routine must be called every frame.
+    ; Play routine for the regular sfx channels.
+    ; Must be called every frame.
 SFXPlay::
     ; Bank to correct bank.
     ldh a, [hPlayQueue]
@@ -510,8 +485,7 @@ SFXPlay::
     ; Nothing to do if it's a null ptr.
     or a, l
     jr nz, .getRegister
-    rst RSTRestoreBank
-    ret
+    jp RSTRestoreBank
 
     ; Otherwise, get the register to write to.
 .getRegister
@@ -522,8 +496,7 @@ SFXPlay::
     cp a, $FE
     jr nz, :+
     rst RSTRestoreBank
-    call SFXProcessQueue
-    ret
+    jp SFXProcessQueue
 
     ; If it's $FF, then we're done for this frame.
 :   cp a, $FF
@@ -546,8 +519,7 @@ SFXPlay::
     ldh [hPlayhead], a
     ld a, h
     ldh [hPlayhead+1], a
-    rst RSTRestoreBank
-    ret
+    jp RSTRestoreBank
 
 
 ENDC
diff --git a/src/sprites.asm b/src/sprites.asm
index aa8c665..143988d 100644
--- a/src/sprites.asm
+++ b/src/sprites.asm
@@ -90,14 +90,15 @@ OAMDMAEnd::
 
 
 SECTION "OAM Functions", ROM0
+    ; Copies the OAM handler to HRAM.
 CopyOAMHandler::
     ld de, OAMDMA
     ld hl, hOAMDMA
     ld bc, OAMDMAEnd - OAMDMA
-    call UnsafeMemCopy
-    ret
+    jp UnsafeMemCopy
 
 
+    ; Clears OAM and shadow OAM.
 ClearOAM::
     ld hl, _OAMRAM
     ld bc, $9F
@@ -106,12 +107,12 @@ ClearOAM::
     ld hl, wShadowOAM
     ld bc, $9F
     ld d, 0
-    call SafeMemSet
-    ret
+    jp UnsafeMemSet
 
 
 
 SECTION "Domain Specific Functions", ROM0
+    ; Puts the mode tells into sprites and displays them.
 ApplyTells::
     ld a, TELLS_BASE_Y
     ld [wSPRModeRNG], a
@@ -155,7 +156,8 @@ ApplyTells::
     ret
 
 
-; Index of next piece in A.
+    ; Draws the next pieces as a sprite.
+    ; Index of next piece in A.
 ApplyNext::
     ; Correct color
     ld [wSPRNext1+3], a
@@ -219,7 +221,6 @@ ApplyNext::
     add a, NEXT_BASE_Y
     ld [wSPRNext4+0], a
 
-
     ; Queue
     ld a, QUEUE_BASE_Y
     ld [wSPRQueue1A], a
@@ -254,17 +255,10 @@ ApplyNext::
     ld [wSPRQueue2B+2], a
     ret
 
-; Index of hold piece in A.
-ApplyHold::
-    cp 255
-    jr nz, .doApplyHold
-    ld hl, wSPRHold1
-    ld bc, 16
-    ld d, 0
-    call UnsafeMemSet
-    ret
 
-.doApplyHold
+    ; Draws the held piece.
+    ; Index of held piece in A.
+ApplyHold::
     ; Correct color
     ld [wSPRHold1+3], a
     ld [wSPRHold2+3], a
@@ -282,7 +276,6 @@ ApplyHold::
     ld a, b
     jr z, .show
 
-
 .hide
     ld b, a
     ld a, TILE_BLANK
@@ -350,8 +343,9 @@ ApplyHold::
     ret
 
 
-; Address of first sprite in hl.
-; Address of first digit in de.
+    ; Generic function to draw a BCD number (6 digits) as 6 sprites.
+    ; Address of first sprite in hl.
+    ; Address of first digit in de.
 ApplyNumbers::
     inc hl
     inc hl
@@ -390,11 +384,10 @@ ApplyNumbers::
     ld a, [de]
     add a, TILE_0
     ld [hl], a
-    add hl, bc
-    inc de
     ret
 
 
+    ; Positions all number sprites for gameplay.
 SetNumberSpritePositions::
     ld a, SCORE_BASE_X
     ld hl, wSPRScore1
diff --git a/src/sram.asm b/src/sram.asm
index f481b29..5447a96 100644
--- a/src/sram.asm
+++ b/src/sram.asm
@@ -34,8 +34,9 @@ rSelectedStartLevel:: ds 2
 
 
 SECTION "SRAM Functions", ROM0
-RestoreSRAM::
     ; Check if our SRAM is initialized and of the correct version.
+    ; Restores it if so, otherwise initializes it.
+RestoreSRAM::
     ld a, [rCheck]
     cp a, LOW(__UTC_YEAR__)
     jr nz, InitializeSRAM
@@ -75,6 +76,7 @@ RestoreSRAM::
     ldh [hStartSpeed+1], a
     ret
 
+    ; Initializes SRAM with default values.
 InitializeSRAM:
     ; Set the magic id.
     ld a, LOW(__UTC_YEAR__)
@@ -125,4 +127,5 @@ InitializeSRAM:
     ld [rSelectedStartLevel+1], a
     ret
 
+
 ENDC
diff --git a/src/state_gameplay.asm b/src/state_gameplay.asm
index 72d5b62..6f72bb6 100644
--- a/src/state_gameplay.asm
+++ b/src/state_gameplay.asm
@@ -48,6 +48,7 @@ hRequestedJingle: ds 1
 
 
 SECTION "Gameplay Functions", ROM0
+    ; Change to game play mode. The event loop will call the event loop and vblank handlers for this mode after this returns.
 SwitchToGameplay::
     ; Turn the screen off if it's on.
     ldh a, [rLCDC]
@@ -113,6 +114,7 @@ SwitchToGameplay::
     ret
 
 
+    ; Main gameplay event loop.
 GamePlayEventLoopHandler::
     ; What mode are we in?
     ld hl, .modejumps
@@ -134,6 +136,7 @@ GamePlayEventLoopHandler::
     jp preGameOverMode
     jp pauseMode
 
+
     ; Draw "READY" and wait a bit.
 leadyMode:
     ldh a, [hModeCounter]
@@ -359,6 +362,7 @@ delayMode:
 
 :   jp drawStaticInfo
 
+
 preGameOverMode:
     ; Spawn the failed piece.
     call ForceSpawnPiece
@@ -578,6 +582,7 @@ drawStaticInfo:
     jp EventLoopPostHandler
 
 
+    ; Do the hold action.
 DoHold:
     ; Mark hold as spent.
     ld a, $FF
diff --git a/src/state_title.asm b/src/state_title.asm
index 7fd6bd2..4b2aa02 100644
--- a/src/state_title.asm
+++ b/src/state_title.asm
@@ -27,6 +27,7 @@ wSelected:: ds 1
 
 
 SECTION "Title Functions", ROM0
+    ; Change to title mode. The event loop will call the event loop and vblank handlers for this mode after this returns.
 SwitchToTitle::
     ; Turn the screen off if it's on.
     ldh a, [rLCDC]
@@ -136,6 +137,7 @@ SwitchToTitle::
     ret
 
 
+    ; Handles title screen input.
 TitleEventLoopHandler::
     call GBCTitleProcess
 
@@ -209,6 +211,8 @@ TitleEventLoopHandler::
 .done
     jp EventLoopPostHandler
 
+
+    ; Decrements the currently selected option.
 DecrementOption:
 .opt0
     ld a, [wSelected]
@@ -307,6 +311,8 @@ DecrementOption:
     jr DecrementLevel
     jp EventLoopPostHandler
 
+
+    ; Decrements start level.
 DecrementLevel:
     ; Decrement
     ldh a, [hStartSpeed]
@@ -324,6 +330,7 @@ DecrementLevel:
     jp CheckLevelRange
 
 
+    ; Increments the selected option.
 IncrementOption:
 .opt0
     ld a, [wSelected]
@@ -422,6 +429,8 @@ IncrementOption:
     jr IncrementLevel
     jp EventLoopPostHandler
 
+
+    ; Increments start level.
 IncrementLevel:
     ; Increment
     ldh a, [hStartSpeed]
@@ -438,11 +447,11 @@ IncrementLevel:
     ld [rSelectedStartLevel+1], a
     jp CheckLevelRange
 
+
+    ; Wipes the start level upon selecting a new speed curve.
 InitSpeedCurve:
     ld a, [wSpeedCurveState]
     call GetStart
-
-.set
     ld a, l
     ldh [hStartSpeed], a
     ld [rSelectedStartLevel], a
@@ -452,7 +461,7 @@ InitSpeedCurve:
     ret
 
 
-
+    ; Gets the end of a speed curve.
 GetEnd:
     ld a, [wSpeedCurveState]
     cp a, SCURVE_DMGT
@@ -478,6 +487,8 @@ GetEnd:
 :   ld bc, sCHILSpeedCurveEnd
     ret
 
+
+    ; Gets the beginning of a speed curve.
 GetStart:
     ld a, [wSpeedCurveState]
     cp a, SCURVE_DMGT
@@ -503,6 +514,8 @@ GetStart:
 :   ld hl, sCHILSpeedCurve
     ret
 
+
+    ; Make sure we don't overflow the level range.
 CheckLevelRange:
     ; At end?
     call GetEnd
@@ -547,6 +560,7 @@ CheckLevelRange:
     jp EventLoopPostHandler
 
 
+    ; Handles the display of the menu.
 TitleVBlankHandler::
     call ToATTR
 
diff --git a/src/time.asm b/src/time.asm
index 0286d15..cd0b4ca 100644
--- a/src/time.asm
+++ b/src/time.asm
@@ -27,22 +27,63 @@ hFrameCtr::  ds 1
 hEvenFrame:: ds 1
 
 
+SECTION "Time Variables", WRAM0
+wMinutes:: ds 1
+wSeconds:: ds 1
+wFrames:: ds 1
+
+
 SECTION "Time Functions", ROM0
+    ; Zeroes all timers and gets the free-running timer ticking.
 TimeInit::
     xor a, a
     ldh [rTMA], a
     ldh [hEvenFrame], a
     ldh [hFrameCtr], a
+    ld [wMinutes], a
+    ld [wSeconds], a
+    ld [wFrames], a
     ld a, TACF_262KHZ | TACF_START
     ldh [rTAC], a
     ret
 
+
+    ; Resets the minute-second timer.
+ResetTime::
+    xor a, a
+    ld [wMinutes], a
+    ld [wSeconds], a
+    ld [wFrames], a
+    ret
+
+
+    ; Increments the global timer. Also saves whether we're on an even frame.
 HandleTimers::
     ldh a, [hFrameCtr]
     inc a
     ldh [hFrameCtr], a
     and 1
     ldh [hEvenFrame], a
+
+    ld a, [wFrames]
+    inc a
+    ld [wFrames], a
+    cp a, 60
+    ret nz
+
+    xor a, a
+    ld [wFrames], a
+    ld a, [wSeconds]
+    inc a
+    ld [wSeconds], a
+    cp a, 60
+    ret nz
+
+    xor a, a
+    ld [wSeconds], a
+    ld a, [wMinutes]
+    inc a
+    ld [wMinutes], a
     ret