Identify remaining Mystery Gift labels and constants

Source: https://projectpokemon.org/home/forums/topic/43930-mystery-gift-reverse-engineering-of-ir-protocol/

12 files changed, 594 insertions, 451 deletions

diff --git a/constants/hardware_constants.asm b/constants/hardware_constants.asm
index 970acd2f..f9014380 100644
--- a/constants/hardware_constants.asm
+++ b/constants/hardware_constants.asm
@@ -71,10 +71,10 @@ rTIMA       EQU $ff05 ; Timer counter (R/W)
 rTMA        EQU $ff06 ; Timer Modulo (R/W)
 rTAC        EQU $ff07 ; Timer Control (R/W)
 rTAC_ON        EQU 2
-rTAC_4096_HZ   EQU 0
-rTAC_262144_HZ EQU 1
-rTAC_65536_HZ  EQU 2
-rTAC_16384_HZ  EQU 3
+rTAC_4096_HZ   EQU %00
+rTAC_262144_HZ EQU %01
+rTAC_65536_HZ  EQU %10
+rTAC_16384_HZ  EQU %11
 rIF         EQU $ff0f ; Interrupt Flag (R/W)
 rNR10       EQU $ff10 ; Channel 1 Sweep register (R/W)
 rNR11       EQU $ff11 ; Channel 1 Sound length/Wave pattern duty (R/W)
@@ -147,6 +147,9 @@ rHDMA3      EQU $ff53 ; CGB Mode Only - New DMA Destination, High
 rHDMA4      EQU $ff54 ; CGB Mode Only - New DMA Destination, Low
 rHDMA5      EQU $ff55 ; CGB Mode Only - New DMA Length/Mode/Start
 rRP         EQU $ff56 ; CGB Mode Only - Infrared Communications Port
+rRP_LED_ON EQU 0
+rRP_RECEIVING EQU 1
+rRP_ENABLE_READ_MASK EQU %11000000
 rBGPI       EQU $ff68 ; CGB Mode Only - Background Palette Index
 rBGPI_AUTO_INCREMENT EQU 7 ; increment rBGPI after write to rBGPD
 rBGPD       EQU $ff69 ; CGB Mode Only - Background Palette Data
diff --git a/constants/misc_constants.asm b/constants/misc_constants.asm
index ca9bc937..3847cf89 100644
--- a/constants/misc_constants.asm
+++ b/constants/misc_constants.asm
@@ -18,6 +18,8 @@ GS_VERSION EQU 0
 ELIF DEF(_SILVER)
 GS_VERSION EQU 1
 ENDC
+; Pokémon Pikachu 2, a step counter / virtual pet device (used by Mystery Gift)
+POKEMON_PIKACHU_2_VERSION EQU 3
 
 ; save file corruption check values
 SAVE_CHECK_VALUE_1 EQU 99
diff --git a/constants/serial_constants.asm b/constants/serial_constants.asm
index 81eadbf4..fd87e4a5 100644
--- a/constants/serial_constants.asm
+++ b/constants/serial_constants.asm
@@ -29,3 +29,5 @@ SERIAL_NO_DATA_BYTE               EQU $fe
 SERIAL_PATCH_LIST_PART_TERMINATOR EQU $ff
 
 SERIAL_PREAMBLE_LENGTH EQU 6
+
+MAX_MYSTERY_GIFT_PARTNERS EQU 5
diff --git a/engine/link/mystery_gift.asm b/engine/link/mystery_gift.asm
index 0d90ba9d..881845db 100644
--- a/engine/link/mystery_gift.asm
+++ b/engine/link/mystery_gift.asm
@@ -1,3 +1,27 @@
+; hMGRole values
+IR_RECEIVER EQU 1
+IR_SENDER   EQU 2
+
+; hMGStatusFlags error bits
+MG_WRONG_CHECKSUM_F EQU 0
+MG_TIMED_OUT_F      EQU 1
+MG_CANCELED_F       EQU 4
+MG_WRONG_PREFIX_F   EQU 7
+
+; hMGStatusFlags values
+MG_WRONG_CHECKSUM EQU 1 << MG_WRONG_CHECKSUM_F
+MG_TIMED_OUT      EQU 1 << MG_TIMED_OUT_F
+MG_CANCELED       EQU 1 << MG_CANCELED_F
+MG_WRONG_PREFIX   EQU 1 << MG_WRONG_PREFIX_F
+MG_NOT_OKAY       EQU MG_WRONG_CHECKSUM | MG_TIMED_OUT | MG_CANCELED | MG_WRONG_PREFIX
+MG_OKAY           EQU $ff ^ MG_NOT_OKAY
+MG_START_END      EQU %11111111
+
+REGION_PREFIX EQU $96
+REGION_CODE   EQU $90 ; USA
+
+MESSAGE_PREFIX EQU $5a
+
 DoMysteryGift:
 	call ClearTilemap
 	call ClearSprites
@@ -7,22 +31,24 @@ DoMysteryGift:
 	ld de, .String_PressAToLink_BToCancel
 	call PlaceString
 	call WaitBGMap
-	farcall PrepMysteryGiftDataToSend
-	call MysteryGift_ClearTrainerData
-	ld a, $2
-	ld [wc901], a
-	ld a, $14
-	ld [wc902], a
-	ldh a, [rIE]
-	push af
 
-	call Function29fc9
+	; Prepare the first of two messages for wMysteryGiftPartnerData
+	farcall StageDataForMysteryGift
+	call ClearMysteryGiftTrainer
+	ld a, 2
+	ld [wMysteryGiftMessageCount], a
+	ld a, wMysteryGiftPartnerDataEnd - wMysteryGiftPartnerData
+	ld [wMysteryGiftStagedDataLength], a
 
+	ldh a, [rIE]
+	push af
+	call ExchangeMysteryGiftData
 	ld d, a
 	xor a
 	ldh [rIF], a
 	pop af
 	ldh [rIE], a
+
 	push de
 	call ClearTilemap
 	call EnableLCD
@@ -31,15 +57,16 @@ DoMysteryGift:
 	call GetSGBLayout
 	call SetPalettes
 	pop de
+
 	hlcoord 2, 8
 	ld a, d
 	ld de, .MysteryGiftCanceledText ; Link has been canceled
-	cp $10
+	cp MG_CANCELED
 	jp z, .LinkCanceled
-	cp $6c
+	cp MG_OKAY
 	jp nz, .CommunicationError
-	ld a, [wc800]
-	cp 3
+	ld a, [wMysteryGiftGameVersion]
+	cp POKEMON_PIKACHU_2_VERSION
 	jr z, .skip_checks
 	call .CheckAlreadyGotFiveGiftsToday
 	ld hl, .MysteryGiftFiveADayText ; Only 5 gifts a day
@@ -54,25 +81,27 @@ DoMysteryGift:
 	ld a, [wMysteryGiftPartnerBackupItem]
 	and a
 	jr nz, .FriendNotReady
-	ld a, [wc800]
-	cp 3
+	ld a, [wMysteryGiftGameVersion]
+	cp POKEMON_PIKACHU_2_VERSION
 	jr z, .skip_append_save
 	call .AddMysteryGiftPartnerID
-	ld a, [wc800]
-	cp 4
+	ld a, [wMysteryGiftGameVersion]
+	cp 4 ; ???
 	jr z, .skip_append_save
 	call .SaveMysteryGiftTrainerName
 .skip_append_save
 	ld a, [wMysteryGiftPartnerSentDeco]
 	and a
-	jr z, .item
+	jr z, .SentItem
+; sent decoration
 	ld a, [wMysteryGiftPartnerWhichDeco]
 	ld c, a
 	farcall MysteryGiftGetDecoration
 	push bc
-	call MysteryGift_CheckAndSetDecorationAlreadyReceived
+	call CheckAndSetMysteryGiftDecorationAlreadyReceived
 	pop bc
-	jr nz, .item
+	jr nz, .SentItem
+; keep the decoration if it wasn't already received
 	callfar GetDecorationName_c
 	ld h, d
 	ld l, e
@@ -82,17 +111,17 @@ DoMysteryGift:
 	ld hl, .MysteryGiftSentHomeText ; sent decoration to home
 	jr .PrintTextAndExit
 
-.item
+.SentItem:
 	call GetMysteryGiftBank
 	ld a, [wMysteryGiftPartnerWhichItem]
 	ld c, a
-	farcall MysteryGiftGetItemHeldEffect
+	farcall MysteryGiftGetItem
 	ld a, c
 	ld [sBackupMysteryGiftItem], a
 	ld [wNamedObjectIndexBuffer], a
 	call CloseSRAM
 	call GetItemName
-	ld hl, .MysteryGiftSentText ; sent item
+	ld hl, .MysteryGiftSentText ; sent item/decoration
 	jr .PrintTextAndExit
 
 .LinkCanceled:
@@ -110,6 +139,7 @@ DoMysteryGift:
 
 .FriendNotReady:
 	ld hl, .YourFriendIsNotReadyText ; friend not ready
+	; fallthrough
 
 .PrintTextAndExit:
 	call PrintText
@@ -159,7 +189,7 @@ DoMysteryGift:
 .CheckAlreadyGotFiveGiftsToday:
 	call GetMysteryGiftBank
 	ld a, [sNumDailyMysteryGiftPartnerIDs]
-	cp $5
+	cp MAX_MYSTERY_GIFT_PARTNERS
 	jp CloseSRAM
 
 .CheckAlreadyGotAGiftFromThatPerson:
@@ -195,9 +225,9 @@ DoMysteryGift:
 	ld hl, sNumDailyMysteryGiftPartnerIDs
 	ld a, [hl]
 	inc [hl]
-	ld hl, sDailyMysteryGiftPartnerIDs ; inc hl
+	ld hl, sDailyMysteryGiftPartnerIDs ; could have done "inc hl" instead
 	ld e, a
-	ld d, $0
+	ld d, 0
 	add hl, de
 	add hl, de
 	ld a, [wMysteryGiftPartnerID]
@@ -208,223 +238,264 @@ DoMysteryGift:
 
 .SaveMysteryGiftTrainerName:
 	call GetMysteryGiftBank
-	ld a, $1
+	ld a, TRUE
 	ld [sMysteryGiftTrainerHouseFlag], a
 	ld hl, wMysteryGiftPartnerName
 	ld de, sMysteryGiftPartnerName
 	ld bc, NAME_LENGTH
 	call CopyBytes
-	ld a, $1
+	assert sMysteryGiftPartnerName + NAME_LENGTH == sMysteryGiftUnusedFlag
+	ld a, TRUE
 	ld [de], a
 	inc de
-	ld hl, wMysteryGiftTrainerData
-	ld bc, (1 + 1 + NUM_MOVES) * PARTY_LENGTH + 2
+	assert sMysteryGiftUnusedFlag + 1 == sMysteryGiftTrainer
+	ld hl, wMysteryGiftTrainer
+	ld bc, wMysteryGiftTrainerEnd - wMysteryGiftTrainer
 	call CopyBytes
 	jp CloseSRAM
 
-Function29fc9:
+ExchangeMysteryGiftData:
 	farcall ClearChannels
-	call Function2a18c
+	call InitializeMysteryGiftInterrupts
 
-.loop2
-	call Function2a1c4
-	call Function2a20b
+.restart
+	call BeginIRCommunication
+	call InitializeIRCommunicationRoles
 	ldh a, [hMGStatusFlags]
-	cp $10
-	jp z, Function2a103
-	cp $6c
-	jr nz, .loop2
-
-	ldh a, [hPrintNumBuffer + 8]
-	cp $2
-	jr z, Function2a055
-	ld hl, hPrintNumBuffer
-	ld b, $1
-	call Function2a184
-	jr nz, .ly_loop
-	call Function2a07c
-	jp nz, Function2a103
-	jr Function2a03d
+	cp MG_CANCELED
+	jp z, EndOrContinueIRCommunication
+	cp MG_OKAY
+	jr nz, .restart
+
+	ldh a, [hMGRole]
+	cp IR_SENDER
+	jr z, SenderExchangeMysteryGiftDataPayloads
+; receiver
+	ld hl, hMGExchangedByte
+	ld b, 1
+	call TryReceivingIRDataBlock
+	jr nz, .failed
+	call ReceiveIRDataPayload_GotRegionPrefix
+	jp nz, EndOrContinueIRCommunication
+	jr ReceiverExchangeMysteryGiftDataPayloads_GotPayload
+
+.failed
 	; Delay frame
-.ly_loop
+.wait_frame
 	ldh a, [rLY]
 	cp LY_VBLANK
-	jr c, .ly_loop
+	jr c, .wait_frame
+
 	ld c, LOW(rRP)
-	ld a, $c0
+	ld a, rRP_ENABLE_READ_MASK
 	ldh [c], a
-	ld b, 240 ; This might have been intended as a 4-second timeout buffer.
-	          ; However, it is reset with each frame.
-.loop3
-	push bc
-	call MysteryGift_ReadJoypad
 
-	ld b, $2
+	ld b, 60 * 4 ; 4 seconds
+.continue
+	push bc
+	call MysteryGift_UpdateJoypad
+	ld b, 1 << rRP_RECEIVING
 	ld c, LOW(rRP)
-	; Delay frame
-.ly_loop2
+.in_vblank
 	ldh a, [c]
 	and b
 	ld b, a
 	ldh a, [rLY]
 	cp LY_VBLANK
-	jr nc, .ly_loop2
-.ly_loop3
+	jr nc, .in_vblank
+.wait_vblank
 	ldh a, [c]
 	and b
 	ld b, a
 	ldh a, [rLY]
 	cp LY_VBLANK
-	jr c, .ly_loop3
-
+	jr c, .wait_vblank
 	ld a, b
 	pop bc
+	; Restart if the 4-second timeout has elapsed
 	dec b
-	jr z, .loop2 ; we never jump here
+	jr z, .restart
+	; Restart if rRP is not receiving data
 	or a
-	jr nz, .loop2
-	; Check if we've pressed the B button
+	jr nz, .restart
+	; Check if we've pressed the B button to cancel
 	ldh a, [hMGJoypadReleased]
 	bit B_BUTTON_F, a
-	jr z, .loop3
-	ld a, $10
+	jr z, .continue
+	ld a, MG_CANCELED
 	ldh [hMGStatusFlags], a
-	jp Function2a103
-
-Function2a037:
-	call Function2a073
-	jp nz, Function2a103
-; fallthrough
-Function2a03d:
-	call Function2a166
-	jp nz, Function2a103
-	call Function2a0bb
-	jp nz, Function2a103
-	call Function2a171
-	jp nz, Function2a103
-	call Function2a461
-	jp Function2a103
-
-Function2a055:
-	call Function2a0bb
-	jp nz, Function2a103
-	call Function2a171
-	jp nz, Function2a103
-	call Function2a073
-	jp nz, Function2a103
-	call Function2a166
-	jp nz, Function2a103
-	call Function2a45c
-	jp Function2a103
-
-Function2a073:
-	ld hl, hPrintNumBuffer
-	ld b, $1
-	call Function2a184
+	jp EndOrContinueIRCommunication
+
+ReceiverExchangeMysteryGiftDataPayloads:
+	; Receive the data payload
+	call ReceiveIRDataPayload
+	jp nz, EndOrContinueIRCommunication
+	; fallthrough
+ReceiverExchangeMysteryGiftDataPayloads_GotPayload:
+	; Switch roles
+	call BeginSendingIRCommunication
+	jp nz, EndOrContinueIRCommunication
+	; Send the data payload
+	call SendIRDataPayload
+	jp nz, EndOrContinueIRCommunication
+	; Switch roles
+	call BeginReceivingIRCommunication
+	jp nz, EndOrContinueIRCommunication
+	; Receive an empty block
+	call ReceiveEmptyIRDataBlock
+	jp EndOrContinueIRCommunication
+
+SenderExchangeMysteryGiftDataPayloads:
+	; Send the data payload
+	call SendIRDataPayload
+	jp nz, EndOrContinueIRCommunication
+	; Switch roles
+	call BeginReceivingIRCommunication
+	jp nz, EndOrContinueIRCommunication
+	; Receive the data payload
+	call ReceiveIRDataPayload
+	jp nz, EndOrContinueIRCommunication
+	; Switch roles
+	call BeginSendingIRCommunication
+	jp nz, EndOrContinueIRCommunication
+	; Send an empty block
+	call SendEmptyIRDataBlock
+	jp EndOrContinueIRCommunication
+
+ReceiveIRDataPayload:
+	; Receive the region prefix
+	ld hl, hMGExchangedByte
+	ld b, 1
+	call TryReceivingIRDataBlock
 	ret nz
-; fallthrough
-Function2a07c:
-	call Function2a461
+	; fallthrough
+ReceiveIRDataPayload_GotRegionPrefix:
+	; Receive an empty block
+	call ReceiveEmptyIRDataBlock
 	ldh a, [hMGStatusFlags]
-	cp $6c
+	cp MG_OKAY
 	ret nz
-	ldh a, [hPrintNumBuffer]
-	cp $96
-	jp nz, Function2a160
-	ld a, $90
-	ldh [hPrintNumBuffer], a
-	call Function2a166
+	; Verify the received region prefix
+	ldh a, [hMGExchangedByte]
+	cp REGION_PREFIX
+	jp nz, WrongMysteryGiftRegion
+	ld a, REGION_CODE
+	ldh [hMGExchangedByte], a
+	; Switch roles
+	call BeginSendingIRCommunication
 	ret nz
-	ld hl, hPrintNumBuffer
-	ld b, $1
-	call Function2a17c
+	; Send the region code
+	ld hl, hMGExchangedByte
+	ld b, 1
+	call TrySendingIRDataBlock
 	ret nz
-	call Function2a45c
+	; Send an empty block
+	call SendEmptyIRDataBlock
 	ldh a, [hMGStatusFlags]
-	cp $6c
+	cp MG_OKAY
 	ret nz
-	call Function2a171
+	; Switch roles
+	call BeginReceivingIRCommunication
 	ret nz
-	ld hl, wMysteryGiftTrainerData
-	ld a, [wc902]
+	; Receive the staged data
+	ld hl, wMysteryGiftTrainer
+	ld a, [wMysteryGiftStagedDataLength]
 	ld b, a
-	call Function2a184
+	call TryReceivingIRDataBlock
 	ret nz
-	call Function2a461
+	; Receive an empty block
+	call ReceiveEmptyIRDataBlock
 	ldh a, [hMGStatusFlags]
-	cp $6c
+	cp MG_OKAY
 	ret
 
-Function2a0bb:
-	ld a, $96
-	ldh [hPrintNumBuffer], a
-	ld hl, hPrintNumBuffer
-	ld b, $1
-	call Function2a17c
+SendIRDataPayload:
+	; Send the region prefix
+	ld a, REGION_PREFIX
+	ldh [hMGExchangedByte], a
+	ld hl, hMGExchangedByte
+	ld b, 1
+	call TrySendingIRDataBlock
 	ret nz
-	call Function2a45c
+	; Send an empty block
+	call SendEmptyIRDataBlock
 	ldh a, [hMGStatusFlags]
-	cp $6c
+	cp MG_OKAY
 	ret nz
-	call Function2a171
+	; Switch roles
+	call BeginReceivingIRCommunication
 	ret nz
-	ld hl, hPrintNumBuffer
-	ld b, $1
-	call Function2a184
+	; Receive the region code
+	ld hl, hMGExchangedByte
+	ld b, 1
+	call TryReceivingIRDataBlock
 	ret nz
-	call Function2a461
+	; Receive an empty block
+	call ReceiveEmptyIRDataBlock
 	ldh a, [hMGStatusFlags]
-	cp $6c
+	cp MG_OKAY
 	ret nz
-	ldh a, [hPrintNumBuffer]
-	cp $90
-	jp nz, Function2a160
-	call Function2a166
+	; Verify the received region code
+	ldh a, [hMGExchangedByte]
+	cp REGION_CODE
+	jp nz, WrongMysteryGiftRegion
+	; Switch roles
+	call BeginSendingIRCommunication
 	ret nz
-	ld hl, wLinkData
-	ld a, [wc902]
+	; Send the staged data
+	ld hl, wMysteryGiftStaging
+	ld a, [wMysteryGiftStagedDataLength]
 	ld b, a
-	call Function2a17c
+	call TrySendingIRDataBlock
 	ret nz
-	call Function2a45c
+	; Send an empty block
+	call SendEmptyIRDataBlock
 	ldh a, [hMGStatusFlags]
-	cp $6c
+	cp MG_OKAY
 	ret
 
-Function2a103:
+EndOrContinueIRCommunication:
 	nop
 	ldh a, [hMGStatusFlags]
-	cp $10
+	; Quit if player canceled
+	cp MG_CANCELED
 	jr z, .quit
-	cp $6c
+	; Quit if there was a communication error
+	cp MG_OKAY
 	jr nz, .quit
-	ld hl, wc901
+	; Quit if all messages are sent/received
+	ld hl, wMysteryGiftMessageCount
 	dec [hl]
 	jr z, .quit
-	ld hl, wMysteryGiftTrainerData
+	; Quit if communicating with Pokémon Pikachu 2 device
+	ld hl, wMysteryGiftTrainer
 	ld de, wMysteryGiftPartnerData
 	ld bc, wMysteryGiftPartnerDataEnd - wMysteryGiftPartnerData
 	call CopyBytes
-	ld a, [wMysteryGiftTrainerData]
-	cp $3
+	ld a, [wMysteryGiftTrainer] ; first byte is the version
+	cp POKEMON_PIKACHU_2_VERSION
 	jr nc, .quit
+
+	; Prepare the second message for wMysteryGiftTrainer
 	farcall StagePartyDataForMysteryGift
-	call MysteryGift_ClearTrainerData
-	ld a, $26
-	ld [wc902], a
-	ldh a, [hPrintNumBuffer + 8]
-	cp $2
-	jr z, .asm_2a143
-	call Function2a171
-	jr nz, Function2a103
-	jp Function2a037
-
-.asm_2a143
-	call Function2a166
-	jr nz, Function2a103
-	jp Function2a055
-
-.quit:
+	call ClearMysteryGiftTrainer
+	ld a, wMysteryGiftTrainerEnd - wMysteryGiftTrainer
+	ld [wMysteryGiftStagedDataLength], a
+
+	ldh a, [hMGRole]
+	cp IR_SENDER
+	jr z, .sender
+; receiver
+	call BeginReceivingIRCommunication
+	jr nz, EndOrContinueIRCommunication
+	jp ReceiverExchangeMysteryGiftDataPayloads
+
+.sender
+	call BeginSendingIRCommunication
+	jr nz, EndOrContinueIRCommunication
+	jp SenderExchangeMysteryGiftDataPayloads
+
+.quit
 	xor a
 	ldh [rIF], a
 	ldh a, [rIE]
@@ -434,50 +505,50 @@ Function2a103:
 	call DelayFrame
 	ldh a, [hMGStatusFlags]
 	push af
-	call Function2a1ce
+	call EndIRCommunication
 	pop af
 	ret
 
-Function2a160:
-	ld a, $80
+WrongMysteryGiftRegion:
+	ld a, MG_WRONG_PREFIX
 	ldh [hMGStatusFlags], a
 	and a
 	ret
 
-Function2a166:
-	call Function2a1c4
-	call Function2a274
+BeginSendingIRCommunication:
+	call BeginIRCommunication
+	call SendIRHelloMessage
 	ldh a, [hMGStatusFlags]
-	cp $6c
+	cp MG_OKAY
 	ret
 
-Function2a171:
-	call Function2a1c4
-	call Function2a22c
+BeginReceivingIRCommunication:
+	call BeginIRCommunication
+	call ReceiveIRHelloMessage
 	ldh a, [hMGStatusFlags]
-	cp $6c
+	cp MG_OKAY
 	ret
 
-Function2a17c:
-	call Function2a2c1
+TrySendingIRDataBlock:
+	call SendIRDataBlock
 	ldh a, [hMGStatusFlags]
-	cp $6c
+	cp MG_OKAY
 	ret
 
-Function2a184:
-	call Function2a385
+TryReceivingIRDataBlock:
+	call ReceiveIRDataBlock
 	ldh a, [hMGStatusFlags]
-	cp $6c
+	cp MG_OKAY
 	ret
 
-Function2a18c:
-	call Function2a1a2
+InitializeMysteryGiftInterrupts:
+	call StartFastIRTimer
 	ld a, 1 << TIMER
 	ldh [rIE], a
 	xor a
 	ldh [rIF], a
-	call Function2a1c4
-; runs for ~$40400 cycles
+	call BeginIRCommunication
+; waits for ~$40400 cycles = ~0.25 seconds
 	xor a
 	ld b, a
 .busy_wait
@@ -487,69 +558,76 @@ Function2a18c:
 	jr nz, .busy_wait
 	ret
 
-Function2a1a2:
+StartFastIRTimer:
+; Starts a 65,536 Hz timer that interrupts every 3 increments (21,845 Hz).
 	xor a
 	ldh [rTAC], a
-	ld a, $fe
+	ld a, -2
 	ldh [rTMA], a
 	ldh [rTIMA], a
-	ld a, $2
+	ld a, rTAC_65536_HZ
 	ldh [rTAC], a
-	or $4
+	or 1 << rTAC_ON
 	ldh [rTAC], a
 	ret
 
-Function2a1b4:
+StartSlowIRTimer:
+; Starts a 65,536 Hz timer that interrupts every 256 increments (256 Hz).
 	xor a
 	ldh [rTAC], a
 	ldh [rTMA], a
 	ldh [rTIMA], a
-	ld a, $2
+	ld a, rTAC_65536_HZ
 	ldh [rTAC], a
-	or $4
+	or 1 << rTAC_ON
 	ldh [rTAC], a
 	ret
 
-Function2a1c4:
-	ld a, $c0
-	call Function2a2ba
-	ld a, $1
-	ldh [hPrintNumBuffer + 8], a
+BeginIRCommunication:
+	ld a, rRP_ENABLE_READ_MASK
+	call ToggleIRCommunication
+	ld a, IR_RECEIVER
+	ldh [hMGRole], a
 	ret
 
-Function2a1ce:
+EndIRCommunication:
 	xor a
-	call Function2a2ba
-	ld a, $2
+	call ToggleIRCommunication
+	ld a, rTAC_65536_HZ
 	ldh [rTAC], a
 	ret
 
-Function2a1d7:
+ReceiveInfraredLEDOn:
+; Count interrupts of the partner's IR LED on; quit after 256-d interrupts.
+.recv_loop
 	inc d
 	ret z
 	xor a
 	ldh [rIF], a
 	halt
 	ldh a, [c]
-	bit 1, a
-	jr z, Function2a1d7
+	bit rRP_RECEIVING, a
+	jr z, .recv_loop
 	or a
 	ret
 
-Function2a1e5:
+ReceiveInfraredLEDOff:
+; Count interrupts of the partner's IR LED off; quit after 256-d interrupts.
+.no_recv_loop
 	inc d
 	ret z
 	xor a
 	ldh [rIF], a
 	halt
 	ldh a, [c]
-	bit 1, a
-	jr nz, Function2a1e5
+	bit rRP_RECEIVING, a
+	jr nz, .no_recv_loop
 	or a
 	ret
 
-Function2a1f3:
-	ld a, $c1
+SendInfraredLEDOn:
+; Holds the IR LED on for d-1 interrupts.
+	ld a, rRP_ENABLE_READ_MASK | (1 << rRP_LED_ON)
 	ldh [c], a
 .wait
 	dec d
@@ -559,8 +637,9 @@ Function2a1f3:
 	halt
 	jr .wait
 
-Function2a1ff:
-	ld a, $c0
+SendInfraredLEDOff:
+; Holds the IR LED off for d-1 interrupts.
+	ld a, rRP_ENABLE_READ_MASK
 	ldh [c], a
 .wait
 	dec d
@@ -570,175 +649,204 @@ Function2a1ff:
 	halt
 	jr .wait
 
-Function2a20b:
-	ld d, $0
+InitializeIRCommunicationRoles:
+	ld d, 0
 	ld e, d
-	ld a, $1
-	ldh [hPrintNumBuffer + 8], a
+
+	ld a, IR_RECEIVER
+	ldh [hMGRole], a
 .loop
-	call MysteryGift_ReadJoypad
-	ld b, $2
+	call MysteryGift_UpdateJoypad
+	ld b, 1 << rRP_RECEIVING
 	ld c, LOW(rRP)
+	; Check if we've pressed the B button to cancel
 	ldh a, [hMGJoypadReleased]
 	bit B_BUTTON_F, a
-	jr z, .next
-	ld a, $10
+	jr z, .not_canceled
+	ld a, MG_CANCELED
 	ldh [hMGStatusFlags], a
 	ret
 
-.next
-	bit 0, a
-	jr nz, Function2a268
+.not_canceled
+	; Check if we've pressed the A button to start sending
+	bit A_BUTTON_F, a
+	jr nz, SendIRHelloMessageAfterDelay
+	; If rRP is not receiving data, keep checking for input
 	ldh a, [c]
 	and b
 	jr nz, .loop
+	; fallthrough
 
-Function2a22c:
+ReceiveIRHelloMessage:
 	ld c, LOW(rRP)
-	ld d, $0
+	ld d, 0
 	ld e, d
-	call Function2a1e5
-	jp z, Function2a370
+
+	call ReceiveInfraredLEDOff
+	jp z, InfraredLEDReceiveTimedOut
 	ld d, e
-	call Function2a1d7
-	jp z, Function2a370
-	call Function2a1e5
-	jp z, Function2a370
-	call Function2a1d7
-	jp z, Function2a370
-	ld a, $6c
+	call ReceiveInfraredLEDOn
+	jp z, InfraredLEDReceiveTimedOut
+	call ReceiveInfraredLEDOff
+	jp z, InfraredLEDReceiveTimedOut
+	call ReceiveInfraredLEDOn
+	jp z, InfraredLEDReceiveTimedOut
+
+	ld a, MG_OKAY
 	ldh [hMGStatusFlags], a
-	ld d, $3d
-	call Function2a1ff
-	ld d, $5
-	call Function2a1f3
-	ld d, $15
-	call Function2a1ff
-	ld d, $5
-	call Function2a1f3
-	ld d, $5
-	call Function2a1ff
+
+	ld d, 61
+	call SendInfraredLEDOff
+	ld d, 5
+	call SendInfraredLEDOn
+	ld d, 21
+	call SendInfraredLEDOff
+	ld d, 5
+	call SendInfraredLEDOn
+	ld d, 5
+	call SendInfraredLEDOff
 	ret
 
-Function2a268:
+SendIRHelloMessageAfterDelay:
 	; Wait a random amount of time
 	call Random
 	ld e, a
 	and $f
 	ld d, a
-.loop
+.wait_loop
 	dec de
 	ld a, d
 	or e
-	jr nz, .loop
-Function2a274:
-	ld a, $2
-	ldh [hPrintNumBuffer + 8], a
+	jr nz, .wait_loop
+	; fallthrough
+
+SendIRHelloMessage:
+	ld a, IR_SENDER
+	ldh [hMGRole], a
+
 	ld c, LOW(rRP)
-	ld d, $0
+	ld d, 0
 	ld e, d
-	ld d, $3d
-	call Function2a1ff
-	ld d, $5
-	call Function2a1f3
-	ld d, $15
-	call Function2a1ff
-	ld d, $5
-	call Function2a1f3
-	ld d, $5
-	call Function2a1ff
+
+	ld d, 61
+	call SendInfraredLEDOff
+	ld d, 5
+	call SendInfraredLEDOn
+	ld d, 21
+	call SendInfraredLEDOff
+	ld d, 5
+	call SendInfraredLEDOn
+	ld d, 5
+	call SendInfraredLEDOff
+
 	ld d, e
-	call Function2a1e5
-	jp z, Function2a370
+	call ReceiveInfraredLEDOff
+	jp z, InfraredLEDReceiveTimedOut
 	ld d, e
-	call Function2a1d7
-	jp z, Function2a370
-	call Function2a1e5
-	jp z, Function2a370
-	call Function2a1d7
-	jp z, Function2a370
-	ld d, $3d
-	call Function2a1ff
-	ld a, $6c
+	call ReceiveInfraredLEDOn
+	jp z, InfraredLEDReceiveTimedOut
+	call ReceiveInfraredLEDOff
+	jp z, InfraredLEDReceiveTimedOut
+	call ReceiveInfraredLEDOn
+	jp z, InfraredLEDReceiveTimedOut
+
+	ld d, 61
+	call SendInfraredLEDOff
+
+	ld a, MG_OKAY
 	ldh [hMGStatusFlags], a
 	ret
 
-Function2a2ba:
+ToggleIRCommunication:
 	ldh [rRP], a
-	ld a, $ff
+	ld a, MG_START_END
 	ldh [hMGStatusFlags], a
 	ret
 
-Function2a2c1:
+SendIRDataBlock:
+; Send b bytes of data in three messages:
+; 1. two bytes: MESSAGE_PREFIX and the length b
+; 2. b bytes: the actual data
+; 3. two bytes: a little-endian checksum
+; Then receive a one-byte acknowledgement message: the status.
 	xor a
-	ldh [hPrintNumBuffer + 4], a
-	ldh [hPrintNumBuffer + 5], a
+	ldh [hMGChecksum + 0], a
+	ldh [hMGChecksum + 1], a
 	push hl
 	push bc
 	ld c, LOW(rRP)
-	ld d, $3d
-	call Function2a1ff
-	ld hl, hPrintNumBuffer + 1
-	ld a, $5a
+	ld d, 61
+	call SendInfraredLEDOff
+	ld hl, hMGExchangedWord
+	ld a, MESSAGE_PREFIX
 	ld [hli], a
 	ld [hl], b
 	dec hl
-	ld b, $2
-	call Function2a304
+	ld b, 2
+	call SendIRDataMessage
 	pop bc
 	pop hl
-	call Function2a304
-	ldh a, [hPrintNumBuffer + 4]
-	ldh [hPrintNumBuffer + 1], a
-	ldh a, [hPrintNumBuffer + 5]
-	ldh [hPrintNumBuffer + 2], a
+	call SendIRDataMessage
+	ldh a, [hMGChecksum + 0]
+	ldh [hMGExchangedWord + 0], a
+	ldh a, [hMGChecksum + 1]
+	ldh [hMGExchangedWord + 1], a
 	push hl
-	ld hl, hPrintNumBuffer + 1
-	ld b, $2
-	call Function2a304
+	ld hl, hMGExchangedWord
+	ld b, 2
+	call SendIRDataMessage
 	ld hl, hMGStatusFlags
-	ld b, $1
-	call Function2a3dd
-	ldh a, [hPrintNumBuffer + 1]
-	ldh [hPrintNumBuffer + 4], a
-	ldh a, [hPrintNumBuffer + 2]
-	ldh [hPrintNumBuffer + 5], a
+	ld b, 1
+	call ReceiveIRDataMessage
+	ldh a, [hMGExchangedWord + 0]
+	ldh [hMGChecksum + 0], a
+	ldh a, [hMGExchangedWord + 1]
+	ldh [hMGChecksum + 1], a
 	pop hl
 	ret
 
-Function2a304:
+SendIRDataMessage:
+; Send b bytes of data one bit at a time, and update the checksum.
 	ld c, LOW(rRP)
-	ld d, $5
-	call Function2a1ff
-	ld d, $5
-	call Function2a1f3
-	ld d, $15
-	call Function2a1ff
+
+	ld d, 5
+	call SendInfraredLEDOff
+	ld d, 5
+	call SendInfraredLEDOn
+	ld d, 21
+	call SendInfraredLEDOff
+
+	; b = -b - 1; then count up to 0
 	ld a, b
 	cpl
 	ld b, a
-	ld a, $f4
+
+	ld a, -12
 	ldh [rTMA], a
-.main_loop
+.byte_loop
 	inc b
 	jr z, .done
-	ld a, $8
-	ldh [hPrintNumBuffer + 3], a
+	ld a, 8
+	ldh [hMGNumBits], a
+	; Get the next data byte
 	ld a, [hli]
 	ld e, a
-	ldh a, [hPrintNumBuffer + 4]
+	; Add the next data byte to the checksum
+	ldh a, [hMGChecksum + 0]
 	add e
-	ldh [hPrintNumBuffer + 4], a
-	ldh a, [hPrintNumBuffer + 5]
+	ldh [hMGChecksum + 0], a
+	ldh a, [hMGChecksum + 1]
 	adc 0
-	ldh [hPrintNumBuffer + 5], a
-.inner_loop
+	ldh [hMGChecksum + 1], a
+	; Send each bit of the byte
+.bit_loop
 	xor a
 	ldh [rIF], a
 	halt
-	ld a, $c1
+	ld a, rRP_ENABLE_READ_MASK | (1 << rRP_LED_ON)
 	ldh [rRP], a
-	ld d, $1
+	; Turn the LED off for longer if the bit is 1
+	ld d, 1
 	ld a, e
 	rlca
 	ld e, a
@@ -746,9 +854,9 @@ Function2a304:
 	inc d
 .wait
 	ldh a, [rTIMA]
-	cp $f8
+	cp -8
 	jr c, .wait
-	ld a, $c0
+	ld a, rRP_ENABLE_READ_MASK
 	ldh [rRP], a
 	dec d
 	jr z, .no_halt
@@ -756,133 +864,145 @@ Function2a304:
 	ldh [rIF], a
 	halt
 .no_halt
-	ldh a, [hPrintNumBuffer + 3]
+	ldh a, [hMGNumBits]
 	dec a
-	jr z, .main_loop
-	ldh [hPrintNumBuffer + 3], a
-	jr .inner_loop
+	jr z, .byte_loop
+	ldh [hMGNumBits], a
+	jr .bit_loop
 
 .done
-	ld a, $fe
+	ld a, -2
 	ldh [rTMA], a
 	xor a
 	ldh [rIF], a
 	halt
-	ld d, $5
-	call Function2a1f3
-	ld d, $11
-	call Function2a1ff
+
+	ld d, 5
+	call SendInfraredLEDOn
+	ld d, 17
+	call SendInfraredLEDOff
 	ret
 
-Function2a370:
+InfraredLEDReceiveTimedOut:
 	ldh a, [hMGStatusFlags]
-	or $2
+	or MG_TIMED_OUT
 	ldh [hMGStatusFlags], a
 	ret
 
-Function2a377:
+ReceivedWrongIRChecksum:
 	ldh a, [hMGStatusFlags]
-	or $1
+	or MG_WRONG_CHECKSUM
 	ldh [hMGStatusFlags], a
 	ret
 
-Function2a37e:
+ReceivedWrongIRMessagePrefix:
 	ldh a, [hMGStatusFlags]
-	or $80
+	or MG_WRONG_PREFIX
 	ldh [hMGStatusFlags], a
 	ret
 
-Function2a385:
+ReceiveIRDataBlock:
+; Receive b bytes of data in three messages:
+; 1. two bytes: MESSAGE_PREFIX and the length b
+; 2. b bytes: the actual data
+; 3. two bytes: a little-endian checksum
+; Then send a one-byte acknowledgement message: the status.
 	xor a
-	ldh [hPrintNumBuffer + 4], a
-	ldh [hPrintNumBuffer + 5], a
+	ldh [hMGChecksum + 0], a
+	ldh [hMGChecksum + 1], a
 	push bc
 	push hl
-	ld hl, hPrintNumBuffer + 1
-	ld b, $2
-	call Function2a3dd
-	ldh a, [hPrintNumBuffer + 2]
-	ldh [hPrintNumBuffer + 7], a
+	ld hl, hMGExchangedWord
+	ld b, 2
+	call ReceiveIRDataMessage
+	ldh a, [hMGExchangedWord + 1]
+	ldh [hMGUnusedMsgLength], a
 	ld b, a
 	pop hl
 	pop af
 	cp b
-	jp c, Function2a37e
-	ldh a, [hPrintNumBuffer + 1]
-	cp $5a
-	jp nz, Function2a37e
-	call Function2a3dd
-	ldh a, [hPrintNumBuffer + 4]
+	jp c, ReceivedWrongIRMessagePrefix
+	ldh a, [hMGExchangedWord + 0]
+	cp MESSAGE_PREFIX
+	jp nz, ReceivedWrongIRMessagePrefix
+	call ReceiveIRDataMessage
+	ldh a, [hMGChecksum + 0]
 	ld d, a
-	ldh a, [hPrintNumBuffer + 5]
+	ldh a, [hMGChecksum + 1]
 	ld e, a
 	push hl
 	push de
-	ld hl, hPrintNumBuffer + 1
-	ld b, $2
-	call Function2a3dd
+	ld hl, hMGExchangedWord
+	ld b, 2
+	call ReceiveIRDataMessage
 	pop de
-	ld hl, hPrintNumBuffer + 1
+	ld hl, hMGExchangedWord
 	ld a, [hli]
 	xor d
 	ld b, a
 	ld a, [hl]
 	xor e
 	or b
-	call nz, Function2a377
+	call nz, ReceivedWrongIRChecksum
 	push de
-	ld d, $3d
-	call Function2a1ff
+
+	ld d, 61
+	call SendInfraredLEDOff
+
 	ld hl, hMGStatusFlags
-	ld b, $1
-	call Function2a304
+	ld b, 1
+	call SendIRDataMessage
+
 	pop de
 	pop hl
 	ld a, d
-	ldh [hPrintNumBuffer + 4], a
+	ldh [hMGChecksum + 0], a
 	ld a, e
-	ldh [hPrintNumBuffer + 5], a
+	ldh [hMGChecksum + 1], a
 	ret
 
-Function2a3dd:
+ReceiveIRDataMessage:
 	ld c, LOW(rRP)
-	ld d, $0
-	call Function2a1e5
-	jp z, Function2a370
-	ld d, $0
-	call Function2a1d7
-	jp z, Function2a370
-	ld d, $0
-	call Function2a1e5
-	jp z, Function2a370
+
+	ld d, 0
+	call ReceiveInfraredLEDOff
+	jp z, InfraredLEDReceiveTimedOut
+	ld d, 0
+	call ReceiveInfraredLEDOn
+	jp z, InfraredLEDReceiveTimedOut
+	ld d, 0
+	call ReceiveInfraredLEDOff
+	jp z, InfraredLEDReceiveTimedOut
+
 	ld a, b
 	cpl
 	ld b, a
 	xor a
 	ldh [hMGPrevTIMA], a
-	call Function2a1b4
+
+	call StartSlowIRTimer
 .main_loop
 	inc b
 	jr z, .done
-	ld a, $8
-	ldh [hPrintNumBuffer + 3], a
+	ld a, 8
+	ldh [hMGNumBits], a
 .inner_loop
-	ld d, $0
-.wait_one
+	ld d, 0
+.recv_loop
 	inc d
-	jr z, .got_one
+	jr z, .recv_done
 	ldh a, [c]
-	bit 1, a
-	jr z, .wait_one
-	ld d, $0
-.got_one
-.wait_zero
+	bit rRP_RECEIVING, a
+	jr z, .recv_loop
+	ld d, 0
+.recv_done
+.send_loop
 	inc d
-	jr z, .got_zero
+	jr z, .send_done
 	ldh a, [c]
-	bit 1, a
-	jr nz, .wait_zero
-.got_zero
+	bit rRP_RECEIVING, a
+	jr nz, .send_loop
+.send_done
 	ldh a, [hMGPrevTIMA]
 	ld d, a
 	ldh a, [rTIMA]
@@ -895,9 +1015,9 @@ Function2a3dd:
 .zero
 	res 0, e
 .ok
-	ldh a, [hPrintNumBuffer + 3]
+	ldh a, [hMGNumBits]
 	dec a
-	ldh [hPrintNumBuffer + 3], a
+	ldh [hMGNumBits], a
 	jr z, .continue
 	ld a, e
 	rlca
@@ -907,34 +1027,35 @@ Function2a3dd:
 .continue
 	ld a, e
 	ld [hli], a
-	ldh a, [hPrintNumBuffer + 4]
+	ldh a, [hMGChecksum + 0]
 	add e
-	ldh [hPrintNumBuffer + 4], a
-	ldh a, [hPrintNumBuffer + 5]
+	ldh [hMGChecksum + 0], a
+	ldh a, [hMGChecksum + 1]
 	adc 0
-	ldh [hPrintNumBuffer + 5], a
+	ldh [hMGChecksum + 1], a
 	jr .main_loop
 
 .done
-	call Function2a1a2
+	call StartFastIRTimer
 	xor a
 	ldh [rIF], a
-	ld d, $0
-	call Function2a1d7
-	jp z, Function2a370
-	ld d, $10
-	call Function2a1ff
+	ld d, 0
+	call ReceiveInfraredLEDOn
+	jp z, InfraredLEDReceiveTimedOut
+
+	ld d, 16
+	call SendInfraredLEDOff
 	ret
 
-Function2a45c:
-	ld b, $0
-	jp Function2a2c1
+SendEmptyIRDataBlock:
+	ld b, 0
+	jp SendIRDataBlock
 
-Function2a461:
-	ld b, $0
-	jp Function2a385
+ReceiveEmptyIRDataBlock:
+	ld b, 0
+	jp ReceiveIRDataBlock
 
-MysteryGift_ReadJoypad:
+MysteryGift_UpdateJoypad:
 ; We can only get four inputs at a time.
 ; We take d-pad first for no particular reason.
 	ld a, R_DPAD
@@ -979,9 +1100,10 @@ endr
 	ldh [rJOYP], a
 	ret
 
-MysteryGift_CheckAndSetDecorationAlreadyReceived:
+CheckAndSetMysteryGiftDecorationAlreadyReceived:
+; Return nz if decoration c was already received; otherwise receive it.
 	call GetMysteryGiftBank
-	ld d, $0
+	ld d, 0
 	ld b, CHECK_FLAG
 	ld hl, sMysteryGiftDecorationsReceived
 	lda_predef SmallFarFlagAction
@@ -1001,12 +1123,12 @@ MysteryGift_CheckAndSetDecorationAlreadyReceived:
 	xor a
 	ret
 
-MysteryGift_CopyReceivedDecosToPC:
+CopyMysteryGiftReceivedDecorationsToPC:
 	call GetMysteryGiftBank
-	ld c, $0
+	ld c, 0
 .loop
 	push bc
-	ld d, $0
+	ld d, 0
 	ld b, CHECK_FLAG
 	ld hl, sMysteryGiftDecorationsReceived
 	predef SmallFarFlagAction
@@ -1025,52 +1147,63 @@ MysteryGift_CopyReceivedDecosToPC:
 	jp CloseSRAM
 
 UnlockMysteryGift:
+; If [sMysteryGiftUnlocked] was -1, this sets both
+; [sMysteryGiftUnlocked] and [sMysteryGiftItem] to 0.
 	call GetMysteryGiftBank
 	ld hl, sMysteryGiftUnlocked
 	ld a, [hl]
 	inc a
 	jr nz, .ok
 	ld [hld], a
+	assert sMysteryGiftUnlocked - 1 == sMysteryGiftItem
 	ld [hl], a
 .ok
 	jp CloseSRAM
 
-Function2a4f6:
+ResetDailyMysteryGiftLimitIfUnlocked:
 	call GetMysteryGiftBank
 	ld a, [sNumDailyMysteryGiftPartnerIDs]
-	cp $ff
-	jr z, .okay
+	cp -1 ; locked?
+	jr z, .dont_clear
 	xor a
 	ld [sNumDailyMysteryGiftPartnerIDs], a
-.okay
+.dont_clear
 	jp CloseSRAM
 
 BackupMysteryGift:
+; Copies [sMysteryGiftItem] to [sBackupMysteryGiftItem],
+; and [sMysteryGiftUnlocked] to [sNumDailyMysteryGiftPartnerIDs].
 	call GetMysteryGiftBank
 	ld hl, sMysteryGiftItem
 	ld de, sBackupMysteryGiftItem
 	ld a, [hli]
 	ld [de], a
 	inc de
+	assert sMysteryGiftItem + 1 == sMysteryGiftUnlocked
+	assert sBackupMysteryGiftItem + 1 == sNumDailyMysteryGiftPartnerIDs
 	ld a, [hl]
 	ld [de], a
 	jp CloseSRAM
 
 RestoreMysteryGift:
+; Copies [sBackupMysteryGiftItem] to [sMysteryGiftItem],
+; and [sNumDailyMysteryGiftPartnerIDs] to [sMysteryGiftUnlocked].
 	call GetMysteryGiftBank
 	ld hl, sBackupMysteryGiftItem
 	ld de, sMysteryGiftItem
 	ld a, [hli]
 	ld [de], a
 	inc de
+	assert sBackupMysteryGiftItem + 1 == sNumDailyMysteryGiftPartnerIDs
+	assert sMysteryGiftItem + 1 == sMysteryGiftUnlocked
 	ld a, [hl]
 	ld [de], a
 	jp CloseSRAM
 
-MysteryGift_ClearTrainerData:
-	ld hl, wMysteryGiftTrainerData
+ClearMysteryGiftTrainer:
+	ld hl, wMysteryGiftTrainer
 	xor a
-	ld b, wMysteryGiftTrainerDataEnd - wMysteryGiftTrainerData
+	ld b, wMysteryGiftTrainerEnd - wMysteryGiftTrainer
 .loop
 	ld [hli], a
 	dec b
@@ -1078,5 +1211,5 @@ MysteryGift_ClearTrainerData:
 	ret
 
 GetMysteryGiftBank:
-	ld a, BANK(sBackupMysteryGiftItem)
+	ld a, BANK(sMysteryGiftData)
 	jp OpenSRAM
diff --git a/engine/link/mystery_gift_2.asm b/engine/link/mystery_gift_2.asm
index 9c524182..af3715e0 100644
--- a/engine/link/mystery_gift_2.asm
+++ b/engine/link/mystery_gift_2.asm
@@ -1,6 +1,6 @@
-PrepMysteryGiftDataToSend:
+StageDataForMysteryGift:
 	ld de, wMysteryGiftStaging
-	ld a, $1 + GS_VERSION
+	ld a, GS_VERSION + 1
 	ld [de], a
 	inc de ; wMysteryGiftStaging+1
 	ld a, BANK(sGameData)
@@ -46,10 +46,10 @@ PrepMysteryGiftDataToSend:
 	ld a, [sBackupMysteryGiftItem]
 	ld [de], a
 	inc de
-	ld a, [sBackupMysteryGiftItem + 1]
+	ld a, [sNumDailyMysteryGiftPartnerIDs]
 	ld [de], a
-	ld a, $14
-	ld [wc900], a
+	ld a, wMysteryGiftPlayerDataEnd - wMysteryGiftPlayerData
+	ld [wUnusedMysteryGiftStagedDataLength], a
 	call CloseSRAM
 	ld hl, wMysteryGiftStaging
 	ld de, wMysteryGiftPlayerData
@@ -121,7 +121,7 @@ PrepMysteryGiftDataToSend:
 	pop de
 	ret
 
-MysteryGiftGetItemHeldEffect:
+MysteryGiftGetItem:
 	ld a, c
 	cp MysteryGiftItems.End - MysteryGiftItems
 	jr nc, MysteryGiftFallbackItem
diff --git a/engine/link/mystery_gift_3.asm b/engine/link/mystery_gift_3.asm
index bc12d9c8..4a8d92c4 100644
--- a/engine/link/mystery_gift_3.asm
+++ b/engine/link/mystery_gift_3.asm
@@ -45,8 +45,8 @@ StagePartyDataForMysteryGift:
 .party_end
 	ld a, -1
 	ld [de], a
-	ld a, $26
-	ld [wc900], a
+	ld a, wMysteryGiftTrainerEnd - wMysteryGiftTrainer
+	ld [wUnusedMysteryGiftStagedDataLength], a
 	jp CloseSRAM
 
 InitMysteryGiftLayout:
diff --git a/engine/menus/intro_menu.asm b/engine/menus/intro_menu.asm
index 2155bdc3..2fe285b1 100644
--- a/engine/menus/intro_menu.asm
+++ b/engine/menus/intro_menu.asm
@@ -87,12 +87,13 @@ _ResetWRAM:
 	ld [wRoamMon2MapNumber], a
 	ld [wRoamMon3MapNumber], a
 
-	ld a, BANK(sMysteryGiftItem)
+	ld a, BANK(sMysteryGiftItem) ; aka BANK(sMysteryGiftUnlocked)
 	call OpenSRAM
 	ld hl, sMysteryGiftItem
 	xor a
 	ld [hli], a
-	dec a
+	assert sMysteryGiftItem + 1 == sMysteryGiftUnlocked
+	dec a ; -1
 	ld [hl], a
 	call CloseSRAM
 
@@ -280,7 +281,7 @@ Continue:
 	ld c, 20
 	call DelayFrames
 	farcall JumpRoamMons
-	farcall MysteryGift_CopyReceivedDecosToPC
+	farcall CopyMysteryGiftReceivedDecorationsToPC
 	farcall ClockContinue
 	ld a, [wSpawnAfterChampion]
 	cp SPAWN_LANCE
diff --git a/engine/menus/main_menu.asm b/engine/menus/main_menu.asm
index 20c74336..22308a87 100644
--- a/engine/menus/main_menu.asm
+++ b/engine/menus/main_menu.asm
@@ -132,7 +132,7 @@ MainMenu_GetWhichMenu:
 	ld a, BANK(sNumDailyMysteryGiftPartnerIDs)
 	call OpenSRAM
 	ld a, [sNumDailyMysteryGiftPartnerIDs]
-	cp -1
+	cp -1 ; locked?
 	call CloseSRAM
 	ld a, MAINMENU_CONTINUE
 	ret z
diff --git a/engine/overworld/time.asm b/engine/overworld/time.asm
index 4860c06c..5b4a96b5 100644
--- a/engine/overworld/time.asm
+++ b/engine/overworld/time.asm
@@ -227,7 +227,7 @@ DoMysteryGiftIfDayHasPassed:
 	ld hl, wBuffer1
 	call InitOneDayCountdown
 	call CloseSRAM
-	farcall Function2a4f6
+	farcall ResetDailyMysteryGiftLimitIfUnlocked
 
 .not_timed_out
 	ld a, BANK(sMysteryGiftTimer)
diff --git a/hram.asm b/hram.asm
index edc9599c..a26c4834 100644
--- a/hram.asm
+++ b/hram.asm
@@ -85,8 +85,14 @@ NEXTU
 hPrintNumBuffer:: ds 10
 
 NEXTU
-; miscellaneous
-	ds 9
+; Mystery Gift
+hMGExchangedByte:: db
+hMGExchangedWord:: dw
+hMGNumBits:: db
+hMGChecksum:: dw
+	ds 1
+hMGUnusedMsgLength:: db
+hMGRole:: db
 hMGStatusFlags:: db
 ENDU
 
diff --git a/sram.asm b/sram.asm
index 3627b4aa..3651798a 100644
--- a/sram.asm
+++ b/sram.asm
@@ -55,19 +55,20 @@ sMailbox8Backup::  mailmsg sMailbox8Backup
 sMailbox9Backup::  mailmsg sMailbox9Backup
 sMailbox10Backup:: mailmsg sMailbox10Backup
 
+sMysteryGiftData::
 sMysteryGiftItem:: db
 sMysteryGiftUnlocked:: db
 sBackupMysteryGiftItem:: db
 sNumDailyMysteryGiftPartnerIDs:: db
-sDailyMysteryGiftPartnerIDs:: ds 5 * 2 ; maximum 5 per day, 2 bytes per ID
+sDailyMysteryGiftPartnerIDs:: ds MAX_MYSTERY_GIFT_PARTNERS * 2
 sMysteryGiftDecorationsReceived:: flag_array NUM_NON_TROPHY_DECOS
 	ds 4
 sMysteryGiftTimer:: dw
 	ds 1
 sMysteryGiftTrainerHouseFlag:: db
 sMysteryGiftPartnerName:: ds NAME_LENGTH
-	ds 1
-sMysteryGiftTrainer:: ds (1 + 1 + NUM_MOVES) * PARTY_LENGTH + 2
+sMysteryGiftUnusedFlag:: db
+sMysteryGiftTrainer:: ds wMysteryGiftTrainerEnd - wMysteryGiftTrainer
 sBackupMysteryGiftItemEnd::
 
 	ds $30
diff --git a/wram.asm b/wram.asm
index 3d2f43bd..0c45e405 100644
--- a/wram.asm
+++ b/wram.asm
@@ -569,20 +569,15 @@ ENDU
 
 NEXTU
 ; mystery gift data
-UNION
-wMysteryGiftPartyTemp:: ds (1 + 1 + NUM_MOVES) * PARTY_LENGTH
-
-NEXTU
 wMysteryGiftStaging:: ds 80
-ENDU
 
-wMysteryGiftTrainerData:: ds (1 + 1 + NUM_MOVES) * PARTY_LENGTH + 2
-wMysteryGiftTrainerDataEnd::
+wMysteryGiftTrainer:: ds 1 + (1 + 1 + NUM_MOVES) * PARTY_LENGTH + 1
+wMysteryGiftTrainerEnd::
 
 	ds 138
 
 wMysteryGiftPartnerData::
-wc800:: db
+wMysteryGiftGameVersion:: db
 wMysteryGiftPartnerID:: dw
 wMysteryGiftPartnerName:: ds NAME_LENGTH
 wMysteryGiftPartnerDexCaught:: db
@@ -636,9 +631,9 @@ wCreditsBlankFrame2bppEnd::
 
 NEXTU
 ; mystery gift data
-wc900:: db
-wc901:: db
-wc902:: db
+wUnusedMysteryGiftStagedDataLength:: db
+wMysteryGiftMessageCount:: db
+wMysteryGiftStagedDataLength:: db
 
 NEXTU
 ; link