1 files changed, 296 insertions, 3 deletions
diff --git a/home/serial.asm b/home/serial.asm
index 48d6832..d51e5a6 100644
--- a/home/serial.asm
+++ b/home/serial.asm
@@ -16,7 +16,7 @@ Serial::
 	ldh a, [hSerialSend]
 	ld [rSB], a
 	ldh a, [hLinkPlayerNumber]
-	cp 2
+	cp USING_INTERNAL_CLOCK
 	jr z, .done
 	ld a, 1 << rSC_ON
 	ld [rSC], a
@@ -26,7 +26,7 @@ Serial::
 	ld a, [rSB]
 	ldh [hSerialReceive], a
 	ldh [hLinkPlayerNumber], a
-	cp 2
+	cp USING_INTERNAL_CLOCK
 	jr z, .master
 	xor a
 	ld [rSB], a
@@ -43,7 +43,7 @@ Serial::
 	xor a
 	ld [rSB], a
 .done
-	ld a, 1
+	ld a, TRUE
 	ldh [hSerialReceived], a
 	ld a, SERIAL_NO_DATA_BYTE
 	ldh [hSerialSend], a
@@ -52,3 +52,296 @@ Serial::
 	pop bc
 	pop af
 	reti
+
+Serial_ExchangeBytes:: ; 64c
+	ld a, $1
+	ldh [hSerialIgnoringInitialData], a
+.loop
+	ld a, [hl]
+	ldh [hSerialSend], a
+	call Serial_ExchangeByte
+	push bc
+	ld b, a
+	inc hl
+	ld a, $30
+.wait
+	dec a
+	jr nz, .wait
+	ldh a, [hSerialIgnoringInitialData]
+	and a
+	ld a, b
+	pop bc
+	jr z, .load
+	dec hl
+	cp SERIAL_PREAMBLE_BYTE
+	jr nz, .loop
+	xor a
+	ldh [hSerialIgnoringInitialData], a
+	jr .loop
+
+.load
+	ld [de], a
+	inc de
+	dec bc
+	ld a, b
+	or c
+	jr nz, .loop
+	ret
+
+Serial_ExchangeByte:: ; 677 (0:0677)
+.loop
+	xor a
+	ldh [hSerialReceived], a
+	ldh a, [hLinkPlayerNumber]
+	cp USING_INTERNAL_CLOCK
+	jr nz, .not_player_2
+	ld a, (1 << rSC_ON) | 1
+	ldh [rSC], a
+.not_player_2
+.loop2
+	ldh a, [hSerialReceived]
+	and a
+	jr nz, .reset_ffca
+	ldh a, [hLinkPlayerNumber]
+	cp $1
+	jr nz, .not_player_1_or_wLinkTimeoutFrames_zero
+	call CheckwLinkTimeoutFramesNonzero
+	jr z, .not_player_1_or_wLinkTimeoutFrames_zero
+	call .delay_15_cycles
+	push hl
+	ld hl, wLinkTimeoutFrames + 1
+	inc [hl]
+	jr nz, .no_rollover_up
+	dec hl
+	inc [hl]
+
+.no_rollover_up
+	pop hl
+	call CheckwLinkTimeoutFramesNonzero
+	jr nz, .loop2
+	jp SerialDisconnected
+
+.not_player_1_or_wLinkTimeoutFrames_zero
+	ldh a, [rIE]
+	and (1 << SERIAL) | (1 << TIMER) | (1 << LCD_STAT) | (1 << VBLANK)
+	cp 1 << SERIAL
+	jr nz, .loop2
+	ld a, [wcb58]
+	dec a
+	ld [wcb58], a
+	jr nz, .loop2
+	ld a, [wcb58 + 1]
+	dec a
+	ld [wcb58 + 1], a
+	jr nz, .loop2
+	ldh a, [hLinkPlayerNumber]
+	cp USING_EXTERNAL_CLOCK
+	jr z, .reset_ffca
+
+	ld a, 255
+.delay_255_cycles
+	dec a
+	jr nz, .delay_255_cycles
+
+.reset_ffca
+	xor a
+	ldh [hSerialReceived], a
+	ldh a, [rIE]
+	and (1 << SERIAL) | (1 << TIMER) | (1 << LCD_STAT) | (1 << VBLANK)
+	sub 1 << SERIAL
+	jr nz, .rIE_not_equal_8
+
+	; LOW($5000)
+	ld [wcb58], a
+	ld a, HIGH($5000)
+	ld [wcb58 + 1], a
+
+.rIE_not_equal_8
+	ldh a, [hSerialReceive]
+	cp SERIAL_NO_DATA_BYTE
+	ret nz
+	call CheckwLinkTimeoutFramesNonzero
+	jr z, .linkTimeoutFrames_zero
+	push hl
+	ld hl, wLinkTimeoutFrames + 1
+	ld a, [hl]
+	dec a
+	ld [hld], a
+	inc a
+	jr nz, .no_rollover
+	dec [hl]
+
+.no_rollover
+	pop hl
+	call CheckwLinkTimeoutFramesNonzero
+	jr z, SerialDisconnected
+
+.linkTimeoutFrames_zero
+	ldh a, [rIE]
+	and (1 << SERIAL) | (1 << TIMER) | (1 << LCD_STAT) | (1 << VBLANK)
+	cp 1 << SERIAL
+	ld a, SERIAL_NO_DATA_BYTE
+	ret z
+	ld a, [hl]
+	ldh [hSerialSend], a
+	call DelayFrame
+	jp .loop
+
+.delay_15_cycles: ; 70e (0:070e)
+	ld a, 15
+.delay_cycles
+	dec a
+	jr nz, .delay_cycles
+	ret
+
+CheckwLinkTimeoutFramesNonzero: ; 714 (0:0714)
+	push hl
+	ld hl, wLinkTimeoutFrames
+	ld a, [hli]
+	or [hl]
+	pop hl
+	ret
+
+SerialDisconnected: ; 71c (0:071c)
+	dec a
+	ld [wLinkTimeoutFrames], a
+	ld [wLinkTimeoutFrames + 1], a
+	ret
+
+; This is used to exchange the button press and selected menu item on the link menu.
+; The data is sent thrice and read twice to increase reliability.
+Serial_ExchangeLinkMenuSelection::
+	ld hl, wPlayerLinkAction
+	ld de, wOtherPlayerLinkMode
+	ld c, 2
+	ld a, TRUE
+	ldh [hSerialIgnoringInitialData], a
+.asm_0730
+	call DelayFrame
+	ld a, [hl]
+	ldh [hSerialSend], a
+	call Serial_ExchangeByte
+	ld b, a
+	inc hl
+	ldh a, [hSerialIgnoringInitialData]
+	and a
+	ld a, FALSE
+	ldh [hSerialIgnoringInitialData], a
+	jr nz, .asm_0730
+	ld a, b
+	ld [de], a
+	inc de
+	dec c
+	jr nz, .asm_0730
+	ret
+
+Serial_PrintWaitingTextAndSyncAndExchangeNybble::
+	call BackUpTilesToBuffer
+	callab PlaceWaitingText
+	call WaitLinkTransfer
+	jp ReloadTilesFromBuffer
+
+WaitLinkTransfer:: ; 75c (0:075c)
+	ld a, $ff
+	ld [wOtherPlayerLinkAction], a
+.loop
+	call LinkTransfer
+	call DelayFrame
+	call CheckwLinkTimeoutFramesNonzero
+	jr z, .check
+	push hl
+	ld hl, wLinkTimeoutFrames + 1
+	dec [hl]
+	jr nz, .skip
+	dec hl
+	dec [hl]
+	jr nz, .skip
+	; We might be disconnected
+	pop hl
+	xor a
+	jp SerialDisconnected
+
+.skip
+	pop hl
+.check
+	ld a, [wOtherPlayerLinkAction]
+	inc a
+	jr z, .loop
+
+	ld b, 10
+.receive
+	call DelayFrame
+	call LinkTransfer
+	dec b
+	jr nz, .receive
+
+	ld b, 10
+.acknowledge
+	call DelayFrame
+	call LinkDataReceived
+	dec b
+	jr nz, .acknowledge
+
+	ld a, [wOtherPlayerLinkAction]
+	ld [wOtherPlayerLinkMode], a
+	ret
+
+LinkTransfer:: ; 7a0 (0:07a0)
+	push bc
+	ld b, $60
+	ld a, [wLinkMode]
+	cp $2
+	jr c, .asm_07ac
+	ld b, $70
+
+.asm_07ac
+	call .Receive
+	ld a, [wPlayerLinkAction]
+	add b
+	ldh [hSerialSend], a
+	ldh a, [hLinkPlayerNumber]
+	cp USING_INTERNAL_CLOCK
+	jr nz, .player_1
+	ld a, (1 << rSC_ON) | 1
+	ldh [rSC], a
+
+.player_1
+	call .Receive
+	pop bc
+	ret
+
+.Receive: ; 7c4 (0:07c4)
+	ldh a, [hSerialReceive]
+	ld [wOtherPlayerLinkMode], a
+	and $f0
+	cp b
+	ret nz
+	xor a
+	ldh [hSerialReceive], a
+	ld a, [wOtherPlayerLinkMode]
+	and $f
+	ld [wOtherPlayerLinkAction], a
+	ret
+
+LinkDataReceived:: ; 7d9 (0:07d9)
+; Let the other system know that the data has been received.
+	xor a
+	ldh [hSerialSend], a
+	ldh a, [hLinkPlayerNumber]
+	cp USING_INTERNAL_CLOCK
+	ret nz
+	ld a, (1 << rSC_ON) | 1
+	ldh [rSC], a
+	ret
+
+Unreferenced_Function7e6::
+	ld a, [wLinkMode]
+	and a
+	ret nz
+	ld a, USING_INTERNAL_CLOCK
+	ldh [rSB], a
+	xor a
+	ldh [hSerialReceive], a
+	ld a, (1 << rSC_ON)
+	ldh [rSC], a
+	ret