Use LCD STAT interrupt more efficiently (#2)

constants/hardware_constants.asm

@@ -36,7 +36,8 @@ DEF LCD_STAT   EQU 1
 DEF TIMER      EQU 2
 DEF SERIAL     EQU 3
 DEF JOYPAD     EQU 4
-DEF IE_DEFAULT EQU (1 << SERIAL) | (1 << TIMER) | (1 << LCD_STAT) | (1 << VBLANK)
+DEF IE_DEFAULT EQU (1 << SERIAL) | (1 << LCD_STAT) | (1 << VBLANK)
+DEF IE_DEFAULT_WO_LCD_STAT EQU (1 << SERIAL) | (1 << VBLANK)
 
 ; OAM attribute flags
 DEF OAM_TILE_BANK EQU 3

engine/link/link.asm

@@ -104,7 +104,7 @@ endc
 
 	xor a
 	ldh [rIF], a
-	ld a, (1 << JOYPAD) | (1 << SERIAL) | (1 << TIMER) | (1 << VBLANK)
+	ld a, (1 << JOYPAD) | (1 << SERIAL) | (1 << VBLANK)
 	ldh [rIE], a
 
 	call Link_CopyRandomNumbers
@@ -280,7 +280,7 @@ endc
 
 	xor a
 	ldh [rIF], a
-	ld a, (1 << JOYPAD) | (1 << SERIAL) | (1 << TIMER) | (1 << VBLANK)
+	ld a, (1 << JOYPAD) | (1 << SERIAL) | (1 << VBLANK)
 	ldh [rIE], a
 	ld de, MUSIC_NONE
 	call PlayMusic

engine/menus/cleared_level_screen.asm

@@ -1,6 +1,7 @@
 ClearedLevelScreen:
 	xor a
 	ldh [hMapAnims], a
+	ldh [hLCDStatIntRequired], a
 	ldh [hSCY], a
 	ld a, -$4
 	ldh [hSCX], a

engine/menus/game_menu.asm

@@ -14,6 +14,7 @@ GameMenu:
 GameMenu_KeepMusic:
 	xor a
 	ldh [hMapAnims], a
+	ldh [hLCDStatIntRequired], a
 	call ClearTilemap
 	call LoadFrame
 	call LoadStandardFont

engine/menus/level_selection_menu.asm

@@ -4,6 +4,7 @@ LevelSelectionMenu::
 	ldh [hMapAnims], a
 	ldh [hSCY], a
 	ldh [hSCX], a
+	ldh [hLCDStatIntRequired], a
 	ld a, 1 << DONT_CLEAR_SHADOW_OAM_IN_SPRITE_ANIMS_F
 	ld [wStateFlags], a
 

engine/menus/main_menu.asm

@@ -14,6 +14,7 @@ MainMenu:
 .loop
 	xor a
 	ldh [hMapAnims], a
+	ldh [hLCDStatIntRequired], a
 	call ClearTilemap
 	call LoadFrame
 	call LoadStandardFont

engine/menus/titlescreen.asm

@@ -13,6 +13,8 @@ IntroSequence:
 	; fallthrough
 
 StartTitleScreen:
+	ld a, TRUE
+	ldh [hLCDStatIntRequired], a
 	ldh a, [rSVBK]
 	push af
 	ld a, BANK(wLYOverrides)

engine/movie/credits.asm

@@ -8,6 +8,9 @@ Credits::
 .okay
 	ld [wJumptableIndex], a
 
+	ld a, TRUE
+	ldh [hLCDStatIntRequired], a
+
 	ldh a, [rSVBK]
 	push af
 	ld a, BANK(wGBCPalettes)

engine/movie/intro.asm

@@ -1,4 +1,6 @@
 CrystalIntro:
+	ld a, TRUE
+	ldh [hLCDStatIntRequired], a
 	ldh a, [rSVBK]
 	push af
 	ld a, BANK(wGBCPalettes)

engine/overworld/events.asm

@@ -3,6 +3,8 @@ SECTION "Events", ROMX
 OverworldLoop::
 	xor a ; MAPSTATUS_START
 	ld [wMapStatus], a
+	ld a, TRUE
+	ld [hLCDStatIntRequired], a
 .loop
 	ld a, [wMapStatus]
 	ld hl, .Jumptable

home/init.asm

@@ -151,7 +151,8 @@ Init::
 
 	xor a
 	ldh [rIF], a
-	ld a, IE_DEFAULT
+	ldh [hLCDStatIntRequired], a
+	ld a, IE_DEFAULT_WO_LCD_STAT
 	ldh [rIE], a
 	ei
 

home/serial.asm

@@ -156,7 +156,7 @@ Serial_ExchangeByte::
 
 .not_player_1_or_timed_out
 	ldh a, [rIE]
-	and (1 << SERIAL) | (1 << TIMER) | (1 << LCD_STAT) | (1 << VBLANK)
+	and IE_DEFAULT
 	cp 1 << SERIAL
 	jr nz, .loop
 	ld a, [wLinkByteTimeout]
@@ -180,7 +180,7 @@ Serial_ExchangeByte::
 	xor a
 	ldh [hSerialReceivedNewData], a
 	ldh a, [rIE]
-	and (1 << SERIAL) | (1 << TIMER) | (1 << LCD_STAT) | (1 << VBLANK)
+	and IE_DEFAULT
 	sub 1 << SERIAL
 	jr nz, .non_serial_interrupts_enabled
 
@@ -212,7 +212,7 @@ Serial_ExchangeByte::
 
 .timed_out
 	ldh a, [rIE]
-	and (1 << SERIAL) | (1 << TIMER) | (1 << LCD_STAT) | (1 << VBLANK)
+	and IE_DEFAULT
 	cp 1 << SERIAL
 	ld a, SERIAL_NO_DATA_BYTE
 	ret z

home/vblank.asm

@@ -35,12 +35,12 @@ VBlank::
 	reti
 
 .VBlanks:
-	dw VBlank0
+	dw VBlank0 ; normal operation
-	dw VBlank1
+	dw VBlank1 ; battle transition, battle anims (double speed mode)
-	dw VBlank2
+	dw VBlank2 ; link
-	dw VBlank3
+	dw VBlank3 ; battle anims (regular speed mode)
-	dw VBlank4
+	dw VBlank4 ; printer
-	dw VBlank5
+	dw VBlank5 ; credits
 	dw VBlank6
 	dw VBlank0 ; just in case
 
@@ -118,6 +118,7 @@ VBlank0::
 	ldh [hVBlankOccurred], a
 
 	; if hWindowHUDLY is active, enable interrupts so the LCD interrupt can trigger
+	; while non-vblank-sensitive operations are executed.
 	ldh a, [hWindowHUDLY]
 	and a
 	jr z, .next2
@@ -163,10 +164,9 @@ VBlank0::
 	ldh a, [hROMBankBackup]
 	rst Bankswitch
 
-	; if hWindowHUDLY is not active, we're done
 	ldh a, [hWindowHUDLY]
 	and a
-	ret z
+	jr z, .no_window_hud
 
 	; interrupts must be enabled in the cycle that rLY becomes [hWindowHUDLY] to prevent flickering
 	; wait until [hWindowHUDLY] - [rLY] is NOT between 0 and 2 before disabling interrupts
@@ -178,9 +178,17 @@ VBlank0::
 	cp 2 + 1
 	jr c, .wait_loop
 
-	; restore normal interrupts: enable ints besides joypad and let vblank finish
+.no_window_hud
+	; if hWindowHUDLY is active, only LCD_STAT is enabled.
+	; if hLCDStatIntRequired changeed during last frame, interrupts to request have changed.
+	; so, restore normal interrupts: enable ints besides joypad (and maybe lcd stat) and let vblank finish.
 	di
+	ld a, [hLCDStatIntRequired]
+	and a
 	ld a, IE_DEFAULT
+	jr nz, .enable_ints
+	ld a, IE_DEFAULT_WO_LCD_STAT
+.enable_ints
 	ldh [rIE], a
 
 	ret

ram/hram.asm

@@ -13,6 +13,8 @@ hVBlankOccurred:: db
 
 hROMBank:: db
 hVBlank:: db
+hLCDStatIntRequired:: db
+
 hMapEntryMethod:: db
 
 hJoypadReleased:: db