First mostly playable version

Improved the snake drawing function, made the game go back to the titlescreen after a game over, added a background grid.

ASM/Snake/drawSnake.s

@@ -1,14 +1,48 @@
 .thumb
 
 push	{lr}
-push	{r4-r6}
+push	{r4-r7}
 ldr	r4,=#0x02000000
+@erase old tongue if it exists
+ldr	r0,=bgTilemapsBuffer
+ldr	r0,[r0]
+ldr	r1,=#0x500
+add	r1,r0
+tongueloop:
+cmp	r0,r1
+beq	donetongue
+ldrb	r2,[r0]
+cmp	r2,#1
+beq	erasetongue
+cmp	r2,#6
+beq	erasetongue
+add	r0,#2
+b	tongueloop
+erasetongue:
+mov	r2,#0
+strh	r2,[r0]
+donetongue:
+@erase old tail
+ldrh	r0,[r4,#0x1A]
+cmp	r0,#0
+beq	erasedtail
+ldr	r3,=drawTile
+mov	lr,r3
+ldrb	r2,[r4,#0x1A]	@x
+ldrb	r3,[r4,#0x1B]	@y
+mov	r1,#0		@attribute
+mov	r0,#0		@bg layer
+.short	0xF800
+erasedtail:
 ldrh	r5,[r4]		@size
 cmp	r5,#0
-beq	End
+bne	dontEnd
+b	End
 dontEnd:
 sub	r5,#1
 lsl	r5,#1
+mov	r7,r5
+sub	r7,#4
 
 @get snake size
 sneakLoop:
@@ -30,6 +64,11 @@ nextEntry:
 cmp	r5,#0
 beq	End
 sub	r5,#2
+cmp	r5,r7
+beq	skip
+b	sneakLoop
+skip:
+mov	r7,r5
 b	sneakLoop
 
 drawTail:
@@ -161,6 +200,6 @@ endtongue:
 b	nextEntry
 
 End:
-pop	{r4-r6}
+pop	{r4-r7}
 pop	{r0}
 bx	r0

ASM/boot.s

@@ -34,9 +34,6 @@ mov	r1,#0x10
 add	r2,#4
 strb	r1,[r0,r2]	@start with a black screen
 
-mov	r1,#3
-strb	r1,[r0,#1]	@turn on bg layers 0 and 1
-
 @enable timer 0, 1 and 2
 ldr	r1,=#0x100
 ldr	r2,=#0xEEDB
@@ -58,6 +55,8 @@ mov	r1,#0x1F
 strb	r1,[r0,#9]	@set the offset for the bg map 0
 mov	r1,#0x1E
 strb	r1,[r0,#11]	@set the offset for the bg map 1
+mov	r1,#0x1D
+strb	r1,[r0,#13]	@set the offset for the bg map 2
 
 swi	#5
 

ASM/mainLoop.s

@@ -16,6 +16,14 @@ ldr	r1,[r1,#4]
 ldr	r2,=#0x200
 .short	0xF800
 
+@make the bg2 background
+ldr	r0,=backgroundgridTSA
+ldr	r1,=bgTilemaps
+ldr	r1,[r1,#8]
+ldr	r3,=loadData
+mov	lr,r3
+.short	0xF800
+
 @temporary black border
 ldr	r0,=fillDest
 mov	lr,r0
@@ -30,10 +38,14 @@ ldr	r0,=#0x04000000
 mov	r1,#1
 strb	r1,[r0,#8]
 
-@disable bg 1 for now
-mov	r1,#1
+@disable bg 1 for now, enable bg 2
+mov	r1,#5
 strb	r1,[r0,#1]
 
+@lower bg 2 priority
+mov	r1,#3
+strb	r1,[r0,#0xC]
+
 ldr	r0,=snekIMG
 ldr	r1,=#0x06000000
 ldr	r3,=loadData
@@ -55,10 +67,12 @@ mov	lr,r0
 .short	0xF800
 
 ldr	r0,=#0x02000000
-add	r0,#0x10
+mov	r1,#0
+strb	r1,[r0,#2]	@reset facing direction
+strb	r1,[r0,#0xD]	@reset game state
 mov	r1,#1
-strb	r1,[r0]		@set bg 0 and 1 to be updated
-strb	r1,[r0,#1]
+strb	r1,[r0,#0x10]	@set bg 0 and 1 to be updated
+strb	r1,[r0,#0x11]
 
 ldr	r0,=drawSnake
 mov	lr,r0
@@ -140,6 +154,11 @@ b	skipSnake	@skip game logic
 runSnake:
 strh	r3,[r0,#0x18]	@update counter
 
+@check for game over
+ldrb	r3,[r0,#0xD]
+cmp	r3,#0xFF
+beq	gameover
+
 ldr	r0,=#0x02000000
 add	r0,#0x10
 mov	r1,#1
@@ -170,15 +189,6 @@ ldrb	r0,[r0,#0xD]
 cmp	r0,#0xF0
 bhi	nobg0draw
 
-ldr	r0,=fillDest
-mov	lr,r0
-mov	r0,#0
-ldr	r1,=bgTilemapsBuffer
-ldr	r1,[r1]
-add	r1,#0x80
-ldr	r2,=#0x120
-.short	0xF800
-
 ldr	r0,=drawSnake
 mov	lr,r0
 .short	0xF800
@@ -194,3 +204,12 @@ b	main
 skipSnake:
 swi	#5		@wait for vblank
 b	main
+
+gameover:
+@back to title screen
+ldr	r0,=fadeOut
+mov	lr,r0
+.short	0xF800
+ldr	r0,=titlescreenLoop
+mov	lr,r0
+.short	0xF800

ASM/titlescreenLoop.s

@@ -1,7 +1,10 @@
 .thumb
 
-@set background 0 to 256 colors mode, and change priority
 ldr	r0,=#0x04000000
+mov	r1,#3
+strb	r1,[r0,#1]	@turn on bg layers 0 and 1
+
+@set background 0 to 256 colors mode, and change priority
 mov	r1,#0x81
 strb	r1,[r0,#8]
 

ROM Buildfile.event

@@ -136,14 +136,14 @@ ALIGN 4
 bgTilemapsBuffer:
 WORD $03000000
 WORD $03000800
-WORD $0
+WORD $03001000
 WORD $0
 
 ALIGN 4
 bgTilemaps:
 WORD $0600F800
 WORD $0600F000
-WORD $0
+WORD $0600E800
 WORD $0
 
 ALIGN 4
@@ -181,3 +181,8 @@ presstartTSA:
 SHORT 0 25
 #incbin "Graphics\pressstart.tsa.bin"
 
+ALIGN 4
+backgroundgridTSA:
+SHORT 0 320
+#incbin "Graphics\backgroundgrid.tsa.bin"
+