Added background buffers, updated routines to use them

ASM/Snake/cleanSnake.s

@@ -1,7 +1,9 @@
 .thumb
 
-ldr	r0,=#0x0600F800
-ldr	r1,=#0x0600FD00
+ldr	r0,=bgTilemapsBuffer
+ldr	r0,[r0]
+ldr	r1,=#0x500
+add	r1,r0
 mov	r2,#0
 
 loop:

ASM/copyBuffers.s

@@ -0,0 +1,39 @@
+.thumb
+
+push	{r4-r7}
+mov	r7,#0
+ldr	r4,=bgTilemapsBuffer
+ldr	r5,=bgTilemaps
+
+loop1:
+mov	r6,r7
+lsl	r6,#2
+mov	r2,#0
+ldr	r3,=#0x5000
+ldr	r0,=#0x02000000
+add	r0,#0x10
+ldrb	r0,[r0,r7]
+cmp	r0,#0
+beq	next
+ldr	r0,[r4,r6]
+cmp	r0,#0
+beq	next
+ldr	r1,[r5,r6]
+cmp	r1,#0
+beq	next
+loop2:
+ldr	r6,[r0,r2]
+str	r6,[r1,r2]
+cmp	r2,r3
+beq	next
+add	r2,#4
+b	loop2
+next:
+add	r7,#1
+cmp	r7,#4
+beq	End
+b	loop1
+
+End:
+pop	{r4-r7}
+bx	lr

ASM/drawTile.s

@@ -2,25 +2,24 @@
 
 push	{lr}
 
-@r0 = tile attribute (palette,tile id, flipping?
-@r1 = bg layer
+@r0 = bg layer
+@r1 = tile attribute (palette,tile id, flipping?
 @r2 = x
 @r3 = y
 
 push	{r4,r5}
 mov	r4,r2
 mov	r5,r3
 
-@set starting size of snake
-lsl	r1,#2
-ldr	r2,=bgTilemaps
-add	r1,r2
-ldr	r1,[r1]		@bg layer map offset
+lsl	r0,#2
+ldr	r2,=bgTilemapsBuffer
+add	r0,r2
+ldr	r0,[r0]		@bg layer map offset
 lsl	r4,#1		@x*2 (*2 since each tile is a short)
-add	r1,r4
+add	r0,r4
 lsl	r5,#6		@y*32*2 (32 being the ammount of tiles in a row)
-add	r1,r5		@final offset = bg layer map offset + x*2 + y*32*2
-strh	r0,[r1]
+add	r0,r5		@final offset = bg layer map offset + x*2 + y*32*2
+strh	r1,[r0]
 
 End:
 pop	{r4,r5}

ASM/mainLoop.s

@@ -38,6 +38,15 @@ noButtons:
 
 swi	#5		@wait for vblank
 
+ldr	r0,=copyBuffers
+mov	lr,r0
+.short	0xF800
+
+ldr	r0,=#0x02000000
+add	r0,#0x10
+mov	r1,#0
+strb	r1,[r0]		@set bg 0 to not be updated
+
 ldrb	r0,=#0x02000000
 ldrb	r1,[r0,#3]	@speed
 ldrb	r2,[r0,#4]	@counter
@@ -49,6 +58,11 @@ blo	skipSnake	@if counter is lower than speed, skip game logic and wait another
 mov	r3,#0
 strb	r3,[r0,#4]	@counter
 
+ldr	r0,=#0x02000000
+add	r0,#0x10
+mov	r1,#1
+strb	r1,[r0]		@set bg 0 to be updated
+
 ldr	r0,=turnSnake
 mov	lr,r0
 .short	0xF800

RAM map.txt

@@ -0,0 +1,16 @@
+$02000000  SHORT  Snake current size
+$02000002  BYTE   Snake facing direction
+$02000003  BYTE   Game speed
+$02000004  BYTE   Counter
+$02000005  BYTE   Buttons being pressed
+$02000006  SHORT  Egg coordinates
+$02000008  WORD   RNG seed
+$0200000C  BYTE   This byte is set after the first time RNG is used
+$0200000D  BYTE   Game state
+$0200000E  SHORT  Snake new size
+$02000010  BYTE   Update background map 0 flag
+$02000011  BYTE   Update background map 1 flag
+$02000012  BYTE   Update background map 2 flag
+$02000013  BYTE   Update background map 3 flag
+...
+$02000020  LIST   Snake body piece coordinates

ROM Buildfile.event

@@ -36,6 +36,9 @@ rng:
 drawTile:
 #inctext lyn "ASM\drawTile.elf" //draw tile at given coords and background layer
 
+copyBuffers:
+#inctext lyn "ASM\copyBuffers.elf" //copy the tilemap buffers over to their destination
+
 makeTileAttribute:
 #inctext lyn "ASM\makeTileAttribute.elf" //piece together the short for the tile based on the attributes
 
@@ -79,6 +82,13 @@ facing directions of the snake:
 
 //the snake's longest possible length is 540, so I'm going to limit it to that and cause a game over if it's reched
 
+ALIGN 4
+bgTilemapsBuffer:
+WORD $03000000
+WORD $0
+WORD $0
+WORD $0
+
 ALIGN 4
 bgTilemaps:
 WORD $0600F800