diff --git a/GenerateVRAMTable.py b/GenerateVRAMTable.py
index 2ad086e..11e0c81 100755
--- a/GenerateVRAMTable.py
+++ b/GenerateVRAMTable.py
@@ -6,7 +6,7 @@ import sys
 def main(argv):
 
 	# Prologue
-	print ("vramRowEnds:",end="")
+	print ("vramRowEndsMinusOne:",end="")
 	v = 0x20a0
 	rowCount = 19
 	
@@ -16,7 +16,7 @@ def main(argv):
 			print ("\n\t.word ", end="")
 			rowCount=0
 		
-		print ("$%x" % v, end="")
+		print ("$%x" % (v-1), end="")
 		if (rowCount<19):
 			print (",", end="")
 		v += 160
diff --git a/gscats.2mg b/gscats.2mg
index 93a11e4..1f80779 100644
Binary files a/gscats.2mg and b/gscats.2mg differ
diff --git a/tables.s b/tables.s
index bcf27f4..312181c 100644
--- a/tables.s
+++ b/tables.s
@@ -32,14 +32,14 @@ sineTable:
 	.byte $4F, $52, $55, $58, $5B, $5E, $61, $64
 	.byte $67, $6A, $6D, $70, $74, $77, $7A, $7D
 
-vramRowEnds:
-	.word $20a0,$2140,$21e0,$2280,$2320,$23c0,$2460,$2500,$25a0,$2640,$26e0,$2780,$2820,$28c0,$2960,$2a00,$2aa0,$2b40,$2be0,$2c80
-	.word $2d20,$2dc0,$2e60,$2f00,$2fa0,$3040,$30e0,$3180,$3220,$32c0,$3360,$3400,$34a0,$3540,$35e0,$3680,$3720,$37c0,$3860,$3900
-	.word $39a0,$3a40,$3ae0,$3b80,$3c20,$3cc0,$3d60,$3e00,$3ea0,$3f40,$3fe0,$4080,$4120,$41c0,$4260,$4300,$43a0,$4440,$44e0,$4580
-	.word $4620,$46c0,$4760,$4800,$48a0,$4940,$49e0,$4a80,$4b20,$4bc0,$4c60,$4d00,$4da0,$4e40,$4ee0,$4f80,$5020,$50c0,$5160,$5200
-	.word $52a0,$5340,$53e0,$5480,$5520,$55c0,$5660,$5700,$57a0,$5840,$58e0,$5980,$5a20,$5ac0,$5b60,$5c00,$5ca0,$5d40,$5de0,$5e80
-	.word $5f20,$5fc0,$6060,$6100,$61a0,$6240,$62e0,$6380,$6420,$64c0,$6560,$6600,$66a0,$6740,$67e0,$6880,$6920,$69c0,$6a60,$6b00
-	.word $6ba0,$6c40,$6ce0,$6d80,$6e20,$6ec0,$6f60,$7000,$70a0,$7140,$71e0,$7280,$7320,$73c0,$7460,$7500,$75a0,$7640,$76e0,$7780
-	.word $7820,$78c0,$7960,$7a00,$7aa0,$7b40,$7be0,$7c80,$7d20,$7dc0,$7e60,$7f00,$7fa0,$8040,$80e0,$8180,$8220,$82c0,$8360,$8400
-	.word $84a0,$8540,$85e0,$8680,$8720,$87c0,$8860,$8900,$89a0,$8a40,$8ae0,$8b80,$8c20,$8cc0,$8d60,$8e00,$8ea0,$8f40,$8fe0,$9080
-	.word $9120,$91c0,$9260,$9300,$93a0,$9440,$94e0,$9580,$9620,$96c0,$9760,$9800,$98a0,$9940,$99e0,$9a80,$9b20,$9bc0,$9c60,$9d00
+vramRowEndsMinusOne:
+	.word $209f,$213f,$21df,$227f,$231f,$23bf,$245f,$24ff,$259f,$263f,$26df,$277f,$281f,$28bf,$295f,$29ff,$2a9f,$2b3f,$2bdf,$2c7f
+	.word $2d1f,$2dbf,$2e5f,$2eff,$2f9f,$303f,$30df,$317f,$321f,$32bf,$335f,$33ff,$349f,$353f,$35df,$367f,$371f,$37bf,$385f,$38ff
+	.word $399f,$3a3f,$3adf,$3b7f,$3c1f,$3cbf,$3d5f,$3dff,$3e9f,$3f3f,$3fdf,$407f,$411f,$41bf,$425f,$42ff,$439f,$443f,$44df,$457f
+	.word $461f,$46bf,$475f,$47ff,$489f,$493f,$49df,$4a7f,$4b1f,$4bbf,$4c5f,$4cff,$4d9f,$4e3f,$4edf,$4f7f,$501f,$50bf,$515f,$51ff
+	.word $529f,$533f,$53df,$547f,$551f,$55bf,$565f,$56ff,$579f,$583f,$58df,$597f,$5a1f,$5abf,$5b5f,$5bff,$5c9f,$5d3f,$5ddf,$5e7f
+	.word $5f1f,$5fbf,$605f,$60ff,$619f,$623f,$62df,$637f,$641f,$64bf,$655f,$65ff,$669f,$673f,$67df,$687f,$691f,$69bf,$6a5f,$6aff
+	.word $6b9f,$6c3f,$6cdf,$6d7f,$6e1f,$6ebf,$6f5f,$6fff,$709f,$713f,$71df,$727f,$731f,$73bf,$745f,$74ff,$759f,$763f,$76df,$777f
+	.word $781f,$78bf,$795f,$79ff,$7a9f,$7b3f,$7bdf,$7c7f,$7d1f,$7dbf,$7e5f,$7eff,$7f9f,$803f,$80df,$817f,$821f,$82bf,$835f,$83ff
+	.word $849f,$853f,$85df,$867f,$871f,$87bf,$885f,$88ff,$899f,$8a3f,$8adf,$8b7f,$8c1f,$8cbf,$8d5f,$8dff,$8e9f,$8f3f,$8fdf,$907f
+	.word $911f,$91bf,$925f,$92ff,$939f,$943f,$94df,$957f,$961f,$96bf,$975f,$97ff,$989f,$993f,$99df,$9a7f,$9b1f,$9bbf,$9c5f,$9cff
diff --git a/terrain.s b/terrain.s
index a3aa6b1..de0fe61 100644
--- a/terrain.s
+++ b/terrain.s
@@ -8,6 +8,218 @@
 TERRAINWIDTH = 640		; In pixels
 MAXTERRAINHEIGHT = 100	; In pixels
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; renderTerrain
+;
+; No stack operations permitted here!
+;
+renderTerrain:
+	lda #199*2
+	sta <ROWINDEX
+	sty <MAPSCROLLPOS
+
+	FASTGRAPHICS
+
+renderTerrainLoop:
+	; = 29 cycles per row
+	ldy <ROWINDEX		; 3
+	lda vramRowEndsMinusOne,y	; 4   Point stack to end of VRAM row
+	tcs					; 2
+
+	jmp renderClippedSpanChain	; 3
+
+renderSpanChainComplete:
+	lda <ROWINDEX			; 3
+	dec						; 2
+	dec						; 2
+	cmp #(200-MAXTERRAINHEIGHT)*2	; 2
+	beq renderTerrainDone	; 2/3
+	sta <ROWINDEX			; 3
+	bra renderTerrainLoop	; 2/3
+
+renderTerrainDone:
+	SLOWGRAPHICS
+	rts
+
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; renderClippedSpanChain
+;
+; No stack operations permitted here!
+;
+;
+renderClippedSpanChain:
+
+	; Prepare our state
+	; = 24 cycles per row + 80 cycles for actual pixels
+	lda #80					; 2
+	sta <XLEFT				; 3
+	lda #$1111				; 2
+	sta <CURRMAPPIXELS		; 3
+	ldy #spanChainEnd-spanChain-2	; 2
+	lda <MAPSCROLLPOS				; 3
+	sta <RIGHTEDGE					; 3
+	lda #renderClippedSpanChainRenderNext	; 2
+	sta renderSpanComplete+1		; 4
+
+	; Find right edge of screen within span chains
+	; = 27 cycles per skipped span
+renderClippedSpanChainLoop:
+
+	lda spanChain,y		; 5
+	sec					; 2
+	sbc <RIGHTEDGE		; 3
+	bmi renderClippedSpanChainNextSpan	; 2/3
+	beq renderClippedSpanChainNextSpan	; 2/3
+
+renderClippedSpanChainLoop2:
+	; Now render spans until left edge of screen
+	; = 28 cycles per span rendered
+	cmp <XLEFT			; 3
+	bcs renderClippedSpanChainLastSpan	; 2/3
+
+	; Render this span
+	ldx spanColors,y	; 4
+	stx <CURRMAPPIXELS	; 3
+
+	asl					; 2
+	tax					; 2
+	jmp (renderSpanJumpTable,x)	; 6   (jmp back = 6)
+
+renderSpanComplete:
+	; This is modified to redirect return from the
+	; unrolled span rendering blocks
+	jmp renderClippedSpanChainRenderNext	; 3
+
+
+renderClippedSpanChainRenderNext:
+	; Track remaining words until left edge
+	; = 26 cycles per span rendered
+	lsr					; 2
+	eor #$ffff			; 2
+	inc					; 2
+	clc					; 2
+	adc <XLEFT			; 3
+	sta <XLEFT			; 3
+	dey					; 2
+	dey					; 2
+
+	; For mid-stream spans, bypass the right-edge clipping code
+	lda spanChain,y		; 5
+	bra renderClippedSpanChainLoop2	; 3
+
+renderClippedSpanChainNextSpan:
+	; Track remaining distance from right edge and
+	; continue searching for visible right edge
+	eor #$ffff			; 2
+	inc					; 2
+	sta <RIGHTEDGE		; 3
+	dey					; 2
+	dey					; 2
+	bra renderClippedSpanChainLoop	; 3
+
+renderClippedSpanChainLastSpan:
+	; Render visible portion of last visible span
+	; = 26 cycles per row
+	ldx spanColors,y	; 4
+	stx <CURRMAPPIXELS	; 3
+
+	lda <XLEFT			; 3
+	asl					; 2
+	tax					; 2
+
+	lda #renderSpanChainComplete	; 2
+	sta renderSpanComplete+1	; 4
+	jmp (renderSpanJumpTable,x)	; 6
+
+
+
+; Clipping state in zero page. All distances in words (4 px)
+MAPSCROLLPOS	= $06	; Right edge of visible region
+XLEFT			= $08	; Remaining horizontal distance to render
+RIGHTEDGE		= $19	; Distance from right edge of terrain to right edge of visible region
+CURRMAPPIXELS	= $67	; 4 pixels being rendered right now
+ROWINDEX		= $69	; Index of row being rendered
+
+spanChain:
+	.word 20,40,10,5,5,5,5,10,40,20
+spanChainEnd:
+	
+spanColors:
+	.word $1111,$0000,$1111,$0000,$1111,$0000,$1111,$0000,$1111,$0000
+
+spanChainIndex:
+	.word 0
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; generateTerrain
+;
+; Trashes A and Y
+;
+
+generateTerrain:
+	ldy #0
+	lda #terrainData
+	sta SCRATCHL
+
+generateTerrainLoop:
+
+	phy
+	tya		; Pull an interesting value out of the sine table
+	and #$00ff
+	tay
+	lda sineTable,y
+	and #$7f7f
+	ply
+
+	sta (SCRATCHL),y
+	iny
+	cpy #TERRAINWIDTH/4
+	bne generateTerrainLoop
+
+	rts
+
+
+.include "spanRender.s"
+
+; Terrain data, stored as height values 4 pixels wide
+
+terrainData:
+	.repeat TERRAINWIDTH/2
+	.byte 0
+	.endrepeat
+
+
+.if 0
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; renderSpanChain
+;
+; Trashes all registers
+; No stack operations permitted here!
+; This is fast, but doesn't support scrolling, so probably not useful
+;
+
+renderSpanChain:
+	stz spanChainIndex
+
+renderSpanChainLoop:
+	ldx spanChainIndex
+	ldy spanChain+2,x
+	lda spanChain,x
+	beq renderSpanChainComplete
+	dec
+	asl
+	tax
+	jmp (renderSpanJumpTable,x)
+
+;renderSpanComplete:
+	inc spanChainIndex
+	inc spanChainIndex
+	inc spanChainIndex
+	inc spanChainIndex
+	bra renderSpanChainLoop
+
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ; renderTerrainColumn
 ;
@@ -93,209 +305,5 @@ renderTerrainColumnsLoop:
 
 renderTerrainColumnsDone:
 	rts
+.endif
 
-
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-; renderTerrain
-;
-; No stack operations permitted here!
-;
-renderTerrain:
-	lda #199
-	sta spanChainIndex
-	sty <MAPSCROLLPOS
-
-	FASTGRAPHICS
-
-renderTerrainLoop:
-	lda spanChainIndex
-	asl
-	tay
-	lda vramRowEnds,y ;$9d00-1	; Point stack to end of VRAM row
-	dec
-	tcs
-
-	jmp renderClippedSpanChain
-
-renderSpanChainComplete:
-	lda spanChainIndex
-	dec
-	cmp #200-MAXTERRAINHEIGHT
-	beq renderTerrainDone
-	sta spanChainIndex
-	bra renderTerrainLoop
-
-renderTerrainDone:
-	SLOWGRAPHICS
-	rts
-
-
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-; renderSpanChain
-;
-; Trashes all registers
-; No stack operations permitted here!
-;
-
-renderSpanChain:
-	stz spanChainIndex
-
-renderSpanChainLoop:
-	ldx spanChainIndex
-	ldy spanChain+2,x
-	lda spanChain,x
-	beq renderSpanChainComplete
-	dec
-	asl
-	tax
-	jmp (renderSpanJumpTable,x)
-
-;renderSpanComplete:
-	inc spanChainIndex
-	inc spanChainIndex
-	inc spanChainIndex
-	inc spanChainIndex
-	bra renderSpanChainLoop
-
-
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-; renderClippedSpanChain
-;
-; No stack operations permitted here!
-;
-;
-renderClippedSpanChain:
-
-	; Prepare our state
-	lda #80
-	sta <XLEFT
-	lda #$1111
-	sta <CURRMAPPIXELS
-	ldy #spanChainEnd-spanChain-2
-	lda <MAPSCROLLPOS
-	sta <RIGHTEDGE
-	lda #renderClippedSpanChainRenderNext
-	sta renderSpanComplete+1
-
-	; Find right edge of screen within span chains
-renderClippedSpanChainLoop:
-
-	lda spanChain,y		; 5
-	sec					; 2
-	sbc <RIGHTEDGE		; 3
-	bmi renderClippedSpanChainNextSpan	; 2/3
-	beq renderClippedSpanChainNextSpan	; 2/3
-
-renderClippedSpanChainLoop2:
-	cmp <XLEFT			; 3
-	bcs renderClippedSpanChainLastSpan	; 2/3
-
-	; Render this span
-	ldx spanColors,y	; 4
-	stx <CURRMAPPIXELS	; 3
-
-	asl					; 2
-	tax					; 2
-	jmp (renderSpanJumpTable,x)	; 6
-
-renderSpanComplete:
-	; This is modified to redirect return from the
-	; unrolled span rendering blocks
-	jmp renderClippedSpanChainRenderNext	; 3
-
-
-renderClippedSpanChainRenderNext:
-
-	; Track remaining words until left edge
-	lsr					; 2
-	eor #$ffff			; 2
-	inc					; 2
-	clc					; 2
-	adc <XLEFT			; 3
-	sta <XLEFT			; 3
-	dey					; 2
-	dey					; 2
-
-	; For mid-stream spans, bypass the right-edge clipping code
-	lda spanChain,y		; 5
-	bra renderClippedSpanChainLoop2	; 3
-
-renderClippedSpanChainNextSpan:
-	; Track remaining distance from right edge and
-	; continue searching for visible right edge
-	eor #$ffff			; 2
-	inc					; 2
-	sta <RIGHTEDGE		; 3
-	dey					; 2
-	dey					; 2
-	bra renderClippedSpanChainLoop	; 3
-
-renderClippedSpanChainLastSpan:
-
-	; Render visible portion of last visible span
-	ldx spanColors,y	; 4
-	stx <CURRMAPPIXELS	; 3
-
-	lda <XLEFT			; 3
-	asl					; 2
-	tax					; 2
-
-	lda #renderSpanChainComplete
-	sta renderSpanComplete+1
-	jmp (renderSpanJumpTable,x)	; 6
-
-
-
-; Clipping state in zero page. All distances in words (4 px)
-MAPSCROLLPOS	= $06	; Right edge of visible region
-XLEFT			= $08	; Remaining horizontal distance to render
-RIGHTEDGE		= $19	; Distance from right edge of terrain to right edge of visible region
-CURRMAPPIXELS	= $67	; 4 pixels being rendered right now
-
-spanChain:
-	.word 20,40,10,5,5,5,5,10,40,20
-spanChainEnd:
-	
-spanColors:
-	.word $1111,$0000,$1111,$0000,$1111,$0000,$1111,$0000,$1111,$0000
-
-spanChainIndex:
-	.word 0
-
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-; generateTerrain
-;
-; Trashes A and Y
-;
-
-generateTerrain:
-	ldy #0
-	lda #terrainData
-	sta SCRATCHL
-
-generateTerrainLoop:
-
-	phy
-	tya		; Pull an interesting value out of the sine table
-	and #$00ff
-	tay
-	lda sineTable,y
-	and #$7f7f
-	ply
-
-	sta (SCRATCHL),y
-	iny
-	cpy #TERRAINWIDTH/4
-	bne generateTerrainLoop
-
-	rts
-
-
-.include "spanRender.s"
-
-; Terrain data, stored as height values 4 pixels wide
-
-terrainData:
-	.repeat TERRAINWIDTH/2
-	.byte 0
-	.endrepeat