Draw the scorpion once we are sure the beam has past it on the screen for the previous frame. Adjust the wait for VBL look to look for less than scan line 200 rather than scan line 0. That way, we shouldn't get a frame glitch at 2.8MHz any more.

BuGS/game.s

@@ -30,7 +30,22 @@ game    start
         jsl setColour
 
 gameLoop anop
-        jsl drawDirtyGameTiles
+        
+        _drawDirtyGameRow 0
+        _drawDirtyGameRow 1
+        _drawDirtyGameRow 2
+        _drawDirtyGameRow 3
+        _drawDirtyGameRow 4
+        _drawDirtyGameRow 5
+        _drawDirtyGameRow 6
+        _drawDirtyGameRow 7
+        _drawDirtyGameRow 8
+        _drawDirtyGameRow 9
+        _drawDirtyGameRow 10
+        _drawDirtyGameRow 11
+        _drawDirtyGameRow 12
+        _drawDirtyGameRow 13
+        _drawDirtyGameRow 14
         
         short i,m
         lda >BORDER_COLOUR_REGISTER
@@ -38,7 +53,18 @@ gameLoop anop
         sta >BORDER_COLOUR_REGISTER
         long i,m
         
-        jsl drawSpider
+        jsl drawScorpion
+        
+        _drawDirtyGameRow 15
+        _drawDirtyGameRow 16
+        _drawDirtyGameRow 17
+        _drawDirtyGameRow 18
+        _drawDirtyGameRow 19
+        _drawDirtyGameRow 20
+        _drawDirtyGameRow 21
+        _drawDirtyGameRow 22
+        _drawDirtyGameRow 23
+        _drawDirtyGameRow 24
         
         short i,m
         lda >BORDER_COLOUR_REGISTER
@@ -46,7 +72,7 @@ gameLoop anop
         sta >BORDER_COLOUR_REGISTER
         long i,m
         
-        jsl drawScorpion
+        jsl drawSpider
         
         short i,m
         lda >BORDER_COLOUR_REGISTER
@@ -99,34 +125,6 @@ gameDone anop
         long i,m
         
         rtl
-
-
-drawDirtyGameTiles entry
-        _drawDirtyGameRow 0
-        _drawDirtyGameRow 1
-        _drawDirtyGameRow 2
-        _drawDirtyGameRow 3
-        _drawDirtyGameRow 4
-        _drawDirtyGameRow 5
-        _drawDirtyGameRow 6
-        _drawDirtyGameRow 7
-        _drawDirtyGameRow 8
-        _drawDirtyGameRow 9
-        _drawDirtyGameRow 10
-        _drawDirtyGameRow 11
-        _drawDirtyGameRow 12
-        _drawDirtyGameRow 13
-        _drawDirtyGameRow 14
-        _drawDirtyGameRow 15
-        _drawDirtyGameRow 16
-        _drawDirtyGameRow 17
-        _drawDirtyGameRow 18
-        _drawDirtyGameRow 19
-        _drawDirtyGameRow 20
-        _drawDirtyGameRow 21
-        _drawDirtyGameRow 22
-        _drawDirtyGameRow 23
-        _drawDirtyGameRow 24
         
 
 drawDirtyNonGameTiles entry
@@ -333,7 +331,7 @@ vblLoop anop
         and #$80ff                ; mask out the VBL bits
         asl a                     ; shift the word around
         adc #0                    ; move MSB -> LSB
-        cmp #$100
+        cmp #$1c8
         bge vblLoop
         rtl
         

BuGS/make/config.txt

@@ -8,7 +8,7 @@ s6d2 =
 
 s7d1 = /Users/jrand/Library/Developer/Xcode/DerivedData/BuGS-bffpexoblaghkzcbtjtzxeulnuto/Build/Products/Debug/BuGS.2mg
 
-g_limit_speed = 3
+g_limit_speed = 0
 
 
 bram1[00] = 00 00 00 01 00 00 0d 06 02 01 01 00 01 00 00 00