add cheat for Serpentine

res/history.md

@@ -11,7 +11,7 @@
 
  - Added help screen (press ? in search or browse mode to show)
  - Added global cheat mode (press Ctrl-C in search or browse mode to toggle)
- - Added 53 game cheats
+ - Added 54 game cheats
  - Fixed corrupted graphics in Asteroid Blaster
  - Fixed corrupted graphics in Sneakers game, demo, and screenshots, and now we are entirely done with this I promise
  - Fixed Axis Assassin demo hanging on IIgs

src/prelaunch/serpentine.a

@@ -0,0 +1,32 @@
+;license:MIT
+;(c) 2019 by 4am
+
+!cpu 6502
+!to "build/PRELAUNCH/SERPENTINE",plain
+*=$106
+
+         !source "src/prelaunch/common.a"
+
+         +GET_MACHINE_STATUS
+         and   #CHEATS_ENABLED
+         sta   cheat
+         ldx   #$0E       ; copy patch code to zero page (stack will be destroyed by the time we need to patch)
+-        lda   patch,x
+         sta   $F1,x
+         dex
+         bpl   -
+         lda   #$F1       ; call patch instead of $222
+         sta   $8BE3
+         lda   #$00
+         sta   $8BE4
+         jmp   $43F5      ; decompress and show title
+patch
+         jsr   $0100      ; decompress
+cheat=*+1
+         lda   #0         ; SMC
+         beq   +
+         lda   #$A5
+         sta   $868F      ; patch - don't decrease lives
+                          ; lives are capped at 3 so no further patches
++
+         jmp   $0800

src/prelaunch/up.n.down.a

@@ -10,12 +10,12 @@
          +GET_MACHINE_STATUS
          and   #CHEATS_ENABLED
          sta   patch+1
-         ldx   #7         ; copy patch code to zero page (stack will be destroyed by the time we need to patch)
+         ldx   #$0B       ; copy patch code to zero page (stack will be destroyed by the time we need to patch)
 -        lda   patch,x
-         sta   $F8,x
+         sta   $F4,x
          dex
          bpl   -
-         lda   #$F8       ; call patch instead of $200
+         lda   #$F4       ; call patch instead of $200
          sta   $4061
          lda   #$00
          sta   $4062