add cheat for Threshold

res/history.md

@@ -12,7 +12,7 @@
 
  - 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 61 game cheats
+ - Added 62 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/threshold.a

@@ -0,0 +1,34 @@
+;license:MIT
+;(c) 2019 by 4am
+
+!cpu 6502
+!to "build/PRELAUNCH/THRESHOLD",plain
+*=$106
+
+         !source "src/prelaunch/common.a"
+
+         +ENABLE_ACCEL
+         +GET_MACHINE_STATUS
+         and   #CHEATS_ENABLED
+         sta   patch+1
+         ldx   #(end_patch-patch-1) ; copy patch code to zero page (stack will be destroyed by the time we need to patch)
+-        lda   patch,x
+         sta   $100-end_patch+patch,x
+         dex
+         bpl   -
+         lda   #($100-end_patch+patch)
+         sta   $39F4
+         lda   #$00
+         sta   $39F5
+         jmp   $0800      ; decompress
+patch
+         lda   #0         ; SMC
+         beq   +
+                          ; lives in $778F
+         lda   #$AD
+         sta   $45B0      ; patch - don't decrease lives
+         sta   $7ECD      ; patch - don't increase lives
++
+         +DISABLE_ACCEL
+         jmp   $6B00
+end_patch