cx16: reset rom/ram/monitor banks at program exit to sane values.

codeGenCpu6502/src/prog8/codegen/cpu6502/ProgramAndVarsGen.kt

@@ -127,11 +127,8 @@ internal class ProgramAndVarsGen(
             "cx16" -> {
                 if(options.floats)
                     asmgen.out("  lda  #4 |  sta  $01")    // to use floats, make sure Basic rom is banked in
-                asmgen.out("  jsr  main.start |  lda  #4 |  sta  $01")
-                if(!options.noSysInit)
-                    asmgen.out("  jmp  ${compTarget.name}.cleanup_at_exit")
-                else
-                    asmgen.out("  rts")
+                asmgen.out("  jsr  main.start")
+                asmgen.out("  jmp  ${compTarget.name}.cleanup_at_exit")
             }
             "c64" -> {
                 asmgen.out("  jsr  main.start |  lda  #31 |  sta  $01")

compiler/res/prog8lib/cx16/syslib.p8

@@ -639,8 +639,12 @@ asmsub  init_system_phase2()  {
 
 asmsub  cleanup_at_exit() {
     ; executed when the main subroutine does rts
-    ; just an rts here, nothing special to clean up on cx16
     %asm {{
+        lda  #1
+        sta  $00        ; ram bank 1
+        lda  #4
+        sta  $01        ; rom bank 4 (kernal)
+        stz  $2d        ; hack to reset machine code monitor bank to 0
         rts
     }}
 }

docs/source/todo.rst

@@ -3,9 +3,6 @@ TODO
 
 For next release
 ^^^^^^^^^^^^^^^^
-- cx16 programs seem to poke 0, 56 at exit?
-- assembling hello4.asm prints stray characters in the string
-
 - petaxian roller.p8 line 49  (also see test.p8) generates large code compared to 8.2
 
 - code gen for if statements has become inefficient? vm/6502?