preserve screen holes across demo

src/4cade.a

@@ -13,6 +13,7 @@ FirstMover
 Reenter                              ; self-running demos should call this to exit back to 4cade
          +READ_RAM1_WRITE_RAM1
          jsr   CloseHandles          ; close any open handles to restore ProRWTS state to original
+         jsr   SaveScreenHoles       ; restore screen hole contents from saved copy
 Main
          ldx   #$FF
          txs

src/4cade.init.a

@@ -51,6 +51,11 @@ ProRWTSBuffer
                                      ; so we reuse as much of the 1-time code as possible
                                      ; and fill the rest with zeros
 OneTimeSetup
+         lda   MachineStatus
+         sta   oldstatus
+         jsr   SaveScreenHoles       ; save initial copy of screen hole content
+         lda   #$91
+         sta   holepatch             ; enable restoring of copy from now on
          lda   hddopendir+1          ; save current directory as 'root'
          ldy   hddopendir+3
          +STAY gRootDirectory

src/glue.prorwts2.a

@@ -7,6 +7,8 @@
 ; - LoadFile
 ; - LoadDHRFile
 ; - SaveSmallFile
+; - CloseHandles
+; - SaveScreenHoles
 ;
 ; A general note about paths:
 ;
@@ -240,6 +242,15 @@ traverse
 @go
          rts
 
+;------------------------------------------------------------------------------
+; promote [private]
+;
+; tiny ProDOS-style interface for ProRWTS
+; in:    whatever ProDOS expects for the supported functions
+; out:   carry clear, A=0
+;        X, Y, and other flags clobbered
+;------------------------------------------------------------------------------
+
 promote
 !pseudopc $bf00 {
         lda    $c08b
@@ -269,6 +280,50 @@ ProDOS_prefix=$bfd0
 }
 end_promote
 
+;------------------------------------------------------------------------------
+; SaveScreenHoles
+; preserve screen hole contents across demo execution
+; to avoid crashing later on disk access
+;
+; in:    nothing
+; out:   all flags clobbered
+;        all registers clobbered
+;------------------------------------------------------------------------------
+
+SaveScreenHoles
+    lda    #4
+    sta    namhi
+    ldx    #0
+    stx    namlo
+    sta    bloklo
+--  ldy    #$78
+-   lda    (namlo),y
+    pha
+    lda    holey_stuff,x
+holepatch ;sta->lda
+    lda    (namlo),y
+    pla
+    sta    holey_stuff,x
+    inx
+    tya
+    eor    #$80
+    tay
+    bmi    -
+    iny
+    bpl    -
+    inc    namhi
+    dec    bloklo
+    bne    --
+    lda    oldstatus
+    ldx    MachineStatus
+    sta    MachineStatus
+    sta    oldstatus
+    rts
+oldstatus
+    !byte  0
+holey_stuff
+    !fill  64
+
 ;------------------------------------------------------------------------------
 ; ProDOS_enter
 ; intercept certain ProDOS requests

src/ui.attract.mode.a

@@ -82,6 +82,7 @@ gAttractIndex
 
          +LOAD_FILE_IMM @key
 
+         jsr   SaveScreenHoles       ; save screen hole contents in case game changes them
          ldx   #(End_Prelaunch-Prelaunch-1)
 -        lda   Prelaunch,x           ; copy pre-launch code to main memory
          sta   $100,x