Clear //gs Shadow Page 2 (#532)

* Fix Alternate Display Mode on ROM0 and ROM1 //gs

fixes attract hanging on ROM0 and ROM1 machines

* Clear //gs Shadow Page 2

We now control the horizontal. We now control the vertical. We now control the shadow bank of //gs video memory. Improves The Goonies and Pacman demos on ROM0/1.

src/4cade.init.a

@@ -75,7 +75,7 @@
                                      ;     bit 7 = 1 if joystick
                                      ; and all other bits are 0 (we'll set bit 3 after copying it to LC RAM)
 
-         ; accommodate uppercase-only machines (64K ][+ is supported)
+         ; accommodate uppercase-only machines (64K ][ and ][+ are supported)
          lda   ROM_MACHINEID
          cmp   #$A0
          beq   +                     ; Spectrum ED
@@ -86,6 +86,22 @@
 +        lda   #$FF
          sta   zpCharMask
 
+         ; IIgs fix for Alternate Display Mode (clear shadow page 2)
+         lda   zpMachineStatus
+         and   #IS_IIGS
+         beq   +
+         ldx   #0
+         txa
+!cpu 65816
+-        sta   $E00800,x             ; when Alternate Display Mode is turned off, the "2"s
+         sta   $E00900,x             ; displayed on the screen live at $E00800
+         sta   $E00A00,x             ; (page "2"/$0800 of IIgs bank $E0)
+         sta   $E00B00,x             ; They are initialized by the IIgs boot ROM
+         inx
+         bne   -
+!cpu 6502
++
+
          ; increase text window width so we can print to the edge of the screen without scrolling
          inc   $21
          ; print version or build number in lower right corner

src/demo/gamma.goblins.a

@@ -9,7 +9,6 @@
          !source "src/macros.a"
 
          +GAME_REQUIRES_JOYSTICK
-         +TEST_TEXT_PAGE_2
          +ENABLE_ACCEL_LC
          +LOAD_XSINGLE title
 

src/macros.a

@@ -352,9 +352,9 @@
          +READ_ROM_NO_WRITE
 }
 
-!macro   USES_TEXT_PAGE_2 {
-         lda   ROM_MACHINEID
-         cmp   #$06
+!macro   USES_TEXT_PAGE_2 {          ; If we know we are going into a game one-time
+         lda   ROM_MACHINEID         ; only we can just blindly turn on TEXT2COPY, as
+         cmp   #$06                  ; Alternate Display Mode turns off on reset or reboot.
          bne   +
          sec
          jsr   $FE1F                 ; check for IIgs
@@ -364,10 +364,10 @@
 +
 }
 
-!macro   TEST_TEXT_PAGE_2 {
-         lda   ROM_MACHINEID
-         cmp   #$06
-         bne   ++
+!macro   TEST_TEXT_PAGE_2 {          ; On a ROM3 IIgs we can test if Alternate Display Mode
+         lda   ROM_MACHINEID         ; is already on. ROM0 and ROM1 versions of ADM use
+         cmp   #$06                  ; interrupts and can cause hangs, so safer to just
+         bne   ++                    ; leave it turned off, especially in ATTRACT/DEMO mode.
          sec
          jsr   $FE1F                 ; check for IIgs
          bcs   ++
@@ -434,7 +434,7 @@
          sta   $3F4
 }
 ; for games that clobber $100-$105, the prelaunch code constructs a new reset vector
-; somewhere else and sets its
+; somewhere else and sets the reset vector to point at it.
 !macro   NEW_RESET_VECTOR .addr {
          ldx   #5
 -        lda   $100,x

src/prelaunch/gamma.goblins.a

@@ -7,7 +7,6 @@
 
          !source "src/prelaunch/common.a"
 
-         +USES_TEXT_PAGE_2
          +ENABLE_ACCEL
          lda   #$60
          sta   $2034