set alternate display mode on IIgs

fixes https://github.com/a2-4am/4cade/issues/4

src/4cade.init.a

@@ -19,6 +19,10 @@
          bcs   @no64K
          jsr   DisableAccelerator    ; set to 1 MHz (supports IIgs and many common accelerator cards)
          jsr   IsGS                  ; check for IIgs (allows super hi-res artwork)
+         php
+         bcc   +
+         jsr   ROM_TEXT2COPY         ; set alternate display mode on IIgs (required for some games)
++        plp
          ror   zpMachineStatus
          sta   SETC3ROM
          jsr   HasVidHDCard          ; check for VidHD card (allows super hi-res artwork even on non-IIgs machines)
@@ -31,7 +35,6 @@
                                      ;     bit 5 = 1 if VidHD
                                      ;     bit 6 = 1 if 128K
                                      ;     bit 7 = 1 if joystick
-
          +READ_ROM_WRITE_RAM2
          jsr   init                  ; initialize and relocate ProRWTS2 to $D400 in RAM bank 2
                                      ; ProRWTS2 disk-data live at $D000-D3FF

src/constants.a

@@ -47,6 +47,7 @@ DHIRESOFF =    $C05F      ; double hi-res off switch
 ; ROM routines and addresses
 ; (prefixed because so much of the program runs from LC RAM, so don't call
 ; these without thinking about memory banks first)
+ROM_TEXT2COPY =$F962      ; turn on alternate display mode on IIgs
 ROM_TEXT =     $FB2F
 ROM_MACHINEID =$FBB3
 ROM_HOME =     $FC58