From 33e8319078be087dc7f59050772889e636a646d3 Mon Sep 17 00:00:00 2001
From: Tom Greene <tom@cowgod.org>
Date: Wed, 29 Jul 2020 22:27:46 -0400
Subject: [PATCH] Treat SHR registers as write-only (#318)

* Treat SHR registers as write-only

* Revert "no VidHD"

This reverts commit dffb3b1cda9aeb3b67a228960802d16533786a56.
---
 src/4cade.init.a     | 12 ------------
 src/ui.attract.shr.a |  9 +++------
 src/ui.common.a      |  6 +++---
 3 files changed, 6 insertions(+), 21 deletions(-)

diff --git a/src/4cade.init.a b/src/4cade.init.a
index 8afbbc146..88476543a 100644
--- a/src/4cade.init.a
+++ b/src/4cade.init.a
@@ -35,18 +35,6 @@
          sta   zpMachineStatus
          sta   SETC3ROM
          jsr   HasVidHDCard          ; check for VidHD card (allows super hi-res artwork even on non-IIgs machines)
-         bcc   +
-
-         ldy   #@VidHDlen
--        lda   @s_VidHD,y
-         sta   $68A,y
-         dey
-         bpl   -
-@hang2   bmi   @hang2
-@s_VidHD !scrxor $80,"CANNOT RUN WITH VIDHD"
-@VidHDlen=(*-@s_VidHD)-1
-
-+
          sta   CLRC3ROM
          ror   zpMachineStatus
          lda   ROM_MACHINEID
diff --git a/src/ui.attract.shr.a b/src/ui.attract.shr.a
index 7f0bd8d3e..fac37298b 100644
--- a/src/ui.attract.shr.a
+++ b/src/ui.attract.shr.a
@@ -123,14 +123,12 @@ SHRArtworkCallback
 BlankSHR
          jsr   Home
 
-         lda   NEWVIDEO              ; set GS NEWVIDEO mode to turn on linearize
-         ora   #%01000000            ; can't use TSB here - might not be 65816
+         lda   #%01000001             ; set GS NEWVIDEO mode to turn on linearize
          sta   NEWVIDEO
 
          sta   WRITEAUXMEM           ; writes go to auxmem
 
-         lda   SHADOW                ; enable auxmem-to-bank-E1 shadowing on IIgs
-         and   #$F7                  ; can't use TRB here - might not be 65816
+         lda   #$00                  ; enable auxmem-to-bank-E1 shadowing on IIgs
          sta   SHADOW
 
          lda   #$20                  ; clear $2000..$9FFF in auxmem
@@ -139,8 +137,7 @@ BlankSHR
 
          sta   WRITEMAINMEM          ; writes go to main memory
 
-         lda   NEWVIDEO              ; set GS NEWVIDEO mode to turn on SHR mode
-         ora   #%10000001            ; can't use TSB here - might not be 65816
+         lda   #%11000001            ; set GS NEWVIDEO mode to turn on SHR mode
          sta   NEWVIDEO
 
          rts
diff --git a/src/ui.common.a b/src/ui.common.a
index 59ea601f6..b2198197d 100755
--- a/src/ui.common.a
+++ b/src/ui.common.a
@@ -22,11 +22,11 @@ Home
          lda   MachineStatus
          and   #SUPPORTS_SHR
          beq   @noSHR
-         lda   NEWVIDEO
-         and   #%00011111            ; bit 7 = 0 -> IIgs Apple II-compatible video modes
+         lda   #%00000001            ; bit 7 = 0 -> IIgs Apple II-compatible video modes
                                      ; bit 6 = 0 -> IIgs 128K memory map is the same as the Apple IIe
                                      ; bit 5 = 0 -> IIgs DHGR is color, not monochrome
-                                     ; bits 0-4 unchanged
+                                     ; bits 1-4 reserved
+                                     ; bit 0 = 1 -> disable bank latch
          sta   NEWVIDEO
          lda   #$F0
          sta   TBCOLOR               ; white text on black background