Fix bus conflict error when bank switching

I tried out the ROM in FCEUX 2.2.3, and ran into an issue where it looked like the bank switch wasn't properly working. I did some research, and thought this was caused by a bus conflict. This fixes it (along with expanding the CHR-ROM to be a power of 2 [i.e. 4] rather than 3). But I don't know why. See sample code at in zip at https://web.archive.org/web/20170806091648/http://nintendoage.com/forum/messageview.cfm?catid=22&threadid=17074 as well as article at https://wiki.nesdev.com/w/index.php/Bus_conflict
samcan · Jun 28, 2020 · 30f3bfe · 30f3bfe
1 parent a0ab95d
commit 30f3bfe
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Showing 3 changed files with 9 additions and 3 deletions.
diff --git a/src/chrblock.chr b/src/chrblock.chr
diff --git a/src/helper.asm b/src/helper.asm
@@ -246,10 +246,16 @@ clr_sprite_mem:
 ;;;;;;;;;;;;;;;
 ;;
 ;; Clobbers: A, X
+;;
+;; I HAVE NO IDEA WHY THIS WORKS
+;; I THOUGHT WE NEEDED TO WRITE TO $8000 TO
+;; SWITCH BANKS, WHICH WORKED IN MESEN, BUT
+;; NOT IN FCEUX. YOU'RE TELLING ME THAT WE CAN
+;; JUST WRITE TO bankvalues AND THAT SWITCHES
+;; BANKS???? WHYY???????!!!!!!!!
 BankSwitch:
   TAX
-  LDA bankvalues, x
-  STA $8000
+  STA bankvalues, x
   RTS
 ;;;;;;;;;;;;;;;
 ;;

diff --git a/src/westward.asm b/src/westward.asm
@@ -1,5 +1,5 @@
 PRG_COUNT		= 2   ; 2x 16KB PRG code
-CHR_COUNT		= 3   ; 3x  8KB CHR data
+CHR_COUNT		= 4   ; 4x  8KB CHR data
 MAPPER			= 3   ; mapper 3 = CNROM
 MIRRORING		= 1   ; background mirroring