Update Jack Bros. to v1.1

README.md

@@ -7,7 +7,7 @@ Here's a few assembly patches for Virtual Boy games.
   * erase saves with the normal in-game menu under Individual Records
 * `jackbros-save.asm`
   * compatible with `Jack Bros. (USA).vb` **only**
-  * does not apply to the Japan ROM but adds the option to switch language (English/Japanese) by holding the **Start** button while booting the game. Defaults to English, but the language setting *is* saved
+  * does not apply to the Japan ROM but you can use the secret language-swap button code built into the original game (!). Hold **L**, **R** and **Left D-Pad Left** then press **Start** on the title screen; this will switch languages and save the new setting to SRAM
   * saves the most recent password entered *or* received via gameplay. In line with this, the `PASSWORD` option on the title screen is now the `CONTINUE` option
   * latest saved password can be loaded by pressing **Start** on the Continue screen. If a password is available, a prompt is added to the password entry screen
   * enables the [debug mode and Japan-only sound test feature](https://www.virtual-boy.com/games/jack-bros/guides/)

jackbros-save.asm

@@ -64,6 +64,12 @@ FONT_CHECK:
     ld.h 0x00f2[r25], r11
     cmp r0, r11
 
+; Secret language switch built into the game?! Hijack this to switch in SRAM
+!ORG 0x0700461E
+!SEEK 0x0461E
+    jr LANGUAGE_SWAP        ; st.h r6, 0x00F2[r25]
+LANGUAGE_SWAP_RETURN:
+
 ; Read language byte from save (0x600) instead of ROM (0x700) everywhere
 !SEEK 0x0481A
     movhi 0x600, r0, r1
@@ -153,16 +159,8 @@ CHECK_SRAM:
     movhi 0x600, r0, r6
     ld.w 0x0000[r6], r7
     cmp r1, r7
-    be LANGUAGE_CHECK
-    jal CLEAR_SRAM
-LANGUAGE_CHECK:
-    movhi 0x200, r0, r7
-    ld.b 0x0014[r7], r7
-    andi 0x10, r7, r0
     be CLEAR_MEM
-    ld.b 0x0004[r6], r7
-    xori 0xFF, r7, r7
-    st.b r7, 0x0004[r6]
+    jal CLEAR_SRAM
 CLEAR_MEM:
     mov r25, r6
     movea 0x4000, r0, r7
@@ -187,6 +185,15 @@ CLEAR_SRAM:
     ?pop r1, r6, r7
     jmp [lp]
 
+LANGUAGE_SWAP:
+    ?push r7
+    movhi 0x600, r0, r1
+    ld.b 0x0004[r1], r7
+    xor r7, r6
+    st.h r6, 0x0004[r1]
+    ?pop r7
+    jr LANGUAGE_SWAP_RETURN
+
 CONTINUE:
     ?push r6
     ld.h 0x0010[r25], r6