Add banking helpers.

src/bankid.asm

@@ -20,12 +20,21 @@ DEF BANKID_ASM EQU 1
 
 
 SECTION "Bank ID 0", ROM0[$0]
+    REPT 7
+        rst $00
+    ENDR
     db $00
 
 SECTION "Bank ID 1", ROMX[$4000], BANK[1]
+    REPT 7
+        rst $00
+    ENDR
     db $01
 
 SECTION "Bank ID 2", ROMX[$4000], BANK[2]
+    REPT 7
+        rst $00
+    ENDR
     db $02
 
 

src/banking.asm

@@ -0,0 +1,46 @@
+; DMGTRIS
+; Copyright (C) 2023 - Randy Thiemann <randy.thiemann@gmail.com>
+
+; This program is free software: you can redistribute it and/or modify
+; it under the terms of the GNU General Public License as published by
+; the Free Software Foundation, either version 3 of the License, or
+; (at your option) any later version.
+
+; This program is distributed in the hope that it will be useful,
+; but WITHOUT ANY WARRANTY; without even the implied warranty of
+; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+; GNU General Public License for more details.
+
+; You should have received a copy of the GNU General Public License
+; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+
+IF !DEF(BANKING_ASM)
+DEF BANKING_ASM EQU 1
+
+
+INCLUDE "globals.asm"
+
+
+SECTION "High Banking Variables", HRAM
+hBankBackup: ds 1
+
+; 0x00, 0x08, 0x10, 0x18, 0x20, 0x28, 0x30, and 0x38
+SECTION "Switch Bank", ROM0[$08]
+    ; Saves the current bank and switches to the bank in b.
+RSTSwitchBank::
+    ld a, [rBANKID]
+    ldh [hBankBackup], a
+    ld a, b
+    ld [rROMB0], a
+    ret
+
+SECTION "Restore Bank", ROM0[$18]
+    ; Restore the bank previously saved. The current one is not saved.
+RSTRestoreBank::
+    ld a, [hBankBackup]
+    ld [rROMB0], a
+    ret
+
+
+ENDC

src/include/globals.asm

@@ -215,7 +215,7 @@ DEF FIELD_TOP_LEFT      EQU $9800+1
 DEF EASTER_0            EQU $9845
 DEF EASTER_1            EQU $9865
 
-DEF rBANKID             EQU $4000
+DEF rBANKID             EQU $4007
 
 
 ENDC

src/sfx.asm

@@ -2432,10 +2432,8 @@ SFXKill::
     ; This play routine must be called every frame.
 SFXPlay::
     ; Bank to SFX bank.
-    ld a, [rBANKID]
-    ld e, a
-    ld a, BANK("SFX Data")
-    ld [rROMB0], a
+    ld b, BANK("SFX Data")
+    rst RSTSwitchBank
 
     ; Load the playhead position into HL.
     ldh a, [hPlayhead]
@@ -2446,8 +2444,7 @@ SFXPlay::
     ; Nothing to do if it's a null ptr.
     or a, l
     jr nz, .getRegister
-    ld a, e
-    ld [rROMB0], a
+    rst RSTRestoreBank
     ret
 
     ; Otherwise, get the register to write to.
@@ -2458,8 +2455,7 @@ SFXPlay::
     ; If it's $FE, then we're done. Check if there's more for us in the queue.
     cp a, $FE
     jr nz, :+
-    ld a, e
-    ld [rROMB0], a
+    rst RSTRestoreBank
     call SFXProcessQueue
     ret
 
@@ -2484,8 +2480,7 @@ SFXPlay::
     ldh [hPlayhead], a
     ld a, h
     ldh [hPlayhead+1], a
-    ld a, e
-    ld [rROMB0], a
+    rst RSTRestoreBank
     ret