1 files changed, 54 insertions, 0 deletions
diff --git a/common/predef.asm b/common/predef.asm
new file mode 100644
index 000000000..bd34a87a1
--- /dev/null
+++ b/common/predef.asm
@@ -0,0 +1,54 @@
+Predef: ; 2d83
+; Call predefined function a.
+; Preserves bc, de, hl and f.
+
+	ld [PredefID], a
+	ld a, [hROMBank]
+	push af
+
+	ld a, BANK(GetPredefPointer)
+	rst Bankswitch
+	call GetPredefPointer ; stores hl in PredefTemp
+
+; Switch to the new function's bank
+	rst Bankswitch
+
+; Instead of directly calling stuff,
+; push it to the stack in reverse.
+
+	ld hl, .Return
+	push hl
+	
+; Call the Predef function
+	ld a, [PredefAddress]
+	ld h, a
+	ld a, [PredefAddress + 1]
+	ld l, a
+	push hl
+
+; Get hl back
+	ld a, [PredefTemp]
+	ld h, a
+	ld a, [PredefTemp + 1]
+	ld l, a
+	ret
+
+.Return
+; Clean up after the Predef call
+
+	ld a, h
+	ld [PredefTemp], a
+	ld a, l
+	ld [PredefTemp+1], a
+
+	pop hl
+	ld a, h
+	rst Bankswitch
+
+	ld a, [PredefTemp]
+	ld h, a
+	ld a, [PredefTemp + 1]
+	ld l, a
+	ret
+; 2dba
+