From 38e0f03cf1131c2d6456666b126e17dcc835670c Mon Sep 17 00:00:00 2001
From: NewRisingSun <8vytz1+dhp372pv94ebg@sharklasers.com>
Date: Fri, 11 Apr 2025 16:10:27 +0200
Subject: [PATCH] Mapper 023: Add support for odd-sized Contra hacks.

---
 src/boards/21_22_23_25.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/boards/21_22_23_25.c b/src/boards/21_22_23_25.c
index 1524858..da73aa8 100644
--- a/src/boards/21_22_23_25.c
+++ b/src/boards/21_22_23_25.c
@@ -23,9 +23,10 @@
 
 static void sync () {
 	VRC24_syncWRAM(0);
-	VRC24_syncPRG(0x01F, 0x000);
+	VRC24_syncPRG(0x03F, 0x000);  /* A real VRC4 has a PRG-ROM maximum of 256 KiB, but some hacks use more than that. */
 	VRC24_syncCHR(0x1FF, 0x000);
 	VRC24_syncMirror();
+	if (ROM_size &1) setprg16(0xC000, ROM_size -1); /* A number of Contra hacks have a PRG-ROM size of 400 KiB, expecting the last 16 KiB to be determined via subtraction. They would not work on real hardware. */
 }
 
 void Mapper21_Init (CartInfo *info) {