From 130580d70eb55d69ad28899f4ee3ebda9cb8e4dc Mon Sep 17 00:00:00 2001
From: retro-wertz <retro-wertz@users.noreply.github.com>
Date: Sun, 23 Jun 2019 20:15:32 +0800
Subject: [PATCH] BMC-830425C-4391T: Update cpu banking

- Fixes loading Mermaid game.
---
 src/boards/bmc830425C4391t.c | 52 +++++++++++-------------------------
 1 file changed, 16 insertions(+), 36 deletions(-)

diff --git a/src/boards/bmc830425C4391t.c b/src/boards/bmc830425C4391t.c
index db18618..ce64fd2 100644
--- a/src/boards/bmc830425C4391t.c
+++ b/src/boards/bmc830425C4391t.c
@@ -26,66 +26,46 @@
 
 #include "mapinc.h"
 
-static uint8 regs[2];
-static uint8 isMermaid = 0;
+static uint8 bank_size;
+static uint8 inner_bank;
+static uint8 outer_bank;
 
 static SFORMAT StateRegs[] =
 {
-	{ regs, 2, "REGS" },
-	{ &isMermaid, 1, "MERM" },
+	{ &inner_bank, 1, "INNB" },
+	{ &outer_bank, 1, "OUTB" },
+	{ &bank_size, 1, "SIZE" },
 	{ 0 }
 };
 
 static void Sync(void) {
-	uint8 bank_size = (regs[0] & 0x80) ? 0x07: 0x0F;
-	uint8 outer_bank = !isMermaid ? (regs[0] & 0x78) : 0x04;
-	uint8 inner_bank = regs[1];
-	uint8 game_block = regs[0] & 0x78;
-
-	/* TODO: Hacky and forced mapping of outer banks(game block)... */
-	if (!isMermaid) {
-		switch(game_block) {
-		case 0x00: /* botb outerbank=0 */
-		case 0x10: /* rocketeer outerbank=1  */
-		case 0x20: /* contra outerbank=2  */
-		case 0x28: /* ducktales outerbank=3 */
-		case 0x38: /* school fight outerbank=5 */
-			outer_bank = (game_block >> 4) + ((game_block & 0x08) ? 0x01 : 0x00);
-			outer_bank |= (game_block >> 3) & 1;
-			break;
-		case 0x30:
-			/* Mermaid game block is tricky (to me at least). Aim here is
-			 * when this register is selected, ignore any other outer bank reg changes */
-			isMermaid = 1;
-			outer_bank = 0x04;
-			break;
-		}
-	}
-
 	setprg16r(outer_bank, 0x8000, (inner_bank & bank_size));
 	setprg16r(outer_bank, 0xC000, bank_size);
 	setchr8(0);
 }
 
 static DECLFW(M320Write) {
-	if ((A & 0xF0E0) == 0xF0E0) {
-		regs[0] = (A & 0x1F) << 3;
+	const uint8 chip[] = { 0, 0, 1, 0, 2, 3, 4, 5 };
+	/* address mask is inconsistent with that is in the wiki. Mask should be
+	 * 0xFFE0 or Mermaid game will not work. */
+	if ((A & 0xFFE0) == 0xF0E0) {
+		outer_bank = chip[(A & 0x0F)];
+		bank_size = (A & 0x10) ? 0x07 : 0x0F;
 	}
-	regs[1] = V & 0x0F;
+	inner_bank = (V & 0x0F);
 	Sync();
 }
 
 static void M320Power(void) {
-	regs[0] = regs[1] = 0;
-	isMermaid = 0;
+	bank_size = 0x0F;
 	Sync();
 	SetReadHandler(0x8000, 0xFFFF, CartBR);
 	SetWriteHandler(0x8000, 0xFFFF, M320Write);
 }
 
 static void M320Reset(void) {
-	regs[0] = regs[1] = 0;
-	isMermaid = 0;
+	inner_bank = outer_bank = 0;
+	bank_size = 0x0F;
 	Sync();
 }