From 98acb0923614ada8705e314c0916423f0025b3e8 Mon Sep 17 00:00:00 2001
From: Nathaniel Walizer <robots.are.love@gmail.com>
Date: Sat, 7 Dec 2024 02:12:22 -0800
Subject: [PATCH] Fix up MMC3 ROM banks

 - Gun-Nac working great
 - Kirby menus are garbage
 - SMB3 overworld sprites are garbage
---
 Makefile       |  2 +-
 src/map/mmc3.c | 72 +++++++++++++++++++++++++++++++++++---------------
 src/ppu.c      |  1 +
 3 files changed, 53 insertions(+), 22 deletions(-)

diff --git a/Makefile b/Makefile
index 778b508..5540b88 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 CC = gcc
 LD = $(CC)
-PFLAGS = -g
+PFLAGS = -g #-DE6502_DEBUG
 CFLAGS = $(PFLAGS) -Wall -Werror -Wshadow -I..
 LDFLAGS = $(PFLAGS)
 
diff --git a/src/map/mmc3.c b/src/map/mmc3.c
index f237ef9..9914f27 100644
--- a/src/map/mmc3.c
+++ b/src/map/mmc3.c
@@ -25,6 +25,7 @@ typedef struct {
     uint8_t* chr_bank[8]; // 1 KB
     uint8_t* vram_bank[4];
 
+    uint8_t r[8];
     mmc3_Flag flags;
     uint8_t bank_select;
     uint8_t irq_count;
@@ -44,17 +45,8 @@ static inline void mmc3_map_prg(mmc3_mapper* map,
     map->prg_bank[reg] = mmc3_prg_bank(map, bank);
 }
 
-static inline void mmc3_update_rom_mode(mmc3_mapper* map) {
-    if (!(map->bank_select & mmc3_Bank_Select_PRG)) {
-        mmc3_map_prg(map, 2, map->prg_rom_banks - 2);
-    } else {
-        mmc3_map_prg(map, 0, map->prg_rom_banks - 2);
-    }
-}
-
-static inline void mmc3_update_prg(mmc3_mapper* map, uint8_t bank) {
-    int reg = (map->bank_select & mmc3_Bank_Select_Reg);
-
+static inline void mmc3_update_prg(mmc3_mapper* map,
+                                   int reg, uint8_t bank) {
     if (reg == 7) {
         mmc3_map_prg(map, 1, bank);
     } else {
@@ -72,6 +64,11 @@ static inline uint8_t* mmc3_chr_bank(mmc3_mapper* map, int bank) {
 
 static inline void mmc3_map_2k_chr(mmc3_mapper* map,
                                    int reg, int bank) {
+    bank &= ~1;
+    if (bank >= map->chr_rom_banks) {
+        MAP_LOG("CHR ROM OOB: %d > %d", bank, map->chr_rom_banks);
+        bank = bank % map->chr_rom_banks;
+    }
     MAP_LOG("CHR ROM: 2k $%04x <- bank %d + %d", reg << 10, bank & ~1, bank | 1);
     map->chr_bank[reg + 0] = mmc3_chr_bank(map, bank & ~1);
     map->chr_bank[reg + 1] = mmc3_chr_bank(map, bank | 1);
@@ -79,13 +76,16 @@ static inline void mmc3_map_2k_chr(mmc3_mapper* map,
 
 static inline void mmc3_map_1k_chr(mmc3_mapper* map,
                                    int reg, int bank) {
+    if (bank >= map->chr_rom_banks) {
+        MAP_LOG("CHR ROM OOB: %d > %d", bank, map->chr_rom_banks);
+        bank = bank % map->chr_rom_banks;
+    }
     MAP_LOG("CHR ROM: 1k $%04x <- bank %d", reg << 10, bank);
     map->chr_bank[reg] = mmc3_chr_bank(map, bank);
 }
 
-static inline void mmc3_update_chr(mmc3_mapper* map, uint8_t bank) {
-    int reg = (map->bank_select & mmc3_Bank_Select_Reg);
-
+static inline void mmc3_update_chr(mmc3_mapper* map,
+                                   int reg, uint8_t bank) {
     if (!(map->bank_select & mmc3_Bank_Select_CHR)) {
         if (1 >= reg) {
             mmc3_map_2k_chr(map, reg * 2, bank);
@@ -102,6 +102,33 @@ static inline void mmc3_update_chr(mmc3_mapper* map, uint8_t bank) {
     }
 }
 
+static inline void mmc3_update_rom_mode(mmc3_mapper* map, int val) {
+    uint8_t delta = map->bank_select ^ val;
+
+    map->bank_select = val;
+
+    if (delta & mmc3_Bank_Select_PRG) {
+        mmc3_map_prg(map, 1, map->r[7]);
+        if (!(val & mmc3_Bank_Select_PRG)) {
+            mmc3_map_prg(map, 0, map->r[6]);
+            mmc3_map_prg(map, 2, map->prg_rom_banks - 2);
+        } else {
+            mmc3_map_prg(map, 0, map->prg_rom_banks - 2);
+            mmc3_map_prg(map, 2, map->r[6]);
+        }
+
+    }
+
+    if (delta & mmc3_Bank_Select_CHR) {
+        mmc3_update_chr(map, 0, map->r[0]);
+        mmc3_update_chr(map, 1, map->r[1]);
+        mmc3_update_chr(map, 2, map->r[2]);
+        mmc3_update_chr(map, 3, map->r[3]);
+        mmc3_update_chr(map, 4, map->r[4]);
+        mmc3_update_chr(map, 5, map->r[5]);
+    }
+}
+
 static inline void mmc3_update_vram(mmc3_mapper* map) {
     if (!(map->flags & mmc3_Flag_Horizontal)) {
         // Vertical mirroring
@@ -119,10 +146,12 @@ static inline void mmc3_update_vram(mmc3_mapper* map) {
 static void mmc3_reset(nes_mapper* nes_map) {
     mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
     map->flags       = 0;
-    map->bank_select = 0;
+    map->bank_select = mmc3_Bank_Select_PRG |
+                       mmc3_Bank_Select_CHR;
     map->irq_count   = 0;
     map->irq_latch   = 0;
-    map->prg_bank[3] = mmc3_prg_bank(map, map->prg_rom_banks - 1);
+    mmc3_update_rom_mode(map, 0);
+    mmc3_map_prg(map, 3, map->prg_rom_banks - 1);
     mmc3_update_vram(map);
 }
 
@@ -192,15 +221,16 @@ static void mmc3_write(nes_mapper* nes_map,
     } else if (addr < 0xA000U) {
         if (addr & 1) {
             // Bank data
-            if ((map->bank_select & mmc3_Bank_Select_Reg) >= 6) {
-                mmc3_update_prg(map, val);
+            int reg = (map->bank_select & mmc3_Bank_Select_Reg);
+            if (reg >= 6) {
+                mmc3_update_prg(map, reg, val);
             } else {
-                mmc3_update_chr(map, val);
+                mmc3_update_chr(map, reg, val);
             }
+            map->r[reg] = val;
         } else {
             // Bank select
-            map->bank_select = val;
-            mmc3_update_rom_mode(map);
+            mmc3_update_rom_mode(map, val);
         }
 
     } else if (addr < 0xC000U) {
diff --git a/src/ppu.c b/src/ppu.c
index 1f619c7..ff48d78 100644
--- a/src/ppu.c
+++ b/src/ppu.c
@@ -199,6 +199,7 @@ int nes_ppu_run(nes_ppu* ppu, int cycles) {
 
     if (    NULL != ppu->mapper->scanline &&
             ppu->scanline < nes_ppu_render &&
+            (ppu->mask & (ppu_Mask_Back | ppu_Mask_Sprite)) &&
             ppu->cycle < 260 && next_cycle >= 260) {
         ppu->mapper->scanline(ppu->mapper);
     }