From 8d93abbf021d479d52721cd3a42a371bc06ba9d0 Mon Sep 17 00:00:00 2001
From: Nathaniel Walizer <robots.are.love@gmail.com>
Date: Mon, 17 Mar 2025 11:59:56 -0700
Subject: [PATCH] Add Mapper 003 (CNROM); even more mapper init refactoring

---
 src/cart.c       | 21 ++++++++++++++++++---
 src/map/map000.c | 19 -------------------
 src/map/map003.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 src/mapper.c     |  2 ++
 4 files changed, 67 insertions(+), 22 deletions(-)
 create mode 100644 src/map/map003.c

diff --git a/src/cart.c b/src/cart.c
index 3eb7a9f..56e80a6 100644
--- a/src/cart.c
+++ b/src/cart.c
@@ -56,7 +56,7 @@ int nes_cart_load_mem(void* data, int size, nes* sys) {
         int i_mapper = (hdr->flags_7 & ines_Mapper_Nibble_Hi) |
                 ((hdr->flags_6 & ines_Mapper_Nibble_Lo) >> 4);
         const nes_Mapper *mapper = nes_mappers[i_mapper];
-        if (NULL == mapper || NULL == mapper->init) {
+        if (NULL == mapper) {
             LOGE("Mapper %d not supported", i_mapper);
             status = -1;
         } else {
@@ -78,6 +78,19 @@ int nes_cart_load_mem(void* data, int size, nes* sys) {
                 LOGE("Failed to allocate mapper data");
                 status = -1;
             } else {
+                // Default PGM ROM
+                if (mem->n_rom_banks > 2) {
+                    mem->rom_bank[0] = prg_rom_page(mem, 0);
+                    mem->rom_bank[1] = prg_rom_page(mem, 1);
+                    mem->rom_bank[2] = prg_rom_page(mem, 2);
+                    mem->rom_bank[3] = prg_rom_page(mem, 3);
+                } else {
+                    mem->rom_bank[0] = prg_rom_page(mem, 0);
+                    mem->rom_bank[1] = prg_rom_page(mem, 1);
+                    mem->rom_bank[2] = prg_rom_page(mem, 0);
+                    mem->rom_bank[3] = prg_rom_page(mem, 1);
+                }
+
                 // PPU Bank 0 - 7: Default pattern tables
                 for (int page = 0; page < 8; ++page) {
                     mem->ppu.bank[page] = chr_page(&mem->ppu, page);
@@ -98,8 +111,10 @@ int nes_cart_load_mem(void* data, int size, nes* sys) {
                     mem->sram_bank = mem->sram;
                 }
 
-                status = mem->mapper.init(&mem->mapper,
-                                          hdr, mem);
+                if (mem->mapper.init) {
+                    status = mem->mapper.init(&mem->mapper,
+                                              hdr, mem);
+                }
             }
             // TODO: Deallocate mapper data when we're done
         }
diff --git a/src/map/map000.c b/src/map/map000.c
index 31c4ec0..3f6b11f 100644
--- a/src/map/map000.c
+++ b/src/map/map000.c
@@ -1,27 +1,8 @@
 #include "memory.h"
 
 
-static int map000_init(nes_Mapper* map, const ines_Header* hdr,
-                       nes_Memory* mem) {
-    if (mem->n_rom_banks > 2) {
-        mem->rom_bank[0] = prg_rom_page(mem, 0);
-        mem->rom_bank[1] = prg_rom_page(mem, 1);
-        mem->rom_bank[2] = prg_rom_page(mem, 2);
-        mem->rom_bank[3] = prg_rom_page(mem, 3);
-    } else {
-        mem->rom_bank[0] = prg_rom_page(mem, 0);
-        mem->rom_bank[1] = prg_rom_page(mem, 1);
-        mem->rom_bank[2] = prg_rom_page(mem, 0);
-        mem->rom_bank[3] = prg_rom_page(mem, 1);
-    }
-
-    return 0;
-}
-
-
 const nes_Mapper map000 = {
     .name           = "NROM",
     .max_chr_banks  = 8,
     .data_size      = 0,
-    .init           = map000_init,
 };
diff --git a/src/map/map003.c b/src/map/map003.c
new file mode 100644
index 0000000..6ffcb4d
--- /dev/null
+++ b/src/map/map003.c
@@ -0,0 +1,47 @@
+#include "memory.h"
+
+
+typedef struct {
+    uint8_t bank;
+} map003_data;
+
+
+static inline void cnrom_set_bank(map003_data* data,
+                                  nes_Memory* mem,
+                                  uint8_t bank) {
+    data->bank = (bank % (mem->ppu.n_chr_banks / 8));
+    mem->ppu.bank[0] = chr_page(&mem->ppu, (data->bank * 8) + 0);
+    mem->ppu.bank[1] = chr_page(&mem->ppu, (data->bank * 8) + 1);
+    mem->ppu.bank[2] = chr_page(&mem->ppu, (data->bank * 8) + 2);
+    mem->ppu.bank[3] = chr_page(&mem->ppu, (data->bank * 8) + 3);
+    mem->ppu.bank[4] = chr_page(&mem->ppu, (data->bank * 8) + 4);
+    mem->ppu.bank[5] = chr_page(&mem->ppu, (data->bank * 8) + 5);
+    mem->ppu.bank[6] = chr_page(&mem->ppu, (data->bank * 8) + 6);
+    mem->ppu.bank[7] = chr_page(&mem->ppu, (data->bank * 8) + 7);
+}
+
+static void map003_reset(nes_Mapper* map, nes_Memory* mem) {
+    cnrom_set_bank((map003_data*)map->data, mem, 0);
+}
+
+static int map003_init(nes_Mapper* map, const ines_Header* hdr,
+                       nes_Memory* mem) {
+    map003_reset(map, mem);
+    return 0;
+}
+
+static int map003_write_rom(nes_Mapper* map, nes_Memory* mem,
+                            uint16_t addr, uint8_t val) {
+    cnrom_set_bank((map003_data*)map->data, mem, val);
+    return 0;
+}
+
+
+const nes_Mapper map003 = {
+    .name           = "CNROM",
+    .max_chr_banks  = 8,
+    .data_size      = sizeof(map003_data),
+    .init           = map003_init,
+    .reset          = map003_reset,
+    .write_rom      = map003_write_rom,
+};
diff --git a/src/mapper.c b/src/mapper.c
index c499337..54ea98c 100644
--- a/src/mapper.c
+++ b/src/mapper.c
@@ -4,9 +4,11 @@
 extern const nes_Mapper map000;
 extern const nes_Mapper map001;
 extern const nes_Mapper map002;
+extern const nes_Mapper map003;
 
 const nes_Mapper* nes_mappers[256] = {
     &map000,
     &map001,
     &map002,
+    &map003,
 };