diff --git a/src/cart.c b/src/cart.c
index dbaebfe..be210aa 100644
--- a/src/cart.c
+++ b/src/cart.c
@@ -63,7 +63,8 @@ int nes_cart_init_mem(nes_cart* cart, void* mem, int len) {
         }
 
         // Don't initialize the mapper until all flags are set!
-        status = nes_map_init(cart->mapper, cart);
+        cart->map_data = nes_map_init(cart->mapper, cart);
+        status = (NULL == cart->map_data ? -1 : 0);
     }
 
     return status;
@@ -71,8 +72,9 @@ int nes_cart_init_mem(nes_cart* cart, void* mem, int len) {
 
 void nes_cart_done(nes_cart* cart) {
     if (NULL != cart->mapper) {
-        nes_map_done(cart->mapper);
+        nes_map_done(cart->mapper, cart->map_data);
         cart->mapper = NULL;
+        cart->map_data = NULL;
     }
     if (NULL != cart->ines_mem) {
         unmap_file(cart->ines_mem, cart->ines_size);
diff --git a/src/cart.h b/src/cart.h
index eaa61c5..aaf4183 100644
--- a/src/cart.h
+++ b/src/cart.h
@@ -17,7 +17,9 @@ typedef struct nes_cart_t {
     uint8_t* chr_rom;
     int chr_rom_banks;
     nes_Cart_Flags flags;
+
     struct nes_mapper_t* mapper;
+    void* map_data;
 
     void* ines_mem;
     int ines_size;
diff --git a/src/map/cnrom.c b/src/map/cnrom.c
index fa68dd1..9d63c3a 100644
--- a/src/map/cnrom.c
+++ b/src/map/cnrom.c
@@ -24,27 +24,26 @@ static void cnrom_set_bank(cnrom_mapper* map, uint8_t bank) {
         ];
 }
 
-static void cnrom_reset(nes_mapper* nes_map) {
-    cnrom_mapper* map = (cnrom_mapper*)nes_map->data;
+static void cnrom_reset(void* _map) {
+    cnrom_mapper* map = (cnrom_mapper*)_map;
     cnrom_set_bank(map, 0);
 }
 
-static int cnrom_init(nes_mapper* nes_map, nes_cart* cart) {
+static void* cnrom_init(nes_mapper* nes_map, nes_cart* cart) {
     cnrom_mapper* map = calloc(1, sizeof(cnrom_mapper));
-    nes_map->data = map;
     if (NULL != map) {
         map->prg_rom       = cart->prg_rom;
         map->prg_rom_banks = cart->prg_rom_banks;
         map->chr_rom       = cart->chr_rom;
         map->chr_rom_banks = cart->chr_rom_banks;
         map->mirror = (cart->flags & Cart_Flag_Horizontal) ? 0 : 1;
-        cnrom_reset(nes_map);
+        cnrom_reset(map);
     }
-    return (NULL == map ? -1 : 0);
+    return map;
 }
 
-static void cnrom_done(nes_mapper* nes_map) {
-    free(nes_map->data);
+static void cnrom_done(void* _map) {
+    free(_map);
 }
 
 static inline uint8_t* cnrom_prg_addr(cnrom_mapper* map,
@@ -57,37 +56,34 @@ static inline uint8_t* cnrom_prg_addr(cnrom_mapper* map,
 }
 
 
-static uint8_t cnrom_read(nes_mapper* map, uint16_t addr) {
+static uint8_t cnrom_read(void* _map, uint16_t addr) {
     uint8_t val = 0;
     if (addr >= nes_mem_rom_start) {
-        val = *(cnrom_prg_addr((cnrom_mapper*)map->data, addr));
+        val = *(cnrom_prg_addr((cnrom_mapper*)_map, addr));
     }
     return val;
 }
 
-static void cnrom_write(nes_mapper* nes_map,
-                        uint16_t addr, uint8_t val) {
-    cnrom_mapper* map = (cnrom_mapper*)nes_map->data;
+static void cnrom_write(void* _map, uint16_t addr, uint8_t val) {
+    cnrom_mapper* map = (cnrom_mapper*)_map;
     if (addr >= nes_mem_rom_start) {
         cnrom_set_bank(map, val);
     }
 }
 
-static uint8_t* cnrom_chr_addr(nes_mapper* nes_map,
-                              uint16_t addr) {
-    return &((cnrom_mapper*)nes_map->data)->chr_bank[addr];
+static uint8_t* cnrom_chr_addr(void* _map, uint16_t addr) {
+    return &((cnrom_mapper*)_map)->chr_bank[addr];
 }
 
-static uint8_t* cnrom_vram_addr(nes_mapper* nes_map,
-                                uint16_t addr) {
-    cnrom_mapper* map = (cnrom_mapper*)nes_map->data;
+static uint8_t* cnrom_vram_addr(void* _map, uint16_t addr) {
+    cnrom_mapper* map = (cnrom_mapper*)_map;
     int page = addr >> 10U;
     page >>= map->mirror;
     addr = ((page & 1) << 10U) | (addr & 0x3FFU);
     return &map->vram[addr];
 }
 
-static void cnrom_chr_write(nes_mapper* nes_map,
+static void cnrom_chr_write(void* _map,
                             uint16_t addr, uint8_t val) {
     // ROM only.
 }
@@ -95,13 +91,13 @@ static void cnrom_chr_write(nes_mapper* nes_map,
 
 /* Save State */
 
-int cnrom_state_size(const nes_mapper* nes_map) {
-    cnrom_mapper* map = (cnrom_mapper*)nes_map->data;
+static int cnrom_state_size(const void* _map) {
+    cnrom_mapper* map = (cnrom_mapper*)_map;
     return (sizeof(map->bank) + sizeof(map->vram));
 }
 
-int cnrom_state_read(nes_mapper* nes_map, const void* data) {
-    cnrom_mapper* map = (cnrom_mapper*)nes_map->data;
+static int cnrom_state_read(void* _map, const void* data) {
+    cnrom_mapper* map = (cnrom_mapper*)_map;
     const void* ptr = data;
 
     memcpy(&map->bank, ptr, sizeof(map->bank));
@@ -115,8 +111,8 @@ int cnrom_state_read(nes_mapper* nes_map, const void* data) {
     return (ptr - data);
 }
 
-int cnrom_state_write(const nes_mapper* nes_map, void* data) {
-    cnrom_mapper* map = (cnrom_mapper*)nes_map->data;
+static int cnrom_state_write(const void* _map, void* data) {
+    cnrom_mapper* map = (cnrom_mapper*)_map;
     void* ptr = data;
 
     memcpy(ptr, &map->bank, sizeof(map->bank));
diff --git a/src/map/mmc1.c b/src/map/mmc1.c
index 6df73b3..29b9e25 100644
--- a/src/map/mmc1.c
+++ b/src/map/mmc1.c
@@ -90,8 +90,8 @@ static void mmc1_update_prg(mmc1_mapper* map) {
     map->prg_bank[1] = &map->prg_rom[bank_1 * nes_prg_rom_page_size];
 }
 
-static void mmc1_reset(nes_mapper* nes_map) {
-    mmc1_mapper* map = (mmc1_mapper*)nes_map->data;
+static void mmc1_reset(void* data) {
+    mmc1_mapper* map = (mmc1_mapper*)data;
     map->reg_shift   = 0b10000;
     map->reg_control = 0b01100;
     map->reg_chr_0   = 0;
@@ -102,9 +102,8 @@ static void mmc1_reset(nes_mapper* nes_map) {
     mmc1_update_vram(map);
 }
 
-static int mmc1_init(nes_mapper* nes_map, nes_cart* cart) {
+static void* mmc1_init(nes_mapper* nes_map, nes_cart* cart) {
     mmc1_mapper* map = calloc(1, sizeof(mmc1_mapper));
-    nes_map->data = map;
     if (NULL != map) {
         map->prg_rom       = cart->prg_rom;
         map->prg_rom_banks = cart->prg_rom_banks;
@@ -121,15 +120,15 @@ static int mmc1_init(nes_mapper* nes_map, nes_cart* cart) {
 
         map->battery = !!(cart->flags & Cart_Flag_Battery);
 
-        mmc1_reset(nes_map);
+        mmc1_reset(map);
     }
-    return (NULL == map ? -1 : 0);
+    return map;
 }
 
-static void mmc1_done(nes_mapper* nes_map) {
-    if (NULL != nes_map->data) {
-        free(((mmc1_mapper*)nes_map->data)->chr_ram);
-        free(nes_map->data);
+static void mmc1_done(void* data) {
+    if (NULL != data) {
+        free(((mmc1_mapper*)data)->chr_ram);
+        free(data);
     }
 }
 
@@ -145,19 +144,18 @@ static inline uint8_t* mmc1_wram_addr(mmc1_mapper* map,
     return &(map->wram[addr & 0x1FFFU]);
 }
 
-static uint8_t mmc1_read(nes_mapper* map, uint16_t addr) {
+static uint8_t mmc1_read(void* data, uint16_t addr) {
     uint8_t val = 0;
     if (addr >= nes_mem_rom_start) {
-        val = *(mmc1_prg_addr((mmc1_mapper*)map->data, addr));
+        val = *(mmc1_prg_addr((mmc1_mapper*)data, addr));
     } else if (addr >= nes_mem_wram_start) {
-        val = *(mmc1_wram_addr((mmc1_mapper*)map->data, addr));
+        val = *(mmc1_wram_addr((mmc1_mapper*)data, addr));
     }
     return val;
 }
 
-static void mmc1_write(nes_mapper* nes_map,
-                       uint16_t addr, uint8_t val) {
-    mmc1_mapper* map = (mmc1_mapper*)nes_map->data;
+static void mmc1_write(void* data, uint16_t addr, uint8_t val) {
+    mmc1_mapper* map = (mmc1_mapper*)data;
     if (addr >= nes_mem_rom_start) {
         MAP_LOG("Write $%04x < %02x", addr, val);
         if (val & 0x80U) {
@@ -201,53 +199,51 @@ static void mmc1_write(nes_mapper* nes_map,
     }
 }
 
-static uint8_t* mmc1_chr_addr(nes_mapper* nes_map,
-                              uint16_t addr) {
+static uint8_t* mmc1_chr_addr(void* data, uint16_t addr) {
     int page = (addr >> 12) & 1;
     addr &= 0xFFFU;
-    return &((mmc1_mapper*)nes_map->data)->chr_bank[page][addr];
+    return &((mmc1_mapper*)data)->chr_bank[page][addr];
 }
 
-static void mmc1_chr_write(nes_mapper* nes_map,
+static void mmc1_chr_write(void* data,
                            uint16_t addr, uint8_t val) {
-    if (NULL != ((mmc1_mapper*)nes_map->data)->chr_ram) {
-        *(mmc1_chr_addr(nes_map, addr)) = val;
+    if (NULL != ((mmc1_mapper*)data)->chr_ram) {
+        *(mmc1_chr_addr(data, addr)) = val;
     }
 }
 
-static uint8_t* mmc1_vram_addr(nes_mapper* nes_map,
-                               uint16_t addr) {
+static uint8_t* mmc1_vram_addr(void* data, uint16_t addr) {
     int page = (addr >> 10) & 3;
     int loc = addr & 0x3FFU;
 //    MAP_LOG("VRAM $%04x -> %p", addr, ((mmc1_mapper*)nes_map->data)->vram_bank[page]);
-    return &((mmc1_mapper*)nes_map->data)->vram_bank[page][loc];
+    return &((mmc1_mapper*)data)->vram_bank[page][loc];
 }
 
 
-static void* mmc1_sram(nes_mapper* nes_map) {
-    mmc1_mapper* map = (mmc1_mapper*)nes_map->data;
+static void* mmc1_sram(void* data) {
+    mmc1_mapper* map = (mmc1_mapper*)data;
     return (map->battery ? map->wram : NULL);
 }
 
-static int mmc1_sram_size(nes_mapper* nes_map) {
-    mmc1_mapper* map = (mmc1_mapper*)nes_map->data;
+static int mmc1_sram_size(void* data) {
+    mmc1_mapper* map = (mmc1_mapper*)data;
     return (map->battery ? sizeof(map->wram) : 0);
 }
 
 
 /* Save State */
 
-int mmc1_state_size(const nes_mapper* nes_map) {
-    mmc1_mapper* map = (mmc1_mapper*)nes_map->data;
+static int mmc1_state_size(const void* _map) {
+    mmc1_mapper* map = (mmc1_mapper*)_map;
     return (    (void*)map +
                 sizeof(*map) -
                 (void*)&(map->reg_shift));
 }
 
-int mmc1_state_read(nes_mapper* nes_map, const void* data) {
-    mmc1_mapper* map = (mmc1_mapper*)nes_map->data;
+static int mmc1_state_read(void* _map, const void* data) {
+    mmc1_mapper* map = (mmc1_mapper*)_map;
 
-    int size = mmc1_state_size(nes_map);
+    int size = mmc1_state_size(_map);
     memcpy(&(map->reg_shift), data, size);
 
     mmc1_update_prg(map);
@@ -257,9 +253,9 @@ int mmc1_state_read(nes_mapper* nes_map, const void* data) {
     return size;
 }
 
-int mmc1_state_write(const nes_mapper* nes_map, void* data) {
-    mmc1_mapper* map = (mmc1_mapper*)nes_map->data;
-    int size = mmc1_state_size(nes_map);
+static int mmc1_state_write(const void* _map, void* data) {
+    mmc1_mapper* map = (mmc1_mapper*)_map;
+    int size = mmc1_state_size(_map);
     memcpy(data, &(map->reg_shift), size);
     return size;
 }
@@ -267,6 +263,7 @@ int mmc1_state_write(const nes_mapper* nes_map, void* data) {
 
 nes_mapper mapper_mmc1 = {
     .name = "MMC1",
+
     .init = mmc1_init,
     .reset = mmc1_reset,
     .done = mmc1_done,
diff --git a/src/map/mmc3.c b/src/map/mmc3.c
index bc70e65..1437a6f 100644
--- a/src/map/mmc3.c
+++ b/src/map/mmc3.c
@@ -3,6 +3,7 @@
 
 #include "map.h"
 
+
 typedef enum {
     mmc3_Flag_Horizontal   = 0b00000001,
     mmc3_Flag_IRQ_Enabled  = 0b00000010,
@@ -25,6 +26,8 @@ typedef struct {
     uint8_t* chr_rom;
     int chr_rom_banks; // 4 KB / 1 KB = 4
 
+    nes_mapper* mapper;
+
     uint8_t* prg_bank[4]; // 8 KB
     uint8_t* chr_bank[8]; // 1 KB
     uint8_t* vram_bank[4];
@@ -146,8 +149,8 @@ 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;
+static void mmc3_reset(void* data) {
+    mmc3_mapper* map = (mmc3_mapper*)data;
     map->irq_count   = 0;
     map->irq_latch   = 0;
     mmc3_update_rom_mode(map, 0);
@@ -155,10 +158,10 @@ static void mmc3_reset(nes_mapper* nes_map) {
     mmc3_update_vram(map);
 }
 
-static int mmc3_init(nes_mapper* nes_map, nes_cart* cart) {
+static void* mmc3_init(nes_mapper* nes_map, nes_cart* cart) {
     mmc3_mapper* map = calloc(1, sizeof(mmc3_mapper));
-    nes_map->data = map;
     if (NULL != map) {
+        map->mapper = nes_map;
         map->flags = (cart->flags & Cart_Flag_Horizontal) ?
                      mmc3_Flag_Horizontal : 0;
         map->prg_rom       = cart->prg_rom;
@@ -179,18 +182,18 @@ static int mmc3_init(nes_mapper* nes_map, nes_cart* cart) {
         map->bank_select = mmc3_Bank_Select_PRG |
                            mmc3_Bank_Select_CHR;
 
-        mmc3_reset(nes_map);
+        mmc3_reset(map);
     }
-    return (NULL == map ? -1 : 0);
+    return map;
 }
 
-static void mmc3_done(nes_mapper* nes_map) {
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
+static void mmc3_done(void* data) {
+    mmc3_mapper* map = (mmc3_mapper*)data;
     if (NULL != map) {
         if (map->flags & mmc3_Flag_CHR_RAM) {
             free(map->chr_rom);
         }
-        free(nes_map->data);
+        free(map);
     }
 }
 
@@ -204,9 +207,9 @@ static inline uint8_t* mmc3_wram_addr(mmc3_mapper* map,
     return &(map->wram[addr & 0x1FFFU]);
 }
 
-static uint8_t mmc3_read(nes_mapper* nes_map, uint16_t addr) {
+static uint8_t mmc3_read(void* data, uint16_t addr) {
     uint8_t* ptr = NULL;
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
+    mmc3_mapper* map = (mmc3_mapper*)data;
     if (addr >= nes_mem_rom_start) {
         ptr = mmc3_prg_addr(map, addr);
     } else if ( addr >= nes_mem_wram_start &&
@@ -222,9 +225,9 @@ static uint8_t mmc3_read(nes_mapper* nes_map, uint16_t addr) {
     return val;
 }
 
-static void mmc3_write(nes_mapper* nes_map,
+static void mmc3_write(void* data,
                        uint16_t addr, uint8_t val) {
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
+    mmc3_mapper* map = (mmc3_mapper*)data;
 
     if (addr >= nes_mem_rom_start) MAP_LOG("$%04x < %02x", addr, val);
 
@@ -284,13 +287,13 @@ static void mmc3_write(nes_mapper* nes_map,
             map->flags |= mmc3_Flag_IRQ_Enabled;
         } else {
             map->flags &= ~mmc3_Flag_IRQ_Enabled;
-            nes_map_trigger_irq(nes_map, 0);
+            nes_map_trigger_irq(map->mapper, 0);
         }
     }
 }
 
-static void mmc3_scanline(nes_mapper* nes_map) {
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
+static void mmc3_scanline(void* data) {
+    mmc3_mapper* map = (mmc3_mapper*)data;
 
     if (    map->irq_count <= 0 ||
             (map->flags & mmc3_Flag_IRQ_Reload)) {
@@ -303,42 +306,42 @@ static void mmc3_scanline(nes_mapper* nes_map) {
     if (    map->irq_count <= 0 &&
             (map->flags & mmc3_Flag_IRQ_Enabled)) {
         MAP_LOG("IRQ Trigger");
-        nes_map_trigger_irq(nes_map, 1);
+        nes_map_trigger_irq(map->mapper, 1);
         map->irq_count = 0;
     }
 
 }
 
-static uint8_t* mmc3_chr_addr(nes_mapper* nes_map,
+static uint8_t* mmc3_chr_addr(void* data,
                               uint16_t addr) {
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
+    mmc3_mapper* map = (mmc3_mapper*)data;
     return &map->chr_bank[(addr >> 10) & 7][addr & 0x3FFU];
 }
 
-static uint8_t* mmc3_vram_addr(nes_mapper* nes_map,
+static uint8_t* mmc3_vram_addr(void* data,
                                uint16_t addr) {
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
+    mmc3_mapper* map = (mmc3_mapper*)data;
     return &map->vram_bank[(addr >> 10) & 3][addr & 0x3FFU];
 }
 
-static void mmc3_chr_write(nes_mapper* nes_map,
+static void mmc3_chr_write(void* data,
                            uint16_t addr, uint8_t val) {
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
+    mmc3_mapper* map = (mmc3_mapper*)data;
     if (map->flags & mmc3_Flag_CHR_RAM) {
-        *(mmc3_chr_addr(nes_map, addr)) = val;
+        *(mmc3_chr_addr(data, addr)) = val;
     }
 //    MAP_LOG("CHR ROM Write: $%04x < %02x\n", addr, val);
 }
 
 
-static void* mmc3_sram(nes_mapper* nes_map) {
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
+static void* mmc3_sram(void* data) {
+    mmc3_mapper* map = (mmc3_mapper*)data;
     return (    (map->flags & mmc3_Flag_Battery) ?
                 map->wram : NULL);
 }
 
-static int mmc3_sram_size(nes_mapper* nes_map) {
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
+static int mmc3_sram_size(void* data) {
+    mmc3_mapper* map = (mmc3_mapper*)data;
     return (    (map->flags & mmc3_Flag_Battery) ?
                 sizeof(map->wram) : 0);
 }
@@ -346,19 +349,19 @@ static int mmc3_sram_size(nes_mapper* nes_map) {
 
 /* Save State */
 
-int mmc3_state_size(const nes_mapper* nes_map) {
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
+static int mmc3_state_size(const void* data) {
+    const mmc3_mapper* map = (mmc3_mapper*)data;
     return (    (map->wram - map->r) +
                 sizeof(map->wram) +
                 sizeof(map->vram));
 }
 
-int mmc3_state_read(nes_mapper* nes_map, const void* data) {
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
+static int mmc3_state_read(void* _map, const void* data) {
+    mmc3_mapper* map = (mmc3_mapper*)_map;
 
     uint8_t old_bank_select = map->bank_select;
 
-    int size = mmc3_state_size(nes_map);
+    int size = mmc3_state_size(_map);
     memcpy(map->r, data, size);
 
     uint8_t new_bank_select = map->bank_select;
@@ -370,9 +373,9 @@ int mmc3_state_read(nes_mapper* nes_map, const void* data) {
     return size;
 }
 
-int mmc3_state_write(const nes_mapper* nes_map, void* data) {
-    mmc3_mapper* map = (mmc3_mapper*)nes_map->data;
-    int size = mmc3_state_size(nes_map);
+static int mmc3_state_write(const void* _map, void* data) {
+    mmc3_mapper* map = (mmc3_mapper*)_map;
+    int size = mmc3_state_size(_map);
     memcpy(data, map->r, size);
     return size;
 }
@@ -380,6 +383,7 @@ int mmc3_state_write(const nes_mapper* nes_map, void* data) {
 
 nes_mapper mapper_mmc3 = {
     .name = "MMC3",
+
     .init = mmc3_init,
     .reset = mmc3_reset,
     .done = mmc3_done,
diff --git a/src/map/nrom.c b/src/map/nrom.c
index 526d9ca..49e37de 100644
--- a/src/map/nrom.c
+++ b/src/map/nrom.c
@@ -15,11 +15,10 @@ typedef struct {
 } nrom_mapper;
 
 
-static void nrom_reset(nes_mapper* nes_map) {}
+static void nrom_reset(void* data) {}
 
-static int nrom_init(nes_mapper* nes_map, nes_cart* cart) {
+static void* nrom_init(nes_mapper* nes_map, nes_cart* cart) {
     nrom_mapper* map = calloc(1, sizeof(nrom_mapper));
-    nes_map->data = map;
     if (NULL != map) {
         map->prg_rom       = cart->prg_rom;
         map->prg_rom_banks = cart->prg_rom_banks;
@@ -31,16 +30,16 @@ static int nrom_init(nes_mapper* nes_map, nes_cart* cart) {
         map->chr_rom_banks = cart->chr_rom_banks;
         map->mirror = (cart->flags & Cart_Flag_Horizontal) ? 0 : 1;
     }
-    return (NULL == map ? -1 : 0);
+    return map;
 }
 
-static void nrom_done(nes_mapper* nes_map) {
-    nrom_mapper* map = (nrom_mapper*)nes_map->data;
+static void nrom_done(void* data) {
+    nrom_mapper* map = (nrom_mapper*)data;
     if (NULL != map) {
         if (map->chr_rom_banks <= 0) {
             free(map->chr_rom);
         }
-        free(nes_map->data);
+        free(data);
     }
 }
 
@@ -58,42 +57,39 @@ static inline uint8_t* nrom_wram_addr(nrom_mapper* map,
     return &(map->wram[addr & 0x1FFFU]);
 }
 
-static uint8_t nrom_read(nes_mapper* map, uint16_t addr) {
+static uint8_t nrom_read(void* data, uint16_t addr) {
     uint8_t val = 0;
     if (addr >= nes_mem_rom_start) {
-        val = *(nrom_prg_addr((nrom_mapper*)map->data, addr));
+        val = *(nrom_prg_addr((nrom_mapper*)data, addr));
     } else if (addr >= nes_mem_wram_start) {
-        val = *(nrom_wram_addr((nrom_mapper*)map->data, addr));
+        val = *(nrom_wram_addr((nrom_mapper*)data, addr));
     }
     return val;
 }
 
-static void nrom_write(nes_mapper* map,
-                       uint16_t addr, uint8_t val) {
+static void nrom_write(void* data, uint16_t addr, uint8_t val) {
     if (addr < nes_mem_rom_start && addr >= nes_mem_wram_start) {
-        *(nrom_wram_addr((nrom_mapper*)map->data, addr)) = val;
+        *(nrom_wram_addr((nrom_mapper*)data, addr)) = val;
     }
 }
 
-static uint8_t* nrom_chr_addr(nes_mapper* nes_map,
-                              uint16_t addr) {
-    return &(((nrom_mapper*)nes_map->data)->chr_rom[addr]);
+static uint8_t* nrom_chr_addr(void* data, uint16_t addr) {
+    return &(((nrom_mapper*)data)->chr_rom[addr]);
 }
 
-static uint8_t* nrom_vram_addr(nes_mapper* nes_map,
-                               uint16_t addr) {
-    nrom_mapper* map = (nrom_mapper*)nes_map->data;
+static uint8_t* nrom_vram_addr(void* data, uint16_t addr) {
+    nrom_mapper* map = (nrom_mapper*)data;
     int page = addr >> 10U;
     page >>= map->mirror;
     addr = ((page & 1) << 10U) | (addr & 0x3FFU);
     return &map->vram[addr];
 }
 
-static void nrom_chr_write(nes_mapper* nes_map,
+static void nrom_chr_write(void* data,
                            uint16_t addr, uint8_t val) {
-    nrom_mapper* map = (nrom_mapper*)nes_map->data;
+    nrom_mapper* map = (nrom_mapper*)data;
     if (map->chr_rom_banks <= 0) {
-        *(nrom_chr_addr(nes_map, addr)) = val;
+        *(nrom_chr_addr(data, addr)) = val;
     }
 //    printf("CHR ROM Write: $%04x < %02x\n", addr, val);
 }
@@ -101,20 +97,20 @@ static void nrom_chr_write(nes_mapper* nes_map,
 
 /* Save State */
 
-int nrom_state_size(const nes_mapper* nes_map) {
-    nrom_mapper* map = (nrom_mapper*)nes_map->data;
+static int nrom_state_size(const void* _map) {
+    nrom_mapper* map = (nrom_mapper*)_map;
     return (sizeof(map->vram) + sizeof(map->wram));
 }
 
-int nrom_state_read(nes_mapper* nes_map, const void* data) {
-    nrom_mapper* map = (nrom_mapper*)nes_map->data;
+static int nrom_state_read(void* _map, const void* data) {
+    nrom_mapper* map = (nrom_mapper*)_map;
     memcpy(map->vram, data, sizeof(map->vram));
     memcpy(map->wram, data + sizeof(map->vram), sizeof(map->wram));
     return (sizeof(map->vram) + sizeof(map->wram));
 }
 
-int nrom_state_write(const nes_mapper* nes_map, void* data) {
-    nrom_mapper* map = (nrom_mapper*)nes_map->data;
+static int nrom_state_write(const void* _map, void* data) {
+    nrom_mapper* map = (nrom_mapper*)_map;
     memcpy(data, map->vram, sizeof(map->vram));
     memcpy(data + sizeof(map->vram), map->wram, sizeof(map->wram));
     return (sizeof(map->vram) + sizeof(map->wram));
diff --git a/src/map/uxrom.c b/src/map/uxrom.c
index 45c7de1..4dbad8e 100644
--- a/src/map/uxrom.c
+++ b/src/map/uxrom.c
@@ -24,28 +24,27 @@ static void uxrom_set_bank(uxrom_mapper* map, uint8_t bank) {
         ];
 }
 
-static void uxrom_reset(nes_mapper* nes_map) {
-    uxrom_mapper* map = (uxrom_mapper*)nes_map->data;
+static void uxrom_reset(void* data) {
+    uxrom_mapper* map = (uxrom_mapper*)data;
     uxrom_set_bank(map, 0);
     map->prg_bank_lo = map->prg_rom;
 }
 
-static int uxrom_init(nes_mapper* nes_map, nes_cart* cart) {
+static void* uxrom_init(nes_mapper* nes_map, nes_cart* cart) {
     uxrom_mapper* map = calloc(1, sizeof(uxrom_mapper));
-    nes_map->data = map;
     if (NULL != map) {
         map->prg_rom       = cart->prg_rom;
         map->prg_rom_banks = cart->prg_rom_banks;
         map->mirror = (cart->flags & Cart_Flag_Horizontal) ? 0 : 1;
         map->prg_bank_hi = &map->prg_rom[(map->prg_rom_banks - 1) *
                                          nes_prg_rom_page_size];
-        uxrom_reset(nes_map);
+        uxrom_reset(map);
     }
-    return (NULL == map ? -1 : 0);
+    return map;
 }
 
-static void uxrom_done(nes_mapper* nes_map) {
-    free(nes_map->data);
+static void uxrom_done(void* data) {
+    free(data);
 }
 
 static inline uint8_t* uxrom_prg_addr(uxrom_mapper* map,
@@ -56,53 +55,50 @@ static inline uint8_t* uxrom_prg_addr(uxrom_mapper* map,
 }
 
 
-static uint8_t uxrom_read(nes_mapper* map, uint16_t addr) {
+static uint8_t uxrom_read(void* _map, uint16_t addr) {
     uint8_t val = 0;
     if (addr >= nes_mem_rom_start) {
-        val = *(uxrom_prg_addr((uxrom_mapper*)map->data, addr));
+        val = *(uxrom_prg_addr((uxrom_mapper*)_map, addr));
     }
     return val;
 }
 
-static void uxrom_write(nes_mapper* nes_map,
-                        uint16_t addr, uint8_t val) {
-    uxrom_mapper* map = (uxrom_mapper*)nes_map->data;
+static void uxrom_write(void* _map, uint16_t addr, uint8_t val) {
+    uxrom_mapper* map = (uxrom_mapper*)_map;
     if (addr >= nes_mem_rom_start) {
         uxrom_set_bank(map, val);
     }
 }
 
-static uint8_t* uxrom_chr_addr(nes_mapper* nes_map,
-                               uint16_t addr) {
-    return &((uxrom_mapper*)nes_map->data)->chr_ram[addr];
+static uint8_t* uxrom_chr_addr(void* data, uint16_t addr) {
+    return &((uxrom_mapper*)data)->chr_ram[addr];
 }
 
-static uint8_t* uxrom_vram_addr(nes_mapper* nes_map,
-                                uint16_t addr) {
-    uxrom_mapper* map = (uxrom_mapper*)nes_map->data;
+static uint8_t* uxrom_vram_addr(void* data, uint16_t addr) {
+    uxrom_mapper* map = (uxrom_mapper*)data;
     int page = addr >> 10U;
     page >>= map->mirror;
     addr = ((page & 1) << 10U) | (addr & 0x3FFU);
     return &map->vram[addr];
 }
 
-static void uxrom_chr_write(nes_mapper* nes_map,
+static void uxrom_chr_write(void* data,
                             uint16_t addr, uint8_t val) {
-    ((uxrom_mapper*)nes_map->data)->chr_ram[addr] = val;
+    ((uxrom_mapper*)data)->chr_ram[addr] = val;
 }
 
 
 /* Save State */
 
-int uxrom_state_size(const nes_mapper* nes_map) {
-    uxrom_mapper* map = (uxrom_mapper*)nes_map->data;
+int uxrom_state_size(const void* _map) {
+    uxrom_mapper* map = (uxrom_mapper*)_map;
     return (    sizeof(uint32_t) +
                 sizeof(map->vram) +
                 sizeof(map->chr_ram));
 }
 
-int uxrom_state_read(nes_mapper* nes_map, const void* data) {
-    uxrom_mapper* map = (uxrom_mapper*)nes_map->data;
+int uxrom_state_read(void* _map, const void* data) {
+    uxrom_mapper* map = (uxrom_mapper*)_map;
     const void* ptr = data;
 
     map->bank = *(uint32_t*)ptr;
@@ -117,8 +113,8 @@ int uxrom_state_read(nes_mapper* nes_map, const void* data) {
     return (ptr - data);
 }
 
-int uxrom_state_write(const nes_mapper* nes_map, void* data) {
-    uxrom_mapper* map = (uxrom_mapper*)nes_map->data;
+int uxrom_state_write(const void* _map, void* data) {
+    uxrom_mapper* map = (uxrom_mapper*)_map;
     void* ptr = data;
 
     uint32_t bank = map->bank;
diff --git a/src/mapper.h b/src/mapper.h
index 6d53c1e..8a13eec 100644
--- a/src/mapper.h
+++ b/src/mapper.h
@@ -12,45 +12,42 @@
 struct nes_cart_t;
 
 typedef struct nes_mapper_t {
-    void* data;
-
     const char* name;
 
-    int (*init)(struct nes_mapper_t*, struct nes_cart_t* cart);
-    void (*reset)(struct nes_mapper_t*);
-    void (*done)(struct nes_mapper_t*);
+    void* (*init)(struct nes_mapper_t*, struct nes_cart_t* cart);
+    void (*reset)(void*);
+    void (*done)(void*);
 
-    uint8_t (*read)(struct nes_mapper_t*, uint16_t addr);
-    void (*write)(struct nes_mapper_t*, uint16_t addr, uint8_t val);
+    uint8_t (*read)(void*, uint16_t addr);
+    void (*write)(void*, uint16_t addr, uint8_t val);
 
-    uint8_t* (*chr_addr)(struct nes_mapper_t*, uint16_t addr);
-    uint8_t* (*vram_addr)(struct nes_mapper_t*, uint16_t addr);
-    void (*chr_write)(struct nes_mapper_t*, uint16_t addr, uint8_t val);
+    uint8_t* (*chr_addr)(void*, uint16_t addr);
+    uint8_t* (*vram_addr)(void*, uint16_t addr);
+    void (*chr_write)(void*, uint16_t addr, uint8_t val);
 
-    void (*scanline)(struct nes_mapper_t*);
-    void (*irq_callback)(void*, int);
+    void (*scanline)(void*);
+    void (*irq_callback)(void* irq_arg, int);
     void* irq_arg;
 
-    void* (*sram)(struct nes_mapper_t*);
-    int (*sram_size)(struct nes_mapper_t*);
-
-    int (*state_size)(const struct nes_mapper_t*);
-    int (*state_read)(struct nes_mapper_t*, const void*);
-    int (*state_write)(const struct nes_mapper_t*, void*);
+    void* (*sram)(void*);
+    int (*sram_size)(void*);
 
+    int (*state_size)(const void* map);
+    int (*state_read)(void* map, const void* data);
+    int (*state_write)(const void* map, void* data);
 } nes_mapper;
 
-static inline int nes_map_init(nes_mapper* map,
-                               struct nes_cart_t* cart) {
+static inline void* nes_map_init(nes_mapper* map,
+                                 struct nes_cart_t* cart) {
     return map->init(map, cart);
 }
 
-static inline void nes_map_reset(nes_mapper* map) {
-    map->reset(map);
+static inline void nes_map_reset(nes_mapper* map, void* data) {
+    map->reset(data);
 }
 
-static inline void nes_map_done(nes_mapper* map) {
-    map->done(map);
+static inline void nes_map_done(nes_mapper* map, void* data) {
+    map->done(data);
 }
 
 static inline void nes_map_set_irq(nes_mapper* map,
@@ -66,44 +63,51 @@ static inline void nes_map_trigger_irq(nes_mapper* map,
 }
 
 static inline uint8_t nes_map_read(nes_mapper* map,
-                                       uint16_t addr) {
-    return map->read(map, addr);
+                                   void* data,
+                                   uint16_t addr) {
+    return map->read(data, addr);
 }
 
 static inline void nes_map_write(nes_mapper* map,
-                                     uint16_t addr,
-                                     uint8_t val) {
-    map->write(map, addr, val);
+                                 void* data,
+                                 uint16_t addr,
+                                 uint8_t val) {
+    map->write(data, addr, val);
 }
 
 static inline uint8_t* nes_map_chr_addr(nes_mapper* map,
-                                       uint16_t addr) {
-    return map->chr_addr(map, addr);
+                                        void* data,
+                                        uint16_t addr) {
+    return map->chr_addr(data, addr);
 }
 
 static inline uint8_t nes_chr_read(nes_mapper* map,
-                                    uint16_t addr) {
-    return *(nes_map_chr_addr(map, addr));
+                                   void* data,
+                                   uint16_t addr) {
+    return *(nes_map_chr_addr(map, data, addr));
 }
 
-static inline void nes_chr_write(nes_mapper* map,
-                                  uint16_t addr, uint8_t val) {
-    return map->chr_write(map, addr, val);
+static inline void nes_chr_write(nes_mapper* map, void* data,
+                                 uint16_t addr, uint8_t val) {
+    return map->chr_write(data, addr, val);
 }
 
 static inline uint8_t* nes_map_vram_addr(nes_mapper* map,
+                                         void* data,
                                          uint16_t addr) {
-    return map->vram_addr(map, addr & 0x1FFFU);
+    return map->vram_addr(data, addr & 0x1FFFU);
 }
 
 static inline uint8_t nes_vram_read(nes_mapper* map,
+                                    void* data,
                                     uint16_t addr) {
-    return *(nes_map_vram_addr(map, addr));
+    return *(nes_map_vram_addr(map, data, addr));
 }
 
 static inline void nes_vram_write(nes_mapper* map,
+                                  void* data,
                                   uint16_t addr, uint8_t val) {
-    *(nes_map_vram_addr(map, addr)) = val;
+    *(nes_map_vram_addr(map, data, addr)) = val;
 }
 
 
diff --git a/src/nes.c b/src/nes.c
index 1ddbf09..7dd89bd 100644
--- a/src/nes.c
+++ b/src/nes.c
@@ -23,7 +23,8 @@ uint8_t nes_mem_read(nes* sys, uint16_t addr) {
         val = nes_apu_read(&sys->apu, addr);
 
     } else {
-        val = nes_map_read(sys->cart.mapper, addr);
+        val = nes_map_read(sys->cart.mapper,
+                           sys->cart.map_data, addr);
     }
 
     return val;
@@ -55,7 +56,8 @@ void nes_mem_write(nes* sys, uint16_t addr, uint8_t val) {
         nes_apu_write(&sys->apu, addr, val);
 
     } else {
-        nes_map_write(sys->cart.mapper, addr, val);
+        nes_map_write(sys->cart.mapper, sys->cart.map_data,
+                      addr, val);
     }
 }
 
@@ -84,6 +86,7 @@ void nes_done(nes* sys) {
 int nes_setup_cart(nes* sys) {
     nes_map_set_irq(sys->cart.mapper, nes_irq, sys);
     sys->ppu.mapper = sys->cart.mapper;
+    sys->ppu.map_data = sys->cart.map_data;
     nes_reset(sys);
     return 0;
 }
diff --git a/src/ppu.c b/src/ppu.c
index d70afe5..53a0a8d 100644
--- a/src/ppu.c
+++ b/src/ppu.c
@@ -43,12 +43,14 @@ uint8_t nes_ppu_read(nes_ppu* ppu, uint16_t addr) {
 
             if (ppu->addr < nes_ppu_mem_vram_start) {
                 PPU_LOG("PPU: CHR MEM READ %04x > %02x\n", ppu->addr, val);
-                ppu->data = nes_chr_read(ppu->mapper, ppu->addr);
+                ppu->data = nes_chr_read(ppu->mapper,
+                                         ppu->map_data,
+                                         ppu->addr);
             } else if (ppu->addr < nes_ppu_mem_vram_start +
                                    nes_ppu_mem_vram_size) {
                 VRAM_LOG("PPU: VRAM READ %04x > %02x\n", ppu->addr, val);
                 ppu->data = nes_vram_read(
-                        ppu->mapper,
+                        ppu->mapper, ppu->map_data,
                         ppu->addr - nes_ppu_mem_vram_start
                     );
             } else if (ppu->addr < nes_ppu_mem_pal_start) {
@@ -186,11 +188,13 @@ void nes_ppu_write(nes_ppu* ppu, uint16_t addr, uint8_t val) {
             }
 #endif // DEBUG_VRAM
 //            printf("PPU: VRAM %04x < %02x\n", vram_addr, val);
-            nes_vram_write(ppu->mapper, vram_addr, val);
+            nes_vram_write(ppu->mapper, ppu->map_data,
+                           vram_addr, val);
 
         } else {
 //            PPU_LOG("PPU: CHR MEM WRITE %04x > %02x\n", ppu->addr, val);
-            nes_chr_write(ppu->mapper, ppu->addr, val);
+            nes_chr_write(ppu->mapper, ppu->map_data,
+                          ppu->addr, val);
         }
 
         ppu->addr += (ppu->control & ppu_Control_VRAM_Inc) ?
@@ -212,6 +216,7 @@ void nes_ppu_reset(nes_ppu* ppu) {
 
 int nes_ppu_init(nes_ppu* ppu, const nes_cart* cart) {
     ppu->mapper   = cart->mapper;
+    ppu->map_data = cart->map_data;
     ppu->status   = 0;
     ppu->oam_addr = 0;
     ppu->addr     = 0;
@@ -237,7 +242,7 @@ nes_ppu_Result nes_ppu_run(nes_ppu* ppu, int cycles) {
             ppu->scanline < nes_ppu_render &&
             (ppu->mask & (ppu_Mask_Back | ppu_Mask_Sprite)) &&
             ppu->cycle < 260 && next_cycle >= 260) {
-        ppu->mapper->scanline(ppu->mapper);
+        ppu->mapper->scanline(ppu->map_data);
     }
 
     ppu->cycle = next_cycle;
diff --git a/src/ppu.h b/src/ppu.h
index 12a4acb..ee5a1e3 100644
--- a/src/ppu.h
+++ b/src/ppu.h
@@ -151,6 +151,7 @@ typedef struct {
 
     // System Interface
     struct nes_mapper_t* mapper;
+    void* map_data;
 } nes_ppu;
 
 uint8_t nes_ppu_read(nes_ppu* ppu, uint16_t addr);
diff --git a/src/save.c b/src/save.c
index b5f9ff3..2f64fd2 100644
--- a/src/save.c
+++ b/src/save.c
@@ -20,9 +20,9 @@ int load_sram(nes_cart* cart, const char* cart_filename) {
     int status = -1;
 
     int sram_size = cart->mapper->sram_size ?
-            cart->mapper->sram_size(cart->mapper) : 0;
+            cart->mapper->sram_size(cart->map_data) : 0;
     void* sram = cart->mapper->sram ?
-            cart->mapper->sram(cart->mapper) : NULL;
+            cart->mapper->sram(cart->map_data) : NULL;
 
     if (sram_size > 0 && NULL != sram) {
         char sram_filename[FILENAME_MAX] = {0};
@@ -39,9 +39,9 @@ int save_sram(const nes_cart* cart, const char* cart_filename) {
 
     if (NULL != cart->mapper) {
         int sram_size = cart->mapper->sram_size ?
-                cart->mapper->sram_size(cart->mapper) : 0;
+                cart->mapper->sram_size(cart->map_data) : 0;
         const void* sram = cart->mapper->sram ?
-                cart->mapper->sram(cart->mapper) : NULL;
+                cart->mapper->sram(cart->map_data) : NULL;
 
         if (sram_size > 0 && NULL != sram) {
             char sram_filename[FILENAME_MAX] = {0};
@@ -230,7 +230,7 @@ int state_size(const nes* sys) {
     size += szChunkHeader + ram_state_size(sys);
     // Cart should already be loaded
     size += szChunkHeader +
-            sys->cart.mapper->state_size(sys->cart.mapper);
+            sys->cart.mapper->state_size(sys->cart.map_data);
 
     return size;
 }
@@ -273,8 +273,10 @@ int state_write(const nes* sys, void* mem, int size) {
     ptr += ram_state_write(sys, ptr);
 
     const nes_mapper* mapper = sys->cart.mapper;
-    ptr = write_header(ptr, tag_mapper, mapper->state_size(mapper));
-    ptr += mapper->state_write(mapper, ptr);
+    const void* map_data = sys->cart.map_data;
+    ptr = write_header(ptr, tag_mapper,
+                       mapper->state_size(map_data));
+    ptr += mapper->state_write(map_data, ptr);
 
     return (ptr - mem);
 }
@@ -336,7 +338,7 @@ int state_read(nes* sys, const void* mem, int mem_size) {
 
         } else if (tag_mapper == tag) {
             n_read = sys->cart.mapper->state_read(
-                    sys->cart.mapper, ptr
+                    sys->cart.map_data, ptr
                 );
             loaded |= Component_Mapper;
 
diff --git a/src/sdl_render.c b/src/sdl_render.c
index d4fe204..78ed2f7 100644
--- a/src/sdl_render.c
+++ b/src/sdl_render.c
@@ -33,7 +33,7 @@ static SDL_Color nes_palette[64] = {
 
 static inline uint8_t* chr_mem(const nes_ppu* ppu,
                                uint16_t addr) {
-    return ppu->mapper->chr_addr(ppu->mapper, addr);
+    return ppu->mapper->chr_addr(ppu->map_data, addr);
 }
 
 
@@ -243,6 +243,7 @@ static inline void render_bg_scanline_area(
     y = y % 8;
     int bank = (ppu->control & ppu_Control_Back_Bank) ? 0x100 : 0;
     const uint8_t* indexes = nes_map_vram_addr(ppu->mapper,
+                                               ppu->map_data,
                                                page << 10);
     const uint8_t* attrs = indexes + 960U;
     const uint8_t* index = indexes +