From 4cdf2839b3ba0e9f6e1973285e8abcb24e8656a3 Mon Sep 17 00:00:00 2001
From: Nathaniel Walizer <robots.are.love@gmail.com>
Date: Fri, 3 Jan 2025 01:44:29 -0800
Subject: [PATCH] Add UxROM mapper (Castlevania, Mega Man)

---
 Makefile        |  2 +-
 src/map/uxrom.c | 96 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/mapper.c    |  2 ++
 3 files changed, 99 insertions(+), 1 deletion(-)
 create mode 100644 src/map/uxrom.c

diff --git a/Makefile b/Makefile
index c51c00f..e835e30 100644
--- a/Makefile
+++ b/Makefile
@@ -27,7 +27,7 @@ SRC_SRCS_1 += sdl_render.c sdl_input.c
 SRC_SRCS_1 += apu.c
 
 MAPDIR = src/map
-MAP_SRCS_1 = nrom.c mmc1.c cnrom.c mmc3.c
+MAP_SRCS_1 = nrom.c mmc1.c uxrom.c cnrom.c mmc3.c
 
 EXT_SRCS_1 = e6502/e6502.c e6502/opcodes.c blip-buf/blip_buf.c
 
diff --git a/src/map/uxrom.c b/src/map/uxrom.c
new file mode 100644
index 0000000..d420fa5
--- /dev/null
+++ b/src/map/uxrom.c
@@ -0,0 +1,96 @@
+#include <stdlib.h>
+
+#include "map.h"
+
+
+typedef struct {
+    uint8_t* prg_rom;
+    int prg_rom_banks;
+    uint8_t mirror;
+    uint8_t vram[nes_vram_page_size * 2];
+    uint8_t chr_ram[8 * 1024];
+
+    uint8_t* prg_bank_lo;
+    uint8_t* prg_bank_hi;
+} uxrom_mapper;
+
+
+static void uxrom_reset(nes_mapper* nes_map) {
+    uxrom_mapper* map = (uxrom_mapper*)nes_map->data;
+    map->prg_bank_lo = map->prg_rom;
+}
+
+static int 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);
+    }
+    return (NULL == map ? -1 : 0);
+}
+
+static void uxrom_done(nes_mapper* nes_map) {
+    free(nes_map->data);
+}
+
+static inline uint8_t* uxrom_prg_addr(uxrom_mapper* map,
+                                      uint16_t addr) {
+    uint8_t* bank = (   addr < 0xC000U ?
+                        map->prg_bank_lo : map->prg_bank_hi );
+    return &(bank[addr & 0x3FFF]);
+}
+
+
+static uint8_t uxrom_read(nes_mapper* map, uint16_t addr) {
+    uint8_t val = 0;
+    if (addr >= nes_mem_rom_start) {
+        val = *(uxrom_prg_addr((uxrom_mapper*)map->data, 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;
+    if (addr >= nes_mem_rom_start) {
+        map->prg_bank_lo = &map->prg_rom[
+                (val % map->prg_rom_banks) *
+                nes_prg_rom_page_size
+            ];
+    }
+}
+
+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_vram_addr(nes_mapper* nes_map,
+                                uint16_t addr) {
+    uxrom_mapper* map = (uxrom_mapper*)nes_map->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,
+                            uint16_t addr, uint8_t val) {
+    ((uxrom_mapper*)nes_map->data)->chr_ram[addr] = val;
+}
+
+nes_mapper mapper_uxrom = {
+    .init  = uxrom_init,
+    .reset = uxrom_reset,
+    .done  = uxrom_done,
+    .read  = uxrom_read,
+    .write = uxrom_write,
+    .chr_addr  = uxrom_chr_addr,
+    .vram_addr = uxrom_vram_addr,
+    .chr_write = uxrom_chr_write,
+};
diff --git a/src/mapper.c b/src/mapper.c
index 7828047..f20092f 100644
--- a/src/mapper.c
+++ b/src/mapper.c
@@ -3,6 +3,7 @@
 
 extern nes_mapper mapper_nrom;
 extern nes_mapper mapper_mmc1;
+extern nes_mapper mapper_uxrom;
 extern nes_mapper mapper_cnrom;
 extern nes_mapper mapper_mmc3;
 
@@ -10,6 +11,7 @@ extern nes_mapper mapper_mmc3;
 nes_mapper* nes_mappers[256] = {
     [  0] = &mapper_nrom,
     [  1] = &mapper_mmc1,
+    [  2] = &mapper_uxrom,
     [  3] = &mapper_cnrom,
     [  4] = &mapper_mmc3,
 };