save game support, and don't update the timer for now, it breaks things

cli/imgui_example.cpp

@@ -13,6 +13,7 @@ extern "C" {
 #include "cpu.h"
 #include "rom.h"
 #include "lcd.h"
+#include "mbc.h"
 #include "instructions.h"
 }
 
@@ -163,6 +164,7 @@ int main(int argc, char *argv[])
 
     dmg_new(&dmg, &cpu, &rom, &lcd);
     cpu.dmg = &dmg;
+    mbc_load_ram(dmg.rom->mbc, "save.sav");
     // cpu_bind_mem_model(&cpu, &dmg, dmg_read, dmg_write);
 
     cpu.pc = 0x100;
@@ -382,6 +384,7 @@ int main(int argc, char *argv[])
     SDL_DestroyWindow(window);
     SDL_Quit();
 
+    mbc_save_ram(dmg.rom->mbc, "save.sav");
     rom_free(&rom);
 
     return 0;

src/dmg.c

@@ -278,7 +278,7 @@ void dmg_step(void *_dmg)
     // order of dependencies? i think cpu needs to step first then update
     // all other hw
     cpu_step(dmg->cpu);
-    timer_step(dmg);
+    // timer_step(dmg);
 
     // each line takes 456 cycles
     int cycle_diff = dmg->cpu->cycle_count - dmg->last_lcd_update;

src/mbc.c

@@ -57,6 +57,7 @@ struct mbc *mbc_new(int type)
     return NULL;
   }
   mbc.type = type;
+  mbc.has_battery = type == 3;
 
   return &mbc;
 }
@@ -76,3 +77,47 @@ int mbc_write(struct mbc *mbc, struct dmg *dmg, u16 addr, u8 data)
   }
   return mbc1_write(mbc, dmg, addr, data);
 }
+
+int mbc_save_ram(struct mbc *mbc, const char *filename)
+{
+  FILE *fp;
+
+  if (!mbc->has_battery) {
+    return 0;
+  }
+
+  fp = fopen(filename, "w");
+  if (!fp) {
+    return 0;
+  }
+
+  if (fwrite(mbc->ram, 1, RAM_SIZE, fp) < RAM_SIZE) {
+    fclose(fp);
+    return 0;
+  }
+
+  fclose(fp);
+  return 1;
+}
+
+int mbc_load_ram(struct mbc *mbc, const char *filename)
+{
+  FILE *fp;
+
+  if (!mbc->has_battery) {
+    return 0;
+  }
+
+  fp = fopen(filename, "r");
+  if (!fp) {
+    return 0;
+  }
+
+  if (fread(mbc->ram, 1, RAM_SIZE, fp) < RAM_SIZE) {
+    fclose(fp);
+    return 0;
+  }
+
+  fclose(fp);
+  return 1;
+}

src/mbc.h

@@ -3,14 +3,17 @@
 
 #include "types.h"
 
+#define RAM_SIZE 0x8000
+
 struct dmg;
 
 struct mbc {
   int type;
+  int has_battery;
   int rom_bank;
   int ram_bank;
   int ram_enabled;
-  u8 ram[0x8000];
+  u8 ram[RAM_SIZE];
 };
 
 struct mbc *mbc_new(int type);
@@ -19,5 +22,8 @@ struct mbc *mbc_new(int type);
 int mbc_read(struct mbc *mbc, struct dmg *dmg, u16 addr, u8 *out_data);
 // return 1 if handled, return 0 for base dmg behavior
 int mbc_write(struct mbc *mbc, struct dmg *dmg, u16 addr, u8 data);
+// 1 if success, 0 if error
+int mbc_save_ram(struct mbc *mbc, const char *filename);
+int mbc_load_ram(struct mbc *mbc, const char *filename);
 
 #endif