2 files changed, 92 insertions, 2 deletions
diff --git a/src/agb_sram.c b/src/agb_sram.c
new file mode 100644
index 0000000..e58d5fa
--- /dev/null
+++ b/src/agb_sram.c
@@ -0,0 +1,89 @@
+#include "global.h"
+#include "agb_sram.h"
+
+static u16 verifySramFast_Work[80]; // buffer to hold code of VerifySramFast_Core
+static u16 readSramFast_Work[64];  // buffer to hold code of ReadSramFast_Core
+
+u32 (*VerifySramFast)(const u8 *src, u8 *dest, u32 size);  // pointer to verifySramFast_Work
+void (*ReadSramFast)(const u8 *src, u8 *dest, u32 size);  // pointer to readSramFast_Work
+
+void ReadSramFast_Core(const u8 *src, u8 *dest, u32 size)
+{
+    REG_WAITCNT = (REG_WAITCNT & ~3) | 3;
+    while (--size != -1)
+        *dest++ = *src++;
+}
+
+void WriteSramFast(const u8 *src, u8 *dest, u32 size)
+{
+    REG_WAITCNT = (REG_WAITCNT & ~3) | 3;
+    while (--size != -1)
+        *dest++ = *src++;
+}
+
+u32 VerifySramFast_Core(const u8 *src, u8 *dest, u32 size)
+{
+    REG_WAITCNT = (REG_WAITCNT & ~3) | 3;
+    while (--size != -1)
+    {
+        if (*dest++ != *src++)
+            return (u32)(dest - 1);
+    }
+    return 0;
+}
+
+void SetSramFastFunc(void)
+{
+    u16 *src;
+    u16 *dest;
+    u16 size;
+
+    src = (u16 *)ReadSramFast_Core;
+    // clear the least significant bit so that we get the actual start address of the function
+    src = (u16 *)((uintptr_t)src ^ 1);  // NOTE: In Fire Emblem 8, this is '& ~1' instead of '^ 1'.
+    dest = readSramFast_Work;
+    // get the size of the function by subtracting the address of the next function
+    size = ((uintptr_t)WriteSramFast - (uintptr_t)ReadSramFast_Core) / 2;
+    // copy the function into the WRAM buffer
+    while (size != 0)
+    {
+        *dest++ = *src++;
+        size--;
+    }
+    // add 1 to the address of the buffer so that we stay in THUMB mode when bx-ing to the address
+    ReadSramFast = (void *)((uintptr_t)readSramFast_Work + 1);
+
+    src = (u16 *)VerifySramFast_Core;
+    // clear the least significant bit so that we get the actual start address of the function
+    src = (u16 *)((uintptr_t)src ^ 1);  // NOTE: In Fire Emblem 8, this is '& ~1' instead of '^ 1'.
+    dest = verifySramFast_Work;
+    // get the size of the function by subtracting the address of the next function
+    size = ((uintptr_t)SetSramFastFunc - (uintptr_t)VerifySramFast_Core) / 2;
+    // copy the function into the WRAM buffer
+    while (size != 0)
+    {
+        *dest++ = *src++;
+        size--;
+    }
+    // add 1 to the address of the buffer so that we stay in THUMB mode when bx-ing to the address
+    VerifySramFast = (void *)((uintptr_t)verifySramFast_Work + 1);
+
+    REG_WAITCNT = (REG_WAITCNT & ~3) | 3;
+}
+
+u32 WriteAndVerifySramFast(const u8 *src, u8 *dest, u32 size)
+{
+    u8 i;
+    u32 errorAddr;
+
+    // try writing and verifying the data 3 times
+    for (i = 0; i < 3; i++)
+    {
+        WriteSramFast(src, dest, size);
+        errorAddr = VerifySramFast(src, dest, size);
+        if (errorAddr == 0)
+            break;
+    }
+
+    return errorAddr;
+}
diff --git a/src/titlescreen.c b/src/titlescreen.c
index a4e75e7..6a2bcac 100755
--- a/src/titlescreen.c
+++ b/src/titlescreen.c
@@ -1,6 +1,7 @@
 #include "global.h"
-#include "titlescreen.h"
+#include "agb_sram.h"
 #include "m4a.h"
+#include "titlescreen.h"
 #include "main.h"
 
 static void sub_114FC(void);
@@ -852,5 +853,5 @@ void sub_11B74(void)
     sub_52C64();
     sub_52B30();
     gMain.unk40 = 0;
-    sub_55654(&gMain.unk40, 0x0E000544 /* Possibly SRAM address */, 4);
+    WriteAndVerifySramFast((const u8 *)&gMain.unk40, (void *)0x0E000544, 4);
 }