From 936eb1d14c9b56f15e8a4fa5b9973224baa64515 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sun, 17 Sep 2017 15:01:13 -0700
Subject: [PATCH] GBA Savedata: Fix 512 byte EEPROM saving as 8kB (fixes #877)

---
 CHANGES                            |  1 +
 include/mgba/internal/gba/memory.h |  3 ++-
 src/gba/savedata.c                 | 30 ++++++++++++++++++++++++------
 src/platform/libretro/libretro.c   | 11 ++---------
 4 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/CHANGES b/CHANGES
index 339df26ea..591a966f8 100644
--- a/CHANGES
+++ b/CHANGES
@@ -23,6 +23,7 @@ Bugfixes:
  - GB, GBA: Fix sync to video with frameskip
  - GB Audio: Fix NRx2 writes while active (fixes mgba.io/i/866)
  - GBA BIOS: Use core's VRAM variable instead of renderer's
+ - GBA Savedata: Fix 512 byte EEPROM saving as 8kB (fixes mgba.io/i/877)
 Misc:
  - Qt: Don't rebuild library view if style hasn't changed
  - SDL: Fix 2.0.5 build on macOS under some circumstances
diff --git a/include/mgba/internal/gba/memory.h b/include/mgba/internal/gba/memory.h
index 1e5c89890..165d956d0 100644
--- a/include/mgba/internal/gba/memory.h
+++ b/include/mgba/internal/gba/memory.h
@@ -67,7 +67,8 @@ enum {
 	SIZE_CART_SRAM = 0x00010000,
 	SIZE_CART_FLASH512 = 0x00010000,
 	SIZE_CART_FLASH1M = 0x00020000,
-	SIZE_CART_EEPROM = 0x00002000
+	SIZE_CART_EEPROM = 0x00002000,
+	SIZE_CART_EEPROM512 = 0x00000200
 };
 
 enum {
diff --git a/src/gba/savedata.c b/src/gba/savedata.c
index 08eab40aa..3008b9428 100644
--- a/src/gba/savedata.c
+++ b/src/gba/savedata.c
@@ -147,7 +147,7 @@ size_t GBASavedataSize(struct GBASavedata* savedata) {
 	case SAVEDATA_FLASH1M:
 		return SIZE_CART_FLASH1M;
 	case SAVEDATA_EEPROM:
-		return SIZE_CART_EEPROM;
+		return (savedata->vf && savedata->vf->size(savedata->vf) == SIZE_CART_EEPROM512) ? SIZE_CART_EEPROM512 : SIZE_CART_EEPROM;
 	case SAVEDATA_FORCE_NONE:
 		return 0;
 	case SAVEDATA_AUTODETECT:
@@ -257,20 +257,23 @@ void GBASavedataInitEEPROM(struct GBASavedata* savedata, bool realisticTiming) {
 		mLOG(GBA_SAVE, WARN, "Can't re-initialize savedata");
 		return;
 	}
+	int32_t eepromSize = SIZE_CART_EEPROM512;
 	off_t end;
 	if (!savedata->vf) {
 		end = 0;
 		savedata->data = anonymousMemoryMap(SIZE_CART_EEPROM);
 	} else {
 		end = savedata->vf->size(savedata->vf);
-		if (end < SIZE_CART_EEPROM) {
-			savedata->vf->truncate(savedata->vf, SIZE_CART_EEPROM);
+		if (end < SIZE_CART_EEPROM512) {
+			savedata->vf->truncate(savedata->vf, SIZE_CART_EEPROM512);
+		} else if (end > SIZE_CART_EEPROM512) {
+			eepromSize = SIZE_CART_EEPROM;
 		}
-		savedata->data = savedata->vf->map(savedata->vf, SIZE_CART_EEPROM, savedata->mapMode);
+		savedata->data = savedata->vf->map(savedata->vf, eepromSize, savedata->mapMode);
 	}
 	savedata->realisticTiming = realisticTiming;
-	if (end < SIZE_CART_EEPROM) {
-		memset(&savedata->data[end], 0xFF, SIZE_CART_EEPROM - end);
+	if (end < SIZE_CART_EEPROM512) {
+		memset(&savedata->data[end], 0xFF, SIZE_CART_EEPROM512 - end);
 	}
 }
 
@@ -405,6 +408,19 @@ void GBASavedataWriteFlash(struct GBASavedata* savedata, uint16_t address, uint8
 	}
 }
 
+static void _ensureEeprom(struct GBASavedata* savedata, uint32_t size) {
+	if (size < SIZE_CART_EEPROM512) {
+		return;
+	}
+	if (!savedata->vf || savedata->vf->size(savedata->vf) > SIZE_CART_EEPROM512) {
+		return;
+	}
+	savedata->vf->unmap(savedata->vf, savedata->data, SIZE_CART_EEPROM512);
+	savedata->vf->truncate(savedata->vf, SIZE_CART_EEPROM);
+	savedata->data = savedata->vf->map(savedata->vf, SIZE_CART_EEPROM, savedata->mapMode);
+	memset(&savedata->data[SIZE_CART_EEPROM512], 0xFF, SIZE_CART_EEPROM - SIZE_CART_EEPROM512);
+}
+
 void GBASavedataWriteEEPROM(struct GBASavedata* savedata, uint16_t value, uint32_t writeSize) {
 	switch (savedata->command) {
 	// Read header
@@ -430,6 +446,7 @@ void GBASavedataWriteEEPROM(struct GBASavedata* savedata, uint16_t value, uint32
 		} else if (writeSize == 1) {
 			savedata->command = EEPROM_COMMAND_NULL;
 		} else if ((savedata->writeAddress >> 3) < SIZE_CART_EEPROM) {
+			_ensureEeprom(savedata, savedata->writeAddress >> 3);
 			uint8_t current = savedata->data[savedata->writeAddress >> 3];
 			current &= ~(1 << (0x7 - (savedata->writeAddress & 0x7)));
 			current |= (value & 0x1) << (0x7 - (savedata->writeAddress & 0x7));
@@ -471,6 +488,7 @@ uint16_t GBASavedataReadEEPROM(struct GBASavedata* savedata) {
 	if (savedata->readBitsRemaining < 64) {
 		int step = 63 - savedata->readBitsRemaining;
 		uint32_t address = (savedata->readAddress + step) >> 3;
+		_ensureEeprom(savedata, address);
 		if (address >= SIZE_CART_EEPROM) {
 			mLOG(GBA_SAVE, GAME_ERROR, "Reading beyond end of EEPROM: %08X", address);
 			return 0xFF;
diff --git a/src/platform/libretro/libretro.c b/src/platform/libretro/libretro.c
index 8cd5f4637..b843f0873 100644
--- a/src/platform/libretro/libretro.c
+++ b/src/platform/libretro/libretro.c
@@ -528,16 +528,9 @@ size_t retro_get_memory_size(unsigned id) {
 	if (core->platform(core) == PLATFORM_GBA) {
 		switch (((struct GBA*) core->board)->memory.savedata.type) {
 		case SAVEDATA_AUTODETECT:
-		case SAVEDATA_FLASH1M:
 			return SIZE_CART_FLASH1M;
-		case SAVEDATA_FLASH512:
-			return SIZE_CART_FLASH512;
-		case SAVEDATA_EEPROM:
-			return SIZE_CART_EEPROM;
-		case SAVEDATA_SRAM:
-			return SIZE_CART_SRAM;
-		case SAVEDATA_FORCE_NONE:
-			return 0;
+		default:
+			return GBASavedataSize(&((struct GBA*) core->board)->memory.savedata);
 		}
 	}
 #endif