From eee291e00eab0fd6d75af8c003a292fff045b866 Mon Sep 17 00:00:00 2001
From: Jeffrey Pfau <jeffrey@endrift.com>
Date: Mon, 9 Nov 2015 22:44:46 -0800
Subject: [PATCH] GBA: Implement bad I/O register loading

---
 CHANGES                            |  1 +
 src/gba/io.c                       | 32 ++++++++++++++++++++++++++++++
 src/gba/renderers/video-software.c | 12 +++++++----
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/CHANGES b/CHANGES
index f8da4b526..277cc18fb 100644
--- a/CHANGES
+++ b/CHANGES
@@ -38,6 +38,7 @@ Misc:
  - GBA Audio: Implement missing flags on SOUNDCNT_X register
  - Util: Use VFile for configuration
  - GBA Memory: Implement several unimplemented memory access types
+ - GBA: Implement bad I/O register loading
 
 0.3.1: (2015-10-24)
 Bugfixes:
diff --git a/src/gba/io.c b/src/gba/io.c
index d62ceeb42..7c935ddc2 100644
--- a/src/gba/io.c
+++ b/src/gba/io.c
@@ -636,6 +636,38 @@ uint16_t GBAIORead(struct GBA* gba, uint32_t address) {
 	case REG_DMA3CNT_LO:
 		// Write-only register
 		return 0;
+	case REG_BG0HOFS:
+	case REG_BG0VOFS:
+	case REG_BG1HOFS:
+	case REG_BG1VOFS:
+	case REG_BG2HOFS:
+	case REG_BG2VOFS:
+	case REG_BG3HOFS:
+	case REG_BG3VOFS:
+	case REG_BG2PA:
+	case REG_BG2PB:
+	case REG_BG2PC:
+	case REG_BG2PD:
+	case REG_BG2X_LO:
+	case REG_BG2X_HI:
+	case REG_BG2Y_LO:
+	case REG_BG2Y_HI:
+	case REG_BG3PA:
+	case REG_BG3PB:
+	case REG_BG3PC:
+	case REG_BG3PD:
+	case REG_BG3X_LO:
+	case REG_BG3X_HI:
+	case REG_BG3Y_LO:
+	case REG_BG3Y_HI:
+	case REG_WIN0H:
+	case REG_WIN1H:
+	case REG_WIN0V:
+	case REG_WIN1V:
+	case REG_MOSAIC:
+	case REG_BLDY:
+		// Write-only register
+		return GBALoad16(gba->cpu, 0x01000000, 0); // Simulate a bad load
 	case REG_DISPCNT:
 	case REG_DISPSTAT:
 	case REG_VCOUNT:
diff --git a/src/gba/renderers/video-software.c b/src/gba/renderers/video-software.c
index ab9e98b0f..cafd7d7f5 100644
--- a/src/gba/renderers/video-software.c
+++ b/src/gba/renderers/video-software.c
@@ -145,19 +145,19 @@ static uint16_t GBAVideoSoftwareRendererWriteVideoRegister(struct GBAVideoRender
 		GBAVideoSoftwareRendererUpdateDISPCNT(softwareRenderer);
 		break;
 	case REG_BG0CNT:
-		value &= 0xFFCF;
+		value &= 0xDFFF;
 		GBAVideoSoftwareRendererWriteBGCNT(softwareRenderer, &softwareRenderer->bg[0], value);
 		break;
 	case REG_BG1CNT:
-		value &= 0xFFCF;
+		value &= 0xDFFF;
 		GBAVideoSoftwareRendererWriteBGCNT(softwareRenderer, &softwareRenderer->bg[1], value);
 		break;
 	case REG_BG2CNT:
-		value &= 0xFFCF;
+		value &= 0xFFFF;
 		GBAVideoSoftwareRendererWriteBGCNT(softwareRenderer, &softwareRenderer->bg[2], value);
 		break;
 	case REG_BG3CNT:
-		value &= 0xFFCF;
+		value &= 0xFFFF;
 		GBAVideoSoftwareRendererWriteBGCNT(softwareRenderer, &softwareRenderer->bg[3], value);
 		break;
 	case REG_BG0HOFS:
@@ -242,6 +242,7 @@ static uint16_t GBAVideoSoftwareRendererWriteVideoRegister(struct GBAVideoRender
 		break;
 	case REG_BLDCNT:
 		GBAVideoSoftwareRendererWriteBLDCNT(softwareRenderer, value);
+		value &= 0x3FFF;
 		break;
 	case REG_BLDALPHA:
 		softwareRenderer->blda = value & 0x1F;
@@ -252,6 +253,7 @@ static uint16_t GBAVideoSoftwareRendererWriteVideoRegister(struct GBAVideoRender
 		if (softwareRenderer->bldb > 0x10) {
 			softwareRenderer->bldb = 0x10;
 		}
+		value &= 0x1F1F;
 		break;
 	case REG_BLDY:
 		softwareRenderer->bldy = value & 0x1F;
@@ -313,10 +315,12 @@ static uint16_t GBAVideoSoftwareRendererWriteVideoRegister(struct GBAVideoRender
 		}
 		break;
 	case REG_WININ:
+		value &= 0x3F3F;
 		softwareRenderer->winN[0].control.packed = value;
 		softwareRenderer->winN[1].control.packed = value >> 8;
 		break;
 	case REG_WINOUT:
+		value &= 0x3F3F;
 		softwareRenderer->winout.packed = value;
 		softwareRenderer->objwin.packed = value >> 8;
 		break;