From 5596f16cbbd8d10ea0b3f55b4205a3059a657adf Mon Sep 17 00:00:00 2001
From: Snesrev <snesrev@protonmail.com>
Date: Sat, 11 Mar 2023 18:33:53 +0100
Subject: [PATCH] LoadStdBG3andSpriteTilesClearTilemaps does DMA from RAM

---
 src/sm_82.c        | 3 ++-
 src/sm_cpu_infra.c | 3 +++
 src/snes/dma.c     | 8 ++++++++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/sm_82.c b/src/sm_82.c
index 8cd91a4..c0951b7 100644
--- a/src/sm_82.c
+++ b/src/sm_82.c
@@ -249,7 +249,8 @@ void LoadStdBG3andSpriteTilesClearTilemaps(void) {  // 0x8282E2
   WriteReg(VMADDL, 0);
   WriteReg(VMADDH, 0x60u);
   WriteReg(VMAIN, 0x80);
-  static const StartDmaCopy unk_828318 = { 1, 1, 0x18, LONGPTR(0x9ad200), 0x4000 };
+  // Bug fix: Asm code does DMA from RAM here.
+  static const StartDmaCopy unk_828318 = { 1, 1, 0x18, LONGPTR(0x9ad200), 0x2e00 };
   SetupDmaTransfer(&unk_828318);
   WriteReg(MDMAEN, 2u);
   WriteReg(VMADDL, 0);
diff --git a/src/sm_cpu_infra.c b/src/sm_cpu_infra.c
index d3f3ae1..1e3fe81 100644
--- a/src/sm_cpu_infra.c
+++ b/src/sm_cpu_infra.c
@@ -740,6 +740,9 @@ Snes *SnesInit(const char *filename) {
   { uint8 t[] = { 0x18, 0x18, 0x18, 0x80 }; PatchBytes(0x828A80, t, sizeof(t)); } // SfxHandlers_3_WaitForAck
   { uint8 t[] = { 0x06 }; PatchBytes(0x828A67, t, sizeof(t)); } // sfx_clear_delay
 
+  // LoadStdBG3andSpriteTilesClearTilemaps does DMA from RAM
+  { uint8 t[] = { 0x00, 0x2E }; PatchBytes(0x82831E, t, sizeof(t)); }
+
   RtlUpdateSnesPatchForBugfix();
 
   for (size_t i = 0; i != arraysize(kPatchedCarrys); i++) {
diff --git a/src/snes/dma.c b/src/snes/dma.c
index bc7702c..872a3ae 100644
--- a/src/snes/dma.c
+++ b/src/snes/dma.c
@@ -184,6 +184,8 @@ void dma_write(Dma* dma, uint16_t adr, uint8_t val) {
   }
 }
 
+extern bool g_fail;
+
 void dma_doDma(Dma* dma) {
   if(dma->dmaTimer > 0) {
     dma->dmaTimer -= 2;
@@ -201,6 +203,12 @@ void dma_doDma(Dma* dma) {
     dma->dmaBusy = false;
     return;
   }
+
+  if (!dma->channel[i].fromB && (dma->channel[i].aBank & 0x80) && !(dma->channel[i].aAdr & 0x8000) && !g_fail) {
+    printf("Warning! DMA from addr 0x%x\n", dma->channel[i].aBank << 16 | dma->channel[i].aAdr);
+    g_fail = true;
+  }
+
   // do channel i
   dma_transferByte(
     dma, dma->channel[i].aAdr, dma->channel[i].aBank,