From 2cb07bf126fba0d6d8960a1b2e23486809c067d0 Mon Sep 17 00:00:00 2001
From: Arisotura <thetotalworm@gmail.com>
Date: Mon, 7 Jul 2025 02:30:01 +0200
Subject: [PATCH] camera: model FIFO more accurately (avoids weird bugs when
 DMA fails)

---
 src/DSi_Camera.cpp             | 47 ++++++++++++++++++----------------
 src/DSi_Camera.h               |  4 +--
 src/FIFO.h                     |  1 +
 src/frontend/qt_sdl/Window.cpp |  2 +-
 4 files changed, 29 insertions(+), 25 deletions(-)

diff --git a/src/DSi_Camera.cpp b/src/DSi_Camera.cpp
index 38251fd6..d12f1e34 100644
--- a/src/DSi_Camera.cpp
+++ b/src/DSi_Camera.cpp
@@ -67,9 +67,7 @@ void DSi_CamModule::Reset()
     CropStart = 0;
     CropEnd = 0;
 
-    memset(DataBuffer, 0, 512*sizeof(u32));
-    BufferReadPos = 0;
-    BufferWritePos = 0;
+    DataBuffer.Clear();
     BufferNumLines = 0;
     CurCamera = nullptr;
 
@@ -89,6 +87,8 @@ void DSi_CamModule::DoSavestate(Savestate* file)
     file->Var16(&ModuleCnt);
     file->Var16(&Cnt);
 
+    // TODO: should other stuff be savestated? (pixel buffer, etc)
+
     /*file->VarArray(FrameBuffer, sizeof(FrameBuffer));
     file->Var32(&TransferPos);
     file->Var32(&FrameLength);*/
@@ -113,8 +113,6 @@ void DSi_CamModule::IRQ(u32 param)
 
         if (Cnt & (1<<15))
         {
-            BufferReadPos = 0;
-            BufferWritePos = 0;
             BufferNumLines = 0;
             CurCamera = activecam;
             DSi.ScheduleEvent(Event_DSi_CamTransfer, false, kTransferStart, 0, 0);
@@ -126,8 +124,10 @@ void DSi_CamModule::IRQ(u32 param)
 
 void DSi_CamModule::TransferScanline(u32 line)
 {
-    u32* dstbuf = &DataBuffer[BufferWritePos];
-    int maxlen = 512 - BufferWritePos;
+    if (Cnt & (1<<4))
+        return;
+
+    int maxlen = DataBuffer.FreeSpace();
 
     u32 tmpbuf[512];
     int lines_next;
@@ -195,28 +195,28 @@ void DSi_CamModule::TransferScanline(u32 line)
             u32 col1 = (r1 >> 3) | ((g1 >> 3) << 5) | ((b1 >> 3) << 10) | 0x8000;
             u32 col2 = (r2 >> 3) | ((g2 >> 3) << 5) | ((b2 >> 3) << 10) | 0x8000;
 
-            dstbuf[i] = col1 | (col2 << 16);
+            DataBuffer.Write(col1 | (col2 << 16));
         }
     }
     else
     {
         // return raw data
 
-        memcpy(dstbuf, &tmpbuf[copystart], copylen*sizeof(u32));
+        for (u32 i = 0; i < copylen; i++)
+        {
+            u32 val = tmpbuf[copystart + i];
+            DataBuffer.Write(val);
+        }
     }
 
     numscan = Cnt & 0x000F;
     if (BufferNumLines >= numscan)
     {
-        BufferReadPos = 0; // checkme
-        BufferWritePos = 0;
         BufferNumLines = 0;
         DSi.CheckNDMAs(0, 0x0B);
     }
     else
     {
-        BufferWritePos += copylen;
-        if (BufferWritePos > 512) BufferWritePos = 512;
         BufferNumLines++;
     }
 
@@ -225,10 +225,9 @@ skip_line:
     {
         // when the frame is finished, transfer any remaining data if needed
         // (if the frame height isn't a multiple of the DMA interval)
+        // (TODO: should it be done earlier?)
         if (BufferNumLines > 0)
         {
-            BufferReadPos = 0;
-            BufferWritePos = 0;
             BufferNumLines = 0;
             DSi.CheckNDMAs(0, 0x0B);
         }
@@ -266,14 +265,19 @@ u32 DSi_CamModule::Read32(u32 addr)
     {
     case 0x04004204:
         {
-            u32 ret = DataBuffer[BufferReadPos];
+            u32 ret;
             if (Cnt & (1<<15))
             {
-                if (BufferReadPos < 511)
-                    BufferReadPos++;
-                // CHECKME!!!!
-                // also presumably we should set bit4 in Cnt if there's no new data to be read
+                if (DataBuffer.IsEmpty())
+                {
+                    ret = 0;
+                    Cnt |= (1<<4);
+                }
+                else
+                    ret = DataBuffer.Read();
             }
+            else
+                ret = DataBuffer.Peek();
 
             return ret;
         }
@@ -339,8 +343,7 @@ void DSi_CamModule::Write16(u32 addr, u16 val)
             if (val & (1<<5))
             {
                 Cnt &= ~(1<<4);
-                BufferReadPos = 0;
-                BufferWritePos = 0;
+                DataBuffer.Clear();
             }
 
             if ((val & (1<<15)) && !(Cnt & (1<<15)))
diff --git a/src/DSi_Camera.h b/src/DSi_Camera.h
index 61934bc8..bd588c72 100644
--- a/src/DSi_Camera.h
+++ b/src/DSi_Camera.h
@@ -22,6 +22,7 @@
 #include "types.h"
 #include "Savestate.h"
 #include "DSi_I2C.h"
+#include "FIFO.h"
 
 namespace melonDS
 {
@@ -119,8 +120,7 @@ private:
     u32 CropStart, CropEnd;
 
     // pixel data buffer holds a maximum of 512 words, regardless of how long scanlines are
-    u32 DataBuffer[512];
-    u32 BufferReadPos, BufferWritePos;
+    FIFO<u32, 512> DataBuffer;
     u32 BufferNumLines;
     DSi_Camera* CurCamera;
 
diff --git a/src/FIFO.h b/src/FIFO.h
index ccb009b1..f8749ad3 100644
--- a/src/FIFO.h
+++ b/src/FIFO.h
@@ -90,6 +90,7 @@ public:
     }
 
     u32 Level() const { return NumOccupied; }
+    u32 FreeSpace() const { return NumEntries - NumOccupied; }
     bool IsEmpty() const { return NumOccupied == 0; }
     bool IsFull() const { return NumOccupied >= NumEntries; }
 
diff --git a/src/frontend/qt_sdl/Window.cpp b/src/frontend/qt_sdl/Window.cpp
index 8e3b2390..b5a9b690 100755
--- a/src/frontend/qt_sdl/Window.cpp
+++ b/src/frontend/qt_sdl/Window.cpp
@@ -979,7 +979,7 @@ void MainWindow::keyPressEvent(QKeyEvent* event)
     if (event->isAutoRepeat()) return;
 
     // TODO!! REMOVE ME IN RELEASE BUILDS!!
-    //if (event->key() == Qt::Key_F11) emuThread->NDS->debug(0);
+    //if (event->key() == Qt::Key_F11) emuInstance->getNDS()->debug(0);
 
     emuInstance->onKeyPress(event);
 }