From 9d2acd69318cedf939b1d4ca0a6e0531d5d9b631 Mon Sep 17 00:00:00 2001
From: mjbudd77 <mjbudd77@gmail.com>
Date: Thu, 19 Aug 2021 21:32:14 -0400
Subject: [PATCH] Added memory write undo functionality for debugger step back.

---
 src/drivers/Qt/ConsoleDebugger.cpp | 32 ++++++++------
 src/drivers/Qt/TraceLogger.cpp     | 68 ++++++++++++++++++++++++++++++
 src/drivers/Qt/TraceLogger.h       |  3 ++
 3 files changed, 91 insertions(+), 12 deletions(-)

diff --git a/src/drivers/Qt/ConsoleDebugger.cpp b/src/drivers/Qt/ConsoleDebugger.cpp
index 900d8f6e..6fec0f27 100644
--- a/src/drivers/Qt/ConsoleDebugger.cpp
+++ b/src/drivers/Qt/ConsoleDebugger.cpp
@@ -818,6 +818,16 @@ QToolBar *ConsoleDebugger::buildToolBar(void)
 
 	toolBar->addAction(act);
 
+	// Debug -> Step Back
+	stepBackToolAct = act = new QAction(tr("Step &Back (F9)"), this);
+	//act->setShortcut(QKeySequence( tr("F9") ) );
+	act->setStatusTip(tr("Step Back"));
+	act->setIcon( QIcon(":icons/StepBack.png") );
+	act->setEnabled(false);
+	connect( act, SIGNAL(triggered()), this, SLOT(debugStepBackCB(void)) );
+
+	toolBar->addAction(act);
+
 	// Debug -> Step Into
 	act = new QAction(tr("Step &Into (F11)"), this);
 	//act->setShortcut(QKeySequence( tr("F11") ) );
@@ -845,16 +855,6 @@ QToolBar *ConsoleDebugger::buildToolBar(void)
 
 	toolBar->addAction(act);
 
-	// Debug -> Step Back
-	stepBackToolAct = act = new QAction(tr("Step &Back (F9)"), this);
-	//act->setShortcut(QKeySequence( tr("F9") ) );
-	act->setStatusTip(tr("Step Back"));
-	act->setIcon( QIcon(":icons/StepBack.png") );
-	act->setEnabled(false);
-	connect( act, SIGNAL(triggered()), this, SLOT(debugStepBackCB(void)) );
-
-	toolBar->addAction(act);
-
 	toolBar->addSeparator();
 
 	// Debug -> Run Line
@@ -4103,8 +4103,16 @@ void ConsoleDebugger::updatePeriodic(void)
 		dbgPauseAct[1]->setEnabled(true);
 	}
 
-	stepBackMenuAct->setEnabled( FCEUD_TraceLoggerRunning() );
-	stepBackToolAct->setEnabled( FCEUD_TraceLoggerRunning() );
+	if ( FCEUD_TraceLoggerRunning() && FCEUI_EmulationPaused() )
+	{
+		stepBackMenuAct->setEnabled(true);
+		stepBackToolAct->setEnabled(true);
+	}
+	else
+	{
+		stepBackMenuAct->setEnabled(false);
+		stepBackToolAct->setEnabled(false);
+	}
 
 	if ( waitingAtBp && (lastBpIdx == BREAK_TYPE_CYCLES_EXCEED) )
 	{
diff --git a/src/drivers/Qt/TraceLogger.cpp b/src/drivers/Qt/TraceLogger.cpp
index b4b5807d..c1680bf1 100644
--- a/src/drivers/Qt/TraceLogger.cpp
+++ b/src/drivers/Qt/TraceLogger.cpp
@@ -1333,6 +1333,59 @@ void FCEUD_TraceInstruction(uint8 *opcode, int size)
 		}
 	}
 
+	switch ( opcode[0] )
+	{
+		// Zero page
+		case 0x85: // STA - Store Accumulator
+		case 0x86: // STX - Store X Register
+		case 0x84: // STY - Store Y Register
+		case 0xC6: // DEC - Decrement Memory
+		case 0xE6: // INC - Increment Memory
+			rec.writeAddr = opcode[1];
+		break;
+		// Absolute
+		case 0x8D: // STA - Store Accumulator
+		case 0x8E: // STX - Store X Register
+		case 0x8C: // STY - Store Y Register
+		case 0xCE: // DEC - Decrement Memory
+		case 0xEE: // INC - Increment Memory
+			rec.writeAddr = opcode[1] | opcode[2] << 8;
+		break;
+		// Indirect X
+		case 0x81: // STA - Store A Register
+			rec.writeAddr = (opcode[1] + X.X) & 0xFF;
+			rec.writeAddr = GetMem((rec.writeAddr)) | (GetMem(((rec.writeAddr)+1)&0xff))<<8;
+		break;
+		// Indirect Y
+		case 0x91: // STA - Store A Register
+			rec.writeAddr  = GetMem(opcode[1]) | (GetMem((opcode[1]+1)&0xff))<<8;
+			rec.writeAddr += X.Y;
+		break;
+		// Zero Page X
+		case 0x95: // STA - Store Accumulator
+		case 0x94: // STY - Store Y Register
+		case 0xD6: // DEC - Decrement Memory
+		case 0xF6: // INC - Increment Memory
+			rec.writeAddr = (opcode[1]+ X.X) & 0xFF;
+		break;
+		// Zero Page Y
+		case 0x96: // STX - Store X Register
+			rec.writeAddr = (opcode[1]+ X.Y) & 0xFF;
+		break;
+		default:
+			rec.writeAddr = -1;
+		break;
+	}
+
+	if ( rec.writeAddr >= 0 )
+	{
+		rec.preWriteVal = GetMem( rec.writeAddr );
+	}
+	else
+	{
+		rec.preWriteVal = 0;
+	}
+
 	pushToLogBuffer(rec);
 
 	return; // TEST
@@ -2485,6 +2538,21 @@ static int undoInstruction( traceRecord_t &rec )
 	X.S  = rec.cpu.S;
 	X.P  = rec.cpu.P;
 
+	if ( rec.writeAddr >= 0 )
+	{
+		if ( rec.writeAddr < 0x8000 )
+		{
+			writefunc wfunc;
+        
+			wfunc = GetWriteHandler (rec.writeAddr);
+        
+			if (wfunc)
+			{
+				wfunc ((uint32) rec.writeAddr,
+				       (uint8) (rec.preWriteVal & 0x000000ff));
+			}
+		}
+	}
 	return 0;
 }
 //----------------------------------------------------
diff --git a/src/drivers/Qt/TraceLogger.h b/src/drivers/Qt/TraceLogger.h
index 25d35df7..a85b0e0e 100644
--- a/src/drivers/Qt/TraceLogger.h
+++ b/src/drivers/Qt/TraceLogger.h
@@ -39,6 +39,7 @@ struct traceRecord_t
 	uint8_t opCode[3];
 	uint8_t opSize;
 	uint8_t asmTxtSize;
+	uint8_t preWriteVal;
 	char asmTxt[64];
 
 	uint64_t frameCount;
@@ -51,6 +52,8 @@ struct traceRecord_t
 	int32_t bank;
 	int32_t skippedLines;
 
+	int32_t writeAddr;
+
 	traceRecord_t(void);
 
 	int appendAsmText(const char *txt);