Implemented data bus state locking, so the debugger won't disturb the

System when it uses peek() to examine memory/TIA/etc.

I'm not entirely sure I put a lockDataBus() call where it will get
executed when the user presses ` to enter the debugger: I put it in
Debugger::start() (does everything call this, or does EventHandler do
something else?), and again in Debugger::state() (which gets called to
build every prompt string).

There are unlockDataBus() calls everywhere in the Debugger where we
execute 6502 code, including Debugger::quit(). Does the EventHandler
call quit() when it exits the debugger (if the user presses ` I mean)?


git-svn-id: svn://svn.code.sf.net/p/stella/code/trunk@630 8b62c5a3-ac7e-4cc8-8f21-d9a121418aba

stella/src/debugger/Debugger.cxx

@@ -13,7 +13,7 @@
 // See the file "license" for information on usage and redistribution of
 // this file, and for a DISCLAIMER OF ALL WARRANTIES.
 //
-// $Id: Debugger.cxx,v 1.57 2005-07-08 17:22:40 stephena Exp $
+// $Id: Debugger.cxx,v 1.58 2005-07-09 23:44:07 urchlay Exp $
 //============================================================================
 
 #include "bspf.hxx"
@@ -216,6 +216,9 @@ const string Debugger::cpuState()
   string result;
   char buf[255];
 
+  // Lock the bus before every prompt, so we don't disturb anything:
+  mySystem->lockDataBus();
+
   CpuState state    = (CpuState&) myCpuDebug->getState();
   CpuState oldstate = (CpuState&) myCpuDebug->getOldState();
 
@@ -489,12 +492,17 @@ bool Debugger::start()
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 void Debugger::quit()
 {
+
   if(myOSystem->eventHandler().state() == EventHandler::S_DEBUGGER) {
+    mySystem->unlockDataBus();
+
     // execute one instruction on quit, IF we're
     // sitting at a breakpoint. This will get us past it.
     // Somehow this feels like a hack to me, but I don't know why
+    // FIXME: do this for traps, too
     if(breakPoints->isSet(myCpuDebug->pc()))
       mySystem->m6502().execute(1);
+
     myOSystem->eventHandler().leaveDebugMode();
   }
 }
@@ -517,7 +525,9 @@ int Debugger::step()
   saveOldState();
 
   int cyc = mySystem->cycles();
+  mySystem->unlockDataBus();
   mySystem->m6502().execute(1);
+  mySystem->lockDataBus();
 
   // FIXME - this doesn't work yet, pending a partial rewrite of TIA class
   myTiaDebug->updateTIA();
@@ -542,15 +552,21 @@ int Debugger::step()
 
 int Debugger::trace()
 {
+
   // 32 is the 6502 JSR instruction:
   if(mySystem->peek(myCpuDebug->pc()) == 32) {
     saveOldState();
 
     int cyc = mySystem->cycles();
     int targetPC = myCpuDebug->pc() + 3; // return address
+
+    mySystem->unlockDataBus();
+
     while(myCpuDebug->pc() != targetPC)
       mySystem->m6502().execute(1);
 
+    mySystem->lockDataBus();
+
     // FIXME - this doesn't work yet, pending a partial rewrite of TIA class
     myTiaDebug->updateTIA();
     myOSystem->frameBuffer().refreshTIA(true);
@@ -645,7 +661,9 @@ string Debugger::disassemble(int start, int lines) {
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 void Debugger::nextFrame(int frames) {
   saveOldState();
+  mySystem->unlockDataBus();
   myOSystem->frameBuffer().advance(frames);
+  mySystem->lockDataBus();
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

stella/src/debugger/TIADebug.cxx

@@ -13,7 +13,7 @@
 // See the file "license" for information on usage and redistribution of
 // this file, and for a DISCLAIMER OF ALL WARRANTIES.
 //
-// $Id: TIADebug.cxx,v 1.9 2005-07-08 17:22:40 stephena Exp $
+// $Id: TIADebug.cxx,v 1.10 2005-07-09 23:44:07 urchlay Exp $
 //============================================================================
 
 #include "System.hxx"
@@ -42,7 +42,7 @@ DebuggerState& TIADebug::getState()
 {
   myState.ram.clear();
   for(int i = 0; i < 0x010; ++i)
-    myState.ram.push_back(mySystem->peek(i));
+    myState.ram.push_back(myTIA->peek(i));
 
   return myState;
 }
@@ -52,7 +52,7 @@ void TIADebug::saveOldState()
 {
   myOldState.ram.clear();
   for(int i = 0; i < 0x010; ++i)
-    myOldState.ram.push_back(mySystem->peek(i));
+    myOldState.ram.push_back(myTIA->peek(i));
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

stella/src/emucore/m6502/src/System.cxx

@@ -13,7 +13,7 @@
 // See the file "license" for information on usage and redistribution of
 // this file, and for a DISCLAIMER OF ALL WARRANTIES.
 //
-// $Id: System.cxx,v 1.12 2005-07-09 12:52:46 stephena Exp $
+// $Id: System.cxx,v 1.13 2005-07-09 23:44:08 urchlay Exp $
 //============================================================================
 
 #include <assert.h>
@@ -57,6 +57,9 @@ System::System(uInt16 n, uInt16 m)
   // Set up (de)serializer in case we are asked to save/load state
   serializer = new Serializer();
   deserializer = new Deserializer();
+
+  // Bus starts out unlocked (in other words, peek() changes myDataBusState)
+  myDataBusLocked = false;
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
@@ -336,7 +339,8 @@ uInt8 System::peek(uInt16 addr)
     result = access.device->peek(addr);
   }
 
-  myDataBusState = result;
+  if(!myDataBusLocked)
+    myDataBusState = result;
 
   return result;
 }
@@ -356,5 +360,17 @@ void System::poke(uInt16 addr, uInt8 value)
     access.device->poke(addr, value);
   }
 
-  myDataBusState = value;
+  if(!myDataBusLocked)
+    myDataBusState = value;
 }
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+void System::lockDataBus() {
+  myDataBusLocked = true;
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+void System::unlockDataBus() {
+  myDataBusLocked = false;
+}
+

stella/src/emucore/m6502/src/System.hxx

@@ -13,7 +13,7 @@
 // See the file "license" for information on usage and redistribution of
 // this file, and for a DISCLAIMER OF ALL WARRANTIES.
 //
-// $Id: System.hxx,v 1.9 2005-07-09 12:52:46 stephena Exp $
+// $Id: System.hxx,v 1.10 2005-07-09 23:44:08 urchlay Exp $
 //============================================================================
 
 #ifndef SYSTEM_HXX
@@ -48,7 +48,7 @@ class Deserializer;
         dynamic code for that page of memory.
 
   @author  Bradford W. Mott
-  @version $Id: System.hxx,v 1.9 2005-07-09 12:52:46 stephena Exp $
+  @version $Id: System.hxx,v 1.10 2005-07-09 23:44:08 urchlay Exp $
 */
 class System
 {
@@ -261,6 +261,18 @@ class System
     */
     void poke(uInt16 address, uInt8 value);
 
+    /**
+      Lock/unlock the data bus. When the bus is locked, peek() and
+      poke() don't update the bus state. The bus should be unlocked
+      while the CPU is running (normal emulation, or when the debugger
+      is stepping/advancing). It should be locked while the debugger
+      is active but not running the CPU. This is so the debugger can
+      use System.peek() to examine memory/registers without changing
+      the state of the system.
+    */
+    void lockDataBus();
+    void unlockDataBus();
+
   public:
     /**
       Structure used to specify access methods for a page
@@ -343,6 +355,11 @@ class System
     // The current state of the Data Bus
     uInt8 myDataBusState;
 
+    // Whether or not peek() updates the data bus state. This
+    // is true during normal emulation, and false when the
+    // debugger is active.
+    bool myDataBusLocked;
+
     // The serializer for the system.  Used to save state.
     Serializer* serializer;