From fa76042790ea544d880a3b654c70e796454eb6a7 Mon Sep 17 00:00:00 2001
From: Christian Speckner <christian.speckner@mayflower.de>
Date: Sat, 24 Jun 2017 00:35:17 +0200
Subject: [PATCH] Make sure that pending RDY is handled after stepping the CPU.
 Closes #155.

---
 src/emucore/M6502.cxx | 23 +++++++++++++++++++----
 src/emucore/M6502.hxx |  5 +++++
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/src/emucore/M6502.cxx b/src/emucore/M6502.cxx
index 4a44fe7be..20bacfa69 100644
--- a/src/emucore/M6502.cxx
+++ b/src/emucore/M6502.cxx
@@ -111,10 +111,7 @@ void M6502::reset()
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 inline uInt8 M6502::peek(uInt16 address, uInt8 flags)
 {
-  if (myHaltRequested) {
-    myOnHaltCallback();
-    myHaltRequested = false;
-  }
+  handleHalt();
 
   ////////////////////////////////////////////////
   // TODO - move this logic directly into CartAR
@@ -175,6 +172,15 @@ void M6502::requestHalt()
   myHaltRequested = true;
 }
 
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+inline void M6502::handleHalt()
+{
+  if (myHaltRequested) {
+    myOnHaltCallback();
+    myHaltRequested = false;
+  }
+}
+
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 bool M6502::execute(uInt32 number)
 {
@@ -241,6 +247,12 @@ bool M6502::execute(uInt32 number)
     // See if execution has been stopped
     if(myExecutionStatus & StopExecutionBit)
     {
+      // Debugger hack: this ensures that stepping a "STA WSYNC" will actually end at the
+      // beginning of the next line (otherwise, the next instruction would be stepped in order for
+      // the halt to take effect). This is safe because as we know that the next cycle will be a read
+      // cycle anyway.
+      handleHalt();
+
       // Yes, so answer that everything finished fine
       return true;
     }
@@ -255,6 +267,9 @@ bool M6502::execute(uInt32 number)
     // See if we've executed the specified number of instructions
     if(number == 0)
     {
+      // See above
+      handleHalt();
+
       // Yes, so answer that everything finished fine
       return true;
     }
diff --git a/src/emucore/M6502.hxx b/src/emucore/M6502.hxx
index ba6a74ef5..a03631337 100644
--- a/src/emucore/M6502.hxx
+++ b/src/emucore/M6502.hxx
@@ -286,6 +286,11 @@ class M6502 : public Serializable
     */
     void interruptHandler();
 
+    /**
+      Check whether halt was requested (RDY low) and notify
+    */
+    void handleHalt();
+
   private:
     /**
       Bit fields used to indicate that certain conditions need to be