From 341f745684cb9f6267b969d4d0e33e5cef9338fb Mon Sep 17 00:00:00 2001
From: Christian Speckner <christian.speckner@mayflower.de>
Date: Sun, 28 Jul 2024 14:13:49 +0200
Subject: [PATCH] Bus stuffing.

---
 src/emucore/elf/BusTransactionQueue.cxx | 7 +++++++
 src/emucore/elf/BusTransactionQueue.hxx | 5 +++++
 src/emucore/elf/VcsLib.cxx              | 9 ++++++++-
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/emucore/elf/BusTransactionQueue.cxx b/src/emucore/elf/BusTransactionQueue.cxx
index bdbca66ea..d9a2cb294 100644
--- a/src/emucore/elf/BusTransactionQueue.cxx
+++ b/src/emucore/elf/BusTransactionQueue.cxx
@@ -92,6 +92,13 @@ BusTransactionQueue& BusTransactionQueue::injectROM(uInt8 value, uInt16 address)
   return *this;
 }
 
+BusTransactionQueue& BusTransactionQueue::stuffByte(uInt8 value, uInt16 address)
+{
+  push(Transaction::transactionDrive(address, value));
+
+  return *this;
+}
+
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 BusTransactionQueue& BusTransactionQueue::yield(uInt16 address)
 {
diff --git a/src/emucore/elf/BusTransactionQueue.hxx b/src/emucore/elf/BusTransactionQueue.hxx
index 0e2c17ab9..c6449c4be 100644
--- a/src/emucore/elf/BusTransactionQueue.hxx
+++ b/src/emucore/elf/BusTransactionQueue.hxx
@@ -43,12 +43,17 @@ class BusTransactionQueue {
 
     BusTransactionQueue& injectROM(uInt8 value);
     BusTransactionQueue& injectROM(uInt8 value, uInt16 address);
+    BusTransactionQueue& stuffByte(uInt8 value, uInt16 address);
 
     BusTransactionQueue& yield(uInt16 address);
 
     bool hasPendingTransaction() const;
     Transaction* getNextTransaction(uInt16 address);
 
+    inline size_t size() const {
+      return myQueueSize;
+    }
+
   private:
     void push(const Transaction& transaction);
 
diff --git a/src/emucore/elf/VcsLib.cxx b/src/emucore/elf/VcsLib.cxx
index ada92a472..f4213215c 100644
--- a/src/emucore/elf/VcsLib.cxx
+++ b/src/emucore/elf/VcsLib.cxx
@@ -146,7 +146,14 @@ CortexM0::err_t VcsLib::fetch16(uInt32 address, uInt16& value, uInt8& op, Cortex
       return returnFromStub(value, op);
 
     case ADDR_VCS_WRITE3:
-      FatalEmulationError::raise("unimplemented: vcsWrite3");
+      arg = cortex.getRegister(0);
+
+      myTransactionQueue
+        .injectROM(0x85)
+        .injectROM(arg)
+        .stuffByte(arg, cortex.getRegister(1));
+
+      return returnFromStub(value, op);
 
     case ADDR_VCS_JMP3:
       myTransactionQueue