From 680b2dca2e02c30bca081fb8156999c2274993f1 Mon Sep 17 00:00:00 2001
From: martti <mysatyre@gmail.com>
Date: Wed, 22 Jun 2011 17:03:10 +0800
Subject: [PATCH] added page wrapping bugs and tests for them

---
 src/py65/devices/mpu6502.py            | 12 ++++---
 src/py65/tests/devices/test_mpu6502.py | 46 ++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 4 deletions(-)

diff --git a/src/py65/devices/mpu6502.py b/src/py65/devices/mpu6502.py
index 2e5c018..845f9c0 100644
--- a/src/py65/devices/mpu6502.py
+++ b/src/py65/devices/mpu6502.py
@@ -73,6 +73,10 @@ class MPU:
   def WordAt(self, addr):
     return self.ByteAt(addr) + (self.ByteAt(addr + 1) << 8)
 
+  def WrapAt(self, addr):
+    wrap = lambda x: (x & 0xff00) + ((x + 1) & 0xff)
+    return self.ByteAt(addr) + (self.ByteAt(wrap(addr)) << 8)
+
   def ProgramCounter(self):
     return self.pc
 
@@ -91,17 +95,17 @@ class MPU:
     return 255 & (self.y + self.ByteAt(self.pc))
 
   def IndirectXAddr(self):
-    return self.WordAt( 255 & (self.ByteAt(self.pc) + self.x))
+    return self.WrapAt( 255 & (self.ByteAt(self.pc) + self.x))
 
   def IndirectYAddr(self):
     if self.addcycles:
-      a1 = self.WordAt(self.ByteAt(self.pc))
+      a1 = self.WrapAt(self.ByteAt(self.pc))
       a2 = (a1+self.y) & 0xffff
       if (a1 & 0xff00) != (a2 & 0xff00):
         self.excycles += 1
       return a2
     else:
-      return (self.WordAt(self.ByteAt(self.pc))+self.y)&0xffff
+      return (self.WrapAt(self.ByteAt(self.pc))+self.y)&0xffff
 
   def AbsoluteAddr(self):
     return self.WordAt(self.pc)
@@ -793,7 +797,7 @@ class MPU:
   @instruction(name="JMP", mode="ind", cycles=5)
   def inst_0x6c(self):
     ta = self.WordAt(self.pc)
-    self.pc = self.WordAt(ta)
+    self.pc = self.WrapAt(ta)
 
   @instruction(name="ADC", mode="abs", cycles=4)
   def inst_0x6d(self):
diff --git a/src/py65/tests/devices/test_mpu6502.py b/src/py65/tests/devices/test_mpu6502.py
index 576b1d5..1260388 100644
--- a/src/py65/tests/devices/test_mpu6502.py
+++ b/src/py65/tests/devices/test_mpu6502.py
@@ -5088,6 +5088,52 @@ class Common6502Tests:
     self.assertEqual(0x03, mpu.a)
     self.assertEqual(0x0008, mpu.pc)
 
+  # page wrapping test
+
+  def test_zeropage_indexed_indirect_wrap(self):
+    mpu = self._make_mpu()
+    mpu.y = 0
+    self._write(mpu.memory, 0xb100, (0x31, ))
+    self._write(mpu.memory, 0xff, (0, ))
+    self._write(mpu.memory, 0, (0xb1, 0xff)) # LDA ($FF),Y
+    mpu.step()
+    self.assertEqual(mpu.a, 0x31)
+
+  def test_zeropage_indexed_wrap(self):
+    mpu = self._make_mpu()
+    mpu.x = 1
+    self._write(mpu.memory, 0, (0xb5, 0xff)) # LDA $FF,X
+    mpu.step()
+    self.assertEqual(mpu.a, 0xb5)
+
+  def test_zeropage_indirect_indexed_wrap(self):
+    mpu = self._make_mpu()
+    mpu.x = 0
+    self._write(mpu.memory, 0xa100, (0x31, ))
+    self._write(mpu.memory, 0xff, (0, ))
+    self._write(mpu.memory, 0, (0xa1, 0xff)) # LDA ($FF,X)
+    mpu.step()
+    self.assertEqual(mpu.a, 0x31)
+
+  def test_zeropage_indirect_indexed_indexwrap(self):
+    mpu = self._make_mpu()
+    mpu.x = 0xff
+    self._write(mpu.memory, 0xa100, (0x31, ))
+    self._write(mpu.memory, 0xff, (0, ))
+    self._write(mpu.memory, 0, (0xa1, 0)) # LDA ($00,X)
+    mpu.step()
+    self.assertEqual(mpu.a, 0x31)
+
+  def test_indirect_wrap(self):
+    mpu = self._make_mpu()
+    mpu.x = 0xff
+    self._write(mpu.memory, 0xff, (0, ))
+    self._write(mpu.memory, 0, (0x6c, 0xff, 0x00)) # LDA ($00,X)
+    mpu.step()
+    self.assertEqual(mpu.pc, 0x6c00)
+
+# decimal flag chaos
+
   # Test Helpers
 
   def _write(self, memory, start_address, bytes):