Flags are now set to 0 on reset.

CHANGES.txt

@@ -13,6 +13,9 @@ Next Release
   - MPU objects now return a two-line string as their __repr__ with 
     the processor status register displayed as binary for readability.  
 
+  - The processor status register is now initialized to 0 on reset.
+    Previously, its unused bit (bit 5) was set to 1 on reset.
+
 0.6 (2009-08-11)
 
   - Added monitor shortcut "a" for "assemble".

src/py65/devices/mpu6502.py

@@ -44,7 +44,7 @@ class MPU:
           "%s: %04x %02x %02x %02x %02x %s" 
     
     return out % (indent, self.name, 
-                  self.pc, self.a, self.x, self.y, self.pc, flags)
+                  self.pc, self.a, self.x, self.y, self.sp, flags)
 
   def step(self):
     instructCode = self.ImmediateByte()
@@ -63,7 +63,7 @@ class MPU:
     self.a = 0
     self.x = 0
     self.y = 0
-    self.flags = self.UNUSED
+    self.flags = 0
     self.processorCycles = 0
 
   # Helpers for addressing modes

src/py65/tests/devices/test_mpu6502.py

@@ -6,6 +6,17 @@ import py65.devices.mpu6502
 class Common6502Tests:
   """Tests common to 6502-based microprocessors"""
 
+  # Reset
+  
+  def test_reset_sets_registers_to_initial_states(self):
+    mpu = self._make_mpu()
+    mpu.reset()
+    self.assertEquals(0xFF, mpu.sp)
+    self.assertEquals(0, mpu.a)
+    self.assertEquals(0, mpu.x)
+    self.assertEquals(0, mpu.y)
+    self.assertEquals(0, mpu.flags)
+
   # ADC Absolute
   
   def test_adc_bcd_off_absolute_carry_clear_in_accumulator_zeroes(self):