clarify and test cycle counting functionality

README.rst

@@ -33,15 +33,20 @@ Example Usage:::
         c.step()
 
         # You can check the registers and memory values to determine what has changed
-        print c.r.a 	# A register
-        print c.r.x 	# X register
-        print c.r.y 	# Y register
-        print c.r.s 	# Stack Pointer
-        print c.r.pc 	# Program Counter
+        print(c.r.a) 	# A register
+        print(c.r.x) 	# X register
+        print(c.r.y) 	# Y register
+        print(c.r.s) 	# Stack Pointer
+        print(c.r.pc) 	# Program Counter
 
-        print c.r.getFlag('C') # Get the value of a flag from the flag register.
+        print(c.cc)     # Print the number of cycles that passed during the last step.
+                        # This number resets for each call to `.step()`
 
-        print mmu.read(0xff) # Read a value from memory
+        print(c.r.getFlag('C')) # Get the value of a flag from the flag register.
+
+        print(mmu.read(0xff)) # Read a value from memory
+
+        
 
 The full set of parameters for CPU is::
 

py65emu/cpu.py

@@ -72,6 +72,7 @@ def __init__(self, mmu=None, pc=None, stack_page=0x1, magic=0xee):
         """
         self.mmu = mmu
         self.r = Registers()
+        # Hold the number of CPU cycles used during the last call to `self.step()`
         self.cc = 0
         # Which page the stack is in.  0x1 means that the stack is from
         # 0x100-0x1ff.  In the 6502 this is always true but it's different
@@ -95,7 +96,6 @@ def reset(self):
 
     def step(self):
         self.cc = 0
-        # pc = self.r.pc
         opcode = self.nextByte()
         self.ops[opcode]()
 

tests/test_cpu.py

@@ -815,6 +815,24 @@ def test_run_rom(self):
         c.step()
         self.assertEqual(c.r.a, 0x55)
 
+    def test_cycle_counting(self):
+        # Adapted from @InvalidCo's test in #7
+        c = self._cpu(romInit=[
+            0xA0, 0x80,
+            0xB9, 0x00, 0x00,
+            0xB9, 0x80, 0x00,
+            0x18,
+            0xB0, 0xFF,
+            0x90, 0x01,
+            0x90, 0x8F
+        ])
+
+        expected_cycles = [2, 4, 5, 2, 2, 3, 4]
+
+        for expected_cycle in expected_cycles:
+            c.step()
+            self.assertEqual(c.cc, expected_cycle)
+
     def tearDown(self):
         pass