Added DEC A and BRA to 65C02

Signed-off-by: Mike Naberezny <mike@naberezny.com>

src/py65/devices/mpu65c02.py

@@ -19,6 +19,9 @@ class MPU(NMOS6502):
     def ZeroPageIndirectAddr(self):
         return self.WordAt( 255 & (self.ByteAt(self.pc)))
 
+    def AccumulatorAddr(self):
+        return self.a
+
     # operations
 
     def opSTZ(self, x):
@@ -137,6 +140,21 @@ class MPU(NMOS6502):
         self.opTRB(self.AbsoluteAddr)
         self.pc += 2
 
+    @instruction(name="DEC", mode="imp", cycles=2)
+    def inst_0x3a(self):
+        tbyte = self.a
+        self.flags &= ~(self.ZERO + self.NEGATIVE)
+        tbyte = (tbyte - 1) & 0xFF
+        if tbyte:
+            self.flags |= tbyte & self.NEGATIVE
+        else:
+            self.flags |= self.ZERO
+        self.a = tbyte
+
+    @instruction(name="BRA", mode="rel", cycles=1, extracycles=1)
+    def inst_0x80(self):
+        self.BranchRelAddr()
+
     @instruction(name="SBC", mode="zpi", cycles=5)
     def inst_0xf2(self):
         self.opSBC(self.ZeroPageIndirectAddr)

src/py65/tests/devices/test_mpu65c02.py

@@ -595,6 +595,47 @@ class MPUTests(unittest.TestCase, Common6502Tests):
         self.assertEquals(0x0003, mpu.pc)
         self.assertEquals(6, mpu.processorCycles)
 
+    def test_dec_a_decreases_a(self):
+        mpu = self._make_mpu(debug=True)
+        self._write(mpu.memory, 0x0000, [0x3A]) #=> DEC A
+        mpu.a = 0x48
+        mpu.step()
+        self.assertEquals(0, mpu.flags & mpu.ZERO)
+        self.assertEquals(0, mpu.flags & mpu.NEGATIVE)
+        self.assertEquals(0x47, mpu.a)
+
+    def test_dec_a_sets_zero_flag(self):
+        mpu = self._make_mpu(debug=True)
+        self._write(mpu.memory, 0x0000, [0x3A]) #=> DEC A
+        mpu.a = 0x01
+        mpu.step()
+        self.assertEquals(mpu.ZERO, mpu.flags & mpu.ZERO)
+        self.assertEquals(0, mpu.flags & mpu.NEGATIVE)
+        self.assertEquals(0x00, mpu.a)
+
+    def test_dec_a_wraps_at_zero(self):
+        mpu = self._make_mpu(debug=True)
+        self._write(mpu.memory, 0x0000, [0x3A]) #=> DEC A
+        mpu.a = 0x00
+        mpu.step()
+        self.assertEquals(0, mpu.flags & mpu.ZERO)
+        self.assertEquals(mpu.NEGATIVE, mpu.flags & mpu.NEGATIVE)
+        self.assertEquals(0xFF, mpu.a)
+
+    def test_bra_forward(self):
+        mpu = self._make_mpu(debug=True)
+        self._write(mpu.memory, 0x0000, [0x80, 0x10]) #=> BRA $10
+        mpu.step()
+        self.assertEquals(0x12, mpu.pc)
+        self.assertEquals(2, mpu.processorCycles)
+
+    def test_bra_backward(self):
+        mpu = self._make_mpu(debug=True)
+        self._write(mpu.memory, 0x0204, [0x80, 0xF0]) #=> BRA $F0
+        mpu.pc = 0x0204
+        mpu.step()
+        self.assertEquals(0x1F6, mpu.pc)
+        self.assertEquals(3, mpu.processorCycles) # Crossed boundry
 
     # Test Helpers