Added calculations for PDO lists

Now there are two functions to perform calculations on PDO lists:
calculate_pdp and follows_power_rules.  calculate_pdp calculates an
estimate of the power supply's PDP, and follows_power_rules tries to
determine if the power supply follows the USB PD Power Rules.  Either
one could run into problems that cannot be detected, but for the
problems that can be detected there's a whole mound of new test code.

pdbuddy/__init__.py

             pdo_list.append(pdo)
 
     return pdo_list
+
+
+def calculate_pdp(pdo_list):
+    """Calculate the PDP in watts of a list of PDOs
+
+    The result is only guaranteed to be correct if the power supply follows
+    the USB Power Delivery standard.  Since quite a few power supplies
+    unfortunately do not, this can really only be considered an estimate.
+    """
+    max_power = 0
+
+    # The Source Power Rules make it so the PDP can be determined by the
+    # highest power available from any fixed supply PDO.
+    for pdo in pdo_list:
+        if pdo.pdo_type == "fixed":
+            max_power = max(max_power, pdo.v / 1000.0 * pdo.i / 1000.0)
+
+    return max_power
+
+
+def follows_power_rules(pdo_list):
+    """Test whether a list of PDOs follows the Power Rules for PD 2.0
+
+    This function is a false-biased approximation; that is, when it returns
+    False it is definitely correct, but when it returns True it might be
+    incorrect.
+    """
+    # First, estimate the PDP assuming the rules are being followed
+    pdp = calculate_pdp(pdo_list)
+
+    # Make sure nothing exceeds the PDP
+    for pdo in pdo_list:
+        if pdo.pdo_type == "fixed":
+            if pdp < pdo.v / 1000.0 * pdo.i / 1000.0:
+                return False
+        # TODO: in the future, there will be more types of PDO checked here
+
+    # Check that the fixed supply PDOs look right
+    seen_5v = False
+    seen_9v = False
+    seen_15v = False
+    seen_20v = False
+    seen_normative_voltages = False
+    if pdp <= 15:
+        # Below 15 W, make sure the PDP is available at 5 V.
+        for pdo in pdo_list:
+            if pdo.pdo_type == "fixed" and pdo.v == 5000:
+                seen_5v = True
+                if pdo.v / 1000.0 * pdo.i / 1000.0 != pdp:
+                    return False
+        seen_normative_voltages = seen_5v
+    elif pdp <= 27:
+        # Between 15 and 27 W, make sure at least 3 A is available at 5 V and
+        # the PDP is available at 9 V.
+        for pdo in pdo_list:
+            if pdo.pdo_type == "fixed" and pdo.v == 5000:
+                seen_5v = True
+                if pdo.i < 3000.0:
+                    return False
+            elif pdo.pdo_type == "fixed" and pdo.v == 9000:
+                seen_9v = True
+                if pdo.v / 1000.0 * pdo.i / 1000.0 != pdp:
+                    return False
+        seen_normative_voltages = seen_5v and seen_9v
+    elif pdp <= 45:
+        # Between 27 and 45 W, make sure at least 3 A is available at 5 and
+        # 9 V, and the PDP is available at 15 V.
+        for pdo in pdo_list:
+            if pdo.pdo_type == "fixed" and pdo.v == 5000:
+                seen_5v = True
+                if pdo.i < 3000.0:
+                    return False
+            elif pdo.pdo_type == "fixed" and pdo.v == 9000:
+                seen_9v = True
+                if pdo.i < 3000.0:
+                    return False
+            elif pdo.pdo_type == "fixed" and pdo.v == 15000:
+                seen_15v = True
+                if pdo.v / 1000.0 * pdo.i / 1000.0 != pdp:
+                    return False
+        seen_normative_voltages = seen_5v and seen_9v and seen_15v
+    else:
+        # Above 45 W, make sure at least 3 A is available at 5, 9, and 15 V,
+        # and the PDP is available at 20 V.
+        for pdo in pdo_list:
+            if pdo.pdo_type == "fixed" and pdo.v == 5000:
+                seen_5v = True
+                if pdo.i < 3000.0:
+                    return False
+            elif pdo.pdo_type == "fixed" and pdo.v == 9000:
+                seen_9v = True
+                if pdo.i < 3000.0:
+                    return False
+            elif pdo.pdo_type == "fixed" and pdo.v == 15000:
+                seen_15v = True
+                if pdo.i < 3000.0:
+                    return False
+            elif pdo.pdo_type == "fixed" and pdo.v == 20000:
+                seen_20v = True
+                if pdo.v / 1000.0 * pdo.i / 1000.0 != pdp:
+                    return False
+        seen_normative_voltages = seen_5v and seen_9v and seen_15v and seen_20v
+
+    if not seen_normative_voltages:
+        return False
+
+    # TODO: there are several things this currently doesn't test, such as
+    # variable and battery PDOs.
+
+    return True

test_pdbuddy/__init__.py

         rp_unknown_notzero = pdbuddy.read_pdo([b"PDO 1: FFFFFFFF"])
         self.assertEqual(self.unknown_notzero, rp_unknown_notzero)
 
+    def test_read_none(self):
+        none_pdo = pdbuddy.read_pdo([b"No Source_Capabilities"])
+        self.assertEqual(none_pdo, None)
+
 
 class ReadPDOListTestCase(unittest.TestCase):
 
         self.assertEqual(pdo_list[1], self.src_fixed_minimal)
         self.assertEqual(pdo_list[2], self.unknown_zero)
         self.assertEqual(pdo_list[3], self.unknown_notzero)
+
+
+class PDOListCalculationsTestCase(unittest.TestCase):
+
+    def setUp(self):
+        self.src_fixed_5v_1p5a = pdbuddy.SrcFixedPDO(False, False, True,
+                False, False, 0, 5000, 1500)
+        self.src_fixed_5v_3a = pdbuddy.SrcFixedPDO(False, False, True, False,
+                False, 0, 5000, 3000)
+        self.src_fixed_9v_1p6a = pdbuddy.SrcFixedPDO(False, False, False,
+                False, False, 0, 9000, 1600)
+        self.src_fixed_9v_3a = pdbuddy.SrcFixedPDO(False, False, False, False,
+                False, 0, 9000, 3000)
+        self.src_fixed_10v_1p5a = pdbuddy.SrcFixedPDO(False, False, False,
+                False, False, 0, 10000, 1500)
+        self.src_fixed_12v_5a = pdbuddy.SrcFixedPDO(False, False, False, False,
+                False, 0, 12000, 5000)
+        self.src_fixed_15v_1p8a = pdbuddy.SrcFixedPDO(False, False, False,
+                False, False, 0, 15000, 1800)
+        self.src_fixed_15v_3a = pdbuddy.SrcFixedPDO(False, False, False, False,
+                False, 0, 15000, 3000)
+        self.src_fixed_20v_2p25a = pdbuddy.SrcFixedPDO(False, False, False,
+                False, False, 0, 20000, 2250)
+        self.src_fixed_20v_5a = pdbuddy.SrcFixedPDO(False, False, False, False,
+                False, 0, 20000, 5000)
+
+    def test_calculate_pdp_15w(self):
+        self.assertEqual(pdbuddy.calculate_pdp([self.src_fixed_5v_3a]), 15)
+        self.assertEqual(pdbuddy.calculate_pdp([self.src_fixed_5v_3a,
+                self.src_fixed_9v_1p6a]), 15)
+
+    def test_calculate_pdp_27w(self):
+        self.assertEqual(pdbuddy.calculate_pdp([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a]), 27)
+        self.assertEqual(pdbuddy.calculate_pdp([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_1p8a]), 27)
+
+    def test_calculate_pdp_45w(self):
+        self.assertEqual(pdbuddy.calculate_pdp([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_3a]), 45)
+        self.assertEqual(pdbuddy.calculate_pdp([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_3a,
+                self.src_fixed_20v_2p25a]), 45)
+
+    def test_calculate_pdp_100w(self):
+        self.assertEqual(pdbuddy.calculate_pdp([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_3a,
+                self.src_fixed_20v_5a]), 100)
+        self.assertEqual(pdbuddy.calculate_pdp([self.src_fixed_5v_1p5a,
+                self.src_fixed_12v_5a, self.src_fixed_20v_5a]), 100)
+
+    def test_follows_power_rules_true(self):
+        # <= 15 W
+        self.assertTrue(pdbuddy.follows_power_rules([self.src_fixed_5v_1p5a]))
+        self.assertTrue(pdbuddy.follows_power_rules([self.src_fixed_5v_3a]))
+        self.assertTrue(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_1p6a]))
+        # <= 27 W
+        self.assertTrue(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a]))
+        self.assertTrue(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_1p8a]))
+        # <= 45 W
+        self.assertTrue(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_3a]))
+        self.assertTrue(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_3a,
+                self.src_fixed_20v_2p25a]))
+        # <= 100 W
+        self.assertTrue(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_3a,
+                self.src_fixed_20v_5a]))
+        self.assertTrue(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_10v_1p5a,
+                self.src_fixed_12v_5a, self.src_fixed_15v_3a,
+                self.src_fixed_20v_5a]))
+
+    def test_follows_power_rules_false(self):
+        # <= 15 W
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_10v_1p5a]))
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_5v_1p5a,
+            self.src_fixed_10v_1p5a]))
+        # <= 27 W
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_9v_3a]))
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_5v_1p5a,
+                self.src_fixed_9v_3a]))
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_1p6a, self.src_fixed_15v_1p8a]))
+        # <= 45 W
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_20v_2p25a]))
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_5v_1p5a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_3a]))
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_1p6a, self.src_fixed_15v_3a]))
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_1p8a,
+                self.src_fixed_20v_2p25a]))
+        # <= 100 W
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_20v_5a]))
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_5v_1p5a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_3a,
+                self.src_fixed_20v_5a]))
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_1p6a, self.src_fixed_15v_3a,
+                self.src_fixed_20v_5a]))
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_15v_1p8a,
+                self.src_fixed_20v_5a]))
+        self.assertFalse(pdbuddy.follows_power_rules([self.src_fixed_5v_3a,
+                self.src_fixed_9v_3a, self.src_fixed_12v_5a,
+                self.src_fixed_15v_3a, self.src_fixed_20v_2p25a]))