Implement reading and writing bits in the plc status dword

schunk_egu_egk_gripper_dummy/src/dummy.py

@@ -15,6 +15,7 @@ def __init__(self):
         self.data = None
         self.plc_input = "0x0040"
         self.plc_output = "0x0048"
+        self.reserved_status_bits = [10, 15] + list(range(18, 31))
 
         enum_config = os.path.join(
             Path(__file__).resolve().parents[1], "config/enum.json"
@@ -101,3 +102,23 @@ def get_plc_input(self):
 
     def get_plc_output(self):
         return [self.plc_output_buffer.hex().upper()]
+
+    def set_status_bit(self, bit: int, value: bool) -> bool:
+        if bit < 0 or bit > 31:
+            return False
+        if bit in self.reserved_status_bits:
+            return False
+        byte_index, bit_index = divmod(bit, 8)
+        if value:
+            self.plc_input_buffer[byte_index] |= 1 << bit_index
+        else:
+            self.plc_input_buffer[byte_index] &= ~(1 << bit_index)
+        return True
+
+    def get_status_bit(self, bit: int) -> int | bool:
+        if bit < 0 or bit > 31:
+            return False
+        if bit in self.reserved_status_bits:
+            return False
+        byte_index, bit_index = divmod(bit, 8)
+        return 1 if self.plc_input_buffer[byte_index] & (1 << bit_index) != 0 else 0

schunk_egu_egk_gripper_dummy/tests/test_plc_communication.py

@@ -16,6 +16,42 @@ def test_dummy_returns_plc_data():
     assert dummy.data[dummy.plc_output] == dummy.get_plc_output()
 
 
+def test_dummy_rejects_writing_reserved_status_bits():
+    dummy = Dummy()
+    invalid_bits = [-1, 999]
+    for bit in invalid_bits + dummy.reserved_status_bits:
+        assert not dummy.set_status_bit(bit, True)
+
+
+def test_dummy_rejects_reading_reserved_status_bits():
+    dummy = Dummy()
+    for bit in dummy.reserved_status_bits:
+        assert isinstance(dummy.get_status_bit(bit), bool)  # call fails
+        assert not dummy.get_status_bit(bit)
+
+
+def test_dummy_supports_reading_and_writing_bits_in_plc_status():
+    dummy = Dummy()
+    valid_bits = list(range(0, 10)) + [11, 12, 13, 14, 16, 17, 31]
+    for bit in valid_bits:
+        dummy.set_status_bit(bit=bit, value=True)
+        result = dummy.get_status_bit(bit=bit)
+        assert isinstance(result, int)  # successful calls get the bit's value
+        assert result == 1
+
+
+def test_dummy_only_touches_specified_bits():
+    dummy = Dummy()
+    before = dummy.get_plc_input()
+    valid_bits = list(range(0, 10)) + [11, 12, 13, 14, 16, 17, 31]
+    for bit in valid_bits:
+        initial_value = dummy.get_status_bit(bit=bit)
+        dummy.set_status_bit(bit=bit, value=True)
+        dummy.set_status_bit(bit=bit, value=initial_value)
+
+    assert dummy.get_plc_input() == before
+
+
 # See p. 24 in
 # Booting and establishing operational readiness [1]