fix: allow CircuitPython UART construction without parity

pslab/bus/busio.py

@@ -440,7 +440,8 @@ def __init__(
         if stop not in (1, 2):
             raise ValueError("Invalid number of stop bits")
 
-        pd += parity.value
+        if parity is not None:
+            pd += parity.value
 
         try:
             self._set_uart_mode(pd, stop - 1)

tests/test_busio_uart_configuration.py

@@ -0,0 +1,81 @@
+"""Hardware-independent regressions for CircuitPython UART configuration."""
+
+from unittest.mock import Mock, call
+
+import pytest
+
+import pslab.protocol as CP
+from pslab.bus.busio import Parity, UART
+from pslab.bus.uart import _UARTPrimitive
+from pslab.connection import ConnectionHandler
+
+
+@pytest.fixture
+def device():
+    """Provide a connection without opening a physical device."""
+    connection = Mock(spec=ConnectionHandler)
+    connection.version = "PSLab V6"
+    return connection
+
+
+@pytest.fixture(autouse=True)
+def restore_uart_configuration():
+    """Keep process-wide cached UART settings independent between cases."""
+    brgval, mode = _UARTPrimitive._brgval, _UARTPrimitive._mode
+    yield
+    _UARTPrimitive._save_config(brgval, mode)
+
+
+@pytest.mark.parametrize(
+    "options, mode",
+    [({}, 0), ({"bits": 9}, 6), ({"stop": 2}, 1), ({"bits": 9, "stop": 2}, 7)],
+)
+def test_uart_without_parity(device, options, mode):
+    """Default and nine-bit UARTs encode no parity without an Enum value."""
+    uart = UART(device, **options)
+
+    assert device.send_byte.call_args_list == [
+        call(CP.UART_2),
+        call(CP.SET_BAUD),
+        call(CP.UART_2),
+        call(CP.SET_MODE),
+        call(mode),
+    ]
+    device.send_int.assert_called_once_with(_UARTPrimitive._get_uart_brgval(9600))
+    assert device.get_ack.call_count == 2
+    assert uart.timeout == 1
+    assert _UARTPrimitive._mode == (mode >> 1, mode & 1)
+
+
+@pytest.mark.parametrize("parity", [Parity.EVEN, Parity.ODD])
+@pytest.mark.parametrize("stop", [1, 2])
+def test_uart_with_parity(device, parity, stop):
+    """Supported parity options retain their existing mode encoding."""
+    UART(device, parity=parity, stop=stop)
+
+    assert device.send_byte.call_args_list[-3:] == [
+        call(CP.UART_2),
+        call(CP.SET_MODE),
+        call((parity.value << 1) | (stop - 1)),
+    ]
+    assert _UARTPrimitive._mode == (parity.value, stop - 1)
+
+
+def test_uart_without_parity_on_older_firmware(device):
+    """No-parity construction retains the unsupported-mode fallback."""
+    device.version = "PSLab V5"
+
+    uart = UART(device, timeout=0.25)
+
+    assert device.send_byte.call_args_list == [call(CP.UART_2), call(CP.SET_BAUD)]
+    assert device.get_ack.call_count == 1
+    assert uart.timeout == 0.25
+
+
+@pytest.mark.parametrize("parity", [Parity.EVEN, Parity.ODD])
+def test_nine_bit_uart_rejects_parity(device, parity):
+    """The no-parity fix does not permit parity with nine data bits."""
+    with pytest.raises(ValueError, match="Invalid parity"):
+        UART(device, bits=9, parity=parity)
+
+    assert device.send_byte.call_args_list == [call(CP.UART_2), call(CP.SET_BAUD)]