Serial port reconfiguration API

.github/workflows/ci.yml

@@ -306,7 +306,7 @@ jobs:
             --cov=serialx \
             -o console_output_style=count \
             -p no:sugar \
-            --adapter-pair /dev/tnt0,/dev/tnt1,no-rts-cts,no-dtr-dsr,no-num-unwritten-bytes,no-reset-write-buffer,no-write-timeout,no-buffer-control \
+            --adapter-pair /dev/tnt0,/dev/tnt1,no-rts-cts,no-dtr-dsr,no-num-unwritten-bytes,no-reset-write-buffer,no-write-timeout,no-buffer-control,no-write-buffering \
             tests
       - name: Upload coverage artifact
         uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
@@ -502,7 +502,7 @@ jobs:
       - name: Set up Bun
         uses: oven-sh/setup-bun@0c5077e51419868618aeaa5fe8019c62421857d6 # v2.2.0
         with:
-          bun-version: 1.3.13
+          bun-version: 1.4.2
       - name: Cache Pyodide package wheels
         uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
         with:

docs/how-to/async-serial.md

@@ -85,6 +85,14 @@ pins = await serial.get_modem_pins()
 assert pins.rts is serialx.PinState.HIGH
 ```
 
+### Reconfiguring
+`reconfigure_port` changes settings on the open port. Only the settings passed are
+changed:
+
+```python
+await serial.reconfigure_port(baudrate=9600, parity=serialx.Parity.EVEN)
+```
+
 ## Async protocols and transports
 While the high-level async API is useful for simple code, libraries and other
 high-performance uses should use asyncio transports and protocols. These have the

docs/how-to/pyodide.md

@@ -28,4 +28,8 @@ reader, writer = await serialx.open_serial_connection(
 
 writer.write(b"ping")
 data = await reader.readexactly(4)
-```
+```
+
+## Limitations
+- Web Serial only accepts port settings on open. `reconfigure_port()` closes and reopens the browser port, which drops DTR and RTS and discards unread bytes. A warning is logged.
+- Software flow control (`xonxoff=True`) is accepted but has no effect.

docs/how-to/pyserial-migration.md

@@ -70,6 +70,9 @@ are listed in the [main API documentation](../api.md). The most common ones are
 | `Serial(do_not_open=False)` | —                          | Not supported; open explicitly via `open()`  |
 | `Serial(rtsdtr_on_open=X)`  | `dtr_on_open=X, rts_on_open=X`   | Now controlled per-pin                  |
 | `Serial(rtsdtr_on_close=X)` | `dtr_on_close=X, rts_on_close=X` | Now controlled per-pin                  |
+| `baudrate = X`              | `reconfigure_port(baudrate=X)` | Setters are deprecated                   |
+| `stop_bits = X`             | `reconfigure_port(stopbits=X)` | Setters are deprecated                   |
+| `data_bits = X`             | `reconfigure_port(byte_size=X)` | Setters are deprecated                  |
 | `SerialPortInfo[i]`         | attribute access           | Slicing `SerialPortInfo` is deprecated       |
 | `SerialPortInfo.description`| `SerialPortInfo.product`   |                                              |
 
@@ -87,6 +90,25 @@ with serialx.serial_for_url("/dev/ttyUSB0", baudrate=115200) as serial:
 
 There is no equivalent for async code because the default `create_serial_connection` and `open_serial_connection` functions already transparently accept URIs.
 
+### Changing port settings
+Use `reconfigure_port(...)` instead of assigning to `baudrate` and other setting properties. Only the settings passed are changed:
+
+```diff
+-serial.baudrate = 9600
+-serial.parity = serial.PARITY_EVEN
++serial.reconfigure_port(baudrate=9600, parity=serialx.Parity.EVEN)
+```
+
+Configuring an unopened port through its properties is deprecated. Pass settings to the `serialx.serial_for_url` constructor:
+
+```diff
+-serial = serial.Serial()
+-serial.baudrate = 9600
+-serial.open()
++serial = serialx.serial_for_url("/dev/ttyUSB0", baudrate=9600)
++serial.open()
+```
+
 ## Constants
 pyserial exposes parity, stop bit, and byte size settings as module-level constants (`serial.PARITY_NONE`, `serial.STOPBITS_ONE`, etc.). serialx replaces them with the `Parity` and `StopBits` enums. Properties like `serial.parity` and `serial.stopbits` now return enum members instead of raw strings or numbers.
 
@@ -148,6 +170,14 @@ if pins.cts is serialx.PinState.HIGH:
 
 `set_modem_pins` accepts individual pin kwargs or a full `ModemPins` dataclass. Pins omitted from the call are left unchanged. `get_modem_pins` returns a `ModemPins` dataclass of `PinState` enum values, call `.to_bool()` on a pin for a `bool | None`.
 
+### Changing port settings
+Assigning to `transport.serial.baudrate` reconfigures the port on the event loop, which is blocking IO. Use the async method on the transport instead:
+
+```diff
+-transport.serial.baudrate = 9600
++await transport.reconfigure_port(baudrate=9600)
+```
+
 ### Simplified async API
 If you have existing sync code using `serial_for_url` and want to make it async, use `async_serial_for_url`. The method names match the sync API (e.g. `read`, `readexactly`, `readline`, `readuntil`, `write`, `flush`) so the migration is mostly adding `async`/`await`:
 

docs/usage.md

@@ -65,3 +65,17 @@ transport, protocol = await serialx.create_serial_connection(
     baudrate=115200,
 )
 ```
+
+## Reconfiguring a port
+`reconfigure_port` changes settings on an open port. Only the settings passed are changed:
+
+```python
+serial.reconfigure_port(baudrate=9600, parity=serialx.Parity.EVEN)
+```
+
+The async APIs expose the same method as a coroutine:
+
+```python
+await serial.reconfigure_port(baudrate=9600)
+await transport.reconfigure_port(baudrate=9600)
+```

serialx/async_serial.py

@@ -232,6 +232,28 @@ async def set_modem_pins(
             dsr=dsr,
         )
 
+    async def reconfigure_port(
+        self,
+        *,
+        baudrate: int | None = None,
+        parity: Parity | str | None = None,
+        stopbits: StopBits | int | float | None = None,
+        byte_size: int | None = None,
+        xonxoff: bool | None = None,
+        rtscts: bool | None = None,
+        dsrdtr: bool | None = None,
+    ) -> None:
+        """Change serial port settings. Only the settings passed are changed."""
+        await self.transport.reconfigure_port(
+            baudrate=baudrate,
+            parity=parity,
+            stopbits=stopbits,
+            byte_size=byte_size,
+            xonxoff=xonxoff,
+            rtscts=rtscts,
+            dsrdtr=dsrdtr,
+        )
+
     # ---- Settings (proxy to transport) ----
 
     @property