Version 0.1.7

Flow control code added for FTDI driver.

example/usbserial4a_ui_example.py

@@ -90,6 +90,7 @@ class MainApp(App):
         self.device_name_list = []
         self.serial_port = None
         self.read_thread = None
+        self.port_thread_lock = threading.Lock()
         super(MainApp, self).__init__(*args, **kwargs)
 
     def build(self):
@@ -97,7 +98,8 @@ class MainApp(App):
 
     def on_stop(self):
         if self.serial_port:
-            self.serial_port.close()
+            with self.port_thread_lock:
+                self.serial_port.close()
         
     def on_btn_scan_release(self):
         self.uiDict['box_list'].clear_widgets()
@@ -106,7 +108,8 @@ class MainApp(App):
         if platform == 'android':
             usb_device_list = usb.get_usb_device_list()
             self.device_name_list = [
-                device.getDeviceName() for device in usb_device_list]
+                device.getDeviceName() for device in usb_device_list
+            ]
         else:
             usb_device_list = list_ports.comports()
             self.device_name_list = [port.device for port in usb_device_list]
@@ -124,7 +127,8 @@ class MainApp(App):
             device = usb.get_usb_device(device_name)
             if not device:
                 raise SerialException(
-                    "Device {} not present!".format(device_name))
+                    "Device {} not present!".format(device_name)
+                )
             if not usb.has_usb_permission(device):
                 usb.request_usb_permission(device)
                 return
@@ -134,7 +138,8 @@ class MainApp(App):
                 8,
                 'N',
                 1,
-                timeout=1)
+                timeout=1
+            )
         else:
             self.serial_port = Serial(
                 device_name,
@@ -142,7 +147,8 @@ class MainApp(App):
                 8,
                 'N',
                 1,
-                timeout=1)
+                timeout=1
+            )
         
         if self.serial_port.is_open and not self.read_thread:
             self.read_thread = threading.Thread(target = self.read_msg_thread)
@@ -156,24 +162,30 @@ class MainApp(App):
                 data = bytes(self.uiDict['txtInput_write'].text + '\n')
             else:
                 data = bytes(
-                    (self.uiDict['txtInput_write'].text + '\n'), 'utf8')
+                    (self.uiDict['txtInput_write'].text + '\n'),
+                    'utf8'
+                )
             self.serial_port.write(data)
             self.uiDict['txtInput_read'].text += '[Sent]{}\n'.format(
-                self.uiDict['txtInput_write'].text)
+                self.uiDict['txtInput_write'].text
+            )
             self.uiDict['txtInput_write'].text = ''
     
     def read_msg_thread(self):
         while True:
-            if not self.serial_port.is_open:
-                break
             try:
-                received_msg = self.serial_port.read()
+                with self.port_thread_lock:
+                    if not self.serial_port.is_open:
+                        break
+                    received_msg = self.serial_port.read(
+                        self.serial_port.in_waiting
+                    )
                 if received_msg:
                     msg = bytes(received_msg).decode('utf8')
                     self.display_received_msg(msg)
             except Exception as ex:
                 raise ex
-        
+                
     @mainthread
     def display_received_msg(self, msg):
         self.uiDict['txtInput_read'].text += msg

setup.py

@@ -2,7 +2,7 @@ from setuptools import setup
 
 setup(
     name="usbserial4a",
-    version="0.1.6",
+    version="0.1.7",
     description="Python package for Kivy Android USB serial port.",
     long_description="https://github.com/jacklinquan/usbserial4a",
     long_description_content_type="text/markdown",

usbserial4a/__init__.py

@@ -9,4 +9,4 @@ Requires: kivy, pyjnius, pyserial, usb4a
 '''
 
 # Project version
-__version__ = '0.1.6'
+__version__ = '0.1.7'

usbserial4a/ftdiserial4a.py

@@ -4,6 +4,8 @@ Classes:
 FtdiSerial(serial.serialutil.SerialBase)
 '''
 
+from struct import unpack
+import time
 from serial.serialutil import SerialBase, SerialException, to_bytes, \
     portNotOpenError, writeTimeoutError, Timeout
 from usb4a import usb
@@ -14,6 +16,19 @@ class FtdiSerial(SerialBase):
     FtdiSerial extends serial.serialutil.SerialBase.
     It can be used in a similar way to serial.Serial from pyserial.
     '''
+    # Modem status
+    MODEM_CTS = (1 << 4)    # Clear to send
+    MODEM_DSR = (1 << 5)    # Data set ready
+    MODEM_RI = (1 << 6)     # Ring indicator
+    MODEM_RLSD = (1 << 7)   # Carrier detect
+    MODEM_DR = (1 << 8)     # Data ready
+    MODEM_OE = (1 << 9)     # Overrun error
+    MODEM_PE = (1 << 10)    # Parity error
+    MODEM_FE = (1 << 11)    # Framing error
+    MODEM_BI = (1 << 12)    # Break interrupt
+    MODEM_THRE = (1 << 13)  # Transmitter holding register
+    MODEM_TEMT = (1 << 14)  # Transmitter empty
+    MODEM_RCVE = (1 << 15)  # Error in RCVR FIFO
     
     # Requests
     SIO_RESET = 0               # Reset the port
@@ -52,6 +67,28 @@ class FtdiSerial(SerialBase):
     SIO_SET_RTS_HIGH = (SIO_SET_RTS_MASK | (SIO_SET_RTS_MASK << 8))
     SIO_SET_RTS_LOW = (0x0 | (SIO_SET_RTS_MASK << 8))
     
+    # Break type
+    BREAK_OFF, BREAK_ON = range(2)
+    
+    # cts:  Clear to send
+    # dsr:  Data set ready
+    # ri:   Ring indicator
+    # dcd:  Data carrier detect
+    # dr:   Data ready
+    # oe:   Overrun error
+    # pe:   Parity error
+    # fe:   Framing error
+    # bi:   Break interrupt
+    # thre: Transmitter holding register
+    # temt: Transmitter empty
+    # err:  Error in RCVR FIFO
+    MODEM_STATUS = [
+        ('', '', '', '', 'cts', 'dsr', 'ri', 'dcd'),
+        ('dr', 'overrun', 'parity', 'framing', 'break', 'thre', 'txe', 'rcvr')
+    ]
+
+    ERROR_BITS = (0x00, 0x8E)
+    
     # Clocks and baudrates
     BUS_CLOCK_BASE = 6.0E6  # 6 MHz
     BUS_CLOCK_HIGH = 30.0E6  # 30 MHz
@@ -64,11 +101,13 @@ class FtdiSerial(SerialBase):
     FTDI_DEVICE_OUT_REQTYPE = usb.build_usb_control_request_type(
         usb.UsbConstants.USB_DIR_OUT, 
         usb.UsbConstants.USB_TYPE_VENDOR, 
-        usb.USB_RECIPIENT_DEVICE)
+        usb.USB_RECIPIENT_DEVICE
+    )
     FTDI_DEVICE_IN_REQTYPE = usb.build_usb_control_request_type(
         usb.UsbConstants.USB_DIR_IN, 
         usb.UsbConstants.USB_TYPE_VENDOR, 
-        usb.USB_RECIPIENT_DEVICE)
+        usb.USB_RECIPIENT_DEVICE
+    )
     
     DEFAULT_READ_BUFFER_SIZE = 1024
     DEFAULT_WRITE_BUFFER_SIZE = 16 * 1024
@@ -88,6 +127,7 @@ class FtdiSerial(SerialBase):
         self._control_endpoint = None
         self._read_endpoint = None
         self._write_endpoint = None
+        self._lineprop = 0
         self._read_buffer = bytearray()
         super(FtdiSerial, self).__init__(*args, **kwargs)
     
@@ -121,21 +161,28 @@ class FtdiSerial(SerialBase):
                 self._interface = self._device.getInterface(i)
             if not self._connection.claimInterface(
                 self._device.getInterface(i), 
-                True):
+                True
+            ):
                 raise SerialException("Could not claim interface {}.".format(i))
         
         self._index = self._interface.getId() + 1
         
         for i in range(self._interface.getEndpointCount()):
             ep = self._interface.getEndpoint(i)
-            if ((ep.getDirection() == usb.UsbConstants.USB_DIR_IN) and
-                (ep.getType() == usb.UsbConstants.USB_ENDPOINT_XFER_INT)):
+            if (
+                (ep.getDirection() == usb.UsbConstants.USB_DIR_IN) \
+                and (ep.getType() == usb.UsbConstants.USB_ENDPOINT_XFER_INT)
+            ):
                 self._control_endpoint = ep
-            elif ((ep.getDirection() == usb.UsbConstants.USB_DIR_IN) and
-                (ep.getType() == usb.UsbConstants.USB_ENDPOINT_XFER_BULK)):
+            elif (
+                (ep.getDirection() == usb.UsbConstants.USB_DIR_IN) \
+                and (ep.getType() == usb.UsbConstants.USB_ENDPOINT_XFER_BULK)
+            ):
                 self._read_endpoint = ep
-            elif ((ep.getDirection() == usb.UsbConstants.USB_DIR_OUT) and
-                (ep.getType() == usb.UsbConstants.USB_ENDPOINT_XFER_BULK)):
+            elif (
+                (ep.getDirection() == usb.UsbConstants.USB_DIR_OUT) \
+                and (ep.getType() == usb.UsbConstants.USB_ENDPOINT_XFER_BULK)
+            ):
                 self._write_endpoint = ep  
                 
         # Check that all endpoints are good
@@ -145,6 +192,22 @@ class FtdiSerial(SerialBase):
         self.is_open = True
         self._reconfigure_port()
         
+    def _reconfigure_port(self):
+        '''Reconfigure serial port parameters.'''
+        self._setParameters(
+            self.baudrate, 
+            self.bytesize, 
+            self.parity, 
+            self.stopbits
+        )
+            
+        if self._rtscts:
+            self._set_flowctrl('hw')
+        elif self._xonxoff:
+            self._set_flowctrl('sw')
+        else:
+            self._set_flowctrl('')
+    
     def close(self):
         '''Close the serial port.'''
         if self._connection:
@@ -158,10 +221,13 @@ class FtdiSerial(SerialBase):
             result = self._ctrl_transfer_out(
                 self.SIO_RESET, 
                 self.SIO_RESET_SIO, 
-                0)
+                self._index
+            )
             if result != 0:
                 raise SerialException("Reset failed: result={}".format(result))
     
+    #  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -
+    
     @property
     def in_waiting(self):
         '''Return the number of bytes currently in the input buffer.
@@ -173,6 +239,14 @@ class FtdiSerial(SerialBase):
         self._read_buffer.extend(self._read())
         return len(self._read_buffer)
     
+    @property
+    def out_waiting(self):
+        '''Return the number of bytes currently in the output buffer.
+        
+        Always return 0.
+        '''
+        return 0
+    
     def read(self, size=1):
         '''Read data from the serial port.
         
@@ -212,18 +286,21 @@ class FtdiSerial(SerialBase):
         offset = 0
         timeout = int(
             self._write_timeout * 1000 if self._write_timeout \
-                else self.USB_WRITE_TIMEOUT_MILLIS)
+                else self.USB_WRITE_TIMEOUT_MILLIS
+        )
         wrote = 0
         while offset < len(data):
             data_length = min(
                 len(data) - offset, 
-                self.DEFAULT_WRITE_BUFFER_SIZE)
+                self.DEFAULT_WRITE_BUFFER_SIZE
+            )
             buf = data[offset:offset + data_length]
             i = self._connection.bulkTransfer(
                 self._write_endpoint,
                 buf,
                 data_length,
-                timeout)
+                timeout
+            )
             if i <= 0:
                 raise SerialException("Failed to write {}: {}".format(buf, i))
             offset += data_length
@@ -234,7 +311,151 @@ class FtdiSerial(SerialBase):
         '''Simply wait some time to allow all data to be written.'''
         pass
     
-    def purgeHwBuffers(self, purgeReadBuffers, purgeWriteBuffers):
+    def reset_input_buffer(self):
+        '''Clear input buffer, discarding all that is in the buffer.'''
+        if not self.is_open:
+            raise portNotOpenError
+        self._purgeHwBuffers(True, False)
+
+    def reset_output_buffer(self):
+        '''\
+        Clear output buffer, aborting the current output and discarding all
+        that is in the buffer.
+        '''
+        if not self.is_open:
+            raise portNotOpenError
+        self._purgeHwBuffers(False, True)
+
+    def send_break(self, duration=0.25):
+        '''Send break condition.
+        
+        Parameters:
+            duration (float): break time in seconds.
+        '''
+        if not self.is_open:
+            raise portNotOpenError
+        self._set_break(True)
+        time.sleep(duration)
+        self._set_break(False)
+
+    def _update_break_state(self):
+        '''Send break condition.'''
+        self._set_break(self._break_state)
+        
+    def _update_rts_state(self):
+        '''Set terminal status line: Request To Send.'''
+        self._set_rts(self._rts_state)
+
+    def _update_dtr_state(self):
+        '''Set terminal status line: Data Terminal Ready.'''
+        self._set_dtr(self._dtr_state)
+
+    @property
+    def cts(self):
+        '''Read terminal status line: Clear To Send.'''
+        status = self._poll_modem_status()
+        return bool(status & self.MODEM_CTS)
+
+    @property
+    def dsr(self):
+        '''Read terminal status line: Data Set Ready.'''
+        status = self._poll_modem_status()
+        return bool(status & self.MODEM_DSR)
+
+    @property
+    def ri(self):
+        '''Read terminal status line: Ring Indicator.'''
+        status = self._poll_modem_status()
+        return bool(status & self.MODEM_RI)
+
+    @property
+    def cd(self):
+        '''Read terminal status line: Carrier Detect.'''
+        status = self._poll_modem_status()
+        return bool(status & self.MODEM_RLSD)
+
+    #  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -
+    
+    def _ctrl_transfer_out(self, request, value, index):
+        '''USB control transfer out.
+        
+        This function does the USB configuration job.
+        '''
+        return self._connection.controlTransfer(
+            self.FTDI_DEVICE_OUT_REQTYPE, 
+            request, 
+            value, 
+            index, 
+            None, 
+            0, 
+            self.USB_WRITE_TIMEOUT_MILLIS
+        )
+    
+    def _ctrl_transfer_in(self, request, buf, length):
+        '''USB control transfer in.
+        
+        Request for a control message from the device.
+        '''
+        return self._connection.controlTransfer(
+            self.FTDI_DEVICE_IN_REQTYPE,
+            request,
+            0,
+            self._index,
+            buf,
+            length,
+            self.USB_READ_TIMEOUT_MILLIS
+        )
+
+    def _set_break(self, break_):
+        '''Start or stop a break exception event on the serial line.
+        
+        Parameters:
+            break_ (bool): either start or stop break event.
+        '''
+        if break_:
+            value = self._lineprop | (0x01 << 14)
+            if self._ctrl_transfer_out(self.SIO_SET_DATA, value, self._index):
+                raise SerialException('Unable to start break sequence')
+        else:
+            value = self._lineprop & ~(0x01 << 14)
+            if self._ctrl_transfer_out(self.SIO_SET_DATA, value, self._index):
+                raise SerialException('Unable to stop break sequence')
+        self._lineprop = value
+
+    def _set_dtr(self, state):
+        '''Set dtr line.
+        
+        Parameters:
+            state (bool): new DTR logical level.
+        '''
+        value = state and self.SIO_SET_DTR_HIGH or self.SIO_SET_DTR_LOW
+        if self._ctrl_transfer_out(self.SIO_SET_MODEM_CTRL, value, self._index):
+            raise SerialException('Unable to set DTR line')
+
+    def _set_rts(self, state):
+        '''Set rts line.
+        
+        Parameters:
+            state (bool): new RTS logical level.
+        '''
+        value = state and self.SIO_SET_RTS_HIGH or self.SIO_SET_RTS_LOW
+        if self._ctrl_transfer_out(self.SIO_SET_MODEM_CTRL, value, self._index):
+            raise SerialException('Unable to set RTS line')
+
+    def _set_dtr_rts(self, dtr, rts):
+        '''Set dtr and rts lines at once.
+        
+        Parameters:
+            dtr (bool): new DTR logical level.
+            rts (bool): new RTS logical level.
+        '''
+        value = 0
+        value |= dtr and self.SIO_SET_DTR_HIGH or self.SIO_SET_DTR_LOW
+        value |= rts and self.SIO_SET_RTS_HIGH or self.SIO_SET_RTS_LOW
+        if self._ctrl_transfer_out(self.SIO_SET_FLOW_CTRL, value, self._index):
+            raise SerialException('Unable to set DTR/RTS lines')
+
+    def _purgeHwBuffers(self, purgeReadBuffers, purgeWriteBuffers):
         '''Set serial port parameters.
         
         Parameters:
@@ -247,19 +468,22 @@ class FtdiSerial(SerialBase):
             result = self._ctrl_transfer_out(
                 self.SIO_RESET, 
                 self.SIO_RESET_PURGE_RX, 
-                0)
+                self._index
+            )
             if result != 0:
                 raise SerialException(
-                    "Flushing RX failed: result={}".format(result))
+                    "Flushing RX failed: result={}".format(result)
+                )
 
         if purgeWriteBuffers:
             result = self._ctrl_transfer_out(
                 self.SIO_RESET, 
                 self.SIO_RESET_PURGE_TX, 
-                0)
+                self._index)
             if result != 0:
                 raise SerialException(
-                    "Flushing TX failed: result={}".format(result))
+                    "Flushing TX failed: result={}".format(result)
+                )
         
         return True
     
@@ -280,11 +504,14 @@ class FtdiSerial(SerialBase):
             self._read_endpoint, 
             buf, 
             self.DEFAULT_READ_BUFFER_SIZE, 
-            self.USB_READ_TIMEOUT_MILLIS)
+            self.USB_READ_TIMEOUT_MILLIS
+        )
         if totalBytesRead < self.MODEM_STATUS_HEADER_LENGTH:
             raise SerialException(
                 "Expected at least {} bytes".format(
-                    self.MODEM_STATUS_HEADER_LENGTH))
+                    self.MODEM_STATUS_HEADER_LENGTH
+                )
+            )
     
         # Translate raw data into serial port data.
         read = bytearray()
@@ -292,7 +519,8 @@ class FtdiSerial(SerialBase):
             buf, 
             read, 
             totalBytesRead, 
-            self._read_endpoint.getMaxPacketSize())
+            self._read_endpoint.getMaxPacketSize()
+        )
             
         return bytes(read)
     
@@ -315,13 +543,59 @@ class FtdiSerial(SerialBase):
         actual, value, index = self._convert_baudrate(baudrate)
         delta = 100*abs(float(actual-baudrate))/baudrate
         if delta > self.BAUDRATE_TOLERANCE:
-            raise ValueError('Baudrate tolerance exceeded: %.02f%% '
-                             '(wanted %d, achievable %d)' %
-                             (delta, baudrate, actual))
+            raise ValueError(
+                'Baudrate tolerance exceeded: %.02f%% '
+                '(wanted %d, achievable %d)' %
+                (delta, baudrate, actual)
+            )
         result = self._ctrl_transfer_out(self.SIO_SET_BAUDRATE, value, index)
         if result != 0:
-            raise SerialException('Unable to set baudrate')
+            raise SerialException('Unable to set baudrate.')
     
+    def _set_line_property(self, bits, stopbits, parity, break_=0):
+        '''Set serial port line property.
+        
+        Parameters:
+            bits (int): number of bits in data(5, 6, 7 or 8).
+            stopbits (float): number of stop bits(1, 1.5, 2).
+            parity (str): 'N', 'E', 'O', 'M' or 'S'.
+            break_ (int): 0 for break off or 1 for break on.
+        '''
+        value = bits & 0x0F
+        
+        if parity == 'N':
+            value |= (0x00 << 8)
+        elif parity == 'O':
+            value |= (0x01 << 8)
+        elif parity == 'E':
+            value |= (0x02 << 8)
+        elif parity == 'M':
+            value |= (0x03 << 8)
+        elif parity == 'S':
+            value |= (0x04 << 8)
+        else:
+            raise ValueError('Unknown parity value: {}'.format(parity))
+        
+        if stopbits == 1:
+            value |= (0x00 << 11)
+        elif stopbits == 1.5:
+            value |= (0x01 << 11)
+        elif stopbits == 2:
+            value |= (0x02 << 11)
+        else:
+            raise ValueError("Unknown stopbits value: {}".format(stopbits))
+        
+        if break_ == self.BREAK_ON:
+            value |= 0x01 << 14
+        
+        result = self._ctrl_transfer_out(self.SIO_SET_DATA, value, self._index)
+        if result != 0:
+            raise SerialException(
+                'Setting line property failed: result={}'.format(result)
+            )
+                
+        self._lineprop = value
+
     def _setParameters(self, baudrate, databits, parity, stopbits):
         '''Set serial port parameters.
         
@@ -333,57 +607,54 @@ class FtdiSerial(SerialBase):
         '''
     
         self._set_baudrate(baudrate)
+        self._set_line_property(databits, stopbits, parity)
         
-        config = databits
+    def _poll_modem_status(self):
+        '''Poll modem status information.
         
-        if parity == 'N':
-            config |= (0x00 << 8)
-        elif parity == 'O':
-            config |= (0x01 << 8)
-        elif parity == 'E':
-            config |= (0x02 << 8)
-        elif parity == 'M':
-            config |= (0x03 << 8)
-        elif parity == 'S':
-            config |= (0x04 << 8)
-        else:
-            raise ValueError("Unknown parity value: {}".format(parity))
+        This function allows the retrieve the two status bytes of the
+        device, useful in UART mode.
+        FTDI device does not have a so-called USB "interrupt" end-point,
+        event polling on the UART interface is done through the regular
+        control endpoint.
+        Returns:
+            status (int): modem status, as a proprietary bitfield
+        '''
+        buf = bytearray(self.DEFAULT_READ_BUFFER_SIZE)
+        result = self._ctrl_transfer_in(self.SIO_POLL_MODEM_STATUS, buf, 2)
+        if result != 2:
+            raise SerialException('Unable to get modem status.')
+        buf = buf[:2]
+        status, = unpack('<H', bytes(buf))
+        return status
+
+    def _set_flowctrl(self, flowctrl):
+        '''Select flowcontrol in UART mode.
         
-        if stopbits == 1:
-            config |= (0x00 << 11)
-        elif stopbits == 1.5:
-            config |= (0x01 << 11)
-        elif stopbits == 2:
-            config |= (0x02 << 11)
-        else:
-            raise ValueError("Unknown stopbits value: {}".format(stopbits))
+        Either hardware flow control through RTS/CTS UART lines,
+        software or no flow control.
+        Parameters:
+            flowctrl (str): 'hw', 'sw' or ''
+        '''
+        ctrl = {
+            'hw': self.SIO_RTS_CTS_HS,
+            'sw': self.SIO_XON_XOFF_HS,
+            '': self.SIO_DISABLE_FLOW_CTRL
+        }
+        try:
+            value = ctrl[flowctrl] | self._index
+        except KeyError:
+            raise ValueError('Unknown flow control: {}'.format(flowctrl))
         
-        result = self._ctrl_transfer_out(self.SIO_SET_DATA, config, 0)
+        result = self._ctrl_transfer_out(
+            self.SIO_SET_FLOW_CTRL,
+            0,
+            value
+        )
         if result != 0:
             raise SerialException(
-                "Setting parameters failed: result={}".format(result))
-    
-    def _reconfigure_port(self):
-        '''Reconfigure serial port parameters.'''
-        self._setParameters(
-            self.baudrate, 
-            self.bytesize, 
-            self.parity, 
-            self.stopbits)
-    
-    def _ctrl_transfer_out(self, request, value, index):
-        '''USB control transfer.
-        
-        This function does the USB configuration job.
-        '''
-        return self._connection.controlTransfer(
-            self.FTDI_DEVICE_OUT_REQTYPE, 
-            request, 
-            value, 
-            index, 
-            None, 
-            0, 
-            self.USB_WRITE_TIMEOUT_MILLIS)
+                "Setting flow control failed: result={}".format(result)
+            )
     
     def _has_mpsse(self):
         '''Tell whether the device supports MPSSE (I2C, SPI, JTAG, ...).
@@ -500,8 +771,8 @@ class FtdiSerial(SerialBase):
                 if baud_diff == 0:
                     break
         # Encode the best divisor value
-        encoded_divisor = (best_divisor >> 3) | \
-                          (frac_code[best_divisor & 7] << 14)
+        encoded_divisor = (best_divisor >> 3) \
+            | (frac_code[best_divisor & 7] << 14)
         # Deal with special cases for encoded value
         if encoded_divisor == 1:
             encoded_divisor = 0  # 3000000 baud
@@ -531,21 +802,23 @@ class FtdiSerial(SerialBase):
         Returns:
             result (int): the number of payload bytes.
         '''
-        packetsCount = totalBytesRead // maxPacketSize + (
-            0 if totalBytesRead % maxPacketSize == 0 else 1)
+        packetsCount = totalBytesRead // maxPacketSize + \
+            (0 if totalBytesRead % maxPacketSize == 0 else 1)
         for packetIdx in range(packetsCount):
-            count = ((totalBytesRead % maxPacketSize) -
-                self.MODEM_STATUS_HEADER_LENGTH) if (
-                    packetIdx == (packetsCount - 1)) else (
-                    maxPacketSize - self.MODEM_STATUS_HEADER_LENGTH)
+            count = (
+                (totalBytesRead % maxPacketSize) \
+                - self.MODEM_STATUS_HEADER_LENGTH
+                ) if (packetIdx == (packetsCount - 1)) else \
+                (maxPacketSize - self.MODEM_STATUS_HEADER_LENGTH)
             if count > 0:
                 usb.arraycopy(
                     src,
                     packetIdx * maxPacketSize + self.MODEM_STATUS_HEADER_LENGTH,
                     dest,
-                    packetIdx * (
-                        maxPacketSize - self.MODEM_STATUS_HEADER_LENGTH),
-                    count)
+                    packetIdx \
+                        * (maxPacketSize - self.MODEM_STATUS_HEADER_LENGTH),
+                    count
+                )
                 
         return totalBytesRead - (packetsCount * 2)