Source code for can.interfaces.serial.serial_can
"""
A text based interface. For example use over serial ports like
"/dev/ttyS1" or "/dev/ttyUSB0" on Linux machines or "COM1" on Windows.
The interface is a simple implementation that has been used for
recording CAN traces.
See the interface documentation for the format being used.
"""
import io
import logging
import struct
from collections.abc import Sequence
from typing import Any, cast
from can import (
BusABC,
CanInitializationError,
CanInterfaceNotImplementedError,
CanOperationError,
CanProtocol,
CanTimeoutError,
Message,
)
from can.typechecking import AutoDetectedConfig
logger = logging.getLogger("can.serial")
try:
import serial.tools.list_ports
except ImportError:
logger.warning(
"You won't be able to use the serial can backend without "
"the `pyserial` package installed!"
)
serial = None
CAN_ERR_FLAG = 0x20000000
CAN_RTR_FLAG = 0x40000000
CAN_EFF_FLAG = 0x80000000
CAN_ID_MASK_EXT = 0x1FFFFFFF
CAN_ID_MASK_STD = 0x7FF
[docs]
class SerialBus(BusABC):
"""
Enable basic can communication over a serial device.
.. note:: See :meth:`~_recv_internal` for some special semantics.
"""
def __init__(
self,
channel: str,
baudrate: int = 115200,
timeout: float = 0.1,
rtscts: bool = False,
**kwargs: Any,
) -> None:
"""
:param channel:
The serial device to open. For example "/dev/ttyS1" or
"/dev/ttyUSB0" on Linux or "COM1" on Windows systems.
:param baudrate:
Baud rate of the serial device in bit/s (default 115200).
.. warning::
Some serial port implementations don't care about the baudrate.
:param timeout:
Timeout for the serial device in seconds (default 0.1).
:param rtscts:
turn hardware handshake (RTS/CTS) on and off
:raises ~can.exceptions.CanInitializationError:
If the given parameters are invalid.
:raises ~can.exceptions.CanInterfaceNotImplementedError:
If the serial module is not installed.
"""
if not serial:
raise CanInterfaceNotImplementedError("the serial module is not installed")
if not channel:
raise TypeError("Must specify a serial port.")
self.channel_info = f"Serial interface: {channel}"
self._can_protocol = CanProtocol.CAN_20
try:
self._ser = serial.serial_for_url(
channel, baudrate=baudrate, timeout=timeout, rtscts=rtscts
)
except ValueError as error:
raise CanInitializationError(
"could not create the serial device"
) from error
super().__init__(channel, **kwargs)
def shutdown(self) -> None:
"""
Close the serial interface.
"""
super().shutdown()
self._ser.close()
def send(self, msg: Message, timeout: float | None = None) -> None:
"""
Send a message over the serial device.
:param msg:
Message to send.
.. note:: If the timestamp is a float value it will be converted
to an integer.
:param timeout:
This parameter will be ignored. The timeout value of the channel is
used instead.
"""
# Pack timestamp
try:
timestamp = struct.pack("<I", int(msg.timestamp * 1000))
except struct.error:
raise ValueError(f"Timestamp is out of range: {msg.timestamp}") from None
# Pack arbitration ID
if msg.is_extended_id:
arbitration_id = msg.arbitration_id & CAN_ID_MASK_EXT
arbitration_id |= CAN_EFF_FLAG
else:
arbitration_id = msg.arbitration_id & CAN_ID_MASK_STD
if msg.is_error_frame:
arbitration_id |= CAN_ERR_FLAG
if msg.is_remote_frame:
arbitration_id |= CAN_RTR_FLAG
arbitration_id_bytes = struct.pack("<I", arbitration_id)
# Assemble message
byte_msg = bytearray()
byte_msg.append(0xAA)
byte_msg += timestamp
byte_msg.append(msg.dlc)
byte_msg += arbitration_id_bytes
byte_msg += msg.data
byte_msg.append(0xBB)
# Write to serial device
try:
self._ser.write(byte_msg)
except serial.PortNotOpenError as error:
raise CanOperationError("writing to closed port") from error
except serial.SerialTimeoutException as error:
raise CanTimeoutError() from error
[docs]
def _recv_internal(self, timeout: float | None) -> tuple[Message | None, bool]:
"""
Read a message from the serial device.
:param timeout:
.. warning::
This parameter will be ignored. The timeout value of the channel is used.
:returns:
Received message and :obj:`False` (because no filtering as taken place).
"""
try:
rx_byte = self._ser.read()
if rx_byte and ord(rx_byte) == 0xAA:
s = self._ser.read(4)
timestamp = struct.unpack("<I", s)[0]
dlc = ord(self._ser.read())
if dlc > 8:
raise ValueError("received DLC may not exceed 8 bytes")
s = self._ser.read(4)
arbitration_id = struct.unpack("<I", s)[0]
is_extended_id = bool(arbitration_id & CAN_EFF_FLAG)
is_error_frame = bool(arbitration_id & CAN_ERR_FLAG)
is_remote_frame = bool(arbitration_id & CAN_RTR_FLAG)
if is_extended_id:
arbitration_id = arbitration_id & CAN_ID_MASK_EXT
else:
arbitration_id = arbitration_id & CAN_ID_MASK_STD
data = self._ser.read(dlc)
delimiter_byte = ord(self._ser.read())
if delimiter_byte == 0xBB:
# received message data okay
msg = Message(
# TODO: We are only guessing that they are milliseconds
timestamp=timestamp / 1000,
arbitration_id=arbitration_id,
dlc=dlc,
data=data,
is_extended_id=is_extended_id,
is_error_frame=is_error_frame,
is_remote_frame=is_remote_frame,
)
return msg, False
else:
raise CanOperationError(
f"invalid delimiter byte while reading message: {delimiter_byte}"
)
else:
return None, False
except serial.SerialException as error:
raise CanOperationError("could not read from serial") from error
def fileno(self) -> int:
try:
return cast("int", self._ser.fileno())
except io.UnsupportedOperation:
raise NotImplementedError(
"fileno is not implemented using current CAN bus on this platform"
) from None
except Exception as exception:
raise CanOperationError("Cannot fetch fileno") from exception
@staticmethod
def _detect_available_configs() -> Sequence[AutoDetectedConfig]:
configs: list[AutoDetectedConfig] = []
if serial is None:
return configs
for port in serial.tools.list_ports.comports():
configs.append({"interface": "serial", "channel": port.device})
return configs