Bus#
The BusABC
class provides a wrapper around a physical or virtual CAN Bus.
An interface specific instance is created by calling the Bus()
function with a particular interface
, for example:
vector_bus = can.Bus(interface='vector', ...)
The created bus is then able to handle the interface specific software/hardware interactions while giving the user the same top level API.
A thread safe bus wrapper is also available, see Thread safe bus.
Transmitting#
Writing individual messages to the bus is done by calling the send()
method
and passing a Message
instance.
with can.Bus() as bus:
msg = can.Message(
arbitration_id=0xC0FFEE,
data=[0, 25, 0, 1, 3, 1, 4, 1],
is_extended_id=True
)
try:
bus.send(msg)
print(f"Message sent on {bus.channel_info}")
except can.CanError:
print("Message NOT sent")
Periodic sending is controlled by the broadcast manager.
Receiving#
Reading from the bus is achieved by either calling the recv()
method or
by directly iterating over the bus:
with can.Bus() as bus:
for msg in bus:
print(msg.data)
Alternatively the Listener api can be used, which is a list of various
Listener
implementations that receive and handle messages from a Notifier
.
Filtering#
Message filtering can be set up for each bus. Where the interface supports it, this is carried out in the hardware or kernel layer - not in Python. All messages that match at least one filter are returned.
Example defining two filters, one to pass 11-bit ID 0x451
, the other to pass 29-bit ID 0xA0000
:
filters = [
{"can_id": 0x451, "can_mask": 0x7FF, "extended": False},
{"can_id": 0xA0000, "can_mask": 0x1FFFFFFF, "extended": True},
]
bus = can.interface.Bus(channel="can0", interface="socketcan", can_filters=filters)
See set_filters()
for the implementation.
Bus API#
- can.Bus(channel=None, interface=None, config_context=None, ignore_config=False, **kwargs)[source]#
Create a new bus instance with configuration loading.
Instantiates a CAN Bus of the given
interface
, falls back to reading a configuration file from default locations.Note
Please note that while the arguments provided to this class take precedence over any existing values from configuration, it is possible that other parameters from the configuration may be added to the bus instantiation. This could potentially have unintended consequences. To prevent this, you may use the ignore_config parameter to ignore any existing configurations.
- Parameters:
channel (str | int | None) – Channel identification. Expected type is backend dependent. Set to
None
to let it be resolved automatically from the default Configuration.interface (str | None) – See Interface Names for a list of supported interfaces. Set to
None
to let it be resolved automatically from the default Configuration.config_context (str | None) – Extra ‘context’, that is passed to config sources. This can be used to select a section other than ‘default’ in the configuration file.
ignore_config (bool) – If
True
, only the given arguments will be used for the bus instantiation. Existing configuration sources will be ignored.kwargs (Any) –
interface
specific keyword arguments.
- Raises:
CanInterfaceNotImplementedError – if the
interface
isn’t recognized or cannot be loadedCanInitializationError – if the bus cannot be instantiated
ValueError – if the
channel
could not be determined
- Return type:
- class can.BusABC(channel, can_filters=None, **kwargs)[source]#
The CAN Bus Abstract Base Class that serves as the basis for all concrete interfaces.
This class may be used as an iterator over the received messages and as a context manager for auto-closing the bus when done using it.
Please refer to Error Handling for possible exceptions that may be thrown by certain operations on this bus.
- Parameters:
- RECV_LOGGING_LEVEL = 9#
Log level for received messages
- channel_info = 'unknown'#
a string describing the underlying bus and/or channel
- property filters: Sequence[CanFilter | CanFilterExtended] | None#
Modify the filters of this bus. See
set_filters()
for details.
- flush_tx_buffer()[source]#
Discard every message that may be queued in the output buffer(s).
- Return type:
None
- property protocol: CanProtocol#
Return the CAN protocol used by this bus instance.
This value is set at initialization time and does not change during the lifetime of a bus instance.
- recv(timeout=None)[source]#
Block waiting for a message from the Bus.
- Parameters:
timeout (float | None) – seconds to wait for a message or None to wait indefinitely
- Returns:
- Raises:
CanOperationError – If an error occurred while reading
- Return type:
Message | None
- abstract send(msg, timeout=None)[source]#
Transmit a message to the CAN bus.
Override this method to enable the transmit path.
- Parameters:
msg (Message) – A message object.
timeout (float | None) – If > 0, wait up to this many seconds for message to be ACK’ed or for transmit queue to be ready depending on driver implementation. If timeout is exceeded, an exception will be raised. Might not be supported by all interfaces. None blocks indefinitely.
- Raises:
CanOperationError – If an error occurred while sending
- Return type:
None
- send_periodic(msgs, period, duration=None, store_task=True, modifier_callback=None)[source]#
Start sending messages at a given period on this bus.
The task will be active until one of the following conditions are met:
the (optional) duration expires
the Bus instance goes out of scope
the Bus instance is shutdown
stop_all_periodic_tasks()
is calledthe task’s
stop()
method is called.
- Parameters:
period (float) – Period in seconds between each message
duration (float | None) – Approximate duration in seconds to continue sending messages. If no duration is provided, the task will continue indefinitely.
store_task (bool) – If True (the default) the task will be attached to this Bus instance. Disable to instead manage tasks manually.
modifier_callback (Callable[[Message], None] | None) – Function which should be used to modify each message’s data before sending. The callback modifies the
data
of the message and returnsNone
.
- Returns:
A started task instance. Note the task can be stopped (and depending on the backend modified) by calling the task’s
stop()
method.- Return type:
Note
Note the duration before the messages stop being sent may not be exactly the same as the duration specified by the user. In general the message will be sent at the given rate until at least duration seconds.
Note
For extremely long-running Bus instances with many short-lived tasks the default api with
store_task==True
may not be appropriate as the stopped tasks are still taking up memory as they are associated with the Bus instance.
- set_filters(filters=None)[source]#
Apply filtering to all messages received by this Bus.
All messages that match at least one filter are returned. If filters is None or a zero length sequence, all messages are matched.
Calling without passing any filters will reset the applied filters to
None
.- Parameters:
filters (Sequence[CanFilter | CanFilterExtended] | None) –
A iterable of dictionaries each containing a “can_id”, a “can_mask”, and an optional “extended” key:
[{"can_id": 0x11, "can_mask": 0x21, "extended": False}]
A filter matches, when
<received_can_id> & can_mask == can_id & can_mask
. Ifextended
is set as well, it only matches messages where<received_is_extended> == extended
. Else it matches every messages based only on the arbitration ID and mask.- Return type:
None
- shutdown()[source]#
Called to carry out any interface specific cleanup required in shutting down a bus.
This method can be safely called multiple times.
- Return type:
None
- stop_all_periodic_tasks(remove_tasks=True)[source]#
Stop sending any messages that were started using
send_periodic()
.Note
The result is undefined if a single task throws an exception while being stopped.
- Parameters:
remove_tasks (bool) – Stop tracking the stopped tasks.
- Return type:
None
Thread safe bus#
This thread safe version of the BusABC
class can be used by multiple threads at once.
Sending and receiving is locked separately to avoid unnecessary delays.
Conflicting calls are executed by blocking until the bus is accessible.
It can be used exactly like the normal BusABC
:
# 'socketcan' is only an example interface, it works with all the others too
my_bus = can.ThreadSafeBus(interface='socketcan', channel='vcan0')
my_bus.send(...)
my_bus.recv(...)
- class can.ThreadSafeBus(*args, **kwargs)[source]#
Contains a thread safe
can.BusABC
implementation that wraps around an existing interface instance. All public methods of that base class are now safe to be called from multiple threads. The send and receive methods are synchronized separately.Use this as a drop-in replacement for
BusABC
.Note
This approach assumes that both
send()
and_recv_internal()
of the underlying bus instance can be called simultaneously, and that the methods use_recv_internal()
instead ofrecv()
directly.