class CAN – controller area network communication bus

THIS MODULE EXISTS TO PROVIDE CAN SUPPORT FOR THE OPENMV CAM RT1062 AND WILL BE REMOVED ONCE MICROPYTHON PROVIDES A STANDARD MACHINE CAN MODULE. THIS MODULE IS A COPY OF THE PYB.CAN MODULE FOR THE STM32.

CAN implements support for classic CAN controllers. At the physical level CAN bus consists of 2 lines: RX and TX. Note that to connect the board to a CAN bus you must use a CAN transceiver to convert the CAN logic signals from the board to the correct voltage levels on the bus.

Example usage for classic CAN controller in Loopback (transceiver-less) mode:

from machine import CAN
can = CAN(0, CAN.LOOPBACK)
can.setfilter(0, CAN.DUAL, 0, (123, 124))  # set a filter to receive messages with id=123 and 124
can.send('message!', 123)   # send a message with id 123
can.recv(0)                 # receive message on FIFO 0

The following CAN module functions and their arguments are available for classic CAN controllers, unless otherwise stated.

Constructors

class machine.CAN(bus, ...)

Construct a CAN object on the given bus. bus can be 0. With no additional parameters, the CAN object is created but not initialised (it has the settings from the last initialisation of the bus, if any). If extra arguments are given, the bus is initialised. See CAN.init() for parameters of initialisation.

The physical pins of the CAN buses are:

  • CAN(0): (RX, TX) = (P3, P1)

Methods

CAN.init(mode, *, auto_restart=False, baudrate=0)

Initialise the CAN bus with the given parameters:

  • mode is one of: NORMAL, LOOPBACK, SILENT, SILENT_LOOPBACK

  • auto_restart sets whether the controller will automatically try and restart communications after entering the bus-off state; if this is disabled then restart() can be used to leave the bus-off state

  • baudrate sets the baudrate used to connect to the CAN bus

CAN.deinit()

Turn off the CAN bus.

CAN.restart()

Force a software restart of the CAN controller without resetting its configuration.

If the controller enters the bus-off state then it will no longer participate in bus activity. If the controller is not configured to automatically restart (see init()) then this method can be used to trigger a restart, and the controller will follow the CAN protocol to leave the bus-off state and go into the error active state.

CAN.state()

Return the state of the controller. The return value can be one of:

  • CAN.STOPPED – the controller is completely off and reset;

  • CAN.ERROR_ACTIVE – the controller is on and in the Error Active state (both TEC and REC are less than 96);

  • CAN.ERROR_WARNING – the controller is on and in the Error Warning state (at least one of TEC or REC is 96 or greater);

  • CAN.ERROR_PASSIVE – the controller is on and in the Error Passive state (at least one of TEC or REC is 128 or greater);

  • CAN.BUS_OFF – the controller is on but not participating in bus activity (TEC overflowed beyond 255).

CAN.info([list])

Get information about the controller’s error states and TX and RX buffers. If list is provided then it should be a list object with at least 8 entries, which will be filled in with the information. Otherwise a new list will be created and filled in. In both cases the return value of the method is the populated list.

The values in the list are:

  • TEC value

  • REC value

  • number of times the controller enterted the Error Warning state (wrapped around to 0 after 65535)

  • number of times the controller enterted the Error Passive state (wrapped around to 0 after 65535)

  • number of times the controller enterted the Bus Off state (wrapped around to 0 after 65535)

  • number of pending TX messages

  • number of pending RX messages on fifo 0

  • always 0

CAN.setfilter(bank, mode, fifo, params, *, rtr, extframe=False)

Configure a filter bank:

  • bank is the classic CAN controller filter bank to configure.

  • mode is the mode the filter should operate in, see the tables below.

  • fifo is which fifo (0) a message should be stored in, if it is accepted by this filter.

  • params is an array of values the defines the filter. The contents of the array depends on the mode argument.

mode

Contents of params array for classic CAN controller

CAN.LIST32

Two 32 bit ids that will be accepted

CAN.DUAL

Two ids that will be accepted. For example (1, 2)

  • rtr For classic CAN controllers, this is an array of booleans that states if a filter should accept a remote transmission request message. If this argument is not given then it defaults to False for all entries. The length of the array depends on the mode argument.

mode

length of rtr array

CAN.LIST32

2

CAN.DUAL

2

  • extframe If True the frame will have an extended identifier (29 bits), otherwise a standard identifier (11 bits) is used.

CAN.clearfilter(bank, extframe=False)

Clear and disables a filter bank:

  • bank is the classic CAN controller filter bank to clear.

  • extframe ignored

CAN.any(fifo)

Return True if any message waiting on the FIFO, else False.

CAN.recv(fifo, list=None, *, timeout=5000)

Receive data on the bus:

  • fifo is an integer, which is the FIFO to receive on - always 0

  • list is an optional list object to be used as the return value

  • timeout is the timeout in milliseconds to wait for the receive.

Return value: A tuple containing five values.

  • The id of the message.

  • A boolean that indicates if the message ID is standard or extended.

  • A boolean that indicates if the message is an RTR message.

  • The FMI (Filter Match Index) value.

  • An array containing the data.

If list is None then a new tuple will be allocated, as well as a new bytes object to contain the data (as the fifth element in the tuple).

If list is not None then it should be a list object with a least five elements. The fifth element should be a memoryview object which is created from either a bytearray or an array of type ‘B’ or ‘b’, and this array must have enough room for at least 8 bytes. The list object will then be populated with the first four return values above, and the memoryview object will be resized inplace to the size of the data and filled in with that data. The same list and memoryview objects can be reused in subsequent calls to this method, providing a way of receiving data without using the heap. For example:

buf = bytearray(8)
lst = [0, 0, 0, 0, memoryview(buf)]
# No heap memory is allocated in the following call
can.recv(0, lst)
CAN.send(data, id, *, timeout=0, rtr=False, extframe=False)

Send a message on the bus:

  • data is the data to send (an integer to send, or a buffer object).

  • id is the id of the message to be sent.

  • timeout is the timeout in milliseconds to wait for the send.

  • rtr is a boolean that specifies if the message shall be sent as a remote transmission request. If rtr is True then only the length of data is used to fill in the DLC slot of the frame; the actual bytes in data are unused.

  • extframe if True the frame will have an extended identifier (29 bits), otherwise a standard identifier (11 bits) is used.

If timeout is 0 the message is placed in a buffer and the method returns immediately.

If all three buffers are in use an exception is thrown. If timeout is not 0, the method waits until the message is transmitted. If the message can’t be transmitted within the specified time an exception is thrown.

Return value: None.

CAN.rxcallback(fifo, fun)

Register a function to be called when a message is accepted into a empty fifo:

  • fifo is the receiving fifo - always 0.

  • fun is the function to be called when the fifo becomes non empty.

The callback function takes two arguments the first is the can object it self the second is a integer that indicates the reason for the callback.

Reason

0

A message has been accepted into a empty FIFO.

1

The FIFO is full

2

A message has been lost due to a full FIFO

Example use of rxcallback:

def cb0(bus, reason):
  print('cb0')
  if reason == 0:
      print('pending')
  if reason == 1:
      print('full')
  if reason == 2:
      print('overflow')

can = CAN(0, CAN.LOOPBACK)
can.rxcallback(0, cb0)

Constants

CAN.NORMAL
CAN.LOOPBACK
CAN.SILENT
CAN.SILENT_LOOPBACK

The mode of the CAN bus used in init().

CAN.STOPPED
CAN.ERROR_ACTIVE
CAN.ERROR_WARNING
CAN.ERROR_PASSIVE
CAN.BUS_OFF

Possible states of the CAN controller returned from state().

CAN.LIST32
CAN.DUAL

The operation mode of a filter used in setfilter() for classic CAN.