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220 lines
8.8 KiB
220 lines
8.8 KiB
class CAN -- controller area network communication bus
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======================================================
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CAN implements the standard CAN communications protocol. At
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the physical level it consists of 2 lines: RX and TX. Note that
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to connect the pyboard to a CAN bus you must use a CAN transceiver
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to convert the CAN logic signals from the pyboard to the correct
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voltage levels on the bus.
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Example usage (works without anything connected)::
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from pyb import CAN
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can = CAN(1, CAN.LOOPBACK)
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can.setfilter(0, CAN.LIST16, 0, (123, 124, 125, 126)) # set a filter to receive messages with id=123, 124, 125 and 126
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can.send('message!', 123) # send a message with id 123
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can.recv(0) # receive message on FIFO 0
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Constructors
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------------
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.. class:: pyb.CAN(bus, ...)
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Construct a CAN object on the given bus. ``bus`` can be 1-2, or 'YA' or 'YB'.
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With no additional parameters, the CAN object is created but not
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initialised (it has the settings from the last initialisation of
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the bus, if any). If extra arguments are given, the bus is initialised.
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See ``init`` for parameters of initialisation.
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The physical pins of the CAN busses are:
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- ``CAN(1)`` is on ``YA``: ``(RX, TX) = (Y3, Y4) = (PB8, PB9)``
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- ``CAN(2)`` is on ``YB``: ``(RX, TX) = (Y5, Y6) = (PB12, PB13)``
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Class Methods
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-------------
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.. method:: CAN.initfilterbanks(nr)
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Reset and disable all filter banks and assign how many banks should be available for CAN(1).
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STM32F405 has 28 filter banks that are shared between the two available CAN bus controllers.
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This function configures how many filter banks should be assigned to each. ``nr`` is the number of banks
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that will be assigned to CAN(1), the rest of the 28 are assigned to CAN(2).
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At boot, 14 banks are assigned to each controller.
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Methods
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-------
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.. method:: can.init(mode, extframe=False, prescaler=100, \*, sjw=1, bs1=6, bs2=8)
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Initialise the CAN bus with the given parameters:
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- ``mode`` is one of: NORMAL, LOOPBACK, SILENT, SILENT_LOOPBACK
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- if ``extframe`` is True then the bus uses extended identifiers in the frames
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(29 bits); otherwise it uses standard 11 bit identifiers
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- ``prescaler`` is used to set the duration of 1 time quanta; the time quanta
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will be the input clock (PCLK1, see :meth:`pyb.freq()`) divided by the prescaler
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- ``sjw`` is the resynchronisation jump width in units of the time quanta;
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it can be 1, 2, 3, 4
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- ``bs1`` defines the location of the sample point in units of the time quanta;
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it can be between 1 and 1024 inclusive
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- ``bs2`` defines the location of the transmit point in units of the time quanta;
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it can be between 1 and 16 inclusive
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The time quanta tq is the basic unit of time for the CAN bus. tq is the CAN
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prescaler value divided by PCLK1 (the frequency of internal peripheral bus 1);
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see :meth:`pyb.freq()` to determine PCLK1.
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A single bit is made up of the synchronisation segment, which is always 1 tq.
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Then follows bit segment 1, then bit segment 2. The sample point is after bit
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segment 1 finishes. The transmit point is after bit segment 2 finishes.
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The baud rate will be 1/bittime, where the bittime is 1 + BS1 + BS2 multiplied
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by the time quanta tq.
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For example, with PCLK1=42MHz, prescaler=100, sjw=1, bs1=6, bs2=8, the value of
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tq is 2.38 microseconds. The bittime is 35.7 microseconds, and the baudrate
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is 28kHz.
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See page 680 of the STM32F405 datasheet for more details.
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.. method:: can.deinit()
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Turn off the CAN bus.
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.. method:: can.setfilter(bank, mode, fifo, params, \*, rtr)
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Configure a filter bank:
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- ``bank`` is the filter bank that is to be configured.
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- ``mode`` is the mode the filter should operate in.
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- ``fifo`` is which fifo (0 or 1) a message should be stored in, if it is accepted by this filter.
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- ``params`` is an array of values the defines the filter. The contents of the array depends on the ``mode`` argument.
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+-----------+---------------------------------------------------------+
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|``mode`` |contents of parameter array |
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+===========+=========================================================+
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|CAN.LIST16 |Four 16 bit ids that will be accepted |
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+-----------+---------------------------------------------------------+
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|CAN.LIST32 |Two 32 bit ids that will be accepted |
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+-----------+---------------------------------------------------------+
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|CAN.MASK16 |Two 16 bit id/mask pairs. E.g. (1, 3, 4, 4) |
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| | | The first pair, 1 and 3 will accept all ids |
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| | | that have bit 0 = 1 and bit 1 = 0. |
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| | | The second pair, 4 and 4, will accept all ids |
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| | | that have bit 2 = 1. |
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+-----------+---------------------------------------------------------+
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|CAN.MASK32 |As with CAN.MASK16 but with only one 32 bit id/mask pair.|
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+-----------+---------------------------------------------------------+
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- ``rtr`` is an array of booleans that states if a filter should accept a
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remote transmission request message. If this argument is not given
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then it defaults to False for all entries. The length of the array
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depends on the ``mode`` argument.
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+-----------+----------------------+
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|``mode`` |length of rtr array |
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+===========+======================+
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|CAN.LIST16 |4 |
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+-----------+----------------------+
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|CAN.LIST32 |2 |
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+-----------+----------------------+
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|CAN.MASK16 |2 |
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+-----------+----------------------+
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|CAN.MASK32 |1 |
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+-----------+----------------------+
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.. method:: can.clearfilter(bank)
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Clear and disables a filter bank:
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- ``bank`` is the filter bank that is to be cleared.
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.. method:: can.any(fifo)
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Return ``True`` if any message waiting on the FIFO, else ``False``.
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.. method:: can.recv(fifo, \*, timeout=5000)
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Receive data on the bus:
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- ``fifo`` is an integer, which is the FIFO to receive on
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- ``timeout`` is the timeout in milliseconds to wait for the receive.
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Return value: A tuple containing four values.
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- The id of the message.
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- A boolean that indicates if the message is an RTR message.
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- The FMI (Filter Match Index) value.
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- An array containing the data.
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.. method:: can.send(data, id, \*, timeout=0, rtr=False)
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Send a message on the bus:
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- ``data`` is the data to send (an integer to send, or a buffer object).
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- ``id`` is the id of the message to be sent.
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- ``timeout`` is the timeout in milliseconds to wait for the send.
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- ``rtr`` is a boolean that specifies if the message shall be sent as
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a remote transmission request. If ``rtr`` is True then only the length
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of ``data`` is used to fill in the DLC slot of the frame; the actual
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bytes in ``data`` are unused.
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If timeout is 0 the message is placed in a buffer in one of three hardware
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buffers and the method returns immediately. If all three buffers are in use
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an exception is thrown. If timeout is not 0, the method waits until the
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message is transmitted. If the message can't be transmitted within the
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specified time an exception is thrown.
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Return value: ``None``.
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.. method:: can.rxcallback(fifo, fun)
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Register a function to be called when a message is accepted into a empty fifo:
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- ``fifo`` is the receiving fifo.
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- ``fun`` is the function to be called when the fifo becomes non empty.
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The callback function takes two arguments the first is the can object it self the second is
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a integer that indicates the reason for the callback.
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+--------+------------------------------------------------+
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| Reason | |
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+========+================================================+
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| 0 | A message has been accepted into a empty FIFO. |
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+--------+------------------------------------------------+
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| 1 | The FIFO is full |
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+--------+------------------------------------------------+
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| 2 | A message has been lost due to a full FIFO |
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+--------+------------------------------------------------+
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Example use of rxcallback::
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def cb0(bus, reason):
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print('cb0')
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if reason == 0:
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print('pending')
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if reason == 1:
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print('full')
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if reason == 2:
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print('overflow')
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can = CAN(1, CAN.LOOPBACK)
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can.rxcallback(0, cb0)
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Constants
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---------
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.. data:: CAN.NORMAL
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.. data:: CAN.LOOPBACK
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.. data:: CAN.SILENT
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.. data:: CAN.SILENT_LOOPBACK
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the mode of the CAN bus
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.. data:: CAN.LIST16
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.. data:: CAN.MASK16
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.. data:: CAN.LIST32
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.. data:: CAN.MASK32
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the operation mode of a filter
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