Ishraq Ibne Ashraf

NAME

Tinkerforge::BrickletCAN - Communicates with CAN bus devices

CONSTANTS

DEVICE_IDENTIFIER

This constant is used to identify a CAN Bricklet.

The get_identity() subroutine and the CALLBACK_ENUMERATE callback of the IP Connection have a device_identifier parameter to specify the Brick's or Bricklet's type.

DEVICE_DISPLAY_NAME

This constant represents the display name of a CAN Bricklet.

CALLBACK_FRAME_READ

This constant is used with the register_callback() subroutine to specify the CALLBACK_FRAME_READ callback.

FUNCTION_WRITE_FRAME

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_READ_FRAME

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_ENABLE_FRAME_READ_CALLBACK

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_DISABLE_FRAME_READ_CALLBACK

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_IS_FRAME_READ_CALLBACK_ENABLED

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_CONFIGURATION

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_CONFIGURATION

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_READ_FILTER

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_READ_FILTER

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_ERROR_LOG

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_IDENTITY

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTIONS

new()

Creates an object with the unique device ID *uid* and adds it to the IP Connection *ipcon*.

write_frame()

Writes a data or remote frame to the write buffer to be transmitted over the CAN transceiver.

The Bricklet supports the standard 11-bit (CAN 2.0A) and the additional extended 18-bit (CAN 2.0B) identifiers. For standard frames the Bricklet uses bit 0 to 10 from the ``identifier`` parameter as standard 11-bit identifier. For extended frames the Bricklet additionally uses bit 11 to 28 from the ``identifier`` parameter as extended 18-bit identifier.

For remote frames the ``data`` parameter is ignored.

Returns *true* if the frame was successfully added to the write buffer. Returns *false* if the frame could not be added because write buffer is already full.

The write buffer can overflow if frames are written to it at a higher rate than the Bricklet can transmitted them over the CAN transceiver. This may happen if the CAN transceiver is configured as read-only or is using a low baud rate (see :func:`Set Configuration`). It can also happen if the CAN bus is congested and the frame cannot be transmitted because it constantly loses arbitration or because the CAN transceiver is currently disabled due to a high write error level (see :func:`Get Error Log`).

read_frame()

Tries to read the next data or remote frame from the read buffer and return it. If a frame was successfully read, then the ``success`` return value is set to *true* and the other return values contain the frame. If the read buffer is empty and no frame could be read, then the ``success`` return value is set to *false* and the other return values contain invalid data.

The ``identifier`` return value follows the identifier format described for :func:`Write Frame`.

For remote frames the ``data`` return value always contains invalid data.

A configurable read filter can be used to define which frames should be received by the CAN transceiver and put into the read buffer (see :func:`Set Read Filter`).

Instead of polling with this function, you can also use callbacks. See the :func:`Enable Frame Read Callback` function and the :cb:`Frame Read` callback.

enable_frame_read_callback()

Enables the :cb:`Frame Read` callback.

By default the callback is disabled.

disable_frame_read_callback()

Disables the :cb:`Frame Read` callback.

By default the callback is disabled.

is_frame_read_callback_enabled()

Returns *true* if the :cb:`Frame Read` callback is enabled, *false* otherwise.

set_configuration()

Sets the configuration for the CAN bus communication.

The baud rate can be configured in steps between 10 and 1000 kbit/s.

The CAN transceiver has three different modes:

* Normal: Reads from and writes and to the CAN bus and performs active bus error detection and acknowledgement. * Loopback: All reads and writes are performed internally. The transceiver is disconnected from the actual CAN bus. * Read-Only: Only reads from the CAN bus, but does neither active bus error detection nor acknowledgement. Only the receiving part of the transceiver is connected to the CAN bus.

The write timeout has three different modes that define how a failed frame transmission should be handled:

* One-Shot (< 0): Only one transmission attempt will be made. If the transmission fails then the frame is discarded. * Infinite (= 0): Infinite transmission attempts will be made. The frame will never be discarded. * Milliseconds (> 0): A limited number of transmission attempts will be made. If the frame could not be transmitted successfully after the configured number of milliseconds then the frame is discarded.

The default is: 125 kbit/s, normal transceiver mode and infinite write timeout.

get_configuration()

Returns the configuration as set by :func:`Set Configuration`.

set_read_filter()

Set the read filter configuration. This can be used to define which frames should be received by the CAN transceiver and put into the read buffer.

The read filter has five different modes that define if and how the mask and the two filters are applied:

* Disabled: No filtering is applied at all. All frames are received even incomplete and defective frames. This mode should be used for debugging only. * Accept-All: All complete and error-free frames are received. * Match-Standard: Only standard frames with a matching identifier are received. * Match-Standard-and-Data: Only standard frames with matching identifier and data bytes are received. * Match-Extended: Only extended frames with a matching identifier are received.

The mask and filters are used as bit masks. Their usage depends on the mode:

* Disabled: Mask and filters are ignored. * Accept-All: Mask and filters are ignored. * Match-Standard: Bit 0 to 10 (11 bits) of mask and filters are used to match the 11-bit identifier of standard frames. * Match-Standard-and-Data: Bit 0 to 10 (11 bits) of mask and filters are used to match the 11-bit identifier of standard frames. Bit 11 to 18 (8 bits) and bit 19 to 26 (8 bits) of mask and filters are used to match the first and second data byte (if present) of standard frames. * Match-Extended: Bit 0 to 10 (11 bits) of mask and filters are used to match the standard 11-bit identifier part of extended frames. Bit 11 to 28 (18 bits) of mask and filters are used to match the extended 18-bit identifier part of extended frames.

The mask and filters are applied in this way: The mask is used to select the identifier and data bits that should be compared to the corresponding filter bits. All unselected bits are automatically accepted. All selected bits have to match one of the filters to be accepted. If all bits for the selected mode are accepted then the frame is accepted and is added to the read buffer.

.. csv-table:: :header: "Mask Bit", "Filter Bit", "Identifier/Data Bit", "Result" :widths: 10, 10, 10, 10

 0, X, X, Accept
 1, 0, 0, Accept
 1, 0, 1, Reject
 1, 1, 0, Reject
 1, 1, 1, Accept

For example, to receive standard frames with identifier 0x123 only the mode can be set to Match-Standard with 0x7FF as mask and 0x123 as filter 1 and filter 2. The mask of 0x7FF selects all 11 identifier bits for matching so that the identifier has to be exactly 0x123 to be accepted.

To accept identifier 0x123 and identifier 0x456 at the same time, just set filter 2 to 0x456 and keep mask and filter 1 unchanged.

The default mode is accept-all.

get_read_filter()

Returns the read filter as set by :func:`Set Read Filter`.

get_error_log()

Returns information about different kinds of errors.

The write and read error levels indicate the current level of checksum, acknowledgement, form, bit and stuffing errors during CAN bus write and read operations.

When the write error level extends 255 then the CAN transceiver gets disabled and no frames can be transmitted or received anymore. The CAN transceiver will automatically be activated again after the CAN bus is idle for a while.

The write and read error levels are not available in read-only transceiver mode (see :func:`Set Configuration`) and are reset to 0 as a side effect of changing the configuration or the read filter.

The write timeout, read register and buffer overflow counts represents the number of these errors:

* A write timeout occurs if a frame could not be transmitted before the configured write timeout expired (see :func:`Set Configuration`). * A read register overflow occurs if the read register of the CAN transceiver still contains the last received frame when the next frame arrives. In this case the newly arrived frame is lost. This happens if the CAN transceiver receives more frames than the Bricklet can handle. Using the read filter (see :func:`Set Read Filter`) can help to reduce the amount of received frames. This count is not exact, but a lower bound, because the Bricklet might not able detect all overflows if they occur in rapid succession. * A read buffer overflow occurs if the read buffer of the Bricklet is already full when the next frame should be read from the read register of the CAN transceiver. In this case the frame in the read register is lost. This happens if the CAN transceiver receives more frames to be added to the read buffer than are removed from the read buffer using the :func:`Read Frame` function. Using the :cb:`Frame Read` callback ensures that the read buffer can not overflow.

get_identity()

Returns the UID, the UID where the Bricklet is connected to, the position, the hardware and firmware version as well as the device identifier.

The position can be 'a', 'b', 'c' or 'd'.

The device identifier numbers can be found :ref:`here <device_identifier>`. |device_identifier_constant|