Python - CAN Bricklet¶

Loopback¶

Download (example_loopback.py)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49

#!/usr/bin/env python
# -*- coding: utf-8 -*-

HOST = "localhost"
PORT = 4223
UID = "XYZ" # Change XYZ to the UID of your CAN Bricklet

from tinkerforge.ip_connection import IPConnection
from tinkerforge.bricklet_can import BrickletCAN

# Callback function for frame read callback
def cb_frame_read(frame_type, identifier, data, length):
    if frame_type == BrickletCAN.FRAME_TYPE_STANDARD_DATA:
        print("Frame Type: Standard Data")
    elif frame_type == BrickletCAN.FRAME_TYPE_STANDARD_REMOTE:
        print("Frame Type: Standard Remote")
    elif frame_type == BrickletCAN.FRAME_TYPE_EXTENDED_DATA:
        print("Frame Type: Extended Data")
    elif frame_type == BrickletCAN.FRAME_TYPE_EXTENDED_REMOTE:
        print("Frame Type: Extended Remote")

    print("Identifier: " + str(identifier))
    print("Data (Length: " + str(length) + "): " + ", ".join(map(str, data[:min(length, 8)])))
    print("")

if __name__ == "__main__":
    ipcon = IPConnection() # Create IP connection
    can = BrickletCAN(UID, ipcon) # Create device object

    ipcon.connect(HOST, PORT) # Connect to brickd
    # Don't use device before ipcon is connected

    # Configure transceiver for loopback mode
    can.set_configuration(can.BAUD_RATE_1000KBPS, can.TRANSCEIVER_MODE_LOOPBACK, 0)

    # Register frame read callback to function cb_frame_read
    can.register_callback(can.CALLBACK_FRAME_READ, cb_frame_read)

    # Enable frame read callback
    can.enable_frame_read_callback()

    # Write standard data frame with identifier 1742 and 3 bytes of data
    can.write_frame(can.FRAME_TYPE_STANDARD_DATA, 1742, [42, 23, 17, 0, 0, 0, 0, 0], 3)

    input("Press key to exit\n") # Use raw_input() in Python 2

    can.disable_frame_read_callback()

    ipcon.disconnect()

Basic Functions¶

BrickletCAN(uid, ipcon)¶

Parameters:	uid – Type: str ipcon – Type: IPConnection
Returns:	can – Type: BrickletCAN

Creates an object with the unique device ID uid:

can = BrickletCAN("YOUR_DEVICE_UID", ipcon)

This object can then be used after the IP Connection is connected.

BrickletCAN.write_frame(frame_type, identifier, data, length)¶

Parameters:	frame_type – Type: int, Range: See constants identifier – Type: int, Range: [0 to 230 - 1] data – Type: [int, ...], Length: 8, Range: [0 to 255] length – Type: int, Range: [0 to 15]
Returns:	success – Type: bool

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 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 get_error_log()).

The following constants are available for this function:

For frame_type:

• BrickletCAN.FRAME_TYPE_STANDARD_DATA = 0
• BrickletCAN.FRAME_TYPE_STANDARD_REMOTE = 1
• BrickletCAN.FRAME_TYPE_EXTENDED_DATA = 2
• BrickletCAN.FRAME_TYPE_EXTENDED_REMOTE = 3

BrickletCAN.read_frame()¶

Return Object:	success – Type: bool frame_type – Type: int, Range: See constants identifier – Type: int, Range: [0 to 230 - 1] data – Type: [int, ...], Length: 8, Range: [0 to 255] length – Type: int, Range: [0 to 15]

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 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 set_read_filter()).

Instead of polling with this function, you can also use callbacks. See the enable_frame_read_callback() function and the CALLBACK_FRAME_READ callback.

The following constants are available for this function:

For frame_type:

• BrickletCAN.FRAME_TYPE_STANDARD_DATA = 0
• BrickletCAN.FRAME_TYPE_STANDARD_REMOTE = 1
• BrickletCAN.FRAME_TYPE_EXTENDED_DATA = 2
• BrickletCAN.FRAME_TYPE_EXTENDED_REMOTE = 3

BrickletCAN.set_configuration(baud_rate, transceiver_mode, write_timeout)¶

Parameters:	baud_rate – Type: int, Range: See constants, Default: 3 transceiver_mode – Type: int, Range: See constants, Default: 0 write_timeout – Type: int, Range: [-1 to 231 - 1], Default: 0
Returns:	None

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 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 (= -1): 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 following constants are available for this function:

For baud_rate:

• BrickletCAN.BAUD_RATE_10KBPS = 0
• BrickletCAN.BAUD_RATE_20KBPS = 1
• BrickletCAN.BAUD_RATE_50KBPS = 2
• BrickletCAN.BAUD_RATE_125KBPS = 3
• BrickletCAN.BAUD_RATE_250KBPS = 4
• BrickletCAN.BAUD_RATE_500KBPS = 5
• BrickletCAN.BAUD_RATE_800KBPS = 6
• BrickletCAN.BAUD_RATE_1000KBPS = 7

For transceiver_mode:

• BrickletCAN.TRANSCEIVER_MODE_NORMAL = 0
• BrickletCAN.TRANSCEIVER_MODE_LOOPBACK = 1
• BrickletCAN.TRANSCEIVER_MODE_READ_ONLY = 2

BrickletCAN.get_configuration()¶

Return Object:	baud_rate – Type: int, Range: See constants, Default: 3 transceiver_mode – Type: int, Range: See constants, Default: 0 write_timeout – Type: int, Range: [-1 to 231 - 1], Default: 0

Returns the configuration as set by set_configuration().

The following constants are available for this function:

For baud_rate:

• BrickletCAN.BAUD_RATE_10KBPS = 0
• BrickletCAN.BAUD_RATE_20KBPS = 1
• BrickletCAN.BAUD_RATE_50KBPS = 2
• BrickletCAN.BAUD_RATE_125KBPS = 3
• BrickletCAN.BAUD_RATE_250KBPS = 4
• BrickletCAN.BAUD_RATE_500KBPS = 5
• BrickletCAN.BAUD_RATE_800KBPS = 6
• BrickletCAN.BAUD_RATE_1000KBPS = 7

For transceiver_mode:

• BrickletCAN.TRANSCEIVER_MODE_NORMAL = 0
• BrickletCAN.TRANSCEIVER_MODE_LOOPBACK = 1
• BrickletCAN.TRANSCEIVER_MODE_READ_ONLY = 2

Advanced Functions¶

BrickletCAN.set_read_filter(mode, mask, filter1, filter2)¶

Parameters:	mode – Type: int, Range: See constants, Default: 1 mask – Type: int, Range: [0 to 230 - 1] filter1 – Type: int, Range: [0 to 230 - 1] filter2 – Type: int, Range: [0 to 230 - 1]
Returns:	None

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.

Mask Bit	Filter Bit	Identifier/Data Bit	Result
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 following constants are available for this function:

For mode:

• BrickletCAN.FILTER_MODE_DISABLED = 0
• BrickletCAN.FILTER_MODE_ACCEPT_ALL = 1
• BrickletCAN.FILTER_MODE_MATCH_STANDARD = 2
• BrickletCAN.FILTER_MODE_MATCH_STANDARD_AND_DATA = 3
• BrickletCAN.FILTER_MODE_MATCH_EXTENDED = 4

BrickletCAN.get_read_filter()¶

Return Object:	mode – Type: int, Range: See constants, Default: 1 mask – Type: int, Range: [0 to 230 - 1] filter1 – Type: int, Range: [0 to 230 - 1] filter2 – Type: int, Range: [0 to 230 - 1]

Returns the read filter as set by set_read_filter().

The following constants are available for this function:

For mode:

• BrickletCAN.FILTER_MODE_DISABLED = 0
• BrickletCAN.FILTER_MODE_ACCEPT_ALL = 1
• BrickletCAN.FILTER_MODE_MATCH_STANDARD = 2
• BrickletCAN.FILTER_MODE_MATCH_STANDARD_AND_DATA = 3
• BrickletCAN.FILTER_MODE_MATCH_EXTENDED = 4

BrickletCAN.get_error_log()¶

Return Object:	write_error_level – Type: int, Range: [0 to 255] read_error_level – Type: int, Range: [0 to 255] transceiver_disabled – Type: bool write_timeout_count – Type: int, Range: [0 to 232 - 1] read_register_overflow_count – Type: int, Range: [0 to 232 - 1] read_buffer_overflow_count – Type: int, Range: [0 to 232 - 1]

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 exceeds 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 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 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 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 read_frame() function. Using the CALLBACK_FRAME_READ callback ensures that the read buffer can not overflow.

BrickletCAN.get_identity()¶

Return Object:

uid – Type: str, Length: up to 8 connected_uid – Type: str, Length: up to 8 position – Type: chr, Range: ["a" to "h", "z"] hardware_version – Type: [int, ...], Length: 3 0: major – Type: int, Range: [0 to 255] 1: minor – Type: int, Range: [0 to 255] 2: revision – Type: int, Range: [0 to 255] firmware_version – Type: [int, ...], Length: 3 0: major – Type: int, Range: [0 to 255] 1: minor – Type: int, Range: [0 to 255] 2: revision – Type: int, Range: [0 to 255] device_identifier – Type: int, Range: [0 to 216 - 1]

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', 'd', 'e', 'f', 'g' or 'h' (Bricklet Port). A Bricklet connected to an Isolator Bricklet is always at position 'z'.

The device identifier numbers can be found here. There is also a constant for the device identifier of this Bricklet.

Callback Configuration Functions¶

BrickletCAN.register_callback(callback_id, function)¶

Parameters:	callback_id – Type: int function – Type: callable
Returns:	None

Registers the given function with the given callback_id.

The available callback IDs with corresponding function signatures are listed below.

BrickletCAN.enable_frame_read_callback()¶

Returns:	None

Enables the CALLBACK_FRAME_READ callback.

By default the callback is disabled. Enabling this callback will disable the CALLBACK_FRAME_READABLE callback.

BrickletCAN.disable_frame_read_callback()¶

Returns:	None

Disables the CALLBACK_FRAME_READ callback.

By default the callback is disabled.

BrickletCAN.is_frame_read_callback_enabled()¶

Returns:	enabled – Type: bool, Default: False

Returns true if the CALLBACK_FRAME_READ callback is enabled, false otherwise.

BrickletCAN.set_frame_readable_callback_configuration(enabled)¶

Parameters:	enabled – Type: bool, Default: False
Returns:	None

Enables/disables the CALLBACK_FRAME_READABLE callback.

By default the callback is disabled. Enabling this callback will disable the CALLBACK_FRAME_READ callback.

New in version 2.0.1 (Plugin).

BrickletCAN.get_frame_readable_callback_configuration()¶

Returns:	enabled – Type: bool, Default: False

Returns true if the CALLBACK_FRAME_READABLE callback is enabled, false otherwise.

New in version 2.0.1 (Plugin).

Callbacks¶

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the register_callback() function of the device object. The first parameter is the callback ID and the second parameter the callback function:

def my_callback(param):
    print(param)

can.register_callback(BrickletCAN.CALLBACK_EXAMPLE, my_callback)

The available constants with inherent number and type of parameters are described below.

BrickletCAN.CALLBACK_FRAME_READ¶

Callback Parameters:	frame_type – Type: int, Range: See constants identifier – Type: int, Range: [0 to 230 - 1] data – Type: [int, ...], Length: 8, Range: [0 to 255] length – Type: int, Range: [0 to 15]

This callback is triggered if a data or remote frame was received by the CAN transceiver.

The identifier return value follows the identifier format described for write_frame().

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

A configurable read filter can be used to define which frames should be received by the CAN transceiver at all (see set_read_filter()).

To enable this callback, use enable_frame_read_callback().

The following constants are available for this function:

For frame_type:

• BrickletCAN.FRAME_TYPE_STANDARD_DATA = 0
• BrickletCAN.FRAME_TYPE_STANDARD_REMOTE = 1
• BrickletCAN.FRAME_TYPE_EXTENDED_DATA = 2
• BrickletCAN.FRAME_TYPE_EXTENDED_REMOTE = 3

BrickletCAN.CALLBACK_FRAME_READABLE¶

Callback Parameters:	no parameters

This callback is triggered if a data or remote frame was received by the CAN transceiver. The received frame can be read with read_frame(). If additional frames are received, but read_frame() was not called yet, the callback will not trigger again.

A configurable read filter can be used to define which frames should be received by the CAN transceiver and put into the read queue (see set_read_filter()).

To enable this callback, use set_frame_readable_callback_configuration().

New in version 2.0.1 (Plugin).

Virtual Functions¶

Virtual functions don't communicate with the device itself, but operate only on the API bindings device object. They can be called without the corresponding IP Connection object being connected.

BrickletCAN.get_api_version()¶

Return Object:	api_version – Type: [int, ...], Length: 3 0: major – Type: int, Range: [0 to 255] 1: minor – Type: int, Range: [0 to 255] 2: revision – Type: int, Range: [0 to 255]

Returns the version of the API definition implemented by this API bindings. This is neither the release version of this API bindings nor does it tell you anything about the represented Brick or Bricklet.

BrickletCAN.get_response_expected(function_id)¶

Parameters:	function_id – Type: int, Range: See constants
Returns:	response_expected – Type: bool

Returns the response expected flag for the function specified by the function ID parameter. It is true if the function is expected to send a response, false otherwise.

For getter functions this is enabled by default and cannot be disabled, because those functions will always send a response. For callback configuration functions it is enabled by default too, but can be disabled by set_response_expected(). For setter functions it is disabled by default and can be enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is sent and errors are silently ignored, because they cannot be detected.

The following constants are available for this function:

For function_id:

• BrickletCAN.FUNCTION_ENABLE_FRAME_READ_CALLBACK = 3
• BrickletCAN.FUNCTION_DISABLE_FRAME_READ_CALLBACK = 4
• BrickletCAN.FUNCTION_SET_CONFIGURATION = 6
• BrickletCAN.FUNCTION_SET_READ_FILTER = 8
• BrickletCAN.FUNCTION_SET_FRAME_READABLE_CALLBACK_CONFIGURATION = 12

BrickletCAN.set_response_expected(function_id, response_expected)¶

Parameters:	function_id – Type: int, Range: See constants response_expected – Type: bool
Returns:	None

Changes the response expected flag of the function specified by the function ID parameter. This flag can only be changed for setter (default value: false) and callback configuration functions (default value: true). For getter functions it is always enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is sent and errors are silently ignored, because they cannot be detected.

The following constants are available for this function:

For function_id:

• BrickletCAN.FUNCTION_ENABLE_FRAME_READ_CALLBACK = 3
• BrickletCAN.FUNCTION_DISABLE_FRAME_READ_CALLBACK = 4
• BrickletCAN.FUNCTION_SET_CONFIGURATION = 6
• BrickletCAN.FUNCTION_SET_READ_FILTER = 8
• BrickletCAN.FUNCTION_SET_FRAME_READABLE_CALLBACK_CONFIGURATION = 12

BrickletCAN.set_response_expected_all(response_expected)¶

Parameters:	response_expected – Type: bool
Returns:	None

Changes the response expected flag for all setter and callback configuration functions of this device at once.

Constants¶

BrickletCAN.DEVICE_IDENTIFIER¶

This constant is used to identify a CAN Bricklet.

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

BrickletCAN.DEVICE_DISPLAY_NAME¶

This constant represents the human readable name of a CAN Bricklet.