Software / API Bindings / Ruby / API Reference and Examples / Bricklets / CAN Bricklet

Ruby - CAN Bricklet¶

This is the description of the Ruby API bindings for the CAN Bricklet. General information and technical specifications for the CAN Bricklet are summarized in its hardware description.

An installation guide for the Ruby API bindings is part of their general description.

Examples¶

The example code below is Public Domain (CC0 1.0).

Loopback¶

Download (example_loopback.rb)

#!/usr/bin/env ruby
# -*- ruby encoding: utf-8 -*-

require 'tinkerforge/ip_connection'
require 'tinkerforge/bricklet_can'

include Tinkerforge

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

ipcon = IPConnection.new # Create IP connection
can = BrickletCAN.new 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 BrickletCAN::BAUD_RATE_1000KBPS, \
                      BrickletCAN::TRANSCEIVER_MODE_LOOPBACK, 0

# Register frame read callback
can.register_callback(BrickletCAN::CALLBACK_FRAME_READ) do |frame_type, identifier, data,
                                                            length|
  if frame_type == BrickletCAN::FRAME_TYPE_STANDARD_DATA
    puts "Frame Type: Standard Data"
  elsif frame_type == BrickletCAN::FRAME_TYPE_STANDARD_REMOTE
    puts "Frame Type: Standard Remote"
  elsif frame_type == BrickletCAN::FRAME_TYPE_EXTENDED_DATA
    puts "Frame Type: Extended Data"
  elsif frame_type == BrickletCAN::FRAME_TYPE_EXTENDED_REMOTE
    puts "Frame Type: Extended Remote"
  end

  puts "Identifier: #{identifier}"
  puts "Data (Length: #{length}): #{data[0, [length, 8].min].join(' ')}"
  puts ''
end

# Enable frame read callback
can.enable_frame_read_callback

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

puts 'Press key to exit'
$stdin.gets

can.disable_frame_read_callback

ipcon.disconnect

API¶

All functions listed below are thread-safe.

Basic Functions¶

BrickletCAN::new(uid, ipcon) → can¶

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

Creates an object with the unique device ID uid:

can = BrickletCAN.new 'YOUR_DEVICE_UID', ipcon

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

BrickletCAN#write_frame(frame_type, identifier, data, length) → bool¶

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 → [bool, int, int, [int, ...], int]¶

Return Array:	0: success – Type: bool 1: frame_type – Type: int, Range: See constants 2: identifier – Type: int, Range: [0 to 2³⁰ - 1] 3: data – Type: [int, ...], Length: 8, Range: [0 to 255] 4: 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) → nil¶

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

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 → [int, int, int]¶

Return Array:	0: baud_rate – Type: int, Range: See constants, Default: 3 1: transceiver_mode – Type: int, Range: See constants, Default: 0 2: 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) → nil¶

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]

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 → [int, int, int, int]¶

Return Array:	0: mode – Type: int, Range: See constants, Default: 1 1: mask – Type: int, Range: [0 to 2³⁰ - 1] 2: filter1 – Type: int, Range: [0 to 2³⁰ - 1] 3: 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 → [int, int, bool, int, int, int]¶

Return Array:	0: write_error_level – Type: int, Range: [0 to 255] 1: read_error_level – Type: int, Range: [0 to 255] 2: transceiver_disabled – Type: bool 3: write_timeout_count – Type: int, Range: [0 to 2³² - 1] 4: read_register_overflow_count – Type: int, Range: [0 to 2³² - 1] 5: 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 → [str, str, chr, [int, ...], [int, ...], int]¶

Return Array:

Return Array:	0: uid – Type: str, Length: up to 8 1: connected_uid – Type: str, Length: up to 8 2: position – Type: chr, Range: ['a' to 'h', 'z'] 3: 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] 4: 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] 5: device_identifier – Type: int, Range: [0 to 2¹⁶ - 1]

0: uid – Type: str, Length: up to 8
1: connected_uid – Type: str, Length: up to 8
2: position – Type: chr, Range: ['a' to 'h', 'z']
3: 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]

4: 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]

5: 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) { |param [, ...]| block } → nil¶

Parameters:	callback_id – Type: int

Registers the given block with the given callback_id.

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

BrickletCAN#enable_frame_read_callback → nil¶

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 → nil¶

Disables the ::CALLBACK_FRAME_READ callback.

By default the callback is disabled.

BrickletCAN#is_frame_read_callback_enabled → bool¶

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) → nil¶

Parameters:	enabled – Type: bool, Default: false

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 → bool¶

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 is a block:

can.register_callback BrickletCAN::CALLBACK_EXAMPLE, do |param|
  puts "#{param}"
end

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

Note

Using callbacks for recurring events is always preferred compared to using getters. It will use less USB bandwidth and the latency will be a lot better, since there is no round trip time.

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 → [int, ...]¶

Return Array:	0: 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) → bool¶

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) → nil¶

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

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.

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) → nil¶

Parameters:	response_expected – Type: bool

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.