This is the description of the Shell API bindings for the CAN Bricklet 2.0. General information and technical specifications for the CAN Bricklet 2.0 are summarized in its hardware description.
An installation guide for the Shell API bindings is part of their general description.
The example code below is Public Domain (CC0 1.0).
Download (example-loopback.sh)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | #!/bin/sh
# Connects to localhost:4223 by default, use --host and --port to change this
uid=XYZ # Change XYZ to the UID of your CAN Bricklet 2.0
# Configure transceiver for loopback mode
tinkerforge call can-v2-bricklet $uid set-transceiver-configuration 1000000 625 transceiver-mode-loopback
# Handle incoming frame read callbacks
tinkerforge dispatch can-v2-bricklet $uid frame-read &
# Enable frame read callback
tinkerforge call can-v2-bricklet $uid set-frame-read-callback-configuration true
# Write standard data frame with identifier 1742 and 3 bytes of data
tinkerforge call can-v2-bricklet $uid write-frame frame-type-standard-data 1742 42,23,17
echo "Press key to exit"; read dummy
tinkerforge call can-v2-bricklet $uid set-frame-read-callback-configuration false
kill -- -$$ # Stop callback dispatch in background
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Possible exit codes for all tinkerforge commands are:
The common options of the call and dispatch commands are documented here. The specific command structure is shown below.
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The call command is used to call a function of the CAN Bricklet 2.0. It can take several options:
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The dispatch command is used to dispatch a callback of the CAN Bricklet 2.0. It can take several options:
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The <function> to be called can take different options depending of its kind. All functions can take the following options:
Getter functions can take the following options:
Setter functions can take the following options:
The --expect-response option for setter functions allows to detect timeouts and other error conditions calls of setters as well. The device will then send a response for this purpose. If this option is not given for a setter function then no response is send and errors are silently ignored, because they cannot be detected.
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The <callback> to be dispatched can take several options:
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Writes a data or remote frame to the write queue to be transmitted over the CAN transceiver.
The Bricklet supports the standard 11-bit (CAN 2.0A) and the additional extended 29-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 uses bit 0 to 28 from the identifier parameter as extended 29-bit identifier.
The data parameter can be up to 15 bytes long. For data frames up to 8 bytes will be used as the actual data. The length (DLC) field in the data or remote frame will be set to the actual length of the data parameter. This allows to transmit data and remote frames with excess length. For remote frames only the length of the data parameter is used. The actual data bytes are ignored.
Returns true if the frame was successfully added to the write queue. Returns false if the frame could not be added because write queue is already full or because the write buffer or the write backlog are configured with a size of zero (see set-queue-configuration).
The write queue 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-transceiver-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 symbols are available for this function:
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Tries to read the next data or remote frame from the read queue and returns 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 queue 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.
The data return value can be up to 15 bytes long. For data frames up to the first 8 bytes are the actual received data. All bytes after the 8th byte are always zero and only there to indicate the length of a data or remote frame with excess length. For remote frames the length of the data return value represents the requested length. The actual data bytes are always zero.
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-configuration).
Instead of polling with this function, you can also use callbacks. See the set-frame-read-callback-configuration function and the frame-read callback.
The following symbols are available for this function:
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Output: | no output |
Sets the transceiver configuration for the CAN bus communication.
The baud rate can be configured in bit/s between 10 and 1000 kbit/s and the sample point can be configured in 1/10 % between 50 and 90 %.
The CAN transceiver has three different modes:
The default is: 125 kbit/s, 62.5 % and normal transceiver mode.
The following symbols are available for this function:
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Returns the configuration as set by set-transceiver-configuration.
The following symbols are available for this function:
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Output: | no output |
Sets the write and read queue configuration.
The CAN transceiver has 32 buffers in total in hardware for transmitting and receiving frames. Additionally, the Bricklet has a backlog for 768 frames in total in software. The buffers and the backlog can be freely assigned to the write and read queues.
write-frame writes a frame into the write backlog. The Bricklet moves the frame from the backlog into a free write buffer. The CAN transceiver then transmits the frame from the write buffer to the CAN bus. If there are no write buffers (write_buffer_size is zero) or there is no write backlog (write_backlog_size is zero) then no frames can be transmitted and write-frame returns always false.
The CAN transceiver receives a frame from the CAN bus and stores it into a free read buffer. The Bricklet moves the frame from the read buffer into the read backlog. read-frame reads the frame from the read backlog and returns it. If there are no read buffers (read_buffer_sizes is empty) or there is no read backlog (read_backlog_size is zero) then no frames can be received and read-frame returns always false.
There can be multiple read buffers, because the CAN transceiver cannot receive data and remote frames into the same read buffer. A positive read buffer size represents a data frame read buffer and a negative read buffer size represents a remote frame read buffer. A read buffer size of zero is not allowed. By default the first read buffer is configured for data frames and the second read buffer is configured for remote frame. There can be up to 32 different read buffers, assuming that no write buffer is used. Each read buffer has its own filter configuration (see set-read-filter-configuration).
A valid queue configuration fulfills these conditions:
write_buffer_size + read_buffer_size_0 + read_buffer_size_1 + ... + read_buffer_size_31 <= 32
write_backlog_size + read_backlog_size <= 768
The write buffer timeout has three different modes that define how a failed frame transmission should be handled:
The current content of the queues is lost when this function is called.
The default is:
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Returns the queue configuration as set by set-queue-configuration.
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Output: | no output |
Set the read filter configuration for the given read buffer index. 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 four different modes that define if and how the filter mask and the filter identifier are applied:
The filter mask and filter identifier are used as bit masks. Their usage depends on the mode:
The filter mask and filter identifier are applied in this way: The filter mask is used to select the frame identifier bits that should be compared to the corresponding filter identifier bits. All unselected bits are automatically accepted. All selected bits have to match the filter identifier to be accepted. If all bits for the selected mode are accepted then the frame is accepted and is added to the read buffer.
Filter Mask Bit | Filter Identifier Bit | Frame Identifier Bit | Result |
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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-Only with 0x7FF as mask and 0x123 as identifier. 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.
There can be up to 32 different read filters configured at the same time, because there can be up to 32 read buffer (see set-queue-configuration).
The default mode is accept-all for all read buffers.
The following symbols are available for this function:
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Returns the read filter configuration as set by set-read-filter-configuration.
The following symbols are available for this function:
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Returns information about different kinds of errors.
The write and read error levels indicate the current level of stuffing, form, acknowledgement, bit and checksum errors during CAN bus write and read operations. For each of this error kinds there is also an individual counter.
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 buffer timeout, read buffer and backlog overflow counts represents the number of these errors:
The read buffer overflow counter counts the overflows of all configured read buffers. Which read buffer exactly suffered from an overflow can be figured out from the read buffer overflow occurrence list (read_buffer_overflow_error_occurred).
The following symbols are available for this function:
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Output: | no output |
Sets the communication LED configuration. By default the LED shows CAN-Bus traffic, it flickers once for every 40 transmitted or received frames.
You can also turn the LED permanently on/off or show a heartbeat.
If the Bricklet is in bootloader mode, the LED is off.
The following symbols are available for this function:
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Returns the configuration as set by set-communication-led-config
The following symbols are available for this function:
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Output: | no output |
Sets the error LED configuration.
By default (show-transceiver-state) the error LED turns on if the CAN transceiver is passive or disabled state (see get-error-log). If the CAN transceiver is in active state the LED turns off.
If the LED is configured as show-error then the error LED turns on if any error occurs. If you call this function with the show-error option again, the LED will turn off until the next error occurs.
You can also turn the LED permanently on/off or show a heartbeat.
If the Bricklet is in bootloader mode, the LED is off.
The following symbols are available for this function:
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Returns the configuration as set by set-error-led-config.
The following symbols are available for this function:
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Returns the error count for the communication between Brick and Bricklet.
The errors are divided into
The errors counts are for errors that occur on the Bricklet side. All Bricks have a similar function that returns the errors on the Brick side.
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Sets the bootloader mode and returns the status after the requested mode change was instigated.
You can change from bootloader mode to firmware mode and vice versa. A change from bootloader mode to firmware mode will only take place if the entry function, device identifier and CRC are present and correct.
This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.
The following symbols are available for this function:
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Returns the current bootloader mode, see set-bootloader-mode.
The following symbols are available for this function:
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Output: | no output |
Sets the firmware pointer for write-firmware. The pointer has to be increased by chunks of size 64. The data is written to flash every 4 chunks (which equals to one page of size 256).
This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.
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Writes 64 Bytes of firmware at the position as written by set-write-firmware-pointer before. The firmware is written to flash every 4 chunks.
You can only write firmware in bootloader mode.
This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.
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Output: | no output |
Sets the status LED configuration. By default the LED shows communication traffic between Brick and Bricklet, it flickers once for every 10 received data packets.
You can also turn the LED permanently on/off or show a heartbeat.
If the Bricklet is in bootloader mode, the LED is will show heartbeat by default.
The following symbols are available for this function:
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Returns the configuration as set by set-status-led-config
The following symbols are available for this function:
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Returns the temperature in °C as measured inside the microcontroller. The value returned is not the ambient temperature!
The temperature is only proportional to the real temperature and it has bad accuracy. Practically it is only useful as an indicator for temperature changes.
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Calling this function will reset the Bricklet. All configurations will be lost.
After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!
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Output: | no output |
Writes a new UID into flash. If you want to set a new UID you have to decode the Base58 encoded UID string into an integer first.
We recommend that you use Brick Viewer to change the UID.
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Returns the current UID as an integer. Encode as Base58 to get the usual string version.
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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 here.
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Output: | no output |
Enables and disables the frame-read callback.
By default the callback is disabled.
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Returns true if the frame-read callback is enabled, false otherwise.
Callbacks can be used to receive time critical or recurring data from the device:
tinkerforge dispatch can-v2-bricklet <uid> example
The available callbacks 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.
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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 details on the data return value see read-frame.
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-queue-configuration).
To enable this callback, use set-frame-read-callback-configuration.
The following symbols are available for this function: