C/C++ - CAN Bricklet

This is the description of the C/C++ 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 C/C++ API bindings is part of their general description.

Examples

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

Loopback

Download (example_loopback.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_can.h"

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

// Callback function for frame read callback
void cb_frame_read(uint8_t frame_type, uint32_t identifier, uint8_t data[8],
                   uint8_t length, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Frame Type: %d\n", frame_type);
    printf("Identifier: %d\n", identifier);
    printf("Data (Length: %d):", length);

    uint8_t i;
    for (i = 0; i < length && i < 8; ++i) {
        printf(" %d", data[i]);
    }

    printf("\n");
    printf("\n");
}

int main(void) {
    // Create IP connection
    IPConnection ipcon;
    ipcon_create(&ipcon);

    // Create device object
    CAN can;
    can_create(&can, UID, &ipcon);

    // Connect to brickd
    if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
        fprintf(stderr, "Could not connect\n");
        return 1;
    }
    // Don't use device before ipcon is connected

    // Configure transceiver for loopback mode
    can_set_configuration(&can, CAN_BAUD_RATE_1000KBPS, CAN_TRANSCEIVER_MODE_LOOPBACK, 0);

    // Register frame read callback to function cb_frame_read
    can_register_callback(&can,
                          CAN_CALLBACK_FRAME_READ,
                          (void *)cb_frame_read,
                          NULL);

    // Enable frame read callback
    can_enable_frame_read_callback(&can);

    // Write standard data frame with identifier 1742 and 3 bytes of data
    uint8_t data[8] = {42, 23, 17, 0, 0, 0, 0, 0};
    bool success;
    can_write_frame(&can, CAN_FRAME_TYPE_STANDARD_DATA, 1742, data, 3, &success);

    printf("Press key to exit\n");
    getchar();
    can_disable_frame_read_callback(&can);
    can_destroy(&can);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

API

Every function of the C/C++ bindings returns an integer which describes an error code. Data returned from the device, when a getter is called, is handled via call by reference. These parameters are labeled with the ret_ prefix.

Possible error codes are:

  • E_OK = 0
  • E_TIMEOUT = -1
  • E_NO_STREAM_SOCKET = -2
  • E_HOSTNAME_INVALID = -3
  • E_NO_CONNECT = -4
  • E_NO_THREAD = -5
  • E_NOT_ADDED = -6 (unused since bindings version 2.0.0)
  • E_ALREADY_CONNECTED = -7
  • E_NOT_CONNECTED = -8
  • E_INVALID_PARAMETER = -9
  • E_NOT_SUPPORTED = -10
  • E_UNKNOWN_ERROR_CODE = -11
  • E_STREAM_OUT_OF_SYNC = -12

as defined in ip_connection.h.

All functions listed below are thread-safe.

Basic Functions

void can_create(CAN *can, const char *uid, IPConnection *ipcon)

Creates the device object can with the unique device ID uid and adds it to the IPConnection ipcon:

CAN can;
can_create(&can, "YOUR_DEVICE_UID", &ipcon);

This device object can be used after the IP connection has been connected (see examples above).

void can_destroy(CAN *can)

Removes the device object can from its IPConnection and destroys it. The device object cannot be used anymore afterwards.

int can_write_frame(CAN *can, uint8_t frame_type, uint32_t identifier, uint8_t data[8], uint8_t length, bool *ret_success)

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 can_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 can_get_error_log()).

The following defines are available for this function:

  • CAN_FRAME_TYPE_STANDARD_DATA = 0
  • CAN_FRAME_TYPE_STANDARD_REMOTE = 1
  • CAN_FRAME_TYPE_EXTENDED_DATA = 2
  • CAN_FRAME_TYPE_EXTENDED_REMOTE = 3
int can_read_frame(CAN *can, bool *ret_success, uint8_t *ret_frame_type, uint32_t *ret_identifier, uint8_t ret_data[8], uint8_t *ret_length)

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 can_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 can_set_read_filter()).

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

The following defines are available for this function:

  • CAN_FRAME_TYPE_STANDARD_DATA = 0
  • CAN_FRAME_TYPE_STANDARD_REMOTE = 1
  • CAN_FRAME_TYPE_EXTENDED_DATA = 2
  • CAN_FRAME_TYPE_EXTENDED_REMOTE = 3
int can_set_configuration(CAN *can, uint8_t baud_rate, uint8_t transceiver_mode, int32_t write_timeout)

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 (< 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.

The following defines are available for this function:

  • CAN_BAUD_RATE_10KBPS = 0
  • CAN_BAUD_RATE_20KBPS = 1
  • CAN_BAUD_RATE_50KBPS = 2
  • CAN_BAUD_RATE_125KBPS = 3
  • CAN_BAUD_RATE_250KBPS = 4
  • CAN_BAUD_RATE_500KBPS = 5
  • CAN_BAUD_RATE_800KBPS = 6
  • CAN_BAUD_RATE_1000KBPS = 7
  • CAN_TRANSCEIVER_MODE_NORMAL = 0
  • CAN_TRANSCEIVER_MODE_LOOPBACK = 1
  • CAN_TRANSCEIVER_MODE_READ_ONLY = 2
int can_get_configuration(CAN *can, uint8_t *ret_baud_rate, uint8_t *ret_transceiver_mode, int32_t *ret_write_timeout)

Returns the configuration as set by can_set_configuration().

The following defines are available for this function:

  • CAN_BAUD_RATE_10KBPS = 0
  • CAN_BAUD_RATE_20KBPS = 1
  • CAN_BAUD_RATE_50KBPS = 2
  • CAN_BAUD_RATE_125KBPS = 3
  • CAN_BAUD_RATE_250KBPS = 4
  • CAN_BAUD_RATE_500KBPS = 5
  • CAN_BAUD_RATE_800KBPS = 6
  • CAN_BAUD_RATE_1000KBPS = 7
  • CAN_TRANSCEIVER_MODE_NORMAL = 0
  • CAN_TRANSCEIVER_MODE_LOOPBACK = 1
  • CAN_TRANSCEIVER_MODE_READ_ONLY = 2

Advanced Functions

int can_set_read_filter(CAN *can, uint8_t mode, uint32_t mask, uint32_t filter1, uint32_t filter2)

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 default mode is accept-all.

The following defines are available for this function:

  • CAN_FILTER_MODE_DISABLED = 0
  • CAN_FILTER_MODE_ACCEPT_ALL = 1
  • CAN_FILTER_MODE_MATCH_STANDARD = 2
  • CAN_FILTER_MODE_MATCH_STANDARD_AND_DATA = 3
  • CAN_FILTER_MODE_MATCH_EXTENDED = 4
int can_get_read_filter(CAN *can, uint8_t *ret_mode, uint32_t *ret_mask, uint32_t *ret_filter1, uint32_t *ret_filter2)

Returns the read filter as set by can_set_read_filter().

The following defines are available for this function:

  • CAN_FILTER_MODE_DISABLED = 0
  • CAN_FILTER_MODE_ACCEPT_ALL = 1
  • CAN_FILTER_MODE_MATCH_STANDARD = 2
  • CAN_FILTER_MODE_MATCH_STANDARD_AND_DATA = 3
  • CAN_FILTER_MODE_MATCH_EXTENDED = 4
int can_get_error_log(CAN *can, uint8_t *ret_write_error_level, uint8_t *ret_read_error_level, bool *ret_transceiver_disabled, uint32_t *ret_write_timeout_count, uint32_t *ret_read_register_overflow_count, uint32_t *ret_read_buffer_overflow_count)

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 can_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 can_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 can_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 can_read_frame() function. Using the CAN_CALLBACK_FRAME_READ callback ensures that the read buffer can not overflow.
int can_get_api_version(CAN *can, uint8_t ret_api_version[3])

Returns the version of the API definition (major, minor, revision) 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.

int can_get_response_expected(CAN *can, uint8_t function_id, bool *ret_response_expected)

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 can_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 send and errors are silently ignored, because they cannot be detected.

See can_set_response_expected() for the list of function ID defines available for this function.

int can_set_response_expected(CAN *can, uint8_t function_id, bool response_expected)

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 send and errors are silently ignored, because they cannot be detected.

The following function ID defines are available for this function:

  • CAN_FUNCTION_ENABLE_FRAME_READ_CALLBACK = 3
  • CAN_FUNCTION_DISABLE_FRAME_READ_CALLBACK = 4
  • CAN_FUNCTION_SET_CONFIGURATION = 6
  • CAN_FUNCTION_SET_READ_FILTER = 8
int can_set_response_expected_all(CAN *can, bool response_expected)

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

int can_get_identity(CAN *can, char ret_uid[8], char ret_connected_uid[8], char *ret_position, uint8_t ret_hardware_version[3], uint8_t ret_firmware_version[3], uint16_t *ret_device_identifier)

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. There is also a constant for the device identifier of this Bricklet.

Callback Configuration Functions

void can_register_callback(CAN *can, int16_t callback_id, void *function, void *user_data)

Registers the given function with the given callback_id. The user_data will be passed as the last parameter to the function.

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

int can_enable_frame_read_callback(CAN *can)

Enables the CAN_CALLBACK_FRAME_READ callback.

By default the callback is disabled.

int can_disable_frame_read_callback(CAN *can)

Disables the CAN_CALLBACK_FRAME_READ callback.

By default the callback is disabled.

int can_is_frame_read_callback_enabled(CAN *can, bool *ret_enabled)

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

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the can_register_callback() function. The parameters consist of the device object, the callback ID, the callback function and optional user data:

void my_callback(int p, void *user_data) {
    printf("parameter: %d\n", p);
}

can_register_callback(&can, CAN_CALLBACK_EXAMPLE, (void *)my_callback, NULL);

The available constants with corresponding callback function signatures 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.

CAN_CALLBACK_FRAME_READ
void callback(uint8_t frame_type, uint32_t identifier, uint8_t data[8], uint8_t length, void *user_data)

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 can_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 can_set_read_filter()).

To enable this callback, use can_enable_frame_read_callback().

The following defines are available for this function:

  • CAN_FRAME_TYPE_STANDARD_DATA = 0
  • CAN_FRAME_TYPE_STANDARD_REMOTE = 1
  • CAN_FRAME_TYPE_EXTENDED_DATA = 2
  • CAN_FRAME_TYPE_EXTENDED_REMOTE = 3

Constants

CAN_DEVICE_IDENTIFIER

This constant is used to identify a CAN Bricklet.

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

CAN_DEVICE_DISPLAY_NAME

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