C/C++ - Servo Brick

This is the description of the C/C++ API bindings for the Servo Brick. General information and technical specifications for the Servo Brick 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).

Configuration

Download (example_configuration.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "brick_servo.h"

#define HOST "localhost"
#define PORT 4223
#define UID "XXYYZZ" // Change XXYYZZ to the UID of your Servo Brick

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

    // Create device object
    Servo servo;
    servo_create(&servo, 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 two servos with voltage 5.5V
    // Servo 1: Connected to port 0, period of 19.5ms, pulse width of 1 to 2ms
    //          and operating angle -100 to 100°
    //
    // Servo 2: Connected to port 5, period of 20ms, pulse width of 0.95
    //          to 1.95ms and operating angle -90 to 90°
    servo_set_output_voltage(&servo, 5500);

    servo_set_degree(&servo, 0, -10000, 10000);
    servo_set_pulse_width(&servo, 0, 1000, 2000);
    servo_set_period(&servo, 0, 19500);
    servo_set_acceleration(&servo, 0, 1000); // Slow acceleration
    servo_set_velocity(&servo, 0, 65535); // Full speed

    servo_set_degree(&servo, 5, -9000, 9000);
    servo_set_pulse_width(&servo, 5, 950, 1950);
    servo_set_period(&servo, 5, 20000);
    servo_set_acceleration(&servo, 5, 65535); // Full acceleration
    servo_set_velocity(&servo, 5, 65535); // Full speed

    servo_set_position(&servo, 0, 10000); // Set to most right position
    servo_enable(&servo, 0);

    servo_set_position(&servo, 5, -9000); // Set to most left position
    servo_enable(&servo, 5);

    printf("Press key to exit\n");
    getchar();
    servo_disable(&servo, 0);
    servo_disable(&servo, 5);
    servo_destroy(&servo);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

Callback

Download (example_callback.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "brick_servo.h"

#define HOST "localhost"
#define PORT 4223
#define UID "XXYYZZ" // Change XXYYZZ to the UID of your Servo Brick

// Use position reached callback to swing back and forth
void cb_position_reached(uint8_t servo_num, int16_t position, void *user_data) {
    Servo *servo = (Servo *)user_data;

    if(position == 9000) {
        printf("Position: 90°, going to -90°\n");
        servo_set_position(servo, servo_num, -9000);
    } else if(position == -9000) {
        printf("Position: -90°, going to 90°\n");
        servo_set_position(servo, servo_num, 9000);
    } else {
        printf("Error\n"); // Can only happen if another program sets position
    }
}

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

    // Create device object
    Servo servo;
    servo_create(&servo, 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

    // Register position reached callback to function cb_position_reached
    servo_register_callback(&servo,
                            SERVO_CALLBACK_POSITION_REACHED,
                            (void *)cb_position_reached,
                            &servo);

    // Enable position reached callback
    servo_enable_position_reached_callback(&servo);

    // Set velocity to 100°/s. This has to be smaller or equal to the
    // maximum velocity of the servo you are using, otherwise the position
    // reached callback will be called too early
    servo_set_velocity(&servo, 0, 10000);
    servo_set_position(&servo, 0, 9000);
    servo_enable(&servo, 0);

    printf("Press key to exit\n");
    getchar();
    servo_disable(&servo, 0);
    servo_destroy(&servo);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

PWM Generator

Download (example_pwm_generator.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "brick_servo.h"

#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change to your UID

// Due to the internal clock dividing mechanism of the Servo Brick not all
// arbitrary PWM frequency values can be achieved. For example, the upper most
// three available PWM frequency values are 1MHz, 500kHz and 250kHz. The steps
// are coarser on the high frequency end and much finer on the low end. You can
// set any value here between 15Hz and 1MHz and the Servo Brick will try to
// match it as closely as possible.
#define PWM_FREQUENCY 175000 // in Hz [15Hz to 1MHz]
#define PWM_DUTY_CYCLE 20 // in % [0% to 100%]

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

    // Create device object
    Servo servo;
    servo_create(&servo, 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

    // Set degree range to 0-100, this will allow to
    // set the PWM duty cycle in 1% steps
    servo_set_degree(&servo, 0, 0, 100);

    // Set PWM frequency (1-65535µs == 1MHz-15Hz)
    int period = 1000000 / PWM_FREQUENCY;

    if (period < 1) {
        period = 1; // 1MHz
    } else if (period > 65535) {
        period = 65535; // ~15Hz
    }

    servo_set_pulse_width(&servo, 0, 0, period);
    servo_set_period(&servo, 0, period);

    // Fast acceleration and full speed
    servo_set_acceleration(&servo, 0, 65535);
    servo_set_velocity(&servo, 0, 65535);

    // Set PWM duty cycle (0-100 %)
    int position = PWM_DUTY_CYCLE;

    if (position < 0) {
        position = 0;
    } else if (position > 100) {
        position = 100;
    }

    servo_set_position(&servo, 0, position);

    // Enable PWM signal
    servo_enable(&servo, 0);

    printf("Press key to exit\n");
    getchar();
    servo_disable(&servo, 0);
    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.

Every function of the Servo Brick API that has a servo_num parameter can address a servo with the servo number (0 to 6). If it is a setter function then multiple servos can be addressed at once with a bitmask for the servos, if the highest bit is set. For example: 1 will address servo 1, (1 << 1) | (1 << 5) | (1 << 7) will address servos 1 and 5, 0xFF will address all seven servos, etc. This allows to set configurations to several servos with one function call. It is guaranteed that the changes will take effect in the same PWM period for all servos you specified in the bitmask.

Basic Functions

void servo_create(Servo *servo, const char *uid, IPConnection *ipcon)

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

Servo servo;
servo_create(&servo, "YOUR_DEVICE_UID", &ipcon);

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

void servo_destroy(Servo *servo)

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

int servo_enable(Servo *servo, uint8_t servo_num)

Enables a servo (0 to 6). If a servo is enabled, the configured position, velocity, acceleration, etc. are applied immediately.

int servo_disable(Servo *servo, uint8_t servo_num)

Disables a servo (0 to 6). Disabled servos are not driven at all, i.e. a disabled servo will not hold its position if a load is applied.

int servo_is_enabled(Servo *servo, uint8_t servo_num, bool *ret_enabled)

Returns true if the specified servo is enabled, false otherwise.

int servo_set_position(Servo *servo, uint8_t servo_num, int16_t position)

Sets the position in °/100 for the specified servo.

The default range of the position is -9000 to 9000, but it can be specified according to your servo with servo_set_degree().

If you want to control a linear servo or RC brushless motor controller or similar with the Servo Brick, you can also define lengths or speeds with servo_set_degree().

int servo_get_position(Servo *servo, uint8_t servo_num, int16_t *ret_position)

Returns the position of the specified servo as set by servo_set_position().

int servo_get_current_position(Servo *servo, uint8_t servo_num, int16_t *ret_position)

Returns the current position of the specified servo. This may not be the value of servo_set_position() if the servo is currently approaching a position goal.

int servo_set_velocity(Servo *servo, uint8_t servo_num, uint16_t velocity)

Sets the maximum velocity of the specified servo in °/100s. The velocity is accelerated according to the value set by servo_set_acceleration().

The minimum velocity is 0 (no movement) and the maximum velocity is 65535. With a value of 65535 the position will be set immediately (no velocity).

The default value is 65535.

int servo_get_velocity(Servo *servo, uint8_t servo_num, uint16_t *ret_velocity)

Returns the velocity of the specified servo as set by servo_set_velocity().

int servo_get_current_velocity(Servo *servo, uint8_t servo_num, uint16_t *ret_velocity)

Returns the current velocity of the specified servo. This may not be the value of servo_set_velocity() if the servo is currently approaching a velocity goal.

int servo_set_acceleration(Servo *servo, uint8_t servo_num, uint16_t acceleration)

Sets the acceleration of the specified servo in °/100s².

The minimum acceleration is 1 and the maximum acceleration is 65535. With a value of 65535 the velocity will be set immediately (no acceleration).

The default value is 65535.

int servo_get_acceleration(Servo *servo, uint8_t servo_num, uint16_t *ret_acceleration)

Returns the acceleration for the specified servo as set by servo_set_acceleration().

int servo_set_output_voltage(Servo *servo, uint16_t voltage)

Sets the output voltages with which the servos are driven in mV. The minimum output voltage is 2000mV and the maximum output voltage is 9000mV.

Note

We recommend that you set this value to the maximum voltage that is specified for your servo, most servos achieve their maximum force only with high voltages.

The default value is 5000.

int servo_get_output_voltage(Servo *servo, uint16_t *ret_voltage)

Returns the output voltage as specified by servo_set_output_voltage().

int servo_set_pulse_width(Servo *servo, uint8_t servo_num, uint16_t min, uint16_t max)

Sets the minimum and maximum pulse width of the specified servo in µs.

Usually, servos are controlled with a PWM, whereby the length of the pulse controls the position of the servo. Every servo has different minimum and maximum pulse widths, these can be specified with this function.

If you have a datasheet for your servo that specifies the minimum and maximum pulse width, you should set the values accordingly. If your servo comes without any datasheet you have to find the values via trial and error.

Both values have a range from 1 to 65535 (unsigned 16-bit integer). The minimum must be smaller than the maximum.

The default values are 1000µs (1ms) and 2000µs (2ms) for minimum and maximum pulse width.

int servo_get_pulse_width(Servo *servo, uint8_t servo_num, uint16_t *ret_min, uint16_t *ret_max)

Returns the minimum and maximum pulse width for the specified servo as set by servo_set_pulse_width().

int servo_set_degree(Servo *servo, uint8_t servo_num, int16_t min, int16_t max)

Sets the minimum and maximum degree for the specified servo (by default given as °/100).

This only specifies the abstract values between which the minimum and maximum pulse width is scaled. For example: If you specify a pulse width of 1000µs to 2000µs and a degree range of -90° to 90°, a call of servo_set_position() with 0 will result in a pulse width of 1500µs (-90° = 1000µs, 90° = 2000µs, etc.).

Possible usage:

  • The datasheet of your servo specifies a range of 200° with the middle position at 110°. In this case you can set the minimum to -9000 and the maximum to 11000.
  • You measure a range of 220° on your servo and you don't have or need a middle position. In this case you can set the minimum to 0 and the maximum to 22000.
  • You have a linear servo with a drive length of 20cm, In this case you could set the minimum to 0 and the maximum to 20000. Now you can set the Position with servo_set_position() with a resolution of cm/100. Also the velocity will have a resolution of cm/100s and the acceleration will have a resolution of cm/100s².
  • You don't care about units and just want the highest possible resolution. In this case you should set the minimum to -32767 and the maximum to 32767.
  • You have a brushless motor with a maximum speed of 10000 rpm and want to control it with a RC brushless motor controller. In this case you can set the minimum to 0 and the maximum to 10000. servo_set_position() now controls the rpm.

Both values have a possible range from -32767 to 32767 (signed 16-bit integer). The minimum must be smaller than the maximum.

The default values are -9000 and 9000 for the minimum and maximum degree.

int servo_get_degree(Servo *servo, uint8_t servo_num, int16_t *ret_min, int16_t *ret_max)

Returns the minimum and maximum degree for the specified servo as set by servo_set_degree().

int servo_set_period(Servo *servo, uint8_t servo_num, uint16_t period)

Sets the period of the specified servo in µs.

Usually, servos are controlled with a PWM. Different servos expect PWMs with different periods. Most servos run well with a period of about 20ms.

If your servo comes with a datasheet that specifies a period, you should set it accordingly. If you don't have a datasheet and you have no idea what the correct period is, the default value (19.5ms) will most likely work fine.

The minimum possible period is 1µs and the maximum is 65535µs.

The default value is 19.5ms (19500µs).

int servo_get_period(Servo *servo, uint8_t servo_num, uint16_t *ret_period)

Returns the period for the specified servo as set by servo_set_period().

int servo_get_servo_current(Servo *servo, uint8_t servo_num, uint16_t *ret_current)

Returns the current consumption of the specified servo in mA.

int servo_get_overall_current(Servo *servo, uint16_t *ret_current)

Returns the current consumption of all servos together in mA.

int servo_get_stack_input_voltage(Servo *servo, uint16_t *ret_voltage)

Returns the stack input voltage in mV. The stack input voltage is the voltage that is supplied via the stack, i.e. it is given by a Step-Down or Step-Up Power Supply.

int servo_get_external_input_voltage(Servo *servo, uint16_t *ret_voltage)

Returns the external input voltage in mV. The external input voltage is given via the black power input connector on the Servo Brick.

If there is an external input voltage and a stack input voltage, the motors will be driven by the external input voltage. If there is only a stack voltage present, the motors will be driven by this voltage.

Warning

This means, if you have a high stack voltage and a low external voltage, the motors will be driven with the low external voltage. If you then remove the external connection, it will immediately be driven by the high stack voltage

Advanced Functions

int servo_get_api_version(Servo *servo, 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 servo_get_response_expected(Servo *servo, 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 servo_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 servo_set_response_expected() for the list of function ID defines available for this function.

int servo_set_response_expected(Servo *servo, 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:

  • SERVO_FUNCTION_ENABLE = 1
  • SERVO_FUNCTION_DISABLE = 2
  • SERVO_FUNCTION_SET_POSITION = 4
  • SERVO_FUNCTION_SET_VELOCITY = 7
  • SERVO_FUNCTION_SET_ACCELERATION = 10
  • SERVO_FUNCTION_SET_OUTPUT_VOLTAGE = 12
  • SERVO_FUNCTION_SET_PULSE_WIDTH = 14
  • SERVO_FUNCTION_SET_DEGREE = 16
  • SERVO_FUNCTION_SET_PERIOD = 18
  • SERVO_FUNCTION_SET_MINIMUM_VOLTAGE = 24
  • SERVO_FUNCTION_ENABLE_POSITION_REACHED_CALLBACK = 29
  • SERVO_FUNCTION_DISABLE_POSITION_REACHED_CALLBACK = 30
  • SERVO_FUNCTION_ENABLE_VELOCITY_REACHED_CALLBACK = 32
  • SERVO_FUNCTION_DISABLE_VELOCITY_REACHED_CALLBACK = 33
  • SERVO_FUNCTION_SET_SPITFP_BAUDRATE_CONFIG = 231
  • SERVO_FUNCTION_SET_SPITFP_BAUDRATE = 234
  • SERVO_FUNCTION_ENABLE_STATUS_LED = 238
  • SERVO_FUNCTION_DISABLE_STATUS_LED = 239
  • SERVO_FUNCTION_RESET = 243
int servo_set_response_expected_all(Servo *servo, bool response_expected)

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

int servo_set_spitfp_baudrate_config(Servo *servo, bool enable_dynamic_baudrate, uint32_t minimum_dynamic_baudrate)

The SPITF protocol can be used with a dynamic baudrate. If the dynamic baudrate is enabled, the Brick will try to adapt the baudrate for the communication between Bricks and Bricklets according to the amount of data that is transferred.

The baudrate will be increased exponentially if lots of data is send/received and decreased linearly if little data is send/received.

This lowers the baudrate in applications where little data is transferred (e.g. a weather station) and increases the robustness. If there is lots of data to transfer (e.g. Thermal Imaging Bricklet) it automatically increases the baudrate as needed.

In cases where some data has to transferred as fast as possible every few seconds (e.g. RS485 Bricklet with a high baudrate but small payload) you may want to turn the dynamic baudrate off to get the highest possible performance.

The maximum value of the baudrate can be set per port with the function servo_set_spitfp_baudrate(). If the dynamic baudrate is disabled, the baudrate as set by servo_set_spitfp_baudrate() will be used statically.

The minimum dynamic baudrate has a value range of 400000 to 2000000 baud.

By default dynamic baudrate is enabled and the minimum dynamic baudrate is 400000.

New in version 2.3.4 (Firmware).

int servo_get_spitfp_baudrate_config(Servo *servo, bool *ret_enable_dynamic_baudrate, uint32_t *ret_minimum_dynamic_baudrate)

Returns the baudrate config, see servo_set_spitfp_baudrate_config().

New in version 2.3.4 (Firmware).

int servo_get_send_timeout_count(Servo *servo, uint8_t communication_method, uint32_t *ret_timeout_count)

Returns the timeout count for the different communication methods.

The methods 0-2 are available for all Bricks, 3-7 only for Master Bricks.

This function is mostly used for debugging during development, in normal operation the counters should nearly always stay at 0.

The following defines are available for this function:

  • SERVO_COMMUNICATION_METHOD_NONE = 0
  • SERVO_COMMUNICATION_METHOD_USB = 1
  • SERVO_COMMUNICATION_METHOD_SPI_STACK = 2
  • SERVO_COMMUNICATION_METHOD_CHIBI = 3
  • SERVO_COMMUNICATION_METHOD_RS485 = 4
  • SERVO_COMMUNICATION_METHOD_WIFI = 5
  • SERVO_COMMUNICATION_METHOD_ETHERNET = 6
  • SERVO_COMMUNICATION_METHOD_WIFI_V2 = 7

New in version 2.3.2 (Firmware).

int servo_set_spitfp_baudrate(Servo *servo, char bricklet_port, uint32_t baudrate)

Sets the baudrate for a specific Bricklet port ('a' - 'd'). The baudrate can be in the range 400000 to 2000000.

If you want to increase the throughput of Bricklets you can increase the baudrate. If you get a high error count because of high interference (see servo_get_spitfp_error_count()) you can decrease the baudrate.

If the dynamic baudrate feature is enabled, the baudrate set by this function corresponds to the maximum baudrate (see servo_set_spitfp_baudrate_config()).

Regulatory testing is done with the default baudrate. If CE compatibility or similar is necessary in you applications we recommend to not change the baudrate.

The default baudrate for all ports is 1400000.

New in version 2.3.2 (Firmware).

int servo_get_spitfp_baudrate(Servo *servo, char bricklet_port, uint32_t *ret_baudrate)

Returns the baudrate for a given Bricklet port, see servo_set_spitfp_baudrate().

New in version 2.3.2 (Firmware).

int servo_get_spitfp_error_count(Servo *servo, char bricklet_port, uint32_t *ret_error_count_ack_checksum, uint32_t *ret_error_count_message_checksum, uint32_t *ret_error_count_frame, uint32_t *ret_error_count_overflow)

Returns the error count for the communication between Brick and Bricklet.

The errors are divided into

  • ACK checksum errors,
  • message checksum errors,
  • framing errors and
  • overflow errors.

The errors counts are for errors that occur on the Brick side. All Bricklets have a similar function that returns the errors on the Bricklet side.

New in version 2.3.2 (Firmware).

int servo_enable_status_led(Servo *servo)

Enables the status LED.

The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

The default state is enabled.

New in version 2.3.1 (Firmware).

int servo_disable_status_led(Servo *servo)

Disables the status LED.

The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

The default state is enabled.

New in version 2.3.1 (Firmware).

int servo_is_status_led_enabled(Servo *servo, bool *ret_enabled)

Returns true if the status LED is enabled, false otherwise.

New in version 2.3.1 (Firmware).

int servo_get_protocol1_bricklet_name(Servo *servo, char port, uint8_t *ret_protocol_version, uint8_t ret_firmware_version[3], char ret_name[40])

Returns the firmware and protocol version and the name of the Bricklet for a given port.

This functions sole purpose is to allow automatic flashing of v1.x.y Bricklet plugins.

int servo_get_chip_temperature(Servo *servo, int16_t *ret_temperature)

Returns the temperature in °C/10 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 an accuracy of +-15%. Practically it is only useful as an indicator for temperature changes.

int servo_reset(Servo *servo)

Calling this function will reset the Brick. Calling this function on a Brick inside of a stack will reset the whole stack.

After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!

int servo_get_identity(Servo *servo, 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 Brick is connected to, the position, the hardware and firmware version as well as the device identifier.

The position can be '0'-'8' (stack position).

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

Callback Configuration Functions

void servo_register_callback(Servo *servo, 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 servo_set_minimum_voltage(Servo *servo, uint16_t voltage)

Sets the minimum voltage in mV, below which the SERVO_CALLBACK_UNDER_VOLTAGE callback is triggered. The minimum possible value that works with the Servo Brick is 5V. You can use this function to detect the discharge of a battery that is used to drive the stepper motor. If you have a fixed power supply, you likely do not need this functionality.

The default value is 5V (5000mV).

int servo_get_minimum_voltage(Servo *servo, uint16_t *ret_voltage)

Returns the minimum voltage as set by servo_set_minimum_voltage()

int servo_enable_position_reached_callback(Servo *servo)

Enables the SERVO_CALLBACK_POSITION_REACHED callback.

Default is disabled.

New in version 2.0.1 (Firmware).

int servo_disable_position_reached_callback(Servo *servo)

Disables the SERVO_CALLBACK_POSITION_REACHED callback.

Default is disabled.

New in version 2.0.1 (Firmware).

int servo_is_position_reached_callback_enabled(Servo *servo, bool *ret_enabled)

Returns true if SERVO_CALLBACK_POSITION_REACHED callback is enabled, false otherwise.

New in version 2.0.1 (Firmware).

int servo_enable_velocity_reached_callback(Servo *servo)

Enables the SERVO_CALLBACK_VELOCITY_REACHED callback.

Default is disabled.

New in version 2.0.1 (Firmware).

int servo_disable_velocity_reached_callback(Servo *servo)

Disables the SERVO_CALLBACK_VELOCITY_REACHED callback.

Default is disabled.

New in version 2.0.1 (Firmware).

int servo_is_velocity_reached_callback_enabled(Servo *servo, bool *ret_enabled)

Returns true if SERVO_CALLBACK_VELOCITY_REACHED callback is enabled, false otherwise.

New in version 2.0.1 (Firmware).

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the servo_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);
}

servo_register_callback(&servo, SERVO_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.

SERVO_CALLBACK_UNDER_VOLTAGE
void callback(uint16_t voltage, void *user_data)

This callback is triggered when the input voltage drops below the value set by servo_set_minimum_voltage(). The parameter is the current voltage given in mV.

SERVO_CALLBACK_POSITION_REACHED
void callback(uint8_t servo_num, int16_t position, void *user_data)

This callback is triggered when a position set by servo_set_position() is reached. If the new position matches the current position then the callback is not triggered, because the servo didn't move. The parameters are the servo and the position that is reached.

You can enable this callback with servo_enable_position_reached_callback().

Note

Since we can't get any feedback from the servo, this only works if the velocity (see servo_set_velocity()) is set smaller or equal to the maximum velocity of the servo. Otherwise the servo will lag behind the control value and the callback will be triggered too early.

SERVO_CALLBACK_VELOCITY_REACHED
void callback(uint8_t servo_num, int16_t velocity, void *user_data)

This callback is triggered when a velocity set by servo_set_velocity() is reached. The parameters are the servo and the velocity that is reached.

You can enable this callback with servo_enable_velocity_reached_callback().

Note

Since we can't get any feedback from the servo, this only works if the acceleration (see servo_set_acceleration()) is set smaller or equal to the maximum acceleration of the servo. Otherwise the servo will lag behind the control value and the callback will be triggered too early.

Constants

SERVO_DEVICE_IDENTIFIER

This constant is used to identify a Servo Brick.

The servo_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.

SERVO_DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Servo Brick.