Support » Tic Stepper Motor Controller User’s Guide » 12. Writing PC software to control the Tic »
12.11. Example code using the C API
<p>The code below uses the C API provided by the <a href="https://github.com/pololu/pololu-tic-software">Tic software</a> to send and receive data from a Tic over USB. This code is written in C and works on Windows, Linux, and macOS. For a very similar example using the C++ API, see <a href="/docs/0J71/12.12">Section 12.12</a>.</p>
<p>If you have compiled the Tic software from source and installed it on a Unix-like system (including MSYS2 on Windows), and copied the code below to a file named <code>code.c</code>, you should be able to compile the code below by running this command in a shell:</p>
<pre>
gcc code.c $(pkg-config libpololu-tic-1 --cflags --libs)</pre>
<p>You might notice that the Tic only performs the desired movement for about a second before it stops moving and the red LED turns on, indicating an error. This is because of the Tic’s command timeout feature: by default, the Tic’s “Command timeout” error will happen if it does not receive certain commands periodically (see <a href="/docs/0J71/5.4">Section 5.4</a> for details), causing the motor to stop. You can send a “Reset command timeout” command every second to get around this, or you can disable the command timeout feature using the Tic Control Center: uncheck the “Enable command timeout” checkbox in the “Serial” box.</p>
<pre name="code" class="c">
// Uses the Tic's C API to send and receive data from a Tic.
// NOTE: The Tic's control mode must be "Serial / I2C / USB".

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <tic.h>

bool handle_error(tic_error * error)
{
 if (error == NULL) { return false; }
 fprintf(stderr, "Error: %s\n", tic_error_get_message(error));
 tic_error_free(error);
 return true;
}

// Opens a handle to a Tic that can be used for communication.
//
// To open a handle to any Tic:
// tic_handle * handle = open_handle(NULL);
// To open a handle to the Tic with serial number 01234567:
// tic_handle * handle = open_handle("01234567");
tic_handle * open_handle(const char * desired_serial_number)
{
 tic_handle * handle = NULL;

 // Get a list of Tic devices connected via USB.
 tic_device ** list = NULL;
 size_t count = 0;
 tic_error * error = tic_list_connected_devices(&list, &count);
 if (handle_error(error)) { goto cleanup; }

 // Iterate through the list and select one device.
 tic_device * device = NULL;
 for (size_t i = 0; i < count; i++)
 {
 tic_device * candidate = list[i];

 if (desired_serial_number)
 {
 const char * serial_number = tic_device_get_serial_number(candidate);
 if (strcmp(serial_number, desired_serial_number))
 {
 // Found a device with the wrong serial number, so continue on to
 // the next device in the list.
 continue;
 }
 }

 // Select this device as the one we want to connect to, and break
 // out of the loop.
 device = candidate;
 break;
 }

 if (device == NULL)
 {
 fprintf(stderr, "Error: No device found.\n");
 goto cleanup;
 }

 error = tic_handle_open(device, &handle);
 if (handle_error(error)) { goto cleanup; }

cleanup:
 for (size_t i = 0; i < count; i++)
 {
 tic_device_free(list[i]);
 }
 tic_list_free(list);
 return handle;
}

int main()
{
 int exit_code = 1;
 tic_handle * handle = NULL;
 tic_variables * variables = NULL;

 handle = open_handle(NULL);
 if (handle == NULL) { goto cleanup; }

 tic_error * error = tic_get_variables(handle, &variables, false);
 if (handle_error(error)) { goto cleanup; }

 int32_t position = tic_variables_get_current_position(variables);
 printf("Current position is %d.\n", position);

 int32_t new_target = position > 0 ? -200 : 200;
 printf("Setting target position to %d.\n", new_target);

 error = tic_exit_safe_start(handle);
 if (handle_error(error)) { goto cleanup; }

 error = tic_set_target_position(handle, new_target);
 if (handle_error(error)) { goto cleanup; }

 exit_code = 0; // This program ran successfully.

cleanup:
 // Free the resources used by the variables.
 tic_variables_free(variables);

 // Call tic_handle_close() to free its resources and because Windows only
 // allows one open handle per device.
 // (Though, in this program, we are about to return from main, so the program
 // will exit and the operating system will do this for us very soon.)
 tic_handle_close(handle);

 return exit_code;
}</pre>
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