Code

SAM D21 Xplained Pro.

#define PWM_MODULE      EXT1_PWM_MODULE

#define PWM_OUT_PIN     EXT1_PWM_0_PIN

#define PWM_OUT_MUX     EXT1_PWM_0_MUX

SAM D20 Xplained Pro.

#define PWM_MODULE      EXT1_PWM_MODULE

#define PWM_OUT_PIN     EXT1_PWM_0_PIN

#define PWM_OUT_MUX     EXT1_PWM_0_MUX

SAM R21 Xplained Pro.

#define PWM_MODULE      EXT1_PWM_MODULE

#define PWM_OUT_PIN     EXT1_PWM_0_PIN

#define PWM_OUT_MUX     EXT1_PWM_0_MUX

SAM D11 Xplained Pro.

#define PWM_MODULE      EXT1_PWM_MODULE

#define PWM_OUT_PIN     EXT1_PWM_0_PIN

#define PWM_OUT_MUX     EXT1_PWM_0_MUX

SAM L21 Xplained Pro.

#define PWM_MODULE      EXT2_PWM_MODULE

#define PWM_OUT_PIN     EXT2_PWM_0_PIN

#define PWM_OUT_MUX     EXT2_PWM_0_MUX

SAM L22 Xplained Pro.

#define PWM_MODULE      EXT3_PWM_MODULE

#define PWM_OUT_PIN     EXT3_PWM_0_PIN

#define PWM_OUT_MUX     EXT3_PWM_0_MUX

SAM DA1 Xplained Pro.

#define PWM_MODULE      EXT1_PWM_MODULE

#define PWM_OUT_PIN     EXT1_PWM_0_PIN

#define PWM_OUT_MUX     EXT1_PWM_0_MUX

SAM C21 Xplained Pro.

#define PWM_MODULE      EXT1_PWM_MODULE

#define PWM_OUT_PIN     EXT1_PWM_0_PIN

#define PWM_OUT_MUX     EXT1_PWM_0_MUX

Add to the main application source file, outside of any functions:

struct tc_module tc_instance;

Copy-paste the following callback function code to your user application:

void tc_callback_to_change_duty_cycle(
        struct tc_module *const module_inst)
{
    static uint16_t i = 0;

    i += 128;
    tc_set_compare_value(module_inst, TC_COMPARE_CAPTURE_CHANNEL_0, i + 1);
}

Copy-paste the following setup code to your user application:

void configure_tc(void)
{
    struct tc_config config_tc;
    tc_get_config_defaults(&config_tc);

    config_tc.counter_size    = TC_COUNTER_SIZE_16BIT;
    config_tc.wave_generation = TC_WAVE_GENERATION_NORMAL_PWM;
    config_tc.counter_16_bit.compare_capture_channel[0] = 0xFFFF;

    config_tc.pwm_channel[0].enabled = true;
    config_tc.pwm_channel[0].pin_out = PWM_OUT_PIN;
    config_tc.pwm_channel[0].pin_mux = PWM_OUT_MUX;

    tc_init(&tc_instance, PWM_MODULE, &config_tc);

    tc_enable(&tc_instance);
}

void configure_tc_callbacks(void)
{
    tc_register_callback(
            &tc_instance,
            tc_callback_to_change_duty_cycle,
            TC_CALLBACK_CC_CHANNEL0);

    tc_enable_callback(&tc_instance, TC_CALLBACK_CC_CHANNEL0);
}

Add to user application initialization (typically the start of main()):

configure_tc();
configure_tc_callbacks();