Workflow

1.
Configure some GPIO port pins for input and output.
```
config_port_pins();
```
2.
Lock peripheral access for the PORT module; attempting to update the module while it is in a protected state will cause a CPU exception. For SAM D20/D21/D10/D11/R21/DA0/DA1, it is Hard Fault exception; For SAM L21/C21, it is system exception, see SYSTEM_Handler().
```
system_peripheral_lock(SYSTEM_PERIPHERAL_ID(PORT),
        ~SYSTEM_PERIPHERAL_ID(PORT));
```

Enable global interrupts.

#if (SAML21) || (SAML22) || (SAMC21) || defined(__DOXYGEN__)
    system_pac_enable_interrupt();
#endif
    system_interrupt_enable_global();

Loop to wait for a button press before continuing.

while (port_pin_get_input_level(BUTTON_0_PIN)) {
    /* Wait for button press */
}

5.
Enter a critical section, so that the PAC module can be unlocked safely and the peripheral manipulated without the possibility of an interrupt modifying the protected module's state.
```
system_interrupt_enter_critical_section();
```

Unlock the PORT peripheral registers.

system_peripheral_unlock(SYSTEM_PERIPHERAL_ID(PORT),
        ~SYSTEM_PERIPHERAL_ID(PORT));

7.
Toggle pin 11, and clear edge detect flag.
```
port_pin_toggle_output_level(LED_0_PIN);
```

Lock the PORT peripheral registers.

system_peripheral_lock(SYSTEM_PERIPHERAL_ID(PORT),
        ~SYSTEM_PERIPHERAL_ID(PORT));

9.
Exit the critical section to allow interrupts to function normally again.
```
system_interrupt_leave_critical_section();
```
10.
Enter an infinite while loop once the module state has been modified successfully.
```
while (1) {
    /* Do nothing */
}
```