12.8.1.2.2 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));
  3. Enable global interrupts. 
    #if (SAML21) || (SAML22) || (SAMC21) || defined(__DOXYGEN__)
    system_pac_enable_interrupt();
#endif
    system_interrupt_enable_global();
  4. 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();
  6. 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);
  8. 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 */
}