DE2-115 Nios device led demo

Hello ,

I am running a demo which uses the usb device controller in the kit .

The PC is acting as a host and the kit as a usb device .

This is the main file :

LCD_Test();
    disable();
    disconnect_USB();
    usleep(1000000);
    Hal4D13_ResetDevice();
    bUSBCheck_Device_State.State_bits.DEVICE_DEFAULT_STATE = 1;
    bUSBCheck_Device_State.State_bits.DEVICE_ADDRESS_STATE = 0;
    bUSBCheck_Device_State.State_bits.DEVICE_CONFIGURATION_STATE = 0;
    bUSBCheck_Device_State.State_bits.RESET_BITS = 0;  
    usleep(1000000);
    reconnect_USB(); 
    CHECK_CHIP_ID();
    Hal4D13_AcquireD13(USB_DC_IRQ,(void*)usb_isr);
    enable();
    bD13flags.bits.verbose=1;
 while (1)
    {
      if (bUSBCheck_Device_State.State_bits.RESET_BITS == 1)
      {
        disable();
        break;  
      }
      if (bD13flags.bits.suspend)
      {
        disable();
        bD13flags.bits.suspend= 0;
        enable();
        suspend_change();    
      } // Suspend Change Handler
      if (bD13flags.bits.DCP_state == USBFSM4DCP_SETUPPROC)
      {
        disable();
        SetupToken_Handler();
        enable();
      } // Setup Token Handler 
      if ((bD13flags.bits.DCP_state == USBFSM4DCP_REQUESTPROC) && !ControlData.Abort)
      {
        disable();
        bD13flags.bits.DCP_state = 0x00;
        DeviceRequest_Handler();
        enable();
      } // Device Request Handler
      usleep(1);
    }
  return  0;
}
    

I know what functions generally do but I hope that somebody explains why it's written in that sequence and I don't understand how the driver generally works .