- /** Indicates the current device state machine state. When in device mode, this indicates the state\r
- * via one of the values of the \ref USB_Device_States_t enum values.\r
- *\r
- * This value should not be altered by the user application as it is handled automatically by the\r
- * library. The only exception to this rule is if the NO_LIMITED_CONTROLLER_CONNECT token is used\r
- * (see \ref EVENT_USB_Connect() and \ref EVENT_USB_Disconnect() events).\r
- *\r
- * \note This global is only present if the user application can be a USB device.\r
- *\r
- * \note This variable should be treated as read-only in the user application, and never manually\r
- * changed in value except in the circumstances outlined above.\r
- *\r
- * \see \ref USB_Device_States_t for a list of possible device states\r
- *\r
- * \ingroup Group_Device\r
- */\r
- extern volatile uint8_t USB_DeviceState;\r
+ #if !defined(DEVICE_STATE_AS_GPIOR0) || defined(__DOXYGEN__)\r
+ /** Indicates the current device state machine state. When in device mode, this indicates the state\r
+ * via one of the values of the \ref USB_Device_States_t enum values.\r
+ *\r
+ * This value should not be altered by the user application as it is handled automatically by the\r
+ * library. The only exception to this rule is if the NO_LIMITED_CONTROLLER_CONNECT token is used\r
+ * (see \ref EVENT_USB_Connect() and \ref EVENT_USB_Disconnect() events).\r
+ *\r
+ * To reduce program size and speed up checks of this global, it can be placed into the AVR's GPIOR0\r
+ * hardware register instead of RAM by defining the DEVICE_STATE_AS_GPIOR0 token in the project\r
+ * makefile and passing it to the compiler via the -D switch. When defined, the GPIOR0 register should\r
+ * not be used in the user application except implicitly via the library APIs.\r
+ *\r
+ * \note This global is only present if the user application can be a USB device.\r
+ *\r
+ * \note This variable should be treated as read-only in the user application, and never manually\r
+ * changed in value except in the circumstances outlined above.\r
+ *\r
+ * \see \ref USB_Device_States_t for a list of possible device states\r
+ *\r
+ * \ingroup Group_Device\r
+ */\r
+ extern volatile uint8_t USB_DeviceState;\r
+ #else\r
+ #define USB_DeviceState GPIOR0\r
+ #endif\r