usb: document usb_status_event and #ifdef it with USB_STATUS_BY_EVENT

Change-Id: I62cdb8ad71a598279fe99cc91d87eafda26cbbc7
Reviewed-on: http://gerrit.rockbox.org/1095
Reviewed-by: Amaury Pouly <amaury.pouly@gmail.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/firmware/export/usb.h b/firmware/export/usb.h
index 6c9cdac6e1..f13ade2acd 100644
--- a/firmware/export/usb.h
+++ b/firmware/export/usb.h
@@ -110,8 +110,10 @@ void usb_wait_for_disconnect(struct event_queue *q);
 int usb_wait_for_disconnect_w_tmo(struct event_queue *q, int ticks);
 bool usb_inserted(void); /* return the official value, what's been reported to the threads */
 int usb_detect(void); /* return the raw hardware value - nothing/pc/charger */
-/* For tick-less USB monitoring (USB_STATUS_BY_EVENT) */
+#ifdef USB_STATUS_BY_EVENT
+/* Notify USB insertion state (USB_INSERTED or USB_EXTRACTED) */
 void usb_status_event(int current_status);
+#endif
 #ifdef HAVE_USB_POWER
 bool usb_powered(void);
 #ifdef HAVE_USB_CHARGING_ENABLE