led.h File Reference

USB activity LED state management. More...

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Enumerations
enum	led_mode_t { LED_OFF, LED_BLINK_SLOW, LED_TRIP_FAST }
	LED state selection constants. More...

Functions
void	init_led ()
	Initialise the USB activity LED subsystem.
void	set_led_state (const enum led_mode_t mode)
	Put the LED in the desired state.
void	trip_led ()
	Trip the led when the state is set to LED_TRIP_FAST.

Detailed Description

USB activity LED state management.

The USB activity LED is controlled entirely via software, so will not turn on automatically if the power is connected, or when a firmware that is unaware of this LED is running on the device. The LED subsystem needs to be initiated by calling init_led() once, preferably as soon as possible after firmware loading. The LED can be set in three different states using set_led_state():

• Off: Permanently turn off the LED
• Blink (slow): Slowly blink (1Hz rate) the LED
• Trip (fast): Default LED state is on, but a call to trip_led() can be used to shortly turn off the LED.

When the device is not connected via USB, the LED is set to in the Off mode. If the device is connected, the state depends on whether there is an active connection or not. Slow blinking will be used to indicate that USB power is detected, but no bus activity is present (e.g. if the USB hub or PC is in stand-by mode). Trip mode is used when there is an active connection. All communication on the USB bus will be used to trip the LED, either resulting in a short blink every now an then when activity is low, or fast blinking when a lot of data is transferred.

Author

Sander Vanheule (Universiteit Gent)

Enumeration Type Documentation

led_mode_t

enum led_mode_t

LED state selection constants.

Enumerator
LED_OFF	Turn the LED off.
LED_BLINK_SLOW	Slow but continous blinking mode.
LED_TRIP_FAST	On by default, but can be 'tripped' (turned of shortly) with trip_led().