LEDs
====

The Duckbill is equipped with a two-color status LED at the bottom side. Each color
of the LED is wired to a dedicated GPIO pin of the CPU. As usual in Linux, both colors
are modelled as individual LED in the BSP.

During boot process, U-Boot switches the red status LED on shortly to indicate that
a software component is running at all. When linux kernel takes over, it flashes
the green status LED like a heartbeat, to indicate that the kernel is still alive and
running.

+-----------------+-----------------------------------------------------------------------------+
| Attribute       | Status LED                                                                  |
+=================+=====================================+=======================================+
| Color           | red                                 | green                                 |
+-----------------+-------------------------------------+---------------------------------------+
| Linux Device    | /sys/class/leds/duckbill:red:status | /sys/class/leds/duckbill:green:status |
+-----------------+-------------------------------------+---------------------------------------+
| Default trigger | none                                | heartbeat                             |
+-----------------+-------------------------------------+---------------------------------------+

The following table lists various device states.

+---------------------+--------------------------+--------------------------------------------------+
| Status LED          | Duration of this state   | Status / possible solution                       |
+----------+----------+                          |                                                  |
| red      | green    |                          |                                                  |
+==========+==========+==========================+==================================================+
| off      | off      | persistent               | Device is powered off, attach power supply       |
+----------+----------+--------------------------+--------------------------------------------------+
| on       | off      | < 10s                    | U-Boot is running and loading Linux              |
+----------+----------+--------------------------+--------------------------------------------------+
| on       | flashing | < 25s                    | Linux kernel is booting                          |
+----------+----------+--------------------------+--------------------------------------------------+
| on       | off      | persistent               | U-Boot could not start Linux                     |
+----------+----------+--------------------------+--------------------------------------------------+
| off      | flashing | persistent               | Linux system is running                          |
+----------+----------+--------------------------+--------------------------------------------------+
| on       | flashing | persistent               | Linux system is running, but errors during       |
|          |          |                          | initialization                                   |
+----------+----------+--------------------------+--------------------------------------------------+

Additionally, the Duckbill 2 EnOcean has three single LEDs on left side of the case. The red and
green LED are handled by the ser2net application via sysfs. They indicate EnOcean operations
by flashing and are operational after a socket connection to ser2net has been established.

+-----------------+--------------------------------------+----------------------------------------+
| Attribute       | TX LED                               | RX LED                                 |
+=================+======================================+========================================+
| Color           | red                                  | green                                  |
+-----------------+--------------------------------------+----------------------------------------+
| Linux Device    | /sys/class/leds/duckbill:red:enocean | /sys/class/leds/duckbill:green:enocean |
+-----------------+--------------------------------------+----------------------------------------+
| Default trigger | none                                 | none                                   |
+-----------------+--------------------------------------+----------------------------------------+

The blue LED is free to use by custom applications.

+----------------------------------------+-------------+-----------------+
| Linux Device                           | Color       | Default trigger |
+========================================+=============+=================+
| /sys/class/leds/duckbill:blue:enocean  | blue        | none            |
+----------------------------------------+-------------+-----------------+