How to toggle LED on-board on Dragonboard 410c running Linux

Question

There are 4 small green LEDs on the Dragonboard 410c and the heartbeat one on the right is constantly blinking, how do I toggle the other ones via command line.

Answer 1

First thing to note is that how to access the on board LEDs or user LEDs which reside between the two USB connectors as well as how many are available for use depends on which operating system, Android or Linux, you are using.

For both Android and Linux the user LEDs are listed in the folder /sys/class/leds so you can use the adb utility to remote in, and then ls the folder to see what the actual pseudo file names are.

For both you will change the value in the brightness pseudo file located in the pseudo folder for the user LED in order to turn the LED on, a value of 1, or off, a value of 0.

There are other pseudo files associated with each LED one of which is trigger which allows you to set the kernel event to trigger the LED. See this answer in Raspberry Pi StackExchange to How do I control the system LEDs using my software?.

Under Android, looking at several of the trigger pseudo files of several of the pseudo directories in /sys/class/leds gives the following output for the pseudo directories of boot (user LED 4 used for booting indicator with Android), led1 (user LED 1 which is available with Android but not Linux), and wlann (the LAN active indicator).

root@msm8916_64:/sys/class/leds # cat boot/trigger
none bkl-trigger [boot-indication] usb-online mmc0 mmc1 battery-charging-or-full battery-charging battery-full battery-charging-blink-full-solid wlan-indication-led
root@msm8916_64:/sys/class/leds # cat led1/trigger
[none] bkl-trigger boot-indication usb-online mmc0 mmc1 battery-charging-or-full battery-charging battery-full battery-charging-blink-full-solid wlan-indication-led
root@msm8916_64:/sys/class/leds # cat wlan/trigger
none bkl-trigger boot-indication usb-online mmc0 mmc1 battery-charging-or-full battery-charging battery-full battery-charging-blink-full-solid [wlan-indication-led]

Note: in order to use file I/O to the pseudo file, the file permissions must allow the type of access (read, write, read/write) you want to use. The default for the LED pseudo files appear to be read so the chmod command will need to be used as in sudo chmod 777 /sys/class/leds/led1/brightness.

https://www.96boards.org/documentation/consumer/dragonboard/dragonboard410c/guides/led-connectors.md.html

Located by the USB ports are a series of LEDs used to provide information to the user. Their usage is defined as follows:

Debian Images

When Debian-based images are installed, the following table defines the LED usage/behaviors.

+----------------------+----------------------+--------------------------+
| LED Board Identifier | Description          | Behavior                 |
+----------------------+----------------------+--------------------------+
| User LED 1           | Heartbeat            | Green: This LED is       |
|                      |                      | should always be         |
|                      |                      | blinking about once a    |
|                      |                      | second. If solid off or  |
|                      |                      | solid on, the board is   |
|                      |                      | not executing correctly  |
+----------------------+----------------------+--------------------------+
| User LED 2           | eMMC                 | Green: This LED blinks   |
|                      |                      | during accesses to eMMC  |
+----------------------+----------------------+--------------------------+
| User LED 3           | SD                   | Green: This LED blinks   |
|                      |                      | during accesses to SD    |
|                      |                      | Card                     |
+----------------------+----------------------+--------------------------+
| User LED 4           | currently unassigned | N/A                      |
+----------------------+----------------------+--------------------------+
| Wifi                 | Wifi                 | Yellow: This LED blinks  |
|                      |                      | during network accesses  |
|                      |                      | over Wifi                |
+----------------------+----------------------+--------------------------+
| BT                   | Bluetooth            | Yellow: This LED blinks  |
|                      |                      | when Bluetooth is being  |
|                      |                      | used                     |
+----------------------+----------------------+--------------------------+

Android Images

When Android-based images are installed, the following table defines the LED usage/behaviors.

+----------------------+----------------------+--------------------------+
| LED Board Identifier | Description          | Behavior                 |
+----------------------+----------------------+--------------------------+
| User LED 1           | currently unassigned | Green:                   |
+----------------------+----------------------+--------------------------+
| User LED 2           | currently unassigned | Green:                   |
|                      |                      |                          |
+----------------------+----------------------+--------------------------+
| User LED 3           | currently unassigned | Green:                   |
|                      |                      |                          |
|                      |                      |                          |
+----------------------+----------------------+--------------------------+
| User LED 4           | Boot                 | This LED illuminates at  |
|                      |                      | at the start of boot     |
|                      |                      | and turns of after       |
|                      |                      | completion of boot.      |
+----------------------+----------------------+--------------------------+
| Wifi                 | Wifi                 | Yellow: TDB              |
+----------------------+----------------------+--------------------------+
| BT                   | Bluetooth            | Yellow: TBD              |
+----------------------+----------------------+--------------------------+

For Linux, currently 3 of the 4 user LEDs are actively being used by the OS, but user LED 4 is unused and can be turned on with a command line of:

// turn on user LED 4 on Linux.
//     use backslash to escape the colon which is part
//     of the pseudo file name of "apq8016-sbc:green:user4".
echo 1 > /sys/class/leds/apq8016-sbc\:green\:user4/brightness

// turn off user LED 4 on Linux
echo 0 > /sys/class/leds/apq8016-sbc\:green\:user4/brightness

For Android 5.1, 3 of the 4 user LEDs are available. The user LEDs are accessed through the path /sys/class/leds where there are pseudo files for three of the user LEDs: led1, led2, and led3. For example to turn on and off user LED 1 use the following command lines. For user LED 2 replace led1 in the path with led2 and likewise for user LED 3 replace led in the path with led3.

// turn on LED 1 on Android
echo 1 > /sys/class/leds/led1/brightness

// turn off LED 1 Android
echo 0 > /sys/class/leds/led1/brightness

Answer 2

First thing to note is that currently 3 of the 4 LEDs are actively being used, but LED_4 is unused and can be turned on via command line with

// turn on
echo 1 > /sys/class/leds/apq8016-sbc\:green\:user4/brightness

// turn off
echo 0 > /sys/class/leds/apq8016-sbc\:green\:user4/brightness