Change hearbeat led on beaglebone black with device tree overlay

Question

I am using the Debian wheezy filesystem with Robert Nelson's latest kernel. I want to disable the heartbeat led using a device tree overlay.

I understand there are easier ways of doing this but I am only interested in answers using overlays to disable the heartbeat led.

One way I can achieve this is by changing the gpio-leds,led0 leaf in am335x-boneblack.dts from: linux,default-trigger = "heartbeat"; to linux,default-trigger = "none";

then compiling the device tree and rebooting.

However if I try to implement the same thing using the following overlay the heartbeat led continues to flash after I successfully apply the overlay with echo > $SLOTS.
What am I doing wrong?

/dts-v1/;
/plugin/;
/
{
    compatible = "ti,beaglebone", "ti,beaglebone-black";
part-number = "pru";
version = "00A0";
fragment@0
 {
    target = <&ocp>;
    __overlay__
    {
         gpio-leds
        {
            compatible = "gpio-leds";
            pinctrl-names = "default";
            pinctrl-0 = <0x3>;
             led0
             {
                label = "beaglebone:green:usr0";
                gpios = <0x5 0x15 0x0>;
                linux,default-trigger = "none";
                default-state = "off";
            };
        };
    };
};
};

brandon brandon · Accepted Answer · 2013-08-29T22:18:45

There's a systemd service, leds.service, that overrides the device tree settings for this one led (who knows why).

To see the status of the service, run

root@beaglebone:~# systemctl status leds.service

which gives the output

leds.service - Angstrom LED config
          Loaded: loaded (/lib/systemd/system/leds.service; enabled)
          Active: active (exited) since Sat 2000-01-01 18:33:24 UTC; 13 years 7 months ago
          Process: 125 ExecStart=/usr/bin/led-config start (code=exited, status=0/SUCCESS)
          CGroup: name=systemd:/system/leds.service

By looking at the "Loaded" field you can see that the service script is located at /lib/systemd/system/leds.service, and the "Process" field says the this service runs the command "/usr/bin/led-config start".

Looking at this file "/usr/bin/led-config" you'll see that it's a shell script that loads defaults from the file "/etc/default/leds":

#file format: name trigger
beaglebone::usr0 heartbeat

So, you can leave the device tree file alone and set the defaults here, or disable this service with

systemctl disable leds.service

Change hearbeat led on beaglebone black with device tree overlay

2 Answers