![LED location](/img/led/led_location.png)

## On-Board LEDs

| LED number | Color | Software control | Remarks |
|------------|-------|------------------|---------|
| LED1       | Green | Yes | Active-low |
| LED2       | Red   | Yes | Active-low |
| LED3       | Green | Yes | Active-low |
| LED4       | Green | Yes | Active-low |
| LED5       | Green | Yes | Active-low |
| LED6       | Green | Yes | Active-low |
| LED7       | Green | Yes | Active-low |
| LED8       | Green | No  | Power indicator |

!!! info
    LED1 - LED7 is preconfigured for certain indicator under Linux, see [LED under Linux](#led-under-linux)

## Expansion Panel (J18)

Helios4 board was designed to either use the on-board LEDs or use a custom expansion panel (not-available).
If you wish to use the header insure to switch to OFF the DIP switch SW2.

![Dipswitch LED](/img/led/dipswitch_led_off.png)

### Pinout Table

![J18 Pinout](/img/led/gpio_pinout_j18.png)

| Pin | LED number | Remarks |
|-----|------------|---------|
|  1  |  -   |  3.3V supply  |
|  2  |  -   |  Not connected |
|  3  | LED1 | Active-low |
|  4  | LED2 | Active-low |
|  5  | LED3 | Active-low |
|  6  | LED4 | Active-low |
|  7  | LED5 | Active-low |
|  8  | LED6 | Active-low |
|  9  | LED7 | Active-low |
| 10  |  -   | GND |

!!! info
    LED1 - LED7 is preconfigured for certain indicator under Linux, see [LED under Linux](#led-under-linux)

### Wiring Diagram

Since the signals to control the LEDs are active low, connect the pin to LED's cathode.
Below is example of the wiring diagram.

![Wiring Example](/img/led/led_expansion_wiring_diagram.png)


## LED under Linux

| LED  | Name                 | Default Trigger | Remarks |
|------|----------------------|-----------------|---------|
| LED1 | helios4:green:status | heartbeat | Blinking periodically |
| LED2 | helios4:red:fault    | none      | See [Configuring Fault LED](#configuring-fault-led) |
| LED3 | helios4:green:ata1   | ata1      | Blinking on SATA1 activity |
| LED4 | helios4:green:ata2   | ata2      | Blinking on SATA2 activity |
| LED5 | helios4:green:ata3   | ata3      | Blinking on SATA3 activity |
| LED6 | helios4:green:ata4   | ata4      | Blinking on SATA4 activity |
| LED7 | helios4:green:usb    | usb-host  | Blinking on USB activity, any port |

!!! note
    **ata* ** trigger requires additional patch to mainline kernel. The patch can be found from
    [here](/files/led/libata_leds_trigger_mvebu.patch) and is not needed for Armbian.

The LEDs can be accessed under leds class in sysfs.

```
root@helios4:~/# ls -l /sys/class/leds/

lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:ata1 -> ../../devices/platform/io-leds/leds/helios4:green:ata1
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:ata2 -> ../../devices/platform/io-leds/leds/helios4:green:ata2
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:ata3 -> ../../devices/platform/io-leds/leds/helios4:green:ata3
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:ata4 -> ../../devices/platform/io-leds/leds/helios4:green:ata4
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:status -> ../../devices/platform/system-leds/leds/helios4:green:status
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:usb -> ../../devices/platform/io-leds/leds/helios4:green:usb
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:red:fault -> ../../devices/platform/system-leds/leds/helios4:red:fault

```

### LEDs Trigger

- none

No automatic trigger. Manually control the LED by manipulating "brightness".
More info see [Configuring LED trigger](#configuring-led-trigger).

- heartbeat

LED "double" flashes at a load average based rate. The interval might changed during high load.
If the LED no longer blink, that is mean the system lock-up or hung and has to be reset'd.

- ataN

LED blink on any read/write activity at specific SATA port.

- usb-host

LED blink on USB activity at any port.

- panic

This trigger allows LEDs to be configured to blink on a kernel panic.

- timer

This allows LEDs to be controlled by a programmable timer via sysfs. delay_on to set how long
the led turned on and delay_off to set how long the led turned off.


### Configuring LED trigger

To configure, simply set the trigger type. For example to set status led triggered by timer

```
echo timer | sudo tee -a  /sys/class/leds/helios4\:green\:status/trigger
```

and done.

Some of the trigger may exposed additional parameter than can be configured further.

On **none** trigger, to turn on the LED set the brightness bigger than 0.

```
echo 1 | sudo tee -a  /sys/class/leds/helios4\:green\:status/brightness
```

and to turn off the LED set the brightness to 0.

```
echo 0 | sudo tee -a  /sys/class/leds/helios4\:green\:status/brightness
```

On **timer** trigger, it will exposed *delay_on* and *delay_off* with default value both 0.5 seconds.
To change the delay, set the respective parameter (value in milliseconds)

```
echo 1000 | sudo tee -a  /sys/class/leds/helios4\:green\:status/delay_on
echo 200 | sudo tee -a  /sys/class/leds/helios4\:green\:status/delay_off
```

!!! note
    The changes is not retained across reboot. Use startup script or udev rules to make it permanent.

### Configuring Fault LED

While other LEDs are preconfigured, the fault LED remains unconfigured (trigger:**none**).

#### 1. As Kernel Panic Indicator

To configure the LED as Kernel panic indicator, set the trigger to **panic**.
However, this functionality might be redundant with status LED. If the status LED no longer blinking,
that mean the system is hung which can be translated into kernel panic occurred.

To trigger kernel panic to test the LED, run
```
echo c > /proc/sysrq-trigger
```

!!! warning
    Triggering kernel panic can lead to data loss. Use with caution!

#### 2. As MDADM Fault Indicator

To configure the LED as MDADM fault indicator, please refer to [MDADM: Configure Fault LED](/mdadm/#configure-fault-led)

!!! info
    On Armbian, this is the default setting for fault LED.