![LED location](/helios4/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) section.

## 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](/helios4/img/led/dipswitch_led_off.png)

### Pinout Table

![J18 Pinout](/helios4/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) section.

### Wiring Diagram

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

![Wiring Example](/helios4/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 [here](/helios4/files/led/libata_leds_trigger_mvebu.patch). **Armbian** builds are already patched, so no action is required.

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 change during heavy load.
If the LED no longer blinks, it means the system is locked-up or hung and has to be reset.

- ata*N*

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

- usb-host

LED blinks 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
```

Some of the triggers may expose additional parameters that 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 of 0.5 seconds for both.
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, since if a kernel panic occurs and/or system hangs, the Status LED will no longer blink.

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 RAID Fault Indicator

To configure the LED as RAID fault indicator, please refer to [MDADM: Configure Fault LED](/helios4/mdadm/#configure-fault-led)

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