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6. LED Use

6.1. Foreword​

AIO-3288J development board has 2 LEDs, as shown in the table below:

LED         GPIO ref.       GPIO number
Blue        GPIO8_A1        257
Yellow      GPIO8_A2        258

The user can use LED equipment subsystem or directly operate GPIO to control this LED.

6.2. Control LED in the form of equipment​

Standard Linux specially defines LED subsystem for LED equipment. Two LEDs on Firefly-RK3288 development board are defined in the form of equipment.

The user can control these two LEDs through /sys/class/leds/ catalog.

For more detailed descriptions, please refer to leds-class.txt.

The default states of LED on development board include:

  • Blue: turn on when the system is electrified
  • Yellow: user defined

The user can input command to trigger attribute through echo to control each LED:

root@firefly:~ # echo none >/sys/class/leds/firefly:blue:power/trigger
root@firefly:~ # echo default-on >/sys/class/leds/firefly:blue:power/trigger

The user can use cat command to obtain the available value of trigger:

root@firefly:~ # cat /sys/class/leds/firefly:blue:power/trigger
none [ir-power-click] test_ac-online test_battery-charging-or-full test_battery-charging
test_battery-full test_battery-charging-blink-full-solid test_usb-online mmc0 mmc1 mmc2
backlight default-on rfkill0 rfkill1 rfkill2

6.3. Operate LED in kernel​

The steps to operate LED in kernel are as follows:

1.Define LED node “leds” in dts file Define LED node in kernel/arch/arm/boot/dts/firefly-rk3288.dts file; the specific definition is as follows:

 leds {
        compatible = "gpio-leds";
        power {
            label = "firefly:blue:power";
            linux,default-trigger = "ir-power-click";
            default-state = "on";
            gpios = <&gpio8 GPIO_A1 GPIO_ACTIVE_HIGH>;
        &#125;;
        user&#123;
            label = "firefly:yellow:user";
            linux,default-trigger = "ir-user-click";
            default-state = "off";
            gpios = <&gpio8 GPIO_A2 GPIO_ACTIVE_HIGH>;
        &#125;;
  &#125;;

Note: the value of compatible shall coincide to the value of .compatible in drivers/leds/leds-gpio.c.

2.Include header file into driver file

#include <linux/leds.h>

3.Control LED in driver file.

(1). Define LED trigger

DEFINE_LED_TRIGGER(ledtrig_ir_click);

(2). Register this trigger

led_trigger_register_simple("ir-power-click", &ledtrig_ir_click);

(3). Control on/off of LED.

led_trigger_event(ledtrig_ir_click, LED_FULL); //on
led_trigger_event(ledtrig_ir_click, LED_OFF); //off