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LED Use

Introduction​

AIO-3128C development board has 2 LEDs, as shown in the table below:

_images/driver_table2.png

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

Control LED in the form of equipment​

Standard Linux specially defines LED subsystem for LED equipment. Two LEDs on AIO-3128C 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

Operate LED in kernel​

The steps to operate LED in kernel are as follows:

  1. Define LED node in the dts file.Define LED node in file kernel/arch/arm/boot/dts/aio-3128c.dts:
leds {
	compatible = "gpio-leds";
    power {
    	label = "firefly:blue:power";
        linux,default-trigger = "ir-power-click";
        default-state = "on";
        gpios = <&gpio1 GPIO_C7 GPIO_ACTIVE_LOW>;
        &#125;;
    
    user &#123;
    	label = "firefly:yellow:user";
        linux,default-trigger = "ir-user-click";
        default-state = "off";
        gpios-v01 = <&gpio2 GPIO_A3 GPIO_ACTIVE_HIGH>;
        &#125;;
&#125;;

Note: The value of .compatible must match the one in drivers/leds/leds-gpio.c.

  1. Include head files in the driver.
#include <linux/leds.h>
  1. 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