LED Use

Introduction

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

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>;
        };
    
    user {
    	label = "firefly:yellow:user";
        linux,default-trigger = "ir-user-click";
        default-state = "off";
        gpios-v01 = <&gpio2 GPIO_A3 GPIO_ACTIVE_HIGH>;
        };
};

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