LED Use

Introduction

There are 2 LEDs on the Firefly-RK3128 development board, as the following table shows:_images/driver_table2.png

Both are programmable using ether LEDs class devices or GPIOs.

LEDs as Class Devices

Linux has its own LED subsystem for LED devices. In Firefly-RK3128, 2 LEDs are configured as LED class devices.You can control them via /sys/class/leds/.For more information, please read the document leds-class.txt .The default status of the two on-board leds are:

  • Blue: on after the system powers on.

  • Yellow: defined by user.

You can change the behavior of each LED by using the echo command to write command to its trigger property:

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

You can also use the cat command to list all available values of the trigger attribute:

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

Controlling LED in the 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/rk3128-fireprime.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_LOW>;
        };
};

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 a 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