LED
Update time:2018-04-13 Views:2167
1 Introduction
There are 2 LEDs on the Firefly-RK3288 development board, as the following table shows:
LED | GPIO ref. | GPIO number |
---|---|---|
Blue | GPIO8_A1 | 257 |
Yellow | GPIO8_A2 | 258 |
Both are programmable using ether LEDs class devices or GPIOs.
2 LEDs as Class Devices
Linux has its own LED subsystem for LED devices. In AIO-3288J, 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
3 Controlling LED in the Kernel
The steps to control LED in the kernel are shown below:
1. Define LED node in the dts file.
Define LED node in file kernel/arch/arm/boot/dts/firefly-rk3288-AIO.dts:
leds { compatible = "gpio-leds"; power { label = "firefly:blue:power"; linux,default-trigger = "ir-power-click"; default-state = "on"; gpios = <&gpio8 GPIO_A1 GPIO_ACTIVE_LOW>; }; user{ label = "firefly:yellow:user"; linux,default-trigger = "ir-user-click"; default-state = "off"; gpios = <&gpio8 GPIO_A2 GPIO_ACTIVE_LOW>; }; };
Note: The value of .compatible must match the one in drivers/leds/leds-gpio.c.
2. Include head files in the driver.
#include <linux/leds.h>
3. Control the LED in the drivers.
(1). Define a trigger.
DEFINE_LED_TRIGGER(ledtrig_ir_click);
(2). Register the trigger.
led_trigger_register_simple("ir-power-click", &ledtrig_ir_click);
(3). Turn on/off the LED.
led_trigger_event(ledtrig_ir_click, LED_FULL); //ON led_trigger_event(ledtrig_ir_click, LED_OFF); //OFF