Revision as of 06:07, 1 September 2014

The RR has 3 LEDs: green(172), blue(174), red(175).

All can be programmable.

LEDs as class devices

On the latest kernel images (Ubuntu 14.04 server/desktop), the 3 LEDs are configured as LED class devices.

You can control them via /sys/class/leds/

Read the documentation for more information: https://www.kernel.org/doc/Documentation/leds/leds-class.txt

The default status of the three on board leds are:

   RED: On when there is power
   GREEN: Flash twice per second after the kernel booting, it's called heartbeat.
   BLUE: Flash when the uSD card is reading/writing.

LEDs as GPIOs

On the previous kernel images, the LEDs can be controled as GPIOs.

Below is program in different languages to flash the green led on RR.

C

#include <stdio.h>

int main()
{
FILE *fp = fopen("/sys/class/gpio/export", "w");
if( !fp )
{
printf("error open export file");
return 1;
}
fprintf(fp, "%d", 172);
fclose(fp);

fp = fopen("/sys/class/gpio/gpio175/direction", "w");

if( !fp )
{
printf("error open export file");
return 1;
}
fprintf(fp, "%s", "out");
fclose(fp);

fp = fopen("/sys/class/gpio/gpio175/value", "w");

if( !fp )
{
printf("error open export file");
return 1;
}
fprintf(fp, "%d", 1);

}

Python

import time

def initpin(pinnum, mode):
'''
pinnum: pin number, eg. 172, 175 etc.
mode: pin mode, valid values: in or out
'''
with open('/sys/class/gpio/export', 'w') as f:
f.write(str(pinnum))

with open('/sys/class/gpio/gpio' + str(pinnum) + '/direction', 'w') as f:
f.write(str(mode))

def setpin(pinnum, value):

with open('/sys/class/gpio/gpio' + str(pinnum) + '/value', 'w') as f:
f.write(str(value))

if __name__ == '__main__':
initpin(172, 'out')
while True:
setpin(172, 0)
time.sleep(1)
setpin(172, 1)
time.sleep(1)

Shell

#!/bin/sh

# enable the gpio 172 -> green led
echo 172 > /sys/class/gpio/export

# set the direction to output
echo "out" > /sys/class/gpio/gpio172/direction
while true;
do
echo 0 > /sys/class/gpio/gpio172/value #led on
sleep 1
echo 1 > /sys/class/gpio/gpio172/value #led off
sleep 1
done

Difference between revisions of "Rock/LED"

Revision as of 06:07, 1 September 2014

Contents

LEDs as class devices

LEDs as GPIOs

C

Python

Shell

@@ Line 12: / Line 12: @@
 Read the documentation for more information: https://www.kernel.org/doc/Documentation/leds/leds-class.txt
+The default status of the three on board leds are:
+    RED: On when there is power
+    GREEN: Flash twice per second after the kernel booting, it's called heartbeat.
+    BLUE: Flash when the uSD card is reading/writing.
 = LEDs as GPIOs =