Kontron KTAM3874-pITX - Manual (Page 84)

KTD-S0057-I Page 80 Linux® Programming Examples (DebianTM)
KTAM3874/pITX Software Guide
10.9 Backlight Example
An easy way to modify the backlight brightness value consists in use of the sysfs interface. The directory
/sys/class/backlight/ktam3874-lcd/ contains the following entries (please note - this directory appears
only if an LCD panel is enabled):
actual_brightness Actual brightness value (read only)
brightness Changeable brightness value
max_brightness Maximal brightness value (read only)
bl_power Changeable power state (on/off)
The program below gives an overview regarding the possible setting options.
/* Backlight test program
* Copyright (c) 2013 Kontron Technology A/S
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License.
*/
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
#define MAX_BKL_VAL 255
#define MAX_BKL_POW 1 /* 0 = enable, 1 = disable */
#define WRITE_DELAY 20
#define POWER_DELAY 100
static const char *dev_pow = "/sys/class/backlight/ktam3874-lcd/bl_power";
static const char *dev_val = "/sys/class/backlight/ktam3874-lcd/brightness";
static const char *dev_act = "/sys/class/backlight/ktam3874-lcd/actual_brightness";
int write_bkl_val (int val)
{
int
fd;
char str[8];
if ((val < 0) || (val > MAX_BKL_VAL))
return -1;
fd = open (dev_val, O_WRONLY);
if (fd < 0)
return -1;
sprintf (str, "%d", val);
if (write (fd, str, strlen (str)) != strlen (str))
{
close (fd);
return -1;
}
close (fd);
return 0;
}