Basic backlight support for MacBook Pro

11/09/2006 / Felipe Alfaro Solana

I made some modifications to the original bl1.c program from Nicolas Boichat. In summary, this modifications allow:

Specify an absolute brightness value

Let x be the absolute brightness value, such that 0<x<16, that is, the value must between 1 and 15, where 1 is the minimum brightness level before turning off the screen, and 15 is the maximum brightness supported by the LCD screen.

For example:

./bl1 15
./bl1 1

Specify an increment or decrement (delta)

Let d be the delta, and x the current brightness value, then the new brightness value y is y=x+d, and 0<y<16.

y = min(max(1, x + d), 15)

Source code

/*
 * Apple Macbook Pro LCD backlight control
 *
 * Copyright (C) 2006 Nicolas Boichat <nicolas @boichat.ch>
 * Copyright (C) 2006 Felipe Alfaro Solana <felipe_alfaro @linuxmail.org>
 *
 * 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, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 */

#include <stdio .h>
#include <sys /io.h>
#include <stdlib .h>

void init()
{
	if (ioperm(0xB2, 0xB3, 1) < 0)
	{
		perror("ioperm failed (you should be root).");
		exit(2);
	}
}

int get_current_value()
{
	outb(0x03, 0xB3);
	outb(0xBF, 0xB2);
	char t = inb(0xB3) >> 4;
	return t;
}

int calculate_new_value(const char *arg)
{
	int val, new = atoi(arg);

	if (arg[0] == '+' || arg[0] == '-')
		val = new + get_current_value();
	else
		val = new;

	if (val > 15)
		val = 15;
	else if (val < 1)
		val = 1;

	return val;
}

int main(int argc, char** argv)
{
	if (argc > 2)
	{
		printf("Usage:n");
		printf("%s : read current valuen", argv[0]);
		printf("%s value : write value [0-15]n", argv[0]);
		exit(1);
	}

	init();

	if (argc < 2)
	{
		printf("Current value : %dn", get_current_value());
		exit(0);
	}

	if (argc == 2)
	{
		int value = calculate_new_value(argv[1]);
		outb(0x04 | (value << 4), 0xB3);
		outb(0xBF, 0xB2);
		printf("new value: %dn", value);
	}

	return 0;
}

21 thoughts on “Basic backlight support for MacBook Pro”

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windi

08/01/2008 at 11:37 AM

Thank you, this works great on iMac version “5,1” as well (also known as “Late 2006”).
Bouboune

29/03/2008 at 4:27 AM

i’m looking for a toll like that but i’m newbie… i’ve got an iMac Alu (mid 2007) 20″ with ATI HD2400Pro.

How to make bli.c work on my computer (i’m under Ubuntu Gusty – Studio version)
Reply at : bouboulabulle[at]caramail.com
Thx !
AndrewL733

18/05/2008 at 12:28 AM

Hi. I could not get your source file to compile. I fixed one error — extra spaces in the include files. But there must be other errors that I don’t understand. Fortunately, I found a pre-compiled binary on another Ubuntu page. You were credited with program.

Here are the errors:
backlight.increment.c: In function ‘calculate_new_value’:
backlight.increment.c:48: error: stray ‘342’ in program
backlight.increment.c:48: error: stray ‘200’ in program
backlight.increment.c:48: error: stray ‘230’ in program
backlight.increment.c:48: error: stray ‘342’ in program
backlight.increment.c:48: error: stray ‘200’ in program
backlight.increment.c:48: error: stray ‘231’ in program
backlight.increment.c:48: error: expected expression before ‘||’ token
backlight.increment.c:48: error: stray ‘342’ in program
backlight.increment.c:48: error: stray ‘200’ in program
backlight.increment.c:48: error: stray ‘230’ in program
backlight.increment.c:48: error: stray ‘342’ in program
backlight.increment.c:48: error: stray ‘200’ in program
backlight.increment.c:48: error: stray ‘231’ in program
backlight.increment.c: In function ‘main’:
backlight.increment.c:65: error: stray ‘342’ in program
backlight.increment.c:65: error: stray ‘200’ in program
backlight.increment.c:65: error: stray ‘235’ in program
backlight.increment.c:65: error: ‘Usage’ undeclared (first use in this function)
backlight.increment.c:65: error: (Each undeclared identifier is reported only once
backlight.increment.c:65: error: for each function it appears in.)
backlight.increment.c:65: error: expected ‘)’ before ‘:’ token
backlight.increment.c:65: error: stray ‘’ in program
backlight.increment.c:65: error: stray ‘342’ in program
backlight.increment.c:65: error: stray ‘200’ in program
backlight.increment.c:65: error: stray ‘235’ in program
backlight.increment.c:66: error: stray ‘342’ in program
backlight.increment.c:66: error: stray ‘200’ in program
backlight.increment.c:66: error: stray ‘235’ in program
backlight.increment.c:66: error: expected expression before ‘%’ token
backlight.increment.c:66: error: stray ‘’ in program
backlight.increment.c:66: error: stray ‘342’ in program
backlight.increment.c:66: error: stray ‘200’ in program
backlight.increment.c:66: error: stray ‘235’ in program
backlight.increment.c:67: error: stray ‘342’ in program
backlight.increment.c:67: error: stray ‘200’ in program
backlight.increment.c:67: error: stray ‘235’ in program
backlight.increment.c:67: error: expected expression before ‘%’ token
backlight.increment.c:67: error: stray ‘’ in program
backlight.increment.c:67: error: stray ‘342’ in program
backlight.increment.c:67: error: stray ‘200’ in program
backlight.increment.c:67: error: stray ‘235’ in program
backlight.increment.c:75: error: stray ‘342’ in program
backlight.increment.c:75: error: stray ‘200’ in program
backlight.increment.c:75: error: stray ‘235’ in program
backlight.increment.c:75: error: ‘Current’ undeclared (first use in this function)
backlight.increment.c:75: error: expected ‘)’ before ‘value’
backlight.increment.c:75: error: stray ‘’ in program
backlight.increment.c:75: error: stray ‘342’ in program
backlight.increment.c:75: error: stray ‘200’ in program
backlight.increment.c:75: error: stray ‘235’ in program
backlight.increment.c:82: error: stray ‘303’ in program
backlight.increment.c:82: error: stray ‘227’ in program
backlight.increment.c:82: error: expected ‘)’ before numeric constant
backlight.increment.c:82: error: too few arguments to function ‘outb’
backlight.increment.c:84: error: stray ‘342’ in program
backlight.increment.c:84: error: stray ‘200’ in program
backlight.increment.c:84: error: stray ‘235’ in program
backlight.increment.c:84: error: ‘new’ undeclared (first use in this function)
backlight.increment.c:84: error: expected ‘)’ before ‘value’
backlight.increment.c:84: error: stray ‘’ in program
backlight.increment.c:84: error: stray ‘342’ in program
backlight.increment.c:84: error: stray ‘200’ in program
backlight.increment.c:84: error: stray ‘235’ in program
Josephine

02/12/2008 at 11:23 AM

Some compilers (e.g Linux) don’t support back quotes, so you need to review your code and replace any such with quotes you type yourself, particularly if you copied your code from some place.

i.e instead of ” ’n’ ” you should enter ” ‘n’ “
Josephine

02/12/2008 at 11:28 AM

Umm – the back quotes in my example haven’t come out clearly in my posted reply, but I hope you caught my gist :).

Alternatively make sure any double quotes in your program are really double quotes and not read as two adjacent single quotes.
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Edward

04/07/2009 at 7:45 PM

hey can somebody help me set this up i am a complete newbie w/ linux and i am using it on an intel mac but the brightness is KILLING MY EYES. thanks 🙂
dx/dy

23/08/2010 at 2:20 AM

Thank you for this fix! Works great!
Just copied your code into gedit(not my editor of choice) dropped it in my home directory, checked and fixed syntax
ran
cc brightnesscontrol.c
at the command line

then ran sudo ./a.out 11

and now my eyes are happy once more!

cheers 🙂
SukkoPera

17/10/2010 at 11:39 AM

Hi,

seems to be working OK on iMac8,1.

Thanks a lot!
G.
kokoklems

25/10/2010 at 8:58 AM

Hello,
I’m running ubuntu 10.10 on iMac 24″. Compilation of the code was successfull, but then when I run the code, the returned current value is ok, but the brightness is not changed… See:

$ sudo ./a.out
Current value : 15
$ sudo ./a.out 10
new value: 10
$ sudo ./a.out
Current value : 15

This thing is still killing my eyes!! Help!
James

09/12/2010 at 2:53 PM

Works great….had a WAY too bring iMac.
Palkal

15/12/2010 at 4:23 PM

Running ubuntu studio 10.10 on iMac10.1. Code compiled, binary running but not changing the values. Same as “kokoklems”.
Palkal

15/12/2010 at 4:54 PM

Ok, I’m back. I managed to adjust the brightness through the compiz setting manager application (install compizconfig-setting-manager from synaptic). I have maped my brightness keys to do the job although this only works for active aplication. If you find a way to make it work for the whole system please let us know.
Dmitri

13/01/2011 at 5:13 PM

The code works great for me (Ubuntu 10.04 and 10.10 with aliminum iMac 21″ and 27″).

Thanks.
bloom

12/05/2011 at 9:48 PM

Here, on an iMac 10,1 (21.5″, ATI Radeon HD 4670), the code compiles and runs but has no effect.
Quozl

17/05/2011 at 10:31 AM

Here, on an iMac 11,1, the code compiles and runs and has an effect, for brightness levels 0 through to 15, but brightness level 0 is some way above the lowest brightness set by Mac OS X. If I set the brightness to minimum in Mac OS X and then boot to Ubuntu, I get what I want. It is as if there may be another port for the scaling factor.
Stephan Lokietek

21/12/2011 at 3:34 PM

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09/01/2012 at 12:53 PM

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