Basic backlight support for MacBook Pro

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;
}

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21 thoughts on “Basic backlight support for MacBook Pro

  1. Pingback: » Re: installing Ubuntu on Mac - ubuntu.sitebolt.net

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

  3. 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 !

  4. 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

  5. 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’ “

  6. 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.

  7. Pingback: Ubuntu on Intel iMac Review | More Zonkyness

  8. 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 🙂

  9. 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 🙂

  10. 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!

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

  12. 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.

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

    Thanks.

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

  15. 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.

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