firmware/target/arm/rk27xx/backlight-rk27xx.c

   1 /***************************************************************************
   2  *             __________               __   ___.
   3  *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
   4  *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
   5  *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
   6  *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
   7  *                     \/            \/     \/    \/            \/
   8  * $Id$
   9  *
  10  * Copyright (C) 2011 by Marcin Bukat
  11  *
  12  * This program is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU General Public License
  14  * as published by the Free Software Foundation; either version 2
  15  * of the License, or (at your option) any later version.
  16  *
  17  * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
  18  * KIND, either express or implied.
  19  *
  20  ****************************************************************************/
  21 #include <stdbool.h>
  22
  23 #include "config.h"
  24 #include "backlight.h"
  25 #include "backlight-target.h"
  26 #include "system.h"
  27 #include "lcd.h"
  28
  29 static int brightness = DEFAULT_BRIGHTNESS_SETTING;
  30
  31 /* Based on http://www.poynton.com/PDFs/SMPTE93_Gamma.pdf
  32  * CIE standarized function that relates physical luminance
  33  * to perceived lightness
  34  *
  35  * L* = 116*(Y/Yn)^(1/3) - 16 (Y/Yn > 0 008856)
  36  * where Yn is luminance of reference white
  37  *
  38  * Actual function is lightly tweaked to account for the fact
  39  * that fill factor of the PWM below ~15% gives black.
  40  * So the function used to calculate the values in the matrix was:
  41  * f(x) = 42000 * ((100*x/31 + 16)/116)^3 + 8000
  42  */
  43 static const unsigned short lin_brightness[] = {
  44      8110,  8191,  8304,  8455,  8649,  8892,  9189,  9545,
  45      9966, 10457, 11024, 11671, 12406, 13232, 14156, 15182,
  46     16316, 17565, 18932, 20423, 22045, 23801, 25699, 27742,
  47     29937, 32289, 34803, 37485, 40340, 43374, 46592, 50000
  48 };
  49
  50 bool _backlight_init(void)
  51 {
  52     /* configure PD4 as output */
  53     GPIO_PDCON |= (1<<4);
  54
  55     /* set PD4 low (backlight off) */
  56     GPIO_PDDR &= ~(1<<4);
  57
  58     /* IOMUXB - set PWM0 pin as GPIO */
  59     SCU_IOMUXB_CON &= ~(1 << 11); /* type<<11<<channel */
  60
  61     /* DIV/2, PWM reset */
  62     PWMT0_CTRL = (0<<9) | (1<<7);
  63
  64     /* set pwm frequency to 500Hz - my lcd panel can't cope more reliably */
  65     /* (apb_freq/pwm_freq)/pwm_div = (50 000 000/500)/2 */
  66     PWMT0_LRC = 50000;
  67     PWMT0_HRC = lin_brightness[brightness];
  68
  69     /* reset counter */
  70     PWMT0_CNTR = 0x00;
  71
  72     /* DIV/2, PWM output enable, PWM timer enable */
  73     PWMT0_CTRL = (0<<9) | (1<<3) | (1<<0);
  74
  75     return true;
  76 }
  77
  78 void _backlight_on(void)
  79 {
  80 #ifdef HAVE_LCD_ENABLE
  81     lcd_enable(true);
  82 #endif
  83     /* enable PWM clock */
  84     SCU_CLKCFG &= ~(1<<29);
  85
  86     /* set output pin as PWM pin */
  87     SCU_IOMUXB_CON |= (1<<11); /* type<<11<<channel */
  88
  89     /* pwm enable */
  90     PWMT0_CTRL |= (1<<3) | (1<<0);
  91 }
  92
  93 void _backlight_off(void)
  94 {
  95     /* setup PWM0 pin as GPIO which is pulled low */
  96     SCU_IOMUXB_CON &= ~(1<<11);
  97
  98     /* stop pwm timer */
  99     PWMT0_CTRL &= ~(1<<3) | (1<<0);
 100
 101     /* disable PWM clock */
 102     SCU_CLKCFG |= (1<<29);
 103 #ifdef HAVE_LCD_ENABLE
 104     lcd_enable(false);
 105 #endif
 106 }
 107
 108 void _backlight_set_brightness(int val)
 109 {
 110     brightness = val & 0x1f;
 111     PWMT0_HRC = lin_brightness[brightness];
 112 }