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

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/***************************************************************************
* __________ __ ___.
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
* \/ \/ \/ \/ \/
* $Id$
*
* Copyright (C) 2011 by Marcin Bukat
*
* 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 software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/
#include <stdbool.h>
#include "config.h"
#include "backlight.h"
#include "backlight-target.h"
#include "system.h"
#include "lcd.h"
static int brightness = DEFAULT_BRIGHTNESS_SETTING;
/* Based on http://www.poynton.com/PDFs/SMPTE93_Gamma.pdf
* CIE standarized function that relates physical luminance
* to perceived lightness
*
* L* = 116*(Y/Yn)^(1/3) - 16 (Y/Yn > 0 008856)
* where Yn is luminance of reference white
*
* Actual function is lightly tweaked to account for the fact
* that fill factor of the PWM below ~15% gives black.
* So the function used to calculate the values in the matrix was:
* f(x) = 42000 * ((100*x/31 + 16)/116)^3 + 8000
*/
static const unsigned short lin_brightness[] = {
8110, 8191, 8304, 8455, 8649, 8892, 9189, 9545,
9966, 10457, 11024, 11671, 12406, 13232, 14156, 15182,
16316, 17565, 18932, 20423, 22045, 23801, 25699, 27742,
29937, 32289, 34803, 37485, 40340, 43374, 46592, 50000
};
bool _backlight_init(void)
{
/* configure PD4 as output */
GPIO_PDCON |= (1<<4);
/* set PD4 low (backlight off) */
GPIO_PDDR &= ~(1<<4);
/* IOMUXB - set PWM0 pin as GPIO */
SCU_IOMUXB_CON &= ~(1 << 11); /* type<<11<<channel */
/* DIV/2, PWM reset */
PWMT0_CTRL = (0<<9) | (1<<7);
/* set pwm frequency to 500Hz - my lcd panel can't cope more reliably */
/* (apb_freq/pwm_freq)/pwm_div = (50 000 000/500)/2 */
PWMT0_LRC = 50000;
PWMT0_HRC = lin_brightness[brightness];
/* reset counter */
PWMT0_CNTR = 0x00;
/* DIV/2, PWM output enable, PWM timer enable */
PWMT0_CTRL = (0<<9) | (1<<3) | (1<<0);
return true;
}
void _backlight_on(void)
{
#ifdef HAVE_LCD_ENABLE
lcd_enable(true);
#endif
/* enable PWM clock */
SCU_CLKCFG &= ~(1<<29);
/* set output pin as PWM pin */
SCU_IOMUXB_CON |= (1<<11); /* type<<11<<channel */
/* pwm enable */
PWMT0_CTRL |= (1<<3) | (1<<0);
}
void _backlight_off(void)
{
/* setup PWM0 pin as GPIO which is pulled low */
SCU_IOMUXB_CON &= ~(1<<11);
/* stop pwm timer */
PWMT0_CTRL &= ~(1<<3) | (1<<0);
/* disable PWM clock */
SCU_CLKCFG |= (1<<29);
#ifdef HAVE_LCD_ENABLE
lcd_enable(false);
#endif
}
void _backlight_set_brightness(int val)
{
brightness = val & 0x1f;
PWMT0_HRC = lin_brightness[brightness];
}