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