From 306753b1ed328bcb3cf999a199580031f3d29603 Mon Sep 17 00:00:00 2001 From: Bertrik Sikken Date: Sat, 11 Jul 2009 13:43:04 +0000 Subject: Meizu: use hardware PWM instead of interrupts+GPIO to set the backlight brightness level git-svn-id: svn://svn.rockbox.org/rockbox/trunk@21772 a1c6a512-1295-4272-9138-f99709370657 --- firmware/target/arm/s5l8700/backlight-meizu.c | 73 +++++++-------------------- 1 file changed, 19 insertions(+), 54 deletions(-) (limited to 'firmware') diff --git a/firmware/target/arm/s5l8700/backlight-meizu.c b/firmware/target/arm/s5l8700/backlight-meizu.c index 23dcbb1820..bc0c290e05 100644 --- a/firmware/target/arm/s5l8700/backlight-meizu.c +++ b/firmware/target/arm/s5l8700/backlight-meizu.c @@ -26,55 +26,20 @@ #include "system.h" /* - Interrupt-driven backlight driver using the PWM mode of a hardware timer. + Backlight driver using the PWM mode of a hardware timer. - Backlight brightness is implemented by configuring one of the timers in - the SoC for PWM mode. In this mode, two interrupts are generated for each - cycle, one at the start of the cycle and another one sometime between the - first interrupt and the start of the next cycle. The backlight is switched - on at the first interrupt and switched off at the second interrupt. This - way, the position in time of the second interrupt determines the duty cycle - and thereby the brightness of the backlight. - The backlight is switched on and off by means of a GPIO pin. + The PWM duty cycle depends exponentially on the configured brightness + level. This makes the brightness curve more linear to the human eye. */ -void INT_TIMERA(void) -{ - unsigned int tacon = TACON; - - /* clear interrupts */ - TACON = tacon; - - /* TA_INT1, start of PWM cycle: enable backlight */ - if (tacon & (1 << 17)) { - PDAT0 |= (1 << 2); - } - - /* TA_INT0, disable backlight until next cycle */ - if (tacon & (1 << 16)) { - PDAT0 &= ~(1 << 2); - } -} - void _backlight_set_brightness(int brightness) { - static const unsigned char logtable[] = {0, 1, 2, 3, 5, 7, 10, 15, 22, 31, 44, 63, 90, 127, 180, 255}; + /* pwm = (sqrt(2)**x)-1, where brightness level x = 0..16 */ + static const unsigned char logtable[] = + {0, 1, 2, 3, 5, 7, 10, 15, 22, 31, 44, 63, 90, 127, 180, 255}; - if (brightness == MIN_BRIGHTNESS_SETTING) { - /* turn backlight fully off and disable interrupt */ - PDAT0 &= ~(1 << 2); - INTMSK &= ~(1 << 5); - } - else if (brightness == MAX_BRIGHTNESS_SETTING) { - /* turn backlight fully on and disable interrupt */ - PDAT0 |= (1 << 2); - INTMSK &= ~(1 << 5); - } - else { - /* set PWM width and enable interrupt */ - TADATA0 = logtable[brightness]; - INTMSK |= (1 << 5); - } + /* set PWM width */ + TCDATA0 = 255 - logtable[brightness]; } void _backlight_on(void) @@ -89,22 +54,22 @@ void _backlight_off(void) bool _backlight_init(void) { - /* enable backlight pin as GPIO */ - PCON0 = ((PCON0 & ~(3 << 4)) | (1 << 4)); + /* enable backlight pin as timer output */ + PCON0 = ((PCON0 & ~(3 << 4)) | (2 << 4)); /* enable timer clock */ PWRCON &= ~(1 << 4); /* configure timer */ - TACMD = (1 << 1); /* TA_CLR */ - TACMD = (1 << 0); /* TA_EN */ - TACON = (1 << 13) | /* TA_INT1_EN */ - (1 << 12) | /* TA_INT0_EN */ - (1 << 11) | /* TA_START */ - (3 << 8) | /* TA_CS = PCLK / 64 */ - (1 << 4); /* TA_MODE_SEL = PWM mode */ - TADATA1 = 255; /* set PWM period */ - TAPRE = 30; /* prescaler */ + TCCMD = (1 << 1); /* TC_CLR */ + TCCON = (0 << 13) | /* TC_INT1_EN */ + (0 << 12) | /* TC_INT0_EN */ + (0 << 11) | /* TC_START */ + (3 << 8) | /* TC_CS = PCLK / 64 */ + (1 << 4); /* TC_MODE_SEL = PWM mode */ + TCDATA1 = 255; /* set PWM period */ + TCPRE = 30; /* prescaler */ + TCCMD = (1 << 0); /* TC_EN */ _backlight_on(); -- cgit v1.2.3