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authorBertrik Sikken <bertrik@sikken.nl>2009-07-11 13:43:04 +0000
committerBertrik Sikken <bertrik@sikken.nl>2009-07-11 13:43:04 +0000
commit306753b1ed328bcb3cf999a199580031f3d29603 (patch)
tree46dafa69b2270adb64c5ab928b7f4deeb3663315 /firmware/target/arm
parente976c51df8801a40a111c2c3d7fd0a30a0402b71 (diff)
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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
Diffstat (limited to 'firmware/target/arm')
-rw-r--r--firmware/target/arm/s5l8700/backlight-meizu.c73
1 files changed, 19 insertions, 54 deletions
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();