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

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();