Implement software pwm to control c200v2 display brightness.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@25300 a1c6a512-1295-4272-9138-f99709370657

firmware/target/arm/as3525/kernel-as3525.c

@@ -36,7 +36,7 @@
 /* The scrollwheel is polled every 5 ms (the tick tasks only every 10) */
 static int poll_scrollwheel = 0;
 
-void INT_TIMER2(void)
+static inline void do_scrollwheel(void)
 {
     if (!poll_scrollwheel)
         call_tick_tasks();      /* Run through the list of tick tasks
@@ -48,17 +48,132 @@ void INT_TIMER2(void)
     }
 
     poll_scrollwheel ^= 1;
-    TIMER2_INTCLR = 0;  /* clear interrupt */
 }
 #else
-void INT_TIMER2(void)
+static inline void do_scrollwheel(void)
 {
-    call_tick_tasks();  /* Run through the list of tick tasks */
+    call_tick_tasks();      /* Run through the list of tick tasks */
+}
+#endif
+
+#if defined(SANSA_C200V2)
+#include "backlight-target.h"
+
+static int timer2_cycles_per_tick = 0;
+static int timer2_cycles_pwmon = 0;
+static int timer2_cycles_pwmoff = 0;
+static int timer2_pwm_state = 0;
+static int timer2_pwm_on = 0;
+
+void _set_timer2_pwm_ratio(int ratio)
+{
+    int cycles = timer2_cycles_per_tick;
+
+    /*
+     * Rather arbitrary limits, but since the CPU
+     * needs some to time in the interrupt handler
+     * there sure is some limit.
+     * More specifically, if the cycles needed to do
+     * the pwm handling are more than the reloaded counter needs
+     * to reach 0 again it will reload to the old value most
+     * likely leading to a (slight) slowdown in tick rate.
+     */
+
+    if (ratio < 10) {
+        /*
+         * Permanent off, reduce interrupt rate to save power
+         */
+        TIMER2_BGLOAD = cycles;
+        timer2_pwm_on = 0;
+        _backlight_pwm(0);
+        return;
+    }
+
+    if (ratio > 990) {
+        /*
+         * Permanent on, reduce interrupt rate to save power
+         */
+        TIMER2_BGLOAD = cycles;
+        timer2_pwm_on = 0;
+        _backlight_pwm(1);
+        return;
+    }
+
+    timer2_cycles_pwmon = cycles*ratio/1000;
+    timer2_cycles_pwmoff = cycles*(1000-ratio)/1000;
+
+    if (timer2_pwm_on == 0) {
+        timer2_pwm_state = 0;
+        timer2_pwm_on = 1;
+        TIMER2_BGLOAD = timer2_cycles_pwmoff;
+    }
+}
+
+static void set_timer2_cycles_per_tick(int cycles)
+{
+    timer2_cycles_per_tick = cycles;
+}
+
+static inline void do_sw_pwm(void)
+{
+    if (!timer2_pwm_on) {
+        do_scrollwheel();  /* Handle scrollwheel and tick tasks */
+        TIMER2_INTCLR = 0;  /* clear interrupt */
+        return;
+    }
+
+    timer2_pwm_state ^= 1;
+    if (timer2_pwm_state) {
+        TIMER2_BGLOAD = timer2_cycles_pwmoff;
+        _backlight_pwm(1);
+        /*
+         * Always do scrollwheel and tick tasks during the longer cycle for safety,
+         * since the short cycle can be quite short.
+         * (minimum: 1us if ratio is 10 or 990 or 0.5us with scrollwheel,
+         *  or just about 6000 clock cycles at 60MHz)
+         */
+        if (timer2_cycles_pwmon > timer2_cycles_pwmoff)
+            do_scrollwheel();  /* Handle scrollwheel and tick tasks */
+    } else {
+        TIMER2_BGLOAD = timer2_cycles_pwmon;
+        _backlight_pwm(0);
+        if (!(timer2_cycles_pwmon > timer2_cycles_pwmoff))
+            do_scrollwheel();  /* Handle scrollwheel and tick tasks */
+    }
 
     TIMER2_INTCLR = 0;  /* clear interrupt */
 }
+#else
+static inline void do_sw_pwm(void)
+{
+    do_scrollwheel();  /* Handle scrollwheel and tick tasks */
+}
+
+static void set_timer2_cycles_per_tick(int cycles)
+{
+    (void)cycles;
+}
 #endif
 
+
+void INT_TIMER2(void)
+{
+    /*
+     * Timer is stacked as follows:
+     * Lowest layer: Software PWM (if configured)
+     *   Alternates timer2 reload value to implement
+     *   software pwm at 100Hz (no scrollwheel)
+     *   or 200Hz (scrollwheel) with variable pulse width 1% to 99%
+     * Middle layer: Scrollwheel handling (if configured, 200Hz)
+     *   Alternate between polling scrollwheel and running tick
+     *   tasks (includes scrollwheel polling).
+     * Top layer: Run tick tasks at 100Hz
+     */
+    do_sw_pwm();
+
+    TIMER2_INTCLR = 0;  /* clear interrupt */
+}
+
 void tick_start(unsigned int interval_in_ms)
 {
     int cycles = KERNEL_TIMER_FREQ / 1000 * interval_in_ms;
@@ -66,6 +181,7 @@ void tick_start(unsigned int interval_in_ms)
     CGU_PERI |= CGU_TIMER2_CLOCK_ENABLE;    /* enable peripheral */
     VIC_INT_ENABLE = INTERRUPT_TIMER2;     /* enable interrupt */
 
+    set_timer2_cycles_per_tick(cycles);
     TIMER2_LOAD = TIMER2_BGLOAD = cycles;   /* timer period */
 
     /* /!\ bit 4 (reserved) must not be modified

firmware/target/arm/as3525/sansa-c200v2/backlight-c200v2.c

@@ -27,6 +27,32 @@
 #include "as3514.h"
 
 int buttonlight_is_on = 0;
+int backlight_is_on = 0;
+static int backlight_level = 0;
+
+/* logarithmic lookup table for brightness s*/
+static const int brightness_table[MAX_BRIGHTNESS_SETTING+1] = {
+    0, 21, 47, 78, 118, 165, 224, 296, 386, 495, 630, 796, 1000
+};
+
+static void _ll_backlight_on(void)
+{
+    GPIOA_PIN(5) = 1<<5;
+}
+
+static void _ll_backlight_off(void)
+{
+    GPIOA_PIN(5) = 0;
+}
+
+void _backlight_pwm(int on)
+{
+    if (on) {
+        _ll_backlight_on();
+    } else {
+        _ll_backlight_off();
+    }
+}
 
 bool _backlight_init(void)
 {
@@ -36,6 +62,8 @@ bool _backlight_init(void)
 
 void _backlight_set_brightness(int brightness)
 {
+    backlight_level = brightness_table[brightness];
+
     if (brightness > 0)
         _backlight_on();
     else
@@ -47,12 +75,17 @@ void _backlight_on(void)
 #ifdef HAVE_LCD_ENABLE
     lcd_enable(true); /* power on lcd + visible display */
 #endif
-    GPIOA_PIN(5) = 1<<5;
+    if (!backlight_is_on)
+        _ll_backlight_on();
+    _set_timer2_pwm_ratio(backlight_level);
+    backlight_is_on = 1;
 }
 
 void _backlight_off(void)
 {
-    GPIOA_PIN(5) = 0;
+    backlight_is_on = 0;
+    _set_timer2_pwm_ratio(0);
+    _ll_backlight_off();
 #ifdef HAVE_LCD_ENABLE
     lcd_enable(false); /* power off visible display */
 #endif

firmware/target/arm/as3525/sansa-c200v2/backlight-target.h

@@ -24,6 +24,7 @@
 #include <stdbool.h>
 
 bool _backlight_init(void);
+void _backlight_pwm(int on);
 void _backlight_on(void);
 void _backlight_off(void);
 void _backlight_set_brightness(int brightness);
@@ -31,4 +32,10 @@ int  __backlight_is_on(void);
 
 void _buttonlight_on(void);
 void _buttonlight_off(void);
+
+/*
+ * FIXME: This may be better off in kernel.h, but...
+ */
+void _set_timer2_pwm_ratio(int ratio);
+
 #endif