From a9e69d935cb5c2e5ffca1bbc977252ce7661d343 Mon Sep 17 00:00:00 2001
From: Michael Sevakis <jethead71@rockbox.org>
Date: Mon, 27 Oct 2008 16:30:24 +0000
Subject: Strange little kernel optimization to ease targeting the timer tick
 and to limit the number of loops in the tick function to the number of tasks
 added rather than always looping the max number.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@18893 a1c6a512-1295-4272-9138-f99709370657
---
 firmware/kernel.c | 72 +++++++++++++++----------------------------------------
 1 file changed, 19 insertions(+), 53 deletions(-)

(limited to 'firmware/kernel.c')

diff --git a/firmware/kernel.c b/firmware/kernel.c
index fb9c5e2449..70b3e03615 100644
--- a/firmware/kernel.c
+++ b/firmware/kernel.c
@@ -54,7 +54,9 @@
 volatile long current_tick SHAREDDATA_ATTR = 0;
 #endif
 
-void (*tick_funcs[MAX_NUM_TICK_TASKS])(void);
+/* List of tick tasks - final element always NULL for termination */
+void (*tick_funcs[MAX_NUM_TICK_TASKS+1])(void);
+static int num_tick_funcs = 0;
 
 extern struct core_entry cores[NUM_CORES];
 
@@ -128,18 +130,8 @@ void tick_start(unsigned int interval_in_ms)
 void IMIA0(void) __attribute__ ((interrupt_handler));
 void IMIA0(void)
 {
-    int i;
-
     /* Run through the list of tick tasks */
-    for(i = 0;i < MAX_NUM_TICK_TASKS;i++)
-    {
-        if(tick_funcs[i])
-        {
-            tick_funcs[i]();
-        }
-    }
-
-    current_tick++;
+    call_tick_tasks();
 
     TSR0 &= ~0x01;
 }
@@ -178,18 +170,8 @@ void tick_start(unsigned int interval_in_ms)
 void TIMER0(void) __attribute__ ((interrupt_handler));
 void TIMER0(void)
 {
-    int i;
-
     /* Run through the list of tick tasks */
-    for(i = 0;i < MAX_NUM_TICK_TASKS;i++)
-    {
-        if(tick_funcs[i])
-        {
-            tick_funcs[i]();
-        }
-    }
-
-    current_tick++;
+    call_tick_tasks();
 
     TER0 = 0xff; /* Clear all events */
 }
@@ -199,27 +181,17 @@ void TIMER0(void)
 #ifndef BOOTLOADER
 void TIMER1(void)
 {
-    int i;
-
     /* Run through the list of tick tasks (using main core) */
     TIMER1_VAL; /* Read value to ack IRQ */
 
     /* Run through the list of tick tasks using main CPU core - 
        wake up the COP through its control interface to provide pulse */
-    for (i = 0;i < MAX_NUM_TICK_TASKS;i++)
-    {
-        if (tick_funcs[i])
-        {
-            tick_funcs[i]();
-        }
-    }
+    call_tick_tasks();
 
 #if NUM_CORES > 1
     /* Pulse the COP */
     core_wake(COP);
 #endif /* NUM_CORES */
-
-    current_tick++;
 }
 #endif
 
@@ -243,16 +215,8 @@ void tick_start(unsigned int interval_in_ms)
 
 void timer_handler(void)
 {
-    int i;
-
     /* Run through the list of tick tasks */
-    for(i = 0;i < MAX_NUM_TICK_TASKS;i++)
-    {
-        if(tick_funcs[i])
-            tick_funcs[i]();
-    }
-
-    current_tick++;
+    call_tick_tasks();
 
     TIMER0.clr = 0;
 }
@@ -274,19 +238,16 @@ void tick_start(unsigned int interval_in_ms)
 
 int tick_add_task(void (*f)(void))
 {
-    int i;
     int oldlevel = disable_irq_save();
 
     /* Add a task if there is room */
-    for(i = 0;i < MAX_NUM_TICK_TASKS;i++)
+    if(num_tick_funcs < MAX_NUM_TICK_TASKS)
     {
-        if(tick_funcs[i] == NULL)
-        {
-            tick_funcs[i] = f;
-            restore_irq(oldlevel);
-            return 0;
-        }
+        tick_funcs[num_tick_funcs++] = f;
+        restore_irq(oldlevel);
+        return 0;
     }
+
     restore_irq(oldlevel);
     panicf("Error! tick_add_task(): out of tasks");
     return -1;
@@ -298,11 +259,16 @@ int tick_remove_task(void (*f)(void))
     int oldlevel = disable_irq_save();
 
     /* Remove a task if it is there */
-    for(i = 0;i < MAX_NUM_TICK_TASKS;i++)
+    for(i = 0;i < num_tick_funcs;i++)
     {
         if(tick_funcs[i] == f)
         {
-            tick_funcs[i] = NULL;
+            /* Compact function list - propagates NULL-terminator as well */
+            for(; i < num_tick_funcs; i++)
+                tick_funcs[i] = tick_funcs[i+1];
+
+            num_tick_funcs--;
+
             restore_irq(oldlevel);
             return 0;
         }
-- 
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