System tick callback : the basics of OS implementation :)

diff --git a/core/systick.c b/core/systick.c
index cd6f2e2..82672cb 100644 (file)
--- a/core/systick.c
+++ b/core/systick.c
@@ -38,16 +38,55 @@ static volatile uint32_t systick_running = 0;
 /* Wraps every 50 days or so with a 1ms tick */
 static volatile uint32_t global_wrapping_system_ticks = 0;
 
+
+struct systick_callback {
+       void (*callback) (uint32_t);
+       uint16_t period;
+       uint16_t countdown;
+};
+static volatile struct systick_callback cbs[MAX_SYSTICK_CALLBACKS] = {};
+
 /* System Tick Timer Interrupt Handler */
 void SysTick_Handler(void)
 {
+       int i = 0;
        global_wrapping_system_ticks++;
        if (sleep_count != 0) {
                sleep_count--;
        }
+       for (i = 0; i < MAX_SYSTICK_CALLBACKS; i++) {
+               if (cbs[i].callback != NULL) {
+                       cbs[i].countdown--;
+                       if (cbs[i].countdown == 0) {
+                               cbs[i].countdown = cbs[i].period;
+                               cbs[i].callback(global_wrapping_system_ticks);
+                       }
+               }
+       }
 }
 
 
+/* Register a callback to be called every 'period' system ticks with 'param' parameter.
+ * returns the callback number, to be used to remove the callback from the table of callbacks.
+ * returns negative value on error.
+ */
+int add_systick_callback(void (*callback) (uint32_t), uint16_t period)
+{
+       int i = 0;
+       if (period == 0) {
+               return -EINVAL;
+       }
+       for (i = 0; i < MAX_SYSTICK_CALLBACKS; i++) {
+               if (cbs[i].callback == NULL) {
+                       cbs[i].callback = callback;
+                       cbs[i].period = period;
+                       cbs[i].countdown = period;
+                       return i;
+               }
+       }
+       return -EBUSY;
+}
+
 
 /***************************************************************************** */
 /* systick timer control function */

diff --git a/include/core/system.h b/include/core/system.h
index ea037ca..9f791db 100644 (file)
--- a/include/core/system.h
+++ b/include/core/system.h
@@ -135,6 +135,12 @@ void systick_timer_on(uint32_t ms);
 /* Removes the main clock from the selected timer block */
 void systick_timer_off(void);
 
+/* Register a callback to be called every 'period' system ticks with 'param' parameter.
+ * returns the callback number, to be used to remove the callback from the table of callbacks.
+ * returns negative value on error.
+ */
+#define MAX_SYSTICK_CALLBACKS  4
+int add_systick_callback(void (*callback) (uint32_t), uint16_t period);
 
 /***************************************************************************** */
 /* Sleeping functions : these use systick */