Add ticker suspend/resume API

Add an API to suspend and resume the ticker.

hal/mbed_ticker_api.c

@@ -32,6 +32,9 @@ static void initialize(const ticker_data_t *ticker)
     if (ticker->queue->initialized) {
         return;
     }
+    if (ticker->queue->suspended) {
+        return;
+    }
 
     ticker->interface->init();
 
@@ -70,6 +73,7 @@ static void initialize(const ticker_data_t *ticker)
     ticker->queue->max_delta_us = max_delta_us;
     ticker->queue->present_time = 0;
     ticker->queue->dispatching = false;
+    ticker->queue->suspended = false;
     ticker->queue->initialized = true;
 
     update_present_time(ticker);
@@ -121,6 +125,9 @@ static us_timestamp_t convert_timestamp(us_timestamp_t ref, timestamp_t timestam
 static void update_present_time(const ticker_data_t *const ticker)
 {
     ticker_event_queue_t *queue = ticker->queue;
+    if (queue->suspended) {
+        return;
+    }
     uint32_t ticker_time = ticker->interface->read();
     if (ticker_time == ticker->queue->tick_last_read) {
         // No work to do
@@ -230,7 +237,7 @@ int _ticker_match_interval_passed(timestamp_t prev_tick, timestamp_t cur_tick, t
 static void schedule_interrupt(const ticker_data_t *const ticker)
 {
     ticker_event_queue_t *queue = ticker->queue;
-    if (ticker->queue->dispatching) {
+    if (queue->suspended || ticker->queue->dispatching) {
         // Don't schedule the next interrupt until dispatching is
         // finished. This prevents repeated calls to interface->set_interrupt
         return;
@@ -285,6 +292,10 @@ void ticker_irq_handler(const ticker_data_t *const ticker)
     core_util_critical_section_enter();
 
     ticker->interface->clear_interrupt();
+    if (ticker->queue->suspended) {
+        core_util_critical_section_exit();
+        return;
+    }
 
     /* Go through all the pending TimerEvents */
     ticker->queue->dispatching = true;
@@ -430,3 +441,29 @@ int ticker_get_next_timestamp(const ticker_data_t *const data, timestamp_t *time
 
     return ret;
 }
+
+void ticker_suspend(const ticker_data_t *const ticker)
+{
+    core_util_critical_section_enter();
+
+    ticker->queue->suspended = true;
+
+    core_util_critical_section_exit();
+}
+
+void ticker_resume(const ticker_data_t *const ticker)
+{
+    core_util_critical_section_enter();
+
+    ticker->queue->suspended = false;
+    if (ticker->queue->initialized) {
+        ticker->queue->tick_last_read = ticker->interface->read();
+
+        update_present_time(ticker);
+        schedule_interrupt(ticker);
+    } else {
+        initialize(ticker);
+    }
+
+    core_util_critical_section_exit();
+}

hal/ticker_api.h

@@ -82,6 +82,7 @@ typedef struct {
     us_timestamp_t present_time;        /**< Store the timestamp used for present time */
     bool initialized;                   /**< Indicate if the instance is initialized */
     bool dispatching;                   /**< The function ticker_irq_handler is dispatching */
+    bool suspended;                     /**< Indicate if the instance is suspended */
     uint8_t frequency_shifts;           /**< If frequency is a value of 2^n, this is n, otherwise 0 */
 } ticker_event_queue_t;
 
@@ -184,6 +185,27 @@ us_timestamp_t ticker_read_us(const ticker_data_t *const ticker);
  */
 int ticker_get_next_timestamp(const ticker_data_t *const ticker, timestamp_t *timestamp);
 
+/** Suspend this ticker
+ *
+ * When suspended reads will always return the same time and no
+ * events will be dispatched. When suspended the common layer
+ * will only ever call the interface function clear_interrupt()
+ * and that is only if ticker_irq_handler is called.
+ *
+ *
+ * @param ticker        The ticker object.
+ */
+void ticker_suspend(const ticker_data_t *const ticker);
+
+/** Resume this ticker
+ *
+ * When resumed the ticker will ignore any time that has passed
+ * and continue counting up where it left off.
+ *
+ * @param ticker        The ticker object.
+ */
+void ticker_resume(const ticker_data_t *const ticker);
+
 /* Private functions
  *
  * @cond PRIVATE