Merge pull request #6515 from marcemmers/mbed_ticker_api

Only schedule mbed_ticker interrupt if queue->head is changed

TESTS/mbed_hal/ticker/main.cpp

@@ -697,6 +697,7 @@ static void test_legacy_insert_event_multiple_overflow()
     interface_stub.timestamp = 
         last_timestamp_to_insert + 
         ((ref_event_timestamp - last_timestamp_to_insert) / 2);
+    ticker_irq_handler(&ticker_stub);
 
     for (size_t i = 0; i < MBED_ARRAY_SIZE(events); ++i) { 
         ticker_insert_event(

hal/mbed_ticker_api.c

@@ -359,14 +359,12 @@ void ticker_insert_event_us(const ticker_data_t *const ticker, ticker_event_t *o
     /* if prev is NULL we're at the head */
     if (prev == NULL) {
         ticker->queue->head = obj;
+        schedule_interrupt(ticker);
     } else {
         prev->next = obj;
     }
 
-    schedule_interrupt(ticker);
-
     core_util_critical_section_exit();
-
 }
 
 void ticker_remove_event(const ticker_data_t *const ticker, ticker_event_t *obj)