ticker api: Schedule immediately event in the past.

Author: pan-

TESTS/mbed_hal/ticker/main.cpp

@@ -905,9 +905,9 @@ static void test_insert_event_us_in_overflow_range() {
  * When an event is inserted with ticker_insert_event_us and a timestamp less 
  * than timestamp value in the ticker interface.
  * Then 
- *   - The event should not be in the queue
- *   - The interrupt timestamp should be set to 
- *     interface_stub.timestamp + TIMESTAMP_MAX_DELTA.
+ *   - The event should be in the queue
+ *   - The interrupt timestamp should be set to interface_stub.timestamp so it
+ *     is scheduled immediately.
  */
 static void test_insert_event_us_underflow() { 
     ticker_set_handler(&ticker_stub, NULL);
@@ -922,15 +922,16 @@ static void test_insert_event_us_underflow() {
     const uint32_t expected_id = 0xDEADDEAF;
 
     ticker_insert_event_us(
-        &ticker_stub, 
+        &ticker_stub,
         &event, expected_timestamp, expected_id
     );
 
-    TEST_ASSERT_EQUAL_PTR(NULL, queue_stub.head);
+    TEST_ASSERT_EQUAL_PTR(&event, queue_stub.head);
     TEST_ASSERT_EQUAL_UINT32(
-        interface_stub.timestamp + TIMESTAMP_MAX_DELTA, 
+        interface_stub.timestamp, 
         interface_stub.interrupt_timestamp
     );
+    TEST_ASSERT_EQUAL(1, interface_stub.set_interrupt_call);
 
     TEST_ASSERT_EQUAL(0, interface_stub.disable_interrupt_call);
 }  

hal/mbed_ticker_api.c

@@ -109,16 +109,22 @@ static void update_present_time(const ticker_data_t *const ticker)
 static void schedule_interrupt(const ticker_data_t *const ticker)
 {
     update_present_time(ticker);
-    uint32_t duration = MBED_TICKER_INTERRUPT_TIMESTAMP_MAX_DELTA;
+    uint32_t relative_timeout = MBED_TICKER_INTERRUPT_TIMESTAMP_MAX_DELTA;
 
     if (ticker->queue->head) {
-        us_timestamp_t event_interval = (ticker->queue->head->timestamp - ticker->queue->present_time);
-        if (event_interval < MBED_TICKER_INTERRUPT_TIMESTAMP_MAX_DELTA) { 
-            duration = event_interval;
+        us_timestamp_t present = ticker->queue->present_time;
+        us_timestamp_t next_event_timestamp = ticker->queue->head->timestamp;
+
+        // if the event at the head of the queue is in the past then schedule
+        // it immediately.
+        if (next_event_timestamp < present) {
+            relative_timeout = 0;
+        } else if ((next_event_timestamp - present) < MBED_TICKER_INTERRUPT_TIMESTAMP_MAX_DELTA) {
+            relative_timeout = next_event_timestamp - present;
         }
     } 
 
-    ticker->interface->set_interrupt(ticker->queue->present_time + duration);
+    ticker->interface->set_interrupt(ticker->queue->present_time + relative_timeout);
 }
 
 void ticker_set_handler(const ticker_data_t *const ticker, ticker_event_handler handler)
@@ -184,12 +190,6 @@ void ticker_insert_event_us(const ticker_data_t *const ticker, ticker_event_t *o
     // update the current timestamp
     update_present_time(ticker);
 
-    // filter out timestamp in the past 
-    if (timestamp < ticker->queue->present_time) { 
-        schedule_interrupt(ticker);
-        return;
-    }
-
     // initialise our data
     obj->timestamp = timestamp;
     obj->id = id;