Bluetooth: controller: Fix assert due to stale tick count

Fixed assert due to stale tick count in role event
preparation. This happens when ticker timeout expiry is
delayed from the requested realtime anchor, due to thread
mode processing overheads and occurring interrupts therein,
if any, that added a delay between requested anchor tick
and actual scheduling for the requested ticker timeout.

The assert is reproduced in bt shell by starting advertising
and following it with continuous scanning (interval 2.5ms,
window 2.5ms), on nRF51x. If the overheads and/or a
advertiser event delayed the scheduling of scanner by over
2.5ms, then the preparation of scanner asserted.

The assert has been fixed by checking for stale tick count
at expiry in role event preparation and skip the event
gracefully.

Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: cvinayak

subsys/bluetooth/controller/ll_sw/ctrl.c

@@ -4323,20 +4323,26 @@ static void event_stop(u32_t ticks_at_expire, u32_t remainder,
 	LL_ASSERT(!retval);
 }
 
-static void event_common_prepare(u32_t ticks_at_expire,
-				 u32_t remainder,
-				 u32_t *ticks_xtal_to_start,
-				 u32_t *ticks_active_to_start,
-				 u32_t ticks_preempt_to_start,
-				 u8_t ticker_id,
-				 ticker_timeout_func ticker_timeout_fp,
-				 void *context)
+static u32_t event_common_prepare(u32_t ticks_at_expire,
+				  u32_t remainder,
+				  u32_t *ticks_xtal_to_start,
+				  u32_t *ticks_active_to_start,
+				  u32_t ticks_preempt_to_start,
+				  u8_t ticker_id,
+				  ticker_timeout_func ticker_timeout_fp,
+				  void *context)
 {
 	u32_t ticker_status;
 	u32_t _ticks_xtal_to_start = *ticks_xtal_to_start;
 	u32_t _ticks_active_to_start = *ticks_active_to_start;
 	u32_t ticks_to_start;
 
+	/* Check for stale ticks_at_expire */
+	if (ticker_ticks_diff_get(ticker_ticks_now_get(), ticks_at_expire) >
+	    TICKER_US_TO_TICKS(RADIO_TICKER_START_PART_US)) {
+		return 1;
+	}
+
 	/* in case this event is short prepare, xtal to start duration will be
 	 * active to start duration.
 	 */
@@ -4479,6 +4485,8 @@ static void event_common_prepare(u32_t ticks_at_expire,
 		LL_ASSERT(!retval);
 	}
 #endif /* CONFIG_BLUETOOTH_CONTROLLER_XTAL_ADVANCED */
+
+	return 0;
 }
 
 static u8_t chan_sel_remap(u8_t *chan_map, u8_t chan_index)
@@ -4757,19 +4765,23 @@ static void adv_scan_configure(u8_t phy, u8_t flags)
 void radio_event_adv_prepare(u32_t ticks_at_expire, u32_t remainder,
 			     u16_t lazy, void *context)
 {
+	u32_t err;
+
 	ARG_UNUSED(lazy);
 	ARG_UNUSED(context);
 
 	DEBUG_RADIO_PREPARE_A(1);
 
 	LL_ASSERT(!_radio.ticker_id_prepare);
-	_radio.ticker_id_prepare = RADIO_TICKER_ID_ADV;
 
-	event_common_prepare(ticks_at_expire, remainder,
-			     &_radio.advertiser.hdr.ticks_xtal_to_start,
-			     &_radio.advertiser.hdr.ticks_active_to_start,
-			     _radio.advertiser.hdr.ticks_preempt_to_start,
-			     RADIO_TICKER_ID_ADV, event_adv, NULL);
+	err = event_common_prepare(ticks_at_expire, remainder,
+				   &_radio.advertiser.hdr.ticks_xtal_to_start,
+				   &_radio.advertiser.hdr.ticks_active_to_start,
+				   _radio.advertiser.hdr.ticks_preempt_to_start,
+				   RADIO_TICKER_ID_ADV, event_adv, NULL);
+	if (!err) {
+		_radio.ticker_id_prepare = RADIO_TICKER_ID_ADV;
+	}
 
 	DEBUG_RADIO_PREPARE_A(0);
 }
@@ -4972,19 +4984,25 @@ void event_adv_stop(u32_t ticks_at_expire, u32_t remainder, u16_t lazy,
 static void event_scan_prepare(u32_t ticks_at_expire, u32_t remainder,
 			      u16_t lazy, void *context)
 {
+	u32_t err;
+
 	ARG_UNUSED(lazy);
 	ARG_UNUSED(context);
 
 	DEBUG_RADIO_PREPARE_O(1);
 
 	LL_ASSERT(!_radio.ticker_id_prepare);
-	_radio.ticker_id_prepare = RADIO_TICKER_ID_SCAN;
 
-	event_common_prepare(ticks_at_expire, remainder,
-			     &_radio.scanner.hdr.ticks_xtal_to_start,
-			     &_radio.scanner.hdr.ticks_active_to_start,
-			     _radio.scanner.hdr.ticks_preempt_to_start,
-			     RADIO_TICKER_ID_SCAN, event_scan, NULL);
+	err = event_common_prepare(ticks_at_expire, remainder,
+				   &_radio.scanner.hdr.ticks_xtal_to_start,
+				   &_radio.scanner.hdr.ticks_active_to_start,
+				   _radio.scanner.hdr.ticks_preempt_to_start,
+				   RADIO_TICKER_ID_SCAN, event_scan, NULL);
+	if (err) {
+		goto skip;
+	}
+
+	_radio.ticker_id_prepare = RADIO_TICKER_ID_SCAN;
 
 #if defined(CONFIG_BLUETOOTH_CONTROLLER_SCHED_ADVANCED)
 	/* calc next group in us for the anchor where first connection event
@@ -5021,6 +5039,7 @@ static void event_scan_prepare(u32_t ticks_at_expire, u32_t remainder,
 	}
 #endif /* CONFIG_BLUETOOTH_CONTROLLER_SCHED_ADVANCED */
 
+skip:
 	DEBUG_RADIO_PREPARE_O(0);
 }
 
@@ -6360,10 +6379,9 @@ static void event_connection_prepare(u32_t ticks_at_expire,
 				     struct connection *conn)
 {
 	u16_t event_counter;
+	u32_t err;
 
 	LL_ASSERT(!_radio.ticker_id_prepare);
-	_radio.ticker_id_prepare =
-	    RADIO_TICKER_ID_FIRST_CONNECTION + conn->handle;
 
 	/* Calc window widening */
 	if (conn->role.slave.role != 0) {
@@ -6497,17 +6515,23 @@ static void event_connection_prepare(u32_t ticks_at_expire,
 	}
 #endif /* CONFIG_BLUETOOTH_CONTROLLER_DATA_LENGTH */
 
-	/* Setup XTAL startup and radio active events */
-	event_common_prepare(ticks_at_expire, remainder,
-			     &conn->hdr.ticks_xtal_to_start,
-			     &conn->hdr.ticks_active_to_start,
-			     conn->hdr.ticks_preempt_to_start,
-			     (RADIO_TICKER_ID_FIRST_CONNECTION + conn->handle),
-			     (conn->role.slave.role != 0) ? event_slave : event_master,
-			     conn);
-
 	/* store the next event counter value */
 	conn->event_counter = event_counter + 1;
+
+	/* Setup XTAL startup and radio active events */
+	err = event_common_prepare(ticks_at_expire, remainder,
+				   &conn->hdr.ticks_xtal_to_start,
+				   &conn->hdr.ticks_active_to_start,
+				   conn->hdr.ticks_preempt_to_start,
+				   (RADIO_TICKER_ID_FIRST_CONNECTION +
+				    conn->handle),
+				   (conn->role.slave.role != 0) ? event_slave :
+								  event_master,
+				   conn);
+	if (!err) {
+		_radio.ticker_id_prepare = RADIO_TICKER_ID_FIRST_CONNECTION +
+					   conn->handle;
+	}
 }
 
 static void connection_configure(struct connection *conn)