Bluetooth: Controller: Fix stuck forced continuation under throughput

subsys/bluetooth/controller/ll_sw/lll.h

@@ -236,7 +236,8 @@ struct lll_prepare_param {
 #if defined(CONFIG_BT_CTLR_JIT_SCHEDULING)
 	int8_t  prio;
 #endif /* CONFIG_BT_CTLR_JIT_SCHEDULING */
-	uint8_t force;
+	uint8_t force:1;
+	uint8_t defer:1;
 	void *param;
 };
 

subsys/bluetooth/controller/ll_sw/lll_common.c

@@ -62,6 +62,8 @@ int lll_prepare(lll_is_abort_cb_t is_abort_cb, lll_abort_cb_t abort_cb,
 	prepare_param->prio = prio;
 #endif /* CONFIG_BT_CTLR_JIT_SCHEDULING */
 
+	prepare_param->defer = 0U;
+
 	err = lll_prepare_resolve(is_abort_cb, abort_cb, prepare_cb, prepare_param, 0U, 0U);
 
 	return err;

subsys/bluetooth/controller/ll_sw/nordic/lll/lll.c

@@ -807,6 +807,8 @@ void lll_isr_early_abort(void *param)
 {
 	int err;
 
+	radio_status_reset();
+
 	radio_isr_set(isr_race, param);
 	if (!radio_is_idle()) {
 		radio_disable();
@@ -1316,7 +1318,9 @@ static void preempt(void *param)
 		/* Returns -EBUSY when same curr and next state/role, do not
 		 * abort same curr and next event.
 		 */
-		if (err != -EBUSY) {
+		if (err == -EBUSY) {
+			ready->prepare_param.defer = 1U;
+		} else {
 			/* Let preemptor LLL know about the cancelled prepare */
 			ready->is_aborted = 1;
 			ready->abort_cb(&ready->prepare_param, ready->prepare_param.param);

subsys/bluetooth/controller/ll_sw/nordic/lll/lll_central.c

@@ -247,12 +247,24 @@ static int prepare_cb(struct lll_prepare_param *p)
 	overhead = lll_preempt_calc(ull, (TICKER_ID_CONN_BASE + lll->handle), ticks_at_event);
 	/* check if preempt to start has changed */
 	if (overhead) {
-		LL_ASSERT_OVERHEAD(overhead);
+		int err;
+
+		if (p->defer == 1U) {
+			/* We accept the overhead and abort the event; previous event has decided to
+			 * continue and has deferred this event beyond the real time threshold to
+			 * have the radio prepared for this event.
+			 */
+			err = 0;
+		} else {
+			LL_ASSERT_OVERHEAD(overhead);
+
+			err = -ECANCELED;
+		}
 
 		radio_isr_set(lll_isr_abort, lll);
 		radio_disable();
 
-		return -ECANCELED;
+		return err;
 	}
 #endif /* !CONFIG_BT_CTLR_XTAL_ADVANCED */
 

subsys/bluetooth/controller/ll_sw/nordic/lll/lll_conn.c

@@ -69,6 +69,7 @@ static uint8_t crc_valid;
 static uint8_t is_aborted;
 static uint16_t tx_cnt;
 static uint16_t trx_cnt;
+static uint8_t trx_busy_iteration;
 
 #if defined(CONFIG_BT_CTLR_LE_ENC)
 static uint8_t mic_state;
@@ -153,27 +154,38 @@ void lll_conn_prepare_reset(void)
 	crc_valid = 0U;
 	crc_expire = 0U;
 	is_aborted = 0U;
+	trx_busy_iteration = 0U;
 
 #if defined(CONFIG_BT_CTLR_LE_ENC)
 	mic_state = LLL_CONN_MIC_NONE;
 #endif /* CONFIG_BT_CTLR_LE_ENC */
 }
 
 #if defined(CONFIG_BT_CENTRAL)
+/* Number of times central event being aborted by same event instance be skipped */
+/* FIXME: Increasing this causes event pipeline overflow assertion, add LLL implementation to
+ *        gracefully abort the deferred next event when -EBUSY is returned in this is_abort_cb
+ *        interface.
+ */
+#define CENTRAL_TRX_BUSY_ITERATION_MAX 1
+
 int lll_conn_central_is_abort_cb(void *next, void *curr,
 				 lll_prepare_cb_t *resume_cb)
 {
 	struct lll_conn *lll = curr;
 
-	/* Do not abort if near supervision timeout */
-	if (lll->forced) {
-		return 0;
-	}
+	if (next != curr) {
+		/* Do not be aborted by a different event if near supervision timeout */
+		if ((lll->forced == 1U) && (trx_cnt < 1U)) {
+			return 0;
+		}
 
-	/* Do not be aborted by same event if a single central trx has not been
-	 * exchanged.
-	 */
-	if ((next == curr) && (trx_cnt < 1U)) {
+	} else if ((trx_cnt < 1U) && (trx_busy_iteration < CENTRAL_TRX_BUSY_ITERATION_MAX)) {
+		trx_busy_iteration++;
+
+		/* Do not be aborted by same event if a single central's Rx has not completed.
+		 * Cases where single trx duration can be greater than connection interval.
+		 */
 		return -EBUSY;
 	}
 
@@ -182,20 +194,30 @@ int lll_conn_central_is_abort_cb(void *next, void *curr,
 #endif /* CONFIG_BT_CENTRAL */
 
 #if defined(CONFIG_BT_PERIPHERAL)
+/* Number of times peripheral event being aborted by same event instance be skipped */
+/* FIXME: Increasing this causes event pipeline overflow assertion, add LLL implementation to
+ *        gracefully abort the deferred next event when -EBUSY is returned in this is_abort_cb
+ *        interface.
+ */
+#define PERIPHERAL_TRX_BUSY_ITERATION_MAX 1
+
 int lll_conn_peripheral_is_abort_cb(void *next, void *curr,
 				    lll_prepare_cb_t *resume_cb)
 {
 	struct lll_conn *lll = curr;
 
-	/* Do not abort if near supervision timeout */
-	if (lll->forced) {
-		return 0;
-	}
+	if (next != curr) {
+		/* Do not be aborted by a different event if near supervision timeout */
+		if ((lll->forced == 1U) && (tx_cnt < 1U)) {
+			return 0;
+		}
 
-	/* Do not be aborted by same event if a single peripheral trx has not
-	 * been exchanged.
-	 */
-	if ((next == curr) && (tx_cnt < 1U)) {
+	} else if ((tx_cnt < 1U) && (trx_busy_iteration < PERIPHERAL_TRX_BUSY_ITERATION_MAX)) {
+		trx_busy_iteration++;
+
+		/* Do not be aborted by same event if a single peripheral's Tx has not completed.
+		 * Cases where single trx duration can be greater than connection interval.
+		 */
 		return -EBUSY;
 	}
 

subsys/bluetooth/controller/ll_sw/nordic/lll/lll_peripheral.c

@@ -339,12 +339,24 @@ static int prepare_cb(struct lll_prepare_param *p)
 	overhead = lll_preempt_calc(ull, (TICKER_ID_CONN_BASE + lll->handle), ticks_at_event);
 	/* check if preempt to start has changed */
 	if (overhead) {
-		LL_ASSERT_OVERHEAD(overhead);
+		int err;
+
+		if (p->defer == 1U) {
+			/* We accept the overhead and abort the event; previous event has decided to
+			 * continue and has deferred this event beyond the real time threshold to
+			 * have the radio prepared for this event.
+			 */
+			err = 0;
+		} else {
+			LL_ASSERT_OVERHEAD(overhead);
+
+			err = -ECANCELED;
+		}
 
 		radio_isr_set(lll_isr_abort, lll);
 		radio_disable();
 
-		return -ECANCELED;
+		return err;
 	}
 #endif /* CONFIG_BT_CTLR_XTAL_ADVANCED */