nimble/ll: Add option to discard excessive ISO SDUs

See syscfg description for details.

nimble/controller/src/ble_ll_isoal.c

@@ -152,10 +152,24 @@ ble_ll_isoal_mux_event_done(struct ble_ll_isoal_mux *mux)
  mux->last_tx_packet_seq_num = blehdr->txiso.packet_seq_num;
  }
 
+#if MYNEWT_VAL(BLE_LL_ISO_HCI_DISCARD_THRESHOLD)
+ /* Drop queued SDUs if number of queued SDUs exceeds defined threshold.
+ * Threshold is defined as number of ISO events. If number of queued SDUs
+ * exceeds number of SDUs required for single event (i.e. including pt)
+ * and number of subsequent ISO events defined by threshold value, we'll
+ * drop any excessive SDUs and notify host as if they were sent.
+ */
+ uint32_t thr = MYNEWT_VAL(BLE_LL_ISO_HCI_DISCARD_THRESHOLD);
+ if (mux->sdu_q_len > mux->sdu_per_event + thr * mux->sdu_per_interval) {
+ num_sdu = mux->sdu_q_len - mux->sdu_per_event -
+ thr * mux->sdu_per_interval;
+ }
+#endif
+
  while (pkthdr && num_sdu--) {
  OS_ENTER_CRITICAL(sr);
  STAILQ_REMOVE_HEAD(&mux->sdu_q, omp_next);
- assert(mux->sdu_q_len > 0);
+ BLE_LL_ASSERT(mux->sdu_q_len > 0);
  mux->sdu_q_len--;
  OS_EXIT_CRITICAL(sr);
 

nimble/controller/syscfg.yml

@@ -505,6 +505,18 @@ syscfg.defs:
  experimental: 1
  restrictions:
  - BLE_LL_HCI_VS || BLE_LL_ISO_HCI_FEEDBACK_INTERVAL_MS == 0
+ BLE_LL_ISO_HCI_DISCARD_THRESHOLD:
+ description: >
+ Enables automatic discarding of excessive ISO SDUs to avoid exhaustion
+ of HCI ISO buffers in case host sends too many SDUs.
+ Threshold is defined as number of ISO events. If number of queued
+ SDUs exceeds number of SDUs required for single event (i.e. including
+ pre-transmissions) and number of subsequent ISO events defined by
+ threshold value, the controller will drop any excessive SDUs and
+ notify to host as if they were already sent.
+ Set to 0 to disable.
+ value: 0
+ experimental: 1
 
  BLE_LL_SYSINIT_STAGE:
  description: >