nimble/ll: Prevent BIG event preemption by periodic advertising

This update adjusts the scheduling policy for periodic advertising
to ensure it does not preempt BIG events. This ensures stability
and performance of audio.

Author: andrzej-kaczmarek

nimble/controller/src/ble_ll_sched.c

@@ -114,6 +114,16 @@ preempt_any_except_conn(struct ble_ll_sched_item *sch,
     return ble_ll_conn_is_lru(sch->cb_arg, item->cb_arg);
 }
 
+static int
+preempt_any_except_big(struct ble_ll_sched_item *sch, struct ble_ll_sched_item *item)
+{
+    if (item->sched_type == BLE_LL_SCHED_TYPE_BIG) {
+        return 0;
+    }
+
+    return 1;
+}
+
 static inline int
 ble_ll_sched_check_overlap(struct ble_ll_sched_item *sch1,
                            struct ble_ll_sched_item *sch2)
@@ -746,7 +756,7 @@ ble_ll_sched_periodic_adv(struct ble_ll_sched_item *sch, bool first_event)
         rc = ble_ll_sched_insert(sch, BLE_LL_SCHED_MAX_DELAY_ANY,
                                  preempt_none);
     } else {
-        rc = ble_ll_sched_insert(sch, 0, preempt_any);
+        rc = ble_ll_sched_insert(sch, 0, preempt_any_except_big);
     }
 
     OS_EXIT_CRITICAL(sr);