Bluetooth: Controller: Fix prepare overhead in scheduling ISO

Fix double prepare overhead considered in scheduling
extended, periodic and ISO broadcast radio events when using
LOW LAT variant.

ticks_slot maintained in ticker includes the overhead, the
ticks_slot stored in role/state context exclude the overhead
hence take care to include ticks_slot_overhead when value is
used from context and not when value used from ticker nodes.

Add jitter due to ticker resolution unit between scheduled
radio events. This will allow the synchronizing side too to
not overlap due to ticker resolution related jitter.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>

subsys/bluetooth/controller/ll_sw/ull_sched.c

@@ -324,15 +324,16 @@ static int group_free_slot_get(uint8_t user_id, uint32_t ticks_slot_abs,
 #if defined(CONFIG_BT_BROADCASTER) && CONFIG_BT_CTLR_ADV_AUX_SET > 0
 		} else if (IN_RANGE(ticker_id, TICKER_ID_ADV_AUX_BASE,
 				    TICKER_ID_ADV_AUX_LAST)) {
-			const struct ll_adv_aux_set *aux;
-
 			*ticks_anchor += ticks_to_expire;
 			*ticks_anchor += ticks_slot;
+			*ticks_anchor += HAL_TICKER_US_TO_TICKS(
+				EVENT_TICKER_RES_MARGIN_US << 1);
+
+#if defined(CONFIG_BT_CTLR_ADV_PERIODIC)
+			const struct ll_adv_aux_set *aux;
 
 			aux = ull_adv_aux_get(ticker_id -
 					      TICKER_ID_ADV_AUX_BASE);
-
-#if defined(CONFIG_BT_CTLR_ADV_PERIODIC)
 			if (aux->lll.adv->sync) {
 				const struct ll_adv_sync_set *sync;
 
@@ -345,29 +346,15 @@ static int group_free_slot_get(uint8_t user_id, uint32_t ticks_slot_abs,
 			}
 #endif /* CONFIG_BT_CTLR_ADV_PERIODIC */
 
-			if (IS_ENABLED(CONFIG_BT_CTLR_LOW_LAT)) {
-				*ticks_anchor +=
-					MAX(aux->ull.ticks_active_to_start,
-					    aux->ull.ticks_prepare_to_start);
-			}
-
 			return 0;
 
 #if defined(CONFIG_BT_CTLR_ADV_PERIODIC)
 		} else if (IN_RANGE(ticker_id, TICKER_ID_ADV_SYNC_BASE,
 				    TICKER_ID_ADV_SYNC_LAST)) {
 			*ticks_anchor += ticks_to_expire;
 			*ticks_anchor += ticks_slot;
-
-			if (IS_ENABLED(CONFIG_BT_CTLR_LOW_LAT)) {
-				const struct ll_adv_sync_set *sync;
-
-				sync = ull_adv_sync_get(ticker_id -
-							TICKER_ID_ADV_SYNC_BASE);
-				*ticks_anchor +=
-					MAX(sync->ull.ticks_active_to_start,
-					    sync->ull.ticks_prepare_to_start);
-			}
+			*ticks_anchor += HAL_TICKER_US_TO_TICKS(
+				EVENT_TICKER_RES_MARGIN_US << 1);
 
 			return 0;
 
@@ -376,16 +363,8 @@ static int group_free_slot_get(uint8_t user_id, uint32_t ticks_slot_abs,
 				    TICKER_ID_ADV_ISO_LAST)) {
 			*ticks_anchor += ticks_to_expire;
 			*ticks_anchor += ticks_slot;
-
-			if (IS_ENABLED(CONFIG_BT_CTLR_LOW_LAT)) {
-				const struct ll_adv_iso_set *iso;
-
-				iso = ull_adv_iso_get(ticker_id -
-						      TICKER_ID_ADV_ISO_BASE);
-				*ticks_anchor +=
-					MAX(iso->ull.ticks_active_to_start,
-					    iso->ull.ticks_prepare_to_start);
-			}
+			*ticks_anchor += HAL_TICKER_US_TO_TICKS(
+				EVENT_TICKER_RES_MARGIN_US << 1);
 
 			return 0;
 
@@ -398,6 +377,8 @@ static int group_free_slot_get(uint8_t user_id, uint32_t ticks_slot_abs,
 				    TICKER_ID_CONN_LAST)) {
 			*ticks_anchor += ticks_to_expire;
 			*ticks_anchor += ticks_slot;
+			*ticks_anchor += HAL_TICKER_US_TO_TICKS(
+				EVENT_TICKER_RES_MARGIN_US << 1);
 
 			return 0;
 #endif /* CONFIG_BT_CONN */