[nrf fromtree] Bluetooth: Controller: Fix single switch timer use in ISO Sync

Fix implementation of Broadcast ISO Synchronized Receiver
using single switch timer to consider minimum compare value
requirement.

This fix reduces latencies to setup radio receptions and
fixes an assertion in lll_sync_iso when radio_tmr_start_us()
is checked for latencies.

Relates to commit 5dfc58c ("Bluetooth: Controller: Fix
single switch timer minimum compare value").

Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>
(cherry picked from commit 8eae0bf)
Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: cvinayak

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

@@ -1352,22 +1352,25 @@ static void isr_rx(void *param)
 		hcto -= addr_us_get(lll->phy);
 		hcto -= radio_rx_ready_delay_get(lll->phy, PHY_FLAGS_S8);
 
-		overhead_us = radio_rx_chain_delay_get(lll->phy, PHY_FLAGS_S8);
-		overhead_us += addr_us_get(lll->phy);
-		overhead_us += radio_rx_ready_delay_get(lll->phy, PHY_FLAGS_S8);
+		/* Overhead within EVENT_IFS_US to exclude from max. jitter */
+		/* Required radio ready duration, settling time */
+		overhead_us = radio_rx_ready_delay_get(lll->phy, PHY_FLAGS_S8);
+		/* If single timer used, then consider required max. latency */
+		overhead_us += HAL_RADIO_ISR_LATENCY_MAX_US;
+		/* Add chain delay overhead */
+		overhead_us += radio_rx_chain_delay_get(lll->phy, PHY_FLAGS_S8);
+		/* Add base clock jitter overhead */
 		overhead_us += (EVENT_CLOCK_JITTER_US << 1);
-
 		LL_ASSERT(EVENT_IFS_US > overhead_us);
 
+		/* Max. available clock jitter */
 		jitter_max_us = (EVENT_IFS_US - overhead_us) >> 1;
+		/* Max. clock jitter per subevent */
 		jitter_max_us = (jitter_max_us * nse) / (lll->num_bis * lll->nse);
-		overhead_us = HAL_RADIO_TMR_START_DELAY_US;
-		if (jitter_max_us > overhead_us) {
-			jitter_max_us -= overhead_us;
-		} else {
-			jitter_max_us = 0U;
-		}
+		/* Min. clock jitter we shall use */
+		jitter_max_us = MAX(jitter_max_us, (EVENT_CLOCK_JITTER_US << 1));
 
+		/* Jitter for current subevent */
 		jitter_us = (EVENT_CLOCK_JITTER_US << 1) * nse;
 		if (jitter_us > jitter_max_us) {
 			jitter_us = jitter_max_us;