Bluetooth: Controller: Fix single switch timer minimum compare value

Fix implementation of single switch timer minimum compare
value requirement. Do not always add the maximum possible
radio latency duration, but check if the required compare
value is smaller, then use the remainder required as the
extra compare value. This fix reduces latencies to setup
radio receptions and fixes an assertion in lll_scan_aux
when radio_tmr_start_us() is checked for latencies.

Relates to commit bcd28e0 ("Bluetooth: Controller:
Fix sw switch single timer for spurious TXEN/RXEN").

Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: cvinayak

subsys/bluetooth/controller/ll_sw/nordic/hal/nrf5/radio/radio.c

@@ -1349,10 +1349,12 @@ uint32_t radio_tmr_start(uint8_t trx, uint32_t ticks_start, uint32_t remainder)
 	 * by the Radio ISR, the compare will trigger again.
 	 */
 	uint32_t latency_ticks;
+	uint32_t latency_us;
 
-	latency_ticks = HAL_TICKER_US_TO_TICKS(HAL_RADIO_ISR_LATENCY_MAX_US);
+	latency_us = MAX(remainder, HAL_RADIO_ISR_LATENCY_MAX_US) - remainder;
+	latency_ticks = HAL_TICKER_US_TO_TICKS(latency_us);
 	ticks_start -= latency_ticks;
-	remainder += HAL_TICKER_TICKS_TO_US(latency_ticks);
+	remainder += latency_us;
 #endif /* !CONFIG_BT_CTLR_SW_SWITCH_SINGLE_TIMER */
 
 	nrf_timer_task_trigger(EVENT_TIMER, NRF_TIMER_TASK_CLEAR);
@@ -1473,10 +1475,12 @@ uint32_t radio_tmr_start_tick(uint8_t trx, uint32_t ticks_start)
 	 * by the Radio ISR, the compare will trigger again.
 	 */
 	uint32_t latency_ticks;
+	uint32_t latency_us;
 
-	latency_ticks = HAL_TICKER_US_TO_TICKS(HAL_RADIO_ISR_LATENCY_MAX_US);
+	latency_us = MAX(remainder_us, HAL_RADIO_ISR_LATENCY_MAX_US) - remainder_us;
+	latency_ticks = HAL_TICKER_US_TO_TICKS(latency_us);
 	ticks_start -= latency_ticks;
-	remainder_us += HAL_TICKER_TICKS_TO_US(latency_ticks);
+	remainder_us += latency_us;
 #endif /* !CONFIG_BT_CTLR_SW_SWITCH_SINGLE_TIMER */
 
 	nrf_timer_task_trigger(EVENT_TIMER, NRF_TIMER_TASK_STOP);
@@ -1614,10 +1618,10 @@ uint32_t radio_tmr_start_us(uint8_t trx, uint32_t start_us)
 		 * The timer is cleared on Radio End and if the PPI/DPPI is not disabled
 		 * by the Radio ISR, the compare will trigger again.
 		 */
-		uint32_t latency_ticks;
+		uint32_t latency_us;
 
-		latency_ticks = HAL_TICKER_US_TO_TICKS(HAL_RADIO_ISR_LATENCY_MAX_US);
-		actual_us += HAL_TICKER_TICKS_TO_US(latency_ticks);
+		latency_us = MAX(actual_us, HAL_RADIO_ISR_LATENCY_MAX_US) - actual_us;
+		actual_us += latency_us;
 #endif /* !CONFIG_BT_CTLR_SW_SWITCH_SINGLE_TIMER */
 
 		nrf_timer_event_clear(EVENT_TIMER, NRF_TIMER_EVENT_COMPARE0);