samples: bluetooth: central_iso: phase configuration

Demonstrates fine tuning of the offset between the "measurement" (i.e.
production and scheduling of ISO SDUs) and the actual sending of the
corresponding PHY frames on the air interface to minimize latency.

Signed-off-by: Florian Grandel <[email protected]>

samples/bluetooth/central_iso/src/main.c

@@ -22,6 +22,11 @@
 #define LATENCY_MS               10U                   /* 10.0 ms */
 #define INTERVAL_US              (10U * USEC_PER_MSEC) /* 10.0 ms */
 
+/* This is the time it takes to process a measurement inside the controller stack
+ * before it will be sent over the air.
+ */
+#define HCI_PROCESSING_OFFSET_US 2500U                 /*  2.5 ms */
+
 static void start_scan(void);
 
 static struct bt_conn *default_conn;
@@ -101,7 +106,7 @@ static void iso_timer_timeout(struct k_timer *timer)
 	 * delivered with minimal latency and w/o accruing rounding errors.
 	 */
 	next_tick = first_tick +
-		    (((int64_t)seq_num * INTERVAL_US) *
+		    (((int64_t)(seq_num + 1U) * INTERVAL_US - HCI_PROCESSING_OFFSET_US) *
 		     CONFIG_SYS_CLOCK_TICKS_PER_SEC) /
 			    USEC_PER_SEC -
 		    cur_tick;