samples: bluetooth: central_iso: deterministic scheduling

The sample used deferred work to schedule ISO SDUs. The deferred work
API does not guarantee deterministic timing, though.

This commit switches to kernel timers which allow for deterministic
periodic or one-off timing as long as timers are re-scheduled in the
timer callback which runs directly in ISR context.

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

samples/bluetooth/central_iso/src/main.c

@@ -25,14 +25,13 @@
 static void start_scan(void);
 
 static struct bt_conn *default_conn;
-static struct k_work_delayable iso_send_work;
 static struct bt_iso_chan iso_chan;
 static uint32_t seq_num;
 NET_BUF_POOL_FIXED_DEFINE(tx_pool, 1, BT_ISO_SDU_BUF_SIZE(CONFIG_BT_ISO_TX_MTU),
 			  CONFIG_BT_CONN_TX_USER_DATA_SIZE, NULL);
 
 /**
- * @brief Send ISO data on timeout
+ * @brief Send ISO data SDU
  *
  * This will send an increasing amount of ISO data, starting from 1 octet.
  *
@@ -44,14 +43,16 @@ NET_BUF_POOL_FIXED_DEFINE(tx_pool, 1, BT_ISO_SDU_BUF_SIZE(CONFIG_BT_ISO_TX_MTU),
  *
  * @param work Pointer to the work structure
  */
-static void iso_timer_timeout(struct k_work *work)
+static void iso_send_sdu(struct k_work *work)
 {
 	static uint8_t buf_data[CONFIG_BT_ISO_TX_MTU];
 	static size_t len_to_send = 1;
 	static bool data_initialized;
 	struct net_buf *buf;
 	int ret;
 
+	ARG_UNUSED(work);
+
 	if (!data_initialized) {
 		for (int i = 0; i < ARRAY_SIZE(buf_data); i++) {
 			buf_data[i] = (uint8_t)i;
@@ -72,14 +73,24 @@ static void iso_timer_timeout(struct k_work *work)
 		net_buf_unref(buf);
 	}
 
-	k_work_schedule(&iso_send_work, K_USEC(INTERVAL_US));
-
 	len_to_send++;
 	if (len_to_send > ARRAY_SIZE(buf_data)) {
 		len_to_send = 1;
 	}
 }
 
+static K_WORK_DEFINE(iso_send_sdu_work, iso_send_sdu);
+
+static void iso_timer_timeout(struct k_timer *timer)
+{
+	ARG_UNUSED(timer);
+
+	k_work_submit(&iso_send_sdu_work);
+}
+
+static K_TIMER_DEFINE(iso_timer, iso_timer_timeout, NULL);
+
+
 static void device_found(const bt_addr_le_t *addr, int8_t rssi, uint8_t type,
 			 struct net_buf_simple *ad)
 {
@@ -137,13 +148,13 @@ static void iso_connected(struct bt_iso_chan *chan)
 	seq_num = 0U;
 
 	/* Start send timer */
-	k_work_schedule(&iso_send_work, K_MSEC(0));
+	k_timer_start(&iso_timer, K_NO_WAIT, K_USEC(INTERVAL_US));
 }
 
 static void iso_disconnected(struct bt_iso_chan *chan, uint8_t reason)
 {
 	printk("ISO Channel %p disconnected (reason 0x%02x)\n", chan, reason);
-	k_work_cancel_delayable(&iso_send_work);
+	k_timer_stop(&iso_timer);
 }
 
 static struct bt_iso_chan_ops iso_ops = {
@@ -267,6 +278,5 @@ int main(void)
 
 	start_scan();
 
-	k_work_init_delayable(&iso_send_work, iso_timer_timeout);
 	return 0;
 }