Extend number of devices for PAwR (Coded PHY)

[Yannch]

Hi all !

I'm writing this message because I'm having problems trying to increase the number of devices in PAwR (I use Coded PHY).

I based my development on the SDK 2.8.0 example (Periodic_adv_conn / Periodic_sync_conn). I also tried Periodic_adv_rsp / Periodic_sync_rsp examples without success.

I've modified it so that I don't have to connect every time via on the TX side:

bt_conn_le_create_synced function()

On the RX side, I have a fixed subevent and slot numbers to answer to TX.

Based on SDK example, I can exchange data with 25 devices (5 subevents / 5 slots)

I used the following configuration:

#define NUM_RSP_SLOTS 5
#define NUM_SUBEVENTS 5
#define SUBEVENT_INTERVAL 0x30

static const struct bt_le_per_adv_param per_adv_params = {
	.interval_min = 0xFF,
	.interval_max = 0xFF,
	.options = 0,
	.num_subevents = NUM_SUBEVENTS,
	.subevent_interval = SUBEVENT_INTERVAL,
	.response_slot_delay = 0x5,
	.response_slot_spacing = 0x50,
	.num_response_slots = NUM_RSP_SLOTS,
};

When I try to increase the number of devices (8 subevents / 20 slots per subevent), I don't get the same behavior.

Below are the timings I use depending on the number of subevents and slots.

#define NUM_RSP_SLOTS 20
#define NUM_SUBEVENTS 8

static const struct bt_le_per_adv_param per_adv_params = {
	.interval_min = 0x960,
	.interval_max = 0x960,
	.options = 0,
	.num_subevents = NUM_SUBEVENTS,
	.subevent_interval = 0xF0,
	.response_slot_delay = 0x10,
	.response_slot_spacing = 0x50,
	.num_response_slots = NUM_RSP_SLOTS,
};

I saw that the PAwR feature is still experimental in the las version of the SDK, could this be related or is there something I'm doing wrong?

Thank you in advance for your answers or feedbacks.

Yann

[Hieu]

Hi Yann,

Your configurations seem feasible. Could you please provide more details on what kind of failure you are facing?

Are there any logs? What are the symptoms?

Hieu

[Yannch]

Hi Hieu,

Thanks for you answer.

Yes sure, what I can see is that with the initial parameters (5 subevents / 5 slots per subevent) I can synchronize and exchange data between transmitter and receiver.

Transmitter:

[00:00:00.011,535] <inf> bt_hci_core: HW Platform: Nordic Semiconductor (0x0002)
[00:00:00.011,566] <inf> bt_hci_core: HW Variant: nRF52x (0x0002)
[00:00:00.011,596] <inf> bt_hci_core: Firmware: Standard Bluetooth controller (0x00) Version 254.63788 Build 573996906
[00:00:00.012,786] <inf> bt_hci_core: Identity: C8:22:35:1D:70:9F (random)
[00:00:00.012,817] <inf> bt_hci_core: HCI: version 6.0 (0x0e) revision 0x104e, manufacturer 0x0059
[00:00:00.012,847] <inf> bt_hci_core: LMP: version 6.0 (0x0e) subver 0x104e
Start Periodic Advertising
PAwR RSP : Subevent : 0 Slot : 2
PAwR RSP : Subevent : 0 Slot : 2
PAwR RSP : Subevent : 0 Slot : 2
PAwR RSP : Subevent : 0 Slot : 2
PAwR RSP : Subevent : 0 Slot : 2
PAwR RSP : Subevent : 0 Slot : 2

Receiver:

Synced to 69:D7:06:00:1C:75 (random) with 5 subevents
DEBUG - CMD RESP 0x0 0x1 0x0 0x0 0x0
DEBUG - CMD RESP 0x0 0x1 0x0 0x0 0x0
DEBUG - CMD RESP 0x0 0x1 0x0 0x0 0x0
DEBUG - CMD RESP 0x0 0x1 0x0 0x0 0x0
DEBUG - CMD RESP 0x0 0x1 0x0 0x0 0x0
DEBUG - CMD RESP 0x0 0x1 0x0 0x0 0x0
DEBUG - CMD RESP 0x0 0x1 0x0 0x0 0x0
DEBUG - CMD RESP 0x0 0x1 0x0 0x0 0x0
DEBUG - CMD RESP 0x0 0x1 0x0 0x0 0x0
DEBUG - CMD RESP 0x0 0x1 0x0 0x0 0x0

Now if I update parameters (Subevents 8 / Slots per subevent 20)

With these settings, the device receiving the PAwR signals can't synchronize.

Transmitter:

[00:00:00.011,352] <inf> bt_hci_core: HW Platform: Nordic Semiconductor (0x0002)
[00:00:00.011,383] <inf> bt_hci_core: HW Variant: nRF52x (0x0002)
[00:00:00.011,413] <inf> bt_hci_core: Firmware: Standard Bluetooth controller (0x00) Version 254.63788 Build 573996906
[00:00:00.012,573] <inf> bt_hci_core: Identity: C8:22:35:1D:70:9F (random)
[00:00:00.012,634] <inf> bt_hci_core: HCI: version 6.0 (0x0e) revision 0x104e, manufacturer 0x0059
[00:00:00.012,664] <inf> bt_hci_core: LMP: version 6.0 (0x0e) subver 0x104e
Start Periodic Advertising

Receiver:

Synced to 71:31:A2:CE:53:E5 (random) with 8 subevents
Failed to set subevents to sync to (err -5)
DEBUG - CMD RESP 0x0 0x1 0x0 0x0 0x0
Failed to send response (err -5)
Receive Terminated Callback

 

[Hieu]

Hi Yann,

Unfortunately, I am working remotely and do not have enough device to reproduce the issue.

What do you think about starting from the working baseline, and slowly change the configurations, and do incremental tests to see at which point the issue occurs?

I recommend this order:

1. Periodic Advertising Interval
2. Subevent Interval
3. Number of Subevents
4. Response Slot Delay
5. Response Slot Spacing
6. Number of Response Slots

If you are able to detect which one fail, try switching up the order, but of course keep it feasible (e.g., don't increase Number of Subevents before you have widened the Advertising Interval)

It would give us some clues on what is wrong.

[Yannch]

Hi Hieu,

No problem, I can check again from my side if I change parameters step by step and I will tell you.

Just a question, from your side in Nordic did you already tried to use PAwR with more than 25 devices (5 subevents / 5 slots) ?

Thank you,

Yann

[Hieu]

Hi Yann,

We have tested more than 25 devices. We wrote about it a little here:  Getting started with Bluetooth Electronic Shelf Labels (ESL) and Periodic Advertising with Responses (PAwR) .

Regards,

Hieu

[Yannch]

Hi Hieu,

Thank you for your reply. I will have a look on the tutorial.

Best regards,

Yann

[Yannch]

Hi Hieu,

I prepared a modified version of the periodic_adv/sync_conn example with my PAwR timings.

Can you please have a look on it ?

You can try from your side if you want, I used a nrf52840dk for the ADV side and only one nrf52840dk for the SYNC side and it's not possible to exchange data. 

You will find diff to easily see my changes.

ADV Side

diff --git a/src/main.c b/src/main.c
index 49c1c52..b04a8b4 100644
--- a/src/main.c
+++ b/src/main.c
@@ -9,22 +9,40 @@
 #include <zephyr/bluetooth/gap.h>
 #include <zephyr/bluetooth/hci.h>
 
-#define NUM_RSP_SLOTS	  5
-#define NUM_SUBEVENTS	  5
-#define PACKET_SIZE	  5
+#define NUM_RSP_SLOTS	  20
+#define NUM_SUBEVENTS	  8
+// #define NUM_RSP_SLOTS	  5
+// #define NUM_SUBEVENTS	  5
+#define PACKET_SIZE	      5
 #define SUBEVENT_INTERVAL 0x30
 
+#define BT_LE_EXT_ADV_NCONN_CODED BT_LE_ADV_PARAM(BT_LE_ADV_OPT_EXT_ADV | \
+                        BT_LE_ADV_OPT_CODED, \
+					    BT_GAP_ADV_FAST_INT_MIN_2, \
+					    BT_GAP_ADV_FAST_INT_MAX_2, NULL)
+
 static const struct bt_le_per_adv_param per_adv_params = {
-	.interval_min = 0xFF,
-	.interval_max = 0xFF,
+	.interval_min = 0x960,
+	.interval_max = 0x960,
 	.options = 0,
 	.num_subevents = NUM_SUBEVENTS,
-	.subevent_interval = SUBEVENT_INTERVAL,
-	.response_slot_delay = 0x5,
+	.subevent_interval = 0xF0,
+	.response_slot_delay = 0x10,
 	.response_slot_spacing = 0x50,
 	.num_response_slots = NUM_RSP_SLOTS,
 };
 
+// static const struct bt_le_per_adv_param per_adv_params = {
+// 	.interval_min = 0xFF,
+// 	.interval_max = 0xFF,
+// 	.options = 0,
+// 	.num_subevents = NUM_SUBEVENTS,
+// 	.subevent_interval = SUBEVENT_INTERVAL,
+// 	.response_slot_delay = 0x5,
+// 	.response_slot_spacing = 0x50,
+// 	.num_response_slots = NUM_RSP_SLOTS,
+// };
+
 static struct bt_le_per_adv_subevent_data_params subevent_data_params[NUM_SUBEVENTS];
 static struct net_buf_simple bufs[NUM_SUBEVENTS];
 static uint8_t backing_store[NUM_SUBEVENTS][PACKET_SIZE];
@@ -73,46 +91,12 @@ static struct bt_conn *default_conn;
 static void response_cb(struct bt_le_ext_adv *adv, struct bt_le_per_adv_response_info *info,
 			struct net_buf_simple *buf)
 {
-	int err;
-	bt_addr_le_t peer;
-	char addr_str[BT_ADDR_LE_STR_LEN];
-	struct bt_conn_le_create_synced_param synced_param;
-	struct bt_le_conn_param conn_param;
-
 	if (!buf) {
 		return;
 	}
 
-	if (default_conn) {
-		/* Do not initiate new connections while already connected */
-		return;
-	}
-
-	bt_addr_le_copy(&peer, &bt_addr_le_none);
-	bt_data_parse(buf, get_address, &peer);
-	if (bt_addr_le_eq(&peer, &bt_addr_le_none)) {
-		/* No address found */
-		return;
-	}
-
-	bt_addr_le_to_str(&peer, addr_str, sizeof(addr_str));
-	printk("Connecting to %s in subevent %d\n", addr_str, info->subevent);
-
-	synced_param.peer = &peer;
-	synced_param.subevent = info->subevent;
-
-	/* Choose same interval as PAwR advertiser to avoid scheduling conflicts */
-	conn_param.interval_min = SUBEVENT_INTERVAL;
-	conn_param.interval_max = SUBEVENT_INTERVAL;
-
-	/* Default values */
-	conn_param.latency = 0;
-	conn_param.timeout = 400;
-
-	err = bt_conn_le_create_synced(adv, &synced_param, &conn_param, &default_conn);
-	if (err) {
-		printk("Failed to initiate connection (err %d)", err);
-	}
+    printk("RX DATA : SUB %u SLOT %u DATA %X%X%X%X%X\n", info->subevent, info->response_slot,
+        buf->data[0], buf->data[1], buf->data[2], buf->data[3], buf->data[4]);
 }
 
 static const struct bt_le_ext_adv_cb adv_cb = {
@@ -183,7 +167,7 @@ int main(void)
 	}
 
 	/* Create a non-connectable advertising set */
-	err = bt_le_ext_adv_create(BT_LE_EXT_ADV_NCONN, &adv_cb, &pawr_adv);
+	err = bt_le_ext_adv_create(BT_LE_EXT_ADV_NCONN_CODED, &adv_cb, &pawr_adv);
 	if (err) {
 		printk("Failed to create advertising set (err %d)\n", err);
 		return 0;

SYNC side

diff --git a/src/main.c b/src/main.c
index db858ef..172acf8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -57,6 +57,7 @@ static void term_cb(struct bt_le_per_adv_sync *sync,
 static struct bt_le_per_adv_response_params rsp_params;
 
 NET_BUF_SIMPLE_DEFINE_STATIC(rsp_buf, sizeof(bt_addr_le_t) + 2 * sizeof(uint8_t));
+uint8_t myDummyBuf[] = {0x11, 0x22, 0x33, 0x44, 0x55};
 
 static void recv_cb(struct bt_le_per_adv_sync *sync,
 		    const struct bt_le_per_adv_sync_recv_info *info, struct net_buf_simple *buf)
@@ -79,25 +80,17 @@ static void recv_cb(struct bt_le_per_adv_sync *sync,
 		rsp_params.response_subevent = info->subevent;
 		rsp_params.response_slot = 0;
 
-		err = bt_le_oob_get_local(BT_ID_DEFAULT, &oob);
-		if (err) {
-			printk("Failed to get OOB data (err %d)\n", err);
-
-			return;
-		}
-
-		bt_addr_le_to_str(&oob.addr, addr_str, sizeof(addr_str));
-		printk("Responding with own addr: %s\n", addr_str);
-
-		net_buf_simple_add_u8(&rsp_buf, sizeof(bt_addr_le_t));
-		net_buf_simple_add_u8(&rsp_buf, BT_DATA_LE_BT_DEVICE_ADDRESS);
-		net_buf_simple_add_mem(&rsp_buf, &oob.addr.a, sizeof(oob.addr.a));
-		net_buf_simple_add_u8(&rsp_buf, oob.addr.type);
+        net_buf_simple_add_mem(&rsp_buf, myDummyBuf, sizeof(myDummyBuf));
 
 		err = bt_le_per_adv_set_response_data(sync, &rsp_params, &rsp_buf);
 		if (err) {
 			printk("Failed to send response (err %d)\n", err);
 		}
+        else
+        {
+            printk("Response data sent : 0x%2X:0x%2X:0x%2X:0x%2X:0x%2X\n",
+                myDummyBuf[0], myDummyBuf[1], myDummyBuf[2], myDummyBuf[3], myDummyBuf[4]);
+        }
 	} else if (buf) {
 		printk("Received empty indication: subevent %d\n", info->subevent);
 	} else {
@@ -198,7 +191,7 @@ int main(void)
 	bt_le_scan_cb_register(&scan_callbacks);
 	bt_le_per_adv_sync_cb_register(&sync_callbacks);
 
-	err = bt_le_scan_start(BT_LE_SCAN_ACTIVE, NULL);
+	err = bt_le_scan_start(BT_LE_SCAN_CODED_ACTIVE, NULL);
 	if (err) {
 		printk("failed (err %d)\n", err);
 

Thanks,

Yann