Restarting High Duty Cycle Direct Advertising

RE: Restarting High Duty Cycle Direct Advertising

aacosta — Wed, 02 Oct 2024 01:03:27 GMT

Actually, it's racy. As I suspected the advertising work sometimes happens before the connection is deallocated.

Using the `recycled` callback (which I just found about) is much nicer.

RE: Restarting High Duty Cycle Direct Advertising

Vidar Berg — Mon, 30 Sep 2024 13:51:11 GMT

I don't see any issue with adding the advertising start work from the disconnected callback, if that's what you're asking.

RE: Restarting High Duty Cycle Direct Advertising

aacosta — Mon, 30 Sep 2024 11:59:18 GMT

Whenever there is a disconnection in the peripheral snd never prompted by me. I guess that online happens on connection errors?

RE: Restarting High Duty Cycle Direct Advertising

Vidar Berg — Mon, 30 Sep 2024 09:21:51 GMT

Are you attempting to start your directed advertiser when there is a connection error? In that case, the workqueue item should be processed after the connection object has been released.

RE: Restarting High Duty Cycle Direct Advertising

aacosta — Sun, 29 Sep 2024 10:56:13 GMT

Vidar Berg I run into the same problem and your work queue solution works great! Thanks!

I have a question though. Are we sure that the advertising work will never run concurrently with the connection finalization? Wouldn't this be a problem?

RE: Restarting High Duty Cycle Direct Advertising

Vidar Berg — Wed, 20 Sep 2023 11:30:45 GMT

I'm Happy to help! I verified that it worked on my end by using the nRF connect app on Android with 'autoconnect' enabled (Note: it won't work on iOS as it doesn't support directed advertisement). With 'autoconnect' enabled, the phone should try to re-connect when it receives directed advertisement packets from the device after the connection has been lost.

Here are the steps I used to test this:

1. Connect & bond with the device from the nRF connect

2. Enable autoconnect by pressing the 3 dotted button in the top right corner and select "autoconnect"

3. Reset the peripheral to force a disconnect

4. Observe from the app that the connection state transitions from 'connected' to 'disconnected' and then back to 'connected'.

Debug log showing reconnect on the first advertisment after reset

*** Booting Zephyr OS build 28a3fca7da5c ***
[00:00:00.006,561] <inf> fs_nvs: nvs_mount: 6 Sectors of 4096 bytes
[00:00:00.006,561] <inf> fs_nvs: nvs_mount: alloc wra: 0, fb8
[00:00:00.006,591] <inf> fs_nvs: nvs_mount: data wra: 0, b4
[00:00:00.006,713] <inf> bt_sdc_hci_driver: hci_driver_open: SoftDevice Controller build revision: 
                                            e0 7e 2e c1 5e 05 85 23  46 15 dc fa 8e 29 7d 70 |.~..^..# F....)}p
                                            10 93 a5 fc                                      |....             
[00:00:00.009,521] <inf> bt_hci_core: hci_vs_init: HW Platform: Nordic Semiconductor (0x0002)
[00:00:00.009,552] <inf> bt_hci_core: hci_vs_init: HW Variant: nRF52x (0x0002)
[00:00:00.009,582] <inf> bt_hci_core: hci_vs_init: Firmware: Standard Bluetooth controller (0x00) Version 224.11902 Build 2231721665
[00:00:00.009,979] <inf> bt_hci_core: bt_init: No ID address. App must call settings_load()
Bluetooth initialized
[00:00:00.010,803] <inf> bt_hci_core: bt_dev_show_info: Identity: D8:2A:C8:17:11:5C (random)
[00:00:00.010,833] <inf> bt_hci_core: bt_dev_show_info: HCI: version 5.4 (0x0d) revision 0x1077, manufacturer 0x0059
[00:00:00.010,894] <inf> bt_hci_core: bt_dev_show_info: LMP: version 5.4 (0x0d) subver 0x1077
Direct advertising to 6C:DD:BC:29:D8:8E (public)
Advertising successfully started
Connected

I should also add that directed advertisements will not be "Scanner" view when scanning for new devices.

RE: Restarting High Duty Cycle Direct Advertising

lionfish — Wed, 20 Sep 2023 10:11:00 GMT

Thank you for writing all that code for me. It's really appreciated. That appears to be working I guess... but I can't actually tell. I've tried bonding with it via the Nordic nRF connect app, but never see high-duty packets? I also tried looking for them via a separate system running the DA14531 SoC, but I couldn't see them there either (I also tried manually setting the target address equal to my phone and the DA14531's address).

Is there a way of detecting these packets? I assume I can't see them as I've some how messed up the address or something, and direct adv packets that aren't addressed to a device get ignored?

Thanks again for your help.

E.g. Modifying the target address...

err = bt_addr_le_from_str("C0:56:78:9A:BC:DE", "random", &bond_addr);
 if (err) {
 printk("Setting address failed (err %d)\n", err);
 }

RE: Restarting High Duty Cycle Direct Advertising

Vidar Berg — Fri, 15 Sep 2023 09:19:50 GMT

Hello,

The program needs to exit the connection callback before attempting to re-start the advertisement. I think the easiest way to do this is to create a workqueue item to start advertising, then offload this task to the workqueue thread from the connected callback.

Define workqueue item

static void advertising_start(struct k_work *work);
static K_WORK_DEFINE(start_advertising_worker, advertising_start);

advertising_start() implementation

static void advertising_start(struct k_work *work)
{
	int err;
	char addr[BT_ADDR_LE_STR_LEN];
	
	bt_addr_le_copy(&bond_addr, BT_ADDR_LE_NONE);
	bt_foreach_bond(BT_ID_DEFAULT, copy_last_bonded_addr, NULL);

	/* Address is equal to BT_ADDR_LE_NONE if compare returns 0.
	 * This means there is no bond yet.
	 */
	if (bt_addr_le_cmp(&bond_addr, BT_ADDR_LE_NONE) != 0) {
		bt_addr_le_to_str(&bond_addr, addr, sizeof(addr));
		printk("Direct advertising to %s\n", addr);

		//adv_param = *BT_LE_ADV_CONN_DIR_LOW_DUTY(&bond_addr);
		adv_param = *BT_LE_ADV_CONN_DIR(&bond_addr);
		adv_param.options |= BT_LE_ADV_OPT_DIR_ADDR_RPA;
		err = bt_le_adv_start(&adv_param, NULL, 0, NULL, 0);
	} else {
		err = bt_le_adv_start(BT_LE_ADV_CONN_NAME, ad, ARRAY_SIZE(ad), NULL, 0);
	}

	if (err) {
		printk("Advertising failed to start (err %d)\n", err);
	} else {
		printk("Advertising successfully started\n");
	}	
}

Submit "advertising start task" to the workqueue from the connected callback

static void connected(struct bt_conn *conn, uint8_t err)
{
	if (err == BT_HCI_ERR_ADV_TIMEOUT) {
		printk("Trying to re-start directed adv.\n");
		k_work_submit(&start_advertising_worker);
	}
	else if (err) {
		printk("Connection failed (err 0x%02x)\n", err);
	} else {
		printk("Connected\n");
	}
}

I tried this with the direct_adv example, and it seemed to work as expected. Here's the full main.c with at the changes I made:

/*
 * Copyright (c) 2022 Michal Morsisko
 * Copyright (c) 2015-2016 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr/types.h>
#include <stddef.h>
#include <string.h>
#include <errno.h>
#include <zephyr/sys/printk.h>
#include <zephyr/sys/byteorder.h>
#include <zephyr/sys/reboot.h>
#include <zephyr/settings/settings.h>
#include <zephyr/bluetooth/bluetooth.h>
#include <zephyr/bluetooth/hci.h>
#include <zephyr/bluetooth/conn.h>
#include <zephyr/bluetooth/uuid.h>
#include <zephyr/bluetooth/gatt.h>



/* Custom Service Variables */
#define BT_UUID_CUSTOM_SERVICE_VAL \
	BT_UUID_128_ENCODE(0x12345678, 0x1234, 0x5678, 0x1234, 0x56789abcdef0)

static struct bt_uuid_128 primary_service_uuid = BT_UUID_INIT_128(
	BT_UUID_CUSTOM_SERVICE_VAL);

static struct bt_uuid_128 read_characteristic_uuid = BT_UUID_INIT_128(
	BT_UUID_128_ENCODE(0x12345678, 0x1234, 0x5678, 0x1234, 0x56789abcdef1));

static struct bt_uuid_128 write_characteristic_uuid = BT_UUID_INIT_128(
	BT_UUID_128_ENCODE(0x12345678, 0x1234, 0x5678, 0x1234, 0x56789abcdef2));

static int signed_value;
static struct bt_le_adv_param adv_param;
static bt_addr_le_t bond_addr;


static void advertising_start(struct k_work *work);

static K_WORK_DEFINE(start_advertising_worker, advertising_start);

static ssize_t read_signed(struct bt_conn *conn, const struct bt_gatt_attr *attr,
			   void *buf, uint16_t len, uint16_t offset)
{
	int *value = &signed_value;

	return bt_gatt_attr_read(conn, attr, buf, len, offset, value,
				 sizeof(signed_value));
}

static ssize_t write_signed(struct bt_conn *conn, const struct bt_gatt_attr *attr,
			    const void *buf, uint16_t len, uint16_t offset,
			    uint8_t flags)
{
	int *value = &signed_value;

	if (offset + len > sizeof(signed_value)) {
		return BT_GATT_ERR(BT_ATT_ERR_INVALID_OFFSET);
	}

	memcpy(value + offset, buf, len);

	return len;
}

/* Vendor Primary Service Declaration */
BT_GATT_SERVICE_DEFINE(primary_service,
	BT_GATT_PRIMARY_SERVICE(&primary_service_uuid),
	BT_GATT_CHARACTERISTIC(&read_characteristic_uuid.uuid,
			       BT_GATT_CHRC_READ,
			       BT_GATT_PERM_READ,
			       read_signed, NULL, NULL),
	BT_GATT_CHARACTERISTIC(&write_characteristic_uuid.uuid,
			       BT_GATT_CHRC_WRITE,
			       BT_GATT_PERM_WRITE_ENCRYPT,
			       NULL, write_signed, NULL),
);

static const struct bt_data ad[] = {
	BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
	BT_DATA_BYTES(BT_DATA_UUID128_ALL, BT_UUID_CUSTOM_SERVICE_VAL),
};

static void connected(struct bt_conn *conn, uint8_t err)
{
	if (err == BT_HCI_ERR_ADV_TIMEOUT) {
		printk("Trying to re-start directed adv.\n");
		k_work_submit(&start_advertising_worker);
	}
	else if (err) {
		printk("Connection failed (err 0x%02x)\n", err);
	} else {
		printk("Connected\n");
	}
}

static void disconnected(struct bt_conn *conn, uint8_t reason)
{
	printk("Disconnected (reason 0x%02x)\n", reason);
}

BT_CONN_CB_DEFINE(conn_callbacks) = {
	.connected = connected,
	.disconnected = disconnected
};

static void copy_last_bonded_addr(const struct bt_bond_info *info, void *data)
{
	bt_addr_le_copy(&bond_addr, &info->addr);
}

static void advertising_start(struct k_work *work)
{
	int err;
	char addr[BT_ADDR_LE_STR_LEN];
	
	bt_addr_le_copy(&bond_addr, BT_ADDR_LE_NONE);
	bt_foreach_bond(BT_ID_DEFAULT, copy_last_bonded_addr, NULL);

	/* Address is equal to BT_ADDR_LE_NONE if compare returns 0.
	 * This means there is no bond yet.
	 */
	if (bt_addr_le_cmp(&bond_addr, BT_ADDR_LE_NONE) != 0) {
		bt_addr_le_to_str(&bond_addr, addr, sizeof(addr));
		printk("Direct advertising to %s\n", addr);

		//adv_param = *BT_LE_ADV_CONN_DIR_LOW_DUTY(&bond_addr);
		adv_param = *BT_LE_ADV_CONN_DIR(&bond_addr);
		adv_param.options |= BT_LE_ADV_OPT_DIR_ADDR_RPA;
		err = bt_le_adv_start(&adv_param, NULL, 0, NULL, 0);
	} else {
		err = bt_le_adv_start(BT_LE_ADV_CONN_NAME, ad, ARRAY_SIZE(ad), NULL, 0);
	}

	if (err) {
		printk("Advertising failed to start (err %d)\n", err);
	} else {
		printk("Advertising successfully started\n");
	}	
}

static void bt_ready(void)
{

	printk("Bluetooth initialized\n");

	if (IS_ENABLED(CONFIG_SETTINGS)) {
		settings_load();
	}
}

void pairing_complete(struct bt_conn *conn, bool bonded)
{
	printk("Pairing completed. Rebooting in 5 seconds...\n");

	k_sleep(K_SECONDS(5));
	sys_reboot(SYS_REBOOT_WARM);
}

static struct bt_conn_auth_info_cb bt_conn_auth_info = {
	.pairing_complete = pairing_complete
};

int main(void)
{
	int err;

	err = bt_enable(NULL);
	if (err) {
		printk("Bluetooth init failed (err %d)\n", err);
		return 0;
	}

	bt_ready();
	bt_conn_auth_info_cb_register(&bt_conn_auth_info);

	k_work_submit(&start_advertising_worker);

	while (1) {
		k_sleep(K_FOREVER);
	}
	return 0;
}

In my code, I didn't implement this, but you would probably want to limit the number of times you restart the advertisement to prevent battery drainage. Additionally, as you might be aware, the high-duty directed advertisement should only run for 1.28 seconds according to the spec.

Best regards,

Vidar