Bluetooth advertising timeout needs to be modified

[craig.goldman]

I am creating proof of concept software using a nRF52840 Dev Kit.  The code is based on the Nordic UART Service example which uses Zephyr, but has been substantially modified to suit the application.

I use "bt_le_adv_start" to begin Bluetooth advertising.  All is working well except the Bluetooth Advertising stops after approx. 30 seconds.

I cannot find an API to use to change the advertising timeout; is there one?
Is it possible to change the timeout to "never"?

I've noticed that the Nordic SDK has functions which allow for changing of the timeout value; can I mix Zephyr API calls and Nordic SDK API calls?

The application may periodically change the advertised values.  If I change the advertised values using "bt_le_adv_update_data", does the timeout counter reset (and I get another 30 seconds)?

As a final, but less desirable option, I could stop the advertising, then re-start every 15 seconds.  Is there anything I should know about solving the problem this way?

-Craig Goldman

[Edvin]

Hello,

By default the BLE advertisements doesn't time out in NCS (unless that changed recently). Are you sure they time out? How do you know that it does? What do you observe? Is it possible to send the application that you are currently working on so that I can have a look?

I've noticed that the Nordic SDK has functions which allow for changing of the timeout value; can I mix Zephyr API calls and Nordic SDK API calls?

What API do you refer to?

Best regards,

Edvin

[craig.goldman]

Unfortuantely, the application requires specialized hardware connected to the nRF52840 to run; it is also 1000's of lines of code (not including SDK and Zephyr library files) spread over 56 files.
If needed, I can send the file which calls "bt_le-adv_start".

I believe advertsiing has stopped for two reasons
* I am using the J-Link RTT Viewer to monitor code logging.
  I get the following log entry: 00> [00:00:54.335,479] <wrn> bt_adv: Failed to stop advertising: 0
  The source of this is in "adv.c" following a call to "bt_le_adv_stop"; the error code of 0 indicates success
  (BTW this is a really poor debugging message to get on success.)
* I am using NRF Connect App running on an iPAD to monitor advertsing and to connect to the running code.
  If I start NRF Connect after I get the warning message, I view no advetrtisements from the device.
  If I start NRF Connect earlier, I can see the bluetooth advertisements on NRF Connect screen.

The Noridic SDK allow the programmer to define advertising modes which include how timeout is handled.
("ble_advertising_config").  I was referring to the documentation for "ble_advertising_start" which can select one of those modes.  I do not see an API specifically for changing the advertising timeout.

Please remember that I am starting bluetooth advertising using "bt_le_adv_start", which is a Zephyr library call.
This was used in the Nordic UART Service example I followed to create the application.

Thank you
-Craig

[Edvin]

craig.goldman said:

The Noridic SDK allow the programmer to define advertising modes which include how timeout is handled.
("ble_advertising_config").

Ah, you are talking about the nRF5 SDK when you say "Nordic SDK". I understand. (In some cases Nordic SDK can mean nRF Connect SDK, while Zephyr SDK is referred to as the pure Zephyr SDK (which is a standalone code base without nRF Connect SDK).

Regarding your question:

I see. This is not triggered in most (any?) of our samples, but I see that there is a timeout functionality that is started in bt_le_adv_start() if ad_is_limited() returns true. This returns true if the BT_LE_AD_LIMITED flag is set.

So if your advertising data is set up something like this:

static const struct bt_data ad[] = {
	BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_LIMITED | BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
	BT_DATA(BT_DATA_NAME_COMPLETE, DEVICE_NAME, DEVICE_NAME_LEN),
};

Try to remove the BT_LE_AD_LIMITED, so that you are left with this:

static const struct bt_data ad[] = {
	BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
	BT_DATA(BT_DATA_NAME_COMPLETE, DEVICE_NAME, DEVICE_NAME_LEN),
};

Then, the advertisements will not time out. Alternatively, if you want to change the duration of the timeout you can either leave the BT_LE_AD_LIMITED in, and configure the timeout by adding this config to your prj.conf:

CONFIG_BT_LIM_ADV_TIMEOUT 60

(change 60 with the number of seconds you want to use. The range is 1 to 180 seconds). 

If you want something longer than 180 seconds, you should remove the BT_LE_AD_LIMITED, and start a timer to stop the advertisements manually. 

The log warning "Failed to stop advertising: 0" looks very much like a bug from Zephyr. It looks like it was supposed to check the return value (err) before printing that. If it is printed with the value 0, it means that it successfully stopped the advertisements.

Best regards,

Edvin

[craig.goldman]

Thank you for the respone but I don't use BT_LE_AD_LIMITED - just BT_LE_AD_GENERAL and BT_LE_AD_NO_BREDR

My advertising data looks like the following...
advertData[0].type = BT_DATA_FLAGS;
advertData[0].data_len = 1u;
advertData[0].data = (const void*)(BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR);
advertData[1].type = BT_DATA_NAME_COMPLETE;
advertData[1].data_len = 7u;
advertData[1].data = "Sensor";

(The actual device name string in the application is constucted from using the device serial number.)

I would rather disable the timeout, but other less desirable solutions could be used.
Do you know if the timeout re-starts if I periodically call "bt_le_adv_update_data"?
Is there a callback on advetising stop which I could use to re-start the advertising?

-Craig

 

[Edvin]

It looks like this format is a bit different to how it is implemented in our samples. It may work just fine, but it is difficult for me to say exactly why it behaves like it does based on this snippet. Can you please try to debug/add logging to see whether ad_is_limited() returns true inside bt_le_adv_start()?

	if (ad_is_limited(ad, ad_len)) {
		k_work_init_delayable(&adv->lim_adv_timeout_work, adv_timeout);
		k_work_reschedule(&adv->lim_adv_timeout_work,
				  K_SECONDS(CONFIG_BT_LIM_ADV_TIMEOUT));
	}

I suggest you figure out why the timer is started (lim_adv_timeout_work, adv_timeout), rather than figuring out whether it is restarted. 

As far as I can tell, bt_le_adv_update_data() doesn't start/restart the advertising. It just updates the data that is used for advertising, so I don't think this will reset any timers. 

The only way I see that "Failed to stop advertising" is printed to the log is inside adv_timeout(), and the only way this is triggered is from k_work_init_delayable(&adv->lim_adv_timeout_work, adv_timeout); inside the check for ad_is_limited().

Best regards,

Edvin