Extended advertising stops after connection gets established in nRF Connect SDK

[Sukriti]

Hello..

I tried implementing a simple application using nRF Connect SDK, which sends data in a connection event using notifications. This is the base code for a test application which requires the peripheral to operate in the connectable (and non-scannable) undirected advertising mode. According to the BLE specs, this is only achievable using advertising extensions. 

The connection gets established successfully and I am also able to see the notification data using nRF Connect App for Android. However, once the peripheral enters connection, it stops advertising, and does not re-start advertising even after getting disconnected. The only way it starts advertising again is resetting the peripheral. After a lot of struggle, this is the current status:

•  Inside the connection disconnected callback function, I called the extended advertising start function, and this worked perfectly. Once the peripheral gets disconnected, it resumes extended advertising.
• However, this is not the desired behavior. I want the peripheral to keep advertising once it enters the connection mode so that it is also visible to other devices. I searched and came across the following GitHub link and few other links referenced in this discussion that pointed out the exactly same issue:
  
  https://github.com/zephyrproject-rtos/zephyr/issues/33897
  
  The suggested workaround in this discussion is to call the extended advertising start function inside the advertising connected callback (using the bt_le_ext_adv_cb callback struct) inside the bt_le_ext_adv_create() function. I tried doing this, exactly the same way as I called the extended advertising start function inside the disconnected callback function earlier.
  
  But this does not seem to work. I keep on getting either the ENOMEM error (error -12), or the error log shown in the picture:
  
  

The same method works with the disconnected callback but fails with the advertising connected callback. Is there anything that I might have missed?

The proj.config file looks like this:

# Increased stack due to settings API usage

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048

CONFIG_BT=y

CONFIG_BT_DEBUG_LOG=y

CONFIG_BT_SMP=y

CONFIG_BT_SIGNING=y

CONFIG_BT_PERIPHERAL=y

CONFIG_BT_ATT_PREPARE_COUNT=5

CONFIG_BT_PRIVACY=y

CONFIG_BT_DEVICE_NAME="Zephyr Peripheral Sample Long Name"

CONFIG_BT_DEVICE_APPEARANCE=833

CONFIG_BT_DEVICE_NAME_DYNAMIC=y

CONFIG_BT_DEVICE_NAME_MAX=65

CONFIG_BT_KEYS_OVERWRITE_OLDEST=y

CONFIG_BT_SETTINGS=y

CONFIG_FLASH=y

CONFIG_FLASH_PAGE_LAYOUT=y

CONFIG_FLASH_MAP=y

CONFIG_NVS=y

CONFIG_SETTINGS=y

CONFIG_BT_BUF_ACL_RX_SIZE=251

CONFIG_BT_L2CAP_TX_MTU=247

CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

CONFIG_BT_BUF_ACL_TX_SIZE=251

CONFIG_BT_GAP_AUTO_UPDATE_CONN_PARAMS=n

CONFIG_BT_USER_DATA_LEN_UPDATE=y

CONFIG_BT_LL_SW_SPLIT=y

CONFIG_BT_EXT_ADV=y

CONFIG_BT_CTLR_ADV_EXT=y

CONFIG_BT_CTLR_ADVANCED_FEATURES=y

CONFIG_BT_CTLR_ADV_DATA_BUF_MAX=6

CONFIG_BT_MAX_CONN=20

nRF52840 has been used as the peripheral. Could you please look into this once and suggest a suitable workaround? 

[Simonr]

Hi

What exactly does your application do after you connect to a device? Do you tell it to start advertising again after it has connected to the first central device? Can you show me your main file?

Best regards,

Simon

[Sukriti]

Hi Simon,

I have attached both main files.. "adv_connected_cb" throws error, while "disconnected" resumes extended advertising after the peripheral gets disconnected. 

The application has a custom service which contains readable (long) characteristic value. Notifications are also enabled. The same data is transferred to the connected device through both notification and read request/response. Notifications are sent out at intervals of 10 ms. I used nRF Connect Mobile App for Android as Central. This application is just a modified version of the Zephyr Peripheral example. I made changes to the prj.conf file, which I already mentioned in the previous thread.

/cfs-file/__key/communityserver-discussions-components-files/4/disconnected_5F00_cb.c

/cfs-file/__key/communityserver-discussions-components-files/4/adv_5F00_connected_5F00_cb.c

[Simonr]

Hi

One way to go about this would be to implement multiple advertising sets. This lets you start another advertisement once connected to one device for example, either similar or different to the first advertising set. We have a sample application available here. Alternatively if you want to use the same advertising set it's possible to start advertising with that also after connecting to the first device. Similar procedure to what is done in the advertising sets sample I think.

Best regards,

Simon

[Sukriti]

Thanks Simon. So basically, while the peripheral is connected to one device, it is only "visible" to other devices (in a non-connectable mode) and can not connect to them. I'm not sure how the same set can be used with this approach, but I'll give it a try.

If use two sets (as used in the sample) and I make the second advertising set connectable, would it mean allowing two simultaneous connections (using disconnected callbacks for both the sets)?  

[Sukriti]

Simonr said:

Alternatively if you want to use the same advertising set it's possible to start advertising with that also after connecting to the first device

Exactly what I tried doing using the advertising connected callback (bt_le_ext_adv_cb), but I got the errors mentioned in the first thread. I'm unable to figure out how it can be achieved taking the multiple advertising sets sample as a reference, because this sample only starts the second set after the first one gets disconnected.