Re: bt_gatt_is_subscribed - any examples?

Lawrence King

Adding devel@... to the email address.


Lawrence King

Principal Developer



From: users@... <users@...> On Behalf Of Lawrence King
Sent: Thursday, December 5, 2019 4:00 PM
To: users@...
Subject: [Zephyr-users] bt_gatt_is_subscribed - any examples?


Dear All:


I have a similar problem to what Frank Viren is seeing in his thread “bt_gatt_notify multiple characteristics”. How to determine the pointer to the right characteristic.


When my central connects to my device I want to send it several notifications. My device has several characteristics under the primary service. When the central connects (in this case the central is either an iPhone, or an Android phone), if I simply wait 200mS after the connection and sent the notifications with bt_gatt_notify() it ‘almost’ always works. Unfortunately sometimes Android or iOS take a little longer to subscribe for notifications, hence I would like to determine if the phone is ready to receive notifications rather than simply waiting 200mS.


I hunted through the bt_ apis and found bt_gatt_is_subscribed() which looks like I can loop testing to see if the central is ready and then send the notifications. Much better than blindly waiting 200mS.



bool bt_gatt_is_subscribed(struct bt_conn *connconststructbt_gatt_attr *attr, u16_t ccc_value)

Check if connection have subscribed to attribute.

Check if connection has subscribed to attribute value change.

The attribute object can be the so called Characteristic Declaration, which is usually declared with BT_GATT_CHARACTERISTIC followed by BT_GATT_CCC, or the Characteristic Value Declaration which is automatically created after the Characteristic Declaration when using BT_GATT_CHARACTERISTIC, or the Client Characteristic Configuration Descriptor (CCCD) which is created by BT_GATT_CCC.


true if the attribute object has been subscribed.


·        conn: Connection object.

·        attr: Attribute object.

·        ccc_value: The subscription type, either notifications or indications.


OK, based on the documentation, this seems to be what I want, but the parameters are difficult for a newbie to understand:

conn – yes I did declare this with BT_GATT_CHARACTERISTIC I know where it is in my source code, but how do I find a pointer to it?

attr –  this was automatically created with BT_GATT_CCC in the same place, but again how do I get a pointer to the attr?

ccc_value – this is obviously an int, probably with definitions for the bits, but what symbolic enums or defines can I put in this parameter?




Unfortunately a google search of “bt_gatt_is_subscribed” only finds 8 results, the source code, the documentation (on the zephyr site, and on the nordic site), and 2 content aggregators. I did not find a single piece of code that calls this function, but there must be at least one call to the function in at least some test suite. bt_gatt_is_subscribed is never called in any of the zephyr/samples…


Can someone point me to an example please?




Lawrence King

Principal Developer

Connected Transport Market Unit



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