Changing Gatt Characteristic Properties?

RE: Changing Gatt Characteristic Properties?

Christopher — Sun, 20 Mar 2016 21:27:05 GMT

Just a shot note: if a characteristic is both notifiable and indicateable, it is not possible to enable only the indications using the iOS BLE API (see more information here: bluegiga.zendesk.com/.../90962587-How-to-enable-Indications-on-CRP-Client-Configuration-descriptor-from-iOS8-Objective-C-). On Android, you can choose to enable either notifications or indications.

RE: Changing Gatt Characteristic Properties?

Ulrich Myhre — Thu, 18 Sep 2014 12:03:35 GMT

See devzone.nordicsemi.com/.../a00247.html If a value is both indicatable and notifyable, and the peer has written 0x03 to the CCCD (enable both), then you can set the "type" field in the ble_gatts_hvx_params_t struct to either BLE_GATT_HVX_NOTIFICATION or BLE_GATT_HVX_INDICATION. If you send indications, you must then wait for a confirm event (BLE_GATTS_EVT_HVC) before you are allowed to send a new one. With notifications, there is no such limit. Does that answer your question?

RE: Changing Gatt Characteristic Properties?

barmaley — Thu, 18 Sep 2014 11:56:59 GMT

Ulrich, could you please clarify your comment?

RE: Changing Gatt Characteristic Properties?

Petter Myhre — Thu, 18 Sep 2014 09:07:12 GMT

This is not an answer. I edited the question and added it.

RE: Changing Gatt Characteristic Properties?

Ulrich Myhre — Mon, 18 Aug 2014 11:44:28 GMT

In the call to HVX you can choose between setting the notification and the indication flag. In addition, you will not receive a handle value confirmation for the notifications, so any code depending on these should not be run for notifications.

RE: Changing Gatt Characteristic Properties?

barmaley — Sun, 17 Aug 2014 21:47:53 GMT

Hi Ulrich,

Yes indeed it is possible to set both flags: indicate and notify. But how can app select what is wants? Could you please provide the code snippet which does that with assumption that both flags were set.

Thank you.

Bar

RE: Changing Gatt Characteristic Properties?

Ulrich Myhre — Sun, 17 Aug 2014 21:41:49 GMT

No, you cannot change the database on the fly.

In fact, if you do change the database you must enable and indicate the service changed characteristic to the peer. This is because the peer side is allowed to cache the database structure, and any changes done to the structure requires a (partial) rediscovery. Not sending the Service Changed will in that case be breaking the specification. Also, changing the database should generally only be used if you want to reinitialize the device with a new profile, so I think you need to consider other options for your use-case.

I do think it is allowed to let a characteristic be both notifiable and indicateable though, which means you could have both properties at once and decide within the app what you want to do. The peer application must then enable for both indications and notifications (0x0003) to allow you to do both operations.

RE: Changing Gatt Characteristic Properties?

barmaley — Sun, 17 Aug 2014 14:00:32 GMT

Is it possible to change GATT characteristic properties on a fly? How? Thanks.