Struggling to subscribe to gatt notifications and write to a gatt characteristic on nrf52840

RE: Struggling to subscribe to gatt notifications and write to a gatt characteristic on nrf52840

brock.hargreaves — Fri, 20 Jun 2025 20:09:11 GMT

There was two problems, one is that I was using bt_gatt_write_without_response_cb when I should have been using bt_gatt_write, the second is that I was using the wrong CCC handle.

RE: Struggling to subscribe to gatt notifications and write to a gatt characteristic on nrf52840

brock.hargreaves — Wed, 18 Jun 2025 22:43:28 GMT

Hi Sigurd , I'm not sure what I was doing wrong before, but I repeated the same steps and I get the full log now. I'm seeing some errors but not sure what to make of them. Could you take a look?devzone.nordicsemi.com/.../6644.sniffer_5F00_log.pcapng

RE: Struggling to subscribe to gatt notifications and write to a gatt characteristic on nrf52840

brock.hargreaves — Wed, 18 Jun 2025 21:46:25 GMT

Hi Sigurd

I'm struggling to follow the packets into the connection of the peripheral. I'm using the nrf52840 dongle with the 4.1.1 firmware from here: https://www.nordicsemi.com/Products/Development-tools/nRF-Sniffer-for-Bluetooth-LE

I followed the instructions on sniffing a single peripheral connection here: https://docs.nordicsemi.com/bundle/nrfutil/page/nrfutil-ble-sniffer/guides/common_actions_sniffing_conn_single_periph.html

I selected the peripheral from the dropdown. However, I still only receive advertising packets (ADV_IND). If I set Wireshark to receive all packets from all devices, I can see the CONNECT_IND packet that is being sent from the central but that's all I ever get. I don't see any packets involving the MTU exchange, PHY update, enabling notifications, etc.

What am I doing wrong?

RE: Struggling to subscribe to gatt notifications and write to a gatt characteristic on nrf52840

brock.hargreaves — Tue, 17 Jun 2025 20:39:01 GMT

Hi Sigurd, thank you for the suggestion. I will respond again as soon as I acquire the sniffer log.

RE: Struggling to subscribe to gatt notifications and write to a gatt characteristic on nrf52840

Sigurd — Tue, 17 Jun 2025 12:34:54 GMT

Hi!

A sniffer log would be helpful here to see what's happening

https://www.nordicsemi.com/Products/Development-tools/nRF-Sniffer-for-Bluetooth-LE