MTU size is not getting updated with Android

RE: MTU size is not getting updated with Android

Ankit_chauhan — Mon, 19 May 2025 12:37:30 GMT

I will check the sniffer logs.
Thanks for the help.

RE: MTU size is not getting updated with Android

Hung Bui — Mon, 19 May 2025 12:33:16 GMT

Hi Ankit,
Please try to get a sniffer trace.
Is the issue reproducible now. If it does, please describe the process.

RE: MTU size is not getting updated with Android

Ankit_chauhan — Mon, 19 May 2025 10:30:55 GMT

Sorry for the late reply. After some debugging it looks like there is no any issue related to the MTU as I have tested the same with nRF connect app and try to read and write larger data than the MTU and it worked.

So it looks like there must be some issue with the Android OS approach of handling pairing. Because when iOS app initiate the pairing process, my Zephyr code will receive pairing_accept callback and if I return success then only the iOS app shows the pairing pop-up else it will show nothing. While in case of Android, it display the pairing pop-up first and then pairing_accept calls.

RE: MTU size is not getting updated with Android

Hung Bui — Wed, 14 May 2025 13:38:00 GMT

I suspect that the Android phone was paired with your device before. You may want to try erase everything (chip erase or click on the double arrow when you flash) to make sure the device delete all bond before testing.
If you want to allow a device to re-pair at security level 2 , you would need to enable this: CONFIG_BT_SMP_ALLOW_UNAUTH_OVERWRITE=y

RE: MTU size is not getting updated with Android

Ankit_chauhan — Wed, 14 May 2025 12:54:59 GMT

Hi,

Thanks for the reply.

I used bonding with bt_conn_set_security(conn, BT_SECURITY_L2); with below authentication callbacks

static struct bt_conn_auth_cb conn_auth_callbacks = {

.cancel = auth_cancel,

};

With this configuration, the App will have a pop-up to pair or cancel after the connection. The disconnect happens from the App side, as you see the reason 19.

The flow of operation is designed in such a way that if the App does not get the data from the sensor as part of authentication, it will disconnect the sensor and declare a failure.

The app tries to read the characteristic data, but it does not fit into the MTU requirement; hence, it tries to update the MTU, but somehow the request is not reaching the sensor.

Meanwhile, I will get some logs from the sniffer tool to understand the issue more.

RE: MTU size is not getting updated with Android

Hung Bui — Wed, 14 May 2025 12:45:08 GMT

Hi Ankit,
Error 4 you got () means

BT_SECURITY_ERR_AUTH_REQUIREMENT

/** The requested security level could not be reached. */

Which security level did you request from the peripheral ? Or did you request pairing from the central ?

We would need to have a sniffer trace to see what exactly happens between the 2 devices.

I don't see a reason why MTU updating would cause pairing to fail.