RE: nRF53 MAX MTU and DLE

Robert de Brum — Thu, 12 Jan 2023 00:55:39 GMT

Hi,

I am working on a project with the nrf5340 and ncs version 2.2.0 and I am trying to enable large packets. When I try to notify a buffer of 510 bytes, I cannot. I get a warning from here:

When debugging I see that the chan->chan.tx.mtu is 509.

This project is converted from an old nrf5 implementation, where the MTU was set to 576 for an nrf52832. How can I set a similar (again, at least 510) MTU for the nrf5340 in NCS?

RE: nRF53 MAX MTU and DLE

Einar Thorsrud — Fri, 03 Sep 2021 12:59:29 GMT

Hi,

There are several protocol layers. You can have a ATT MTU of 512, but that would have to be split on several GAP packets. The longest possible packet with DLE is 251 bytes.

That means that If you want to fit the ATT MTU in a single packet, that means it can be maximum 247 bytes. This is limited by the Bluetooth specification, and is not implementation specific.