What does the "add value" function in nRF Connect do?

[William Geng]

Hello,

We have a custom device using nRF52832 with a MTU of 20 bytes, and for one of the tests we are trying to write 248 bytes to the device with nRFConnect, can the "add value" function be used to manually fragment the data? or does the nRFConnect automatically fragments the data for you?

Thanks,

William

[Kenneth]

Hello,

I think I need some help to understand the context. Is this "add value" in nRF Connect mobile app or in nRF5 SDK? From a high level typically data will be fragmented by some layer in BLE. In general you may find this useful:
https://punchthrough.com/maximizing-ble-throughput-part-2-use-larger-att-mtu-2/

If the max length field of the characteristic on the nRF52832 is 20bytes, then you would need to fragment the data in several writes to transfer 248bytes I would assume. If the max length is >=248bytes, then it should be fragmented by lower layers in BLE if actual MTU is 20bytes.

Best regards,
Kenneth

[William Geng]

Sorry for the confusion I chose the wrong tag :( I am referring to the nRF Connect mobile app in this case. The max length field of the characteristic on the nRF52832 is 20 bytes, does that mean I would use the add value function to chain 13 byte arrays writes to complete the full transmission?

[Kenneth]

I am not familiar with the ios/android api, but if the characteristic on the peripheral is configured with a max length of 20bytes, then you would need to perform multiple writes to transfer more than 20bytes yes.

Kenneth