BLE data length extention Thingy 52

[Rilleaa]

Hi everyone. 

I want to stream 12kB of ADC data from the thingy 52 via BLE. At the moment this takes around 4 seconds to do which is to slow so i would like to increase throughput by utilising DLE but unsure how to implement it. 

Is it enough to increase the MTU size and send bigger packages to  sd_ble_gatts_hvx() function as the BLE_GAP_DATA_LENGTH_AUTO is on auto? Or what would be the steps needed to implement this supposing that both devices support DLE?

Thankful for help

//Rilleaa 

[Kenneth]

First of all the connection interval should be as short as possible.

Then you should call sd_ble_gatts_hvx() as fast as possible until NRF_ERROR_RESOURCES. Then you need to wait for BLE_GATTS_EVT_HVN_TX_COMPLETE before you can repeat calling sd_ble_gatts_hvx() as fast as possible.

If you include gatt_init() in your application, then the callback provided in gatt_init() should provide you with the max length that is supported in the callback handler after the supported MTU exchange have completed. After that you can call sd_ble_gatts_hvx() with a length that equal the max supported length in the callback handler.

[Rilleaa]

The for the reply Kenneth.

I have implemented something similar by following this thread https://devzone.nordicsemi.com/f/nordic-q-a/553/dealing-large-data-packet-s-through-ble/2839#2839 it works fine and i get around 3kB/s of throughput. Is there any way to increase this even further? I looked at this link:
https://infocenter.nordicsemi.com/index.jsp?topic=%2Fsds_s132%2FSDS%2Fs1xx%2Fble_data_throughput%2Fble_data_throughput.html&cp=3_4_2_0_16 
and it indicates that i would be possible to increase the speed more. Or is it limitations in the central device (in my case a raspberry pi 4) that i cant change thats is limmitning the thorughput speed?

//Rilleaa

[Kenneth]

It is the master that control most of the parameters, so as a peripheral device you can only request for faster interval and longer length. So it could be limited by the rasperry pi yes.

Kenneth

[Rilleaa]

Okey yea mabey that part is out of my control then.

Any way of knowing what MTU size the two devices? From the ble sniffer i see when i connect with my Iphone 6s that it uses MTU size 185 but with the raspberry pie i cant see any MTU size.

I have tried to send bigger packages bigger than 20 bytes from thingy 52 to both iphone and Raspberry pi it works on the iphone but not on the raspberry pi i just recive the first 20 bytes in the array of data that was sent to  sd_ble_gatts_hvx(). 

I attatched my sniffer logs i case you have time to have a look at them :). 

//Rilleaa

ThingyToIphone6s.pcapngThingyToRBP.pcapng