BLE data rate issue - GATT write extremely slow

[Arne M.]

Hello everyone,

please take a look at my minimal reproducable example, which explains the problem and also includes some example measurements. derteufelqwe/nrf-ble-datarate-issue: Minimal reproducable example to show a problem with the BLE data rate (github.com)

TL;DR: During testing I observed that the data rate of BLE is weiredly slow when transmitting from Central -> Peripheral using GATT writes. The other direction performs as expected.
But when running bidirectional traffic (GATT write in one direction and GATT notify in the other) the GATT writes suddenly become way faster.
I also can't reproduce the data rate for GATT writes, which is given in the Nordic Documentation.

Greetings

Arne

[Kenneth]

Hello,

Likely this is due to slave latency is > 0. Typically slave latency is updated during a connection parameter update, and to reduce current of the peripheral it can skip the number of intervals as defines by slave latency, this will in effect reduce the throughput from the central to the peripheral.

Either you need to update connection parameter, but there is also a command that you can call on the peripheral where it will still listen every connection interval even if slave latency is >0. This is:

int hci_vs_sdc_peripheral_latency_mode_set(const sdc_hci_cmd_vs_peripheral_latency_mode_set_t *params);

Documentation here: https://github.com/nrfconnect/sdk-nrfxlib/blob/main/softdevice_controller/include/sdc_hci_vs.h#L1184  

Kenneth