Stable data transmission at ~50 kBit/s with ble_app_uart

[Maria_19]

Hi all,

I have a nRF52DK as peripheral and a nRF52840DK as central. I want to send data from the peripheral to the central with a data rate of 50 kBit/s.

I added a continuous data transmission to the ble_app_uart example. At the moment I have a timer, which calls the ble_nus_data_send() function every 32ms with a payload of 200 Bytes. The timer starts after central and peripheral is connected and MTU_exchange is finished.

The exact time when a NUS-paket is sent by the peripheral or received by the central does not matter. But I shouldn´t get an error. With the default connection parameters of the ble_app_uart example I received a NRF_ERROR_RESOURCES after I called the ble_nus_data_send() function 2-10 times.

My questions:

1. Which connection parameters should I use?

2. Do I have to set the connection parameters on central and peripheral?

3. How can I transmit data with a data-rate of 50 kBit/s without errors?

Thank you all soo much :)

Kind regards,

Maria

[Simonr]

Hi

The NRF_ERROR_RESOURCES in ble_nus_data_send() is caused by queueing too many notifications. Please try increasing the queue size or connection parameters. My colleague Sigurd explains how to increase the queue size in this ticket. 

2. Connection parameters are set in the gap_params_init() function, where you set connection interval, slave latency, connection timeout, etc. To make sure the parameters are what you set them to, you can call a BLE_GAP_EVT_CONN_PARAM_UPDATE_REQUEST in your central device to accept the connection parameters set in the peer device.

3. Is there a specific reason you need the devices to transmit at 50kbps? You will have to do set the parameters to match up with 50kbps, and then tune any difference you see between the observed and expected data rate. This case has an in-depth discussion on the matter.

Best regards,

Simon