NUS increase throughput and data loss

[davidz]

We have been using ble nus service which is working very well. 

There are more than 100,000 bytes of data to be transferred each time. 

We were using BLE_NUS_EVT_TX_RDY  event for flow control, which is working. 

Now we want to improve the data throughput and doing experiments. We found that if we use the following code, then about 20% data are lost.

           do{
                err_code=ble_nus_data_send(&m_nus,data_buf,&data_length,m_conn_handle);
              } while(err_code==NRF_ERROR_BUSY);

What is the best way to maximize the nus throughput without losing data?

[Jørgen Holmefjord]

Hi,

There are many parameters that can help increase the throughput of the application, including PHY (1MBIT vs 2MBIT), connection interval, ATT_MTU size, Data Length Extensions (DLE), Connection Event Length Extensions, etc.

An overview of expected maximum throughput numbers can be found in the softdevice specification (Bluetooth Low Energy data throughput).

As a starting point, I would recommend you to have a look at the nRF52 BLE image transfer demo. This example show how to configure the softdevice for maximum throughput, with a BLE service that is very similar to Nordic UART Service (NUS).

Best regards,
Jørgen

[davidz]

Thanks Jorgen. We have done extensive experiments on PHY, connection interval, MTU size, DLE and extensions on reliable transmission. There are multiple peripherals so our case is more complicated than just 1 to 1 connection. One parameter adjustment may improve on 1 to 1 throughput but affect the overall performance negatively.
As always, your recommendation is very helpful. We will investigate on how to improve based on your suggestions. Lots of tests down the road again.