RE: packet loss issue with nus service

Dan — Tue, 26 Apr 2016 12:42:28 GMT

Thank you for your response, Stefan. My connection interval is currently set to "MSEC_TO_UNITS(8, UNIT_1_25_MS)" which is the least possible value, if I'm right.

And as I've said above, the central (receiver) works fine with other non-Nordic peripheral devices which implement the NUS in a custom profile. Similarly, the Nordic peripheral works properly with the Master Control Panel, without ANY packet loss.

RE: packet loss issue with nus service

Stefan Birnir Sverrisson — Fri, 22 Apr 2016 16:06:43 GMT

Hi Dan

My first thought is that your connection interval is too low. There is a maximum of 6 packets per connection interval. If you are e.g. feeing the softdevice with a packet with 50Hz frequency, but your connection interval is e.g. 200ms, then the packets will pile up in the softdevice and you will have a buffer overflow.

Update 26.4.2016 As far as I can see, the acceptable connection intervals of the central ble_app_uart_c application is the same as in the peripheral ble_app_uart application, i.e. minimum connection interval of 20ms and maximum connection interval of 75ms. I tried connecting the two devices to see what connection interval is actually present when connecting, and it is 75ms.

For S130/S132 2.0.x the RX and TX bandwidth is configurable, individually for peripheral and central links. The default configuration for connections as a central is BLE_CONN_BW_MID (both for TX and RX), and for connections as a peripheral it is BLE_CONN_BW_HIGH (both for TX and RX). The BLE_CONN_BW_MID is 3 packets per connection interval max and BLE_CONN_BW_HIGH is 6 packets per connection interval max. So I suspect the central ble_app_uart_c application is limited to maximum 3 packets per connection interval. The result is that you are able to send in one direction 1/0.075*3 = 40 packets per second. Since you are feeding the softdevice with 50 packets per second, it is logical that you will get a buffer overflow.

So I see two ways of fixing this

Change the connection interval for the central device, e.g. min 20ms and max 40ms
Change the bandwidth of the central links to BLE_CONN_BW_HIGH

To see how to change the bandwidth of the central links, look at the s13x_nrf5x_2.0.0_migration-document, chapter about "Configurable bandwidth". The migration document is bundled with the softdevice download file.