Sniffing min max connection interval with nRF Sniffer

Question

Hello, 
 I'm new to sniffing BLE. I'd like to determine the min and max connection interval and other connection parameters (MTU, slave latency, supervisory timeout, etc.) of a peripheral. I don't have access to the firmware. I have Wireshark+nRF Sniffer for BLE 3.0.0 installed and running my my Mac (10.14.6). I can see advertising, connection requests, etc. I've attached a screen capture. Where do I look to find these connection parameters? 
 Many thanks, 
 Tim

bjorn-spockeli · Accepted Answer

Hi Tim, 
 Tim said: I'm seeing very little latency between GPIO interrupt and call to sd_ble_gatts_hvx(). About 0.091551ms. I'm seeing quite a variation in time between call to sd_ble_gatts_hvx() and SoftDevice calling on_hvx_tx_complete(). Range is from 34 to 84 ms. Is this variation due to packet loss, re-transmission? Or connection interval/window? It would be helpful if I could understand the variation and account for it. 
 Yes, retransmissions due to packets being dropped may be the cause for the delay that is larger than the connection interval, i.e. 30ms. In order to minimize the time between calling sd_ble_gatts_hvx and the packet going on air my suggestion would be to lower the connection interval to its lowest setting, i.e. 7.5ms. 
 You could also use use the 2Mbps Phy, which will shorten the time it takes for the RADIO to transmit all the bytes compared to the 1Mbps PHY. 
 Tim said: Lastly, as we look to a solution for synchronizing internal peripheral clocks, would you recommend the blog post I link to above? All we need is 10ms accuracy between two peripherals. Wondering if the blog post solution is overkill and we could achieve our 10ms requirement with something simpler. 
 I think this is the only synchronization solution that we have any source code for I am afraid. Try lowering the connection interval first. 
 Best regards 
 Bjørn

Sniffing min max connection interval with nRF Sniffer

Top Replies