sniffer detects LL infinite loop

RE: sniffer detects LL infinite loop

Hung Bui — Fri, 18 Nov 2016 08:47:08 GMT

Hi Karel,

It's on the link layer not the ATT layer, so it's doesn't matter if it's notification or write command, if the packet is not ACKed on link layer, it will be re-transmit until it's ACKed or until the connection timeout.

From your trace, it seems that the Slave tried to NACK the packet because it's not possible to take more data (buffer full). It's maybe that the application didn't read the events out of the softdevice as it should and the event buffer is full. Or if you do authorization but failed to approve the write you will also get bufferfull.

Which firmware do you use on the Slave side ?

If you test using our SDK's examples, would you have the same issue ?

RE: sniffer detects LL infinite loop

Karel_TandD — Fri, 18 Nov 2016 00:19:47 GMT

Hi Hung,

I was not fully aware that the protocol did not have a max retry count at the lower layers, is this true also for notifications as well as write-without-ack?
Added the trace file (TI sniffer) to the top of the question.
Don't know the exact chip used, but another one from the same batch has markings
N51822 / QFACA1 / 1620AM The chip on the Nordic Dongle (MasterEmulator side) has markings N51442 / QFACA1 / 1503AD

RE: sniffer detects LL infinite loop

Hung Bui — Thu, 17 Nov 2016 10:15:36 GMT

Hi Karen,

Could you send a full trace ? If possible, please use Nordic Sniffer, we prefer to analyze data capture from that.

From the trace what I can see is that the packet from Slave is often missing and it sent strange NESN. Please make sure you put the sniffer close to the master and slave.

I'm not sure what "The receiving side looks for "holes" (missing block numbers) and requests the re-transmission of those missing blocks." for. BLE is a reliable protocol,there will be no packet missing, packet is always retransmited until it's ACKed.

It's by default that if a packet is not ACKed after a "connection supervision timeout" the connection will be terminated.

How often do you see the issue ? Which nRF51 chip are you testing with (please read the laser marking and compare to the revision overview here )