deadlock possibility on gazell protocol?

[Firek]

Hi all,

In my project I'd like to use gazell for to communicate 2-6 devices with host. Furthermore I use switching between BLE and Gazell (only 1 device support till now) so there is often "out of sync" state occur. I've read out documentation of gazell with Synchronisation, frequency hopping and so forth. And I'm afraid that there is very probable to achieve a deadlock in case of ynchronization of more then one device at the same time. I'm not sure due to no reference in the documentation about synchronization of two device in the same time. So the quesions are: Am I right? The devices have influence each other? How to prevent synchronization in the same time on all the timeslots?

[ovrebekk]

Hi Firek

Will you be doing BLE/Gazell switching on both the device and host side, or just on the device?

The synchronization scheme in Gazell is pretty simple, and I don't think it is possible to get a dead lock as you say. If two devices will start transmitting at exactly the same time the worst thing that can happen is that they both keep retransmitting until they time out. When this happens they will pick a new random channel and try again, and sooner or later the two devices will use either a different frequency or a different time to send their data.

In other words the user might experience higher packet delay (latency) if the two devices crash, but unless you are sending a lot data from both devices I don't think it will happen regularly.

[Firek]

Swtching is only at host side.

[Firek]

Ok so now everything is clear. I didn't know about picking random channel, hence my suspitions. Thanks Torbjorn.

[Firek]

I've found in documentation that channel_index is incremented not random generated. Can You confirm for sure that there is as You said not as documentation.

"When this counter reaches timeslots_per_channel, the timeslot_counter is reset and the channel_index is incremented (cyclically)"